~s Radiance Digest v2n6
Dear Radiance User,

I've been accumulating mail messages for about half a year, and it's
time to send them out before the digest hits the treacherous 100K mark.

As usual, the mail is broken into indexed catagories for more
convenient browsing.  These are the topics covered in this issue:

	BRIGHTNESS MAPPING	- Mapping luminance to display values
	LIGHTING CALCULATIONS	- Lighting and daylighting questions
	SPECULAR APPROXIMATION	- Fresnel approximation changes
	MEMORY USAGE		- Memory used by rpict and oconv
	SGI GAMMA		- Correct gamma setting on Silicon Graphics
	PROGRAM NAMING		- Radiance program name collisions
	RVIEW SURFACE NORMALS	- Learning about surface normals in rview
	WATER			- Modeling water
	STAR FILTER		- Using pfilt star filter in animations
	GLOW			- Details on glow type definition
	TMESH2RAD		- New triangle mesh converter
	LUMINAIRE MODELING	- Modeling unusual luminaire geometry
	GENSKY			- Getting gensky to mimic a measured sky
	COMPILE PROBLEMS	- ANSI-C compilation trauma
	GLASS BRICKS		- Modeling glass bricks
	AMBIENT VALUES		- Setting the ambient value (-av parameter)
	LOCK MANAGER		- Problem with rpiece/rpict on some machines
	SPECKLE			- Source of image speckle
	OBJVIEW			- Using objview to look at a single object
	CSG			- Constructive Solid Geometry (not)
	RAD PROBLEMS		- Strange behavior with rad program

If you wish to be taken off the Radiance mailing list, please send mail
to "radiance-request@hobbes.lbl.gov".

-Greg

==========================================================================
BRIGHTNESS MAPPING

[The following refers back to some material under the same heading in
Radiance digest v2n5, part 2.]

Date: Wed, 17 Nov 1993 12:48:19 GMT
From: lilley@v5.cgu.mcc.ac.uk (Chris Lilley, Computer Graphics Unit)
To: GJWard@lbl.gov
Subject: Re: Radiance Digest, v2n5, Part 2 of 2

Kevin said:

> I also looked up the 
>definition of the candela which is based upon radiance measurements that are
>converted to luminous measurements by a max luminous efficiency of 
>683 lumens/watt is at a wavelength of 545 nm.

You said:

>Luminous efficacy doesn't really have much to do with luminance or the
>perception of brightness.  Luminous efficacy tells how efficiently a
>lamp converts electrical energy into visible light.

I think there may be a misunderstanding here. You are talking about the
luminous efficiency of a light source - light output for power input.
Kevin is actually talking here about the luminous efficiency of the eye
which clearly does relate to the perception of brightness.

He is firstly referring to luminous efficacy, which is where the 683
comes from.  Indeed you later talk about that yourself. And to get
luminous efficacy you take the quoitent of luminous flux by radiant
flux. Luminous flux in general assumes photopic vision, which is where
the 545nm comes from (although Wyszecki & Stiles give it as 555nm). And
the photopic luminous efficiency is also involved - brightness
sensation for light input wrt wavelength, for the standard photometric
observer.

Do you agree with this?

You also said:

>For a standard color monitor, the formula boils down to:

>	exposure = .882/(1.219 + L^0.4)^2.5

Could you explain what you mean by a standard colouyr monitor as there
are a number of standards, mainly related to video broadcast and
encoding rather than computer graphics, which does not use standard
monitors but rather what each workstation manufacturer happens to
supply.

The power of 2.5 looks like a form of gamma correction. (and the 0.4,
its inverse) Where do the .882 and the 1.219 come from though?

Charles Ehrlich said:

>Very little is known about the way our eyes actually measures light

I suspect the CIE would take issue with that statement ;-)

Regards,

Chris Lilley
----------------------------------------------------------------------------
Technical Author, ITTI Computer Graphics and Visualisation Training Project
Computer Graphics Unit, Manchester Computing Centre, Oxford Road, 
Manchester, UK.  M13 9PL                     Internet: C.C.Lilley@mcc.ac.uk 
Voice: +44 61 275 6045   Fax: +44 61 275 6040   Janet: C.C.Lilley@uk.ac.mcc

     "The word 'formal' in this context is a euphemism for 'useless'."
     H.M. Schey, 'Div, Grad, Curl and all that'. Norton: New York  1973
----------------------------------------------------------------------------



Date: Wed, 17 Nov 93 09:50:32 PST
From: greg (Gregory J. Ward)
To: lilley@v5.cgu.mcc.ac.uk
Subject: Re: Radiance Digest, v2n5, Part 2 of 2

Hi Chris,

OK, I apologize for my glib answer to Kevin.  The statement I made
about luminous efficacy not having much to do with luminance or
brightness is clearly wrong -- I was just trying to get him on a
different track.

There are many ways to interpret what Kevin wrote, but it seemed to me
like he was confusing the efficacies of the light sources with the
display of the rendered image, and the two are not really related.  An
incandescent light has an efficacy around 14 lumens/watt because most
of the energy is given off as heat.  The 179 lumens/watt value I use is
the theoretical maximum efficacy of uniform white light over the
visible spectrum.  (You may contest this number, but it's right around
there and it doesn't much matter what value is used as long as it's
used consistently -- see first section in part 1 RD v2n5.)

I do agree with your statements.  (I believe 555 nm is the defined peak
of v(lambda).)

The formula I picked out works for "average" workstation monitors.
Mine is from SGI and has a Sony XBR tube with Mitsubishi electronics
(20" model).  It is derived in a graphics gem I wrote to be published
in Gems IV by Paul Heckbert, Academic Press.  I can mail you a
PostScript version of the text and formulas from it if you like, but
the pictures must be carefully reproduced so I can't offer those as
readily.

The short answer to your questions about the constants' origin is that
they came from Blackwell's fit to his subject data, the same way
everything else "known" about the human visual system is derived.

-Greg

==========================================================================
LIGHTING CALCULATIONS

From greg Fri Nov 19 08:48:05 1993
Return-Path: <greg>
Date: Fri, 19 Nov 93 08:47:39 PST
From: greg (Gregory J. Ward)
To: Francis_Rubinstein@macmail.lbl.gov, RGMARC@engri.psu.edu
Subject: Re: Daylighting
Status: RO

Dear Rick,

Francis forwarded your questions to me, and I will do my best to answer.

> 1. To determine the illuminance at a photocell location, with an appropriate
> view function.

You should probably use rtrace with the -I option -- this returns irradiance
at a given point and surface normal direction in your scene.  As for the
other parameters, it really depends on your scene.  Can you describe it for
me?  (Esp. with regard to how light is getting to the workplane.)

To convert the watts/m^2 you get out of rtrace for red green and blue to
illuminance in lux, pipe the output to "rcalc -e '$1=54*$1+106*$2+20*$3'".

> 2. To determine the distribution of illuminance across the workplane.  (Is it
> possible to do this directly in Radiance?)

Yes, you can do this by sending an array of points to rtrace then converting
the result, like so:

% cnt 10 5 | rcalc -e '$1=($1+.5)*20/10;$2=($2+.5)*10/5;$3=2.5' \
	-e '$3=0;$4=0;$5=1' | rtrace -h -I -ab 1 -av .2 .2 .2 myscene.oct \
	| rcalc -e '$1=54*$1+106*$2+20*$3' > workplane.ill

To understand this command, you should read the manual pages on cnt, rcalc
and rtrace.  Good luck!

-Greg


Date: 19 Nov 1993 11:57:49 -0400 (EDT)
From: "Richard G. Mistrick" <RGMARC@ENGR.PSU.EDU>
Subject: Re: Daylighting
To: greg@hobbes.lbl.gov

Greg:
    Thanks for the advice.  With respect to the photocell condition, what we
plan to study (and Francis may provide input as a member of a student's M.S.
committee) is the preferred photocell response (considering shielding, etc.)
that is most appropriate for daylight dimming systems under sidelighting
conditions.  We will also look at different lighting systems - direct,
indirect, direct/indirect.  So, what we want to do is mimic a detector view
field with the detector either on the ceiling or on the wall.  I suppose that
I can simply put in a reflectance function that would approximate the detector
field of view.
    One addition question that I have is what is the correlation between RGB
and reflectance for diffuse surfaces?  Thanks for your help, and as I write
this I see that I have a new message from you on a new version.
--Rick Mistrick

Date: Fri, 19 Nov 93 10:06:50 PST
From: greg (Gregory J. Ward)
To: RGMARC@ENGR.PSU.EDU
Subject: Re: Daylighting

Hi Rick,

There are two ways to get what you're after.  The most direct is to model
the actual photocell geometry and use rtrace -I at the appropriate position
on the photosensor.  The other way is to generate a hemispherical fisheye
view of the scene and apply some masking to take out the part of the view
appropriate for different (hypothetical) shielding devices.  The options
for such a view (to rview or rpict) are -vth -vv 180 -vh 180.  Just adding
up (averaging) all the non-black pixels in such a picture gives you the
irradiance.

For your second question, the following is a diffuse surface with 75%
reflectance (gray):

void plastic gray75
0
0
5 .75 .75 .75 0 0

If there is a specular component (eg. for glossy paint), the actual
reflectance of the following:

void plastic shiny_gray70
0
0
5 .75 .75 .75 .04 .05

would be .75*(1-.04) + .04, or 76%.  The completely general formula to
get reflectance from the parameters of plastic is:

	(.263*R+.655*G+.082*B)*(1-S) + S

Where R, G and B are the first, second and third parameters, and S is the
fourth parameter.

For metal, the formla is simpler, just (.263*R+.655*G+.082*B), since
the specular component is also modified by the material color.

-Greg

Date: 02 Dec 1993 14:40:49 -0400 (EDT)
From: "Richard G. Mistrick" <RGMARC@engri.psu.edu>
Subject: Radiance questions
To: gjward@lbl.gov

Greg:
    We are slowly learning more about Radiance, but I still have some basic
questions that we have not been able to answer.

1. In commands such as source and glow, what are the R G B values?  

2. For assigning reflectances, it would be nice to have a command in which you
enter the R G B values and the output is the color on the screen and its
reflectance.  Is there such a command?

3. We have followed the daylighting example in the tutorial and are attempting
to get an IES standard clear sky distribution.  One thing that we notice is 
that as we change the turbidity and use RTRACE to determine irradiance, we 
get different irradiances inside the building but not outside.  How do we get
the accurate values for the daylight available on an exterior horizontal or
vertical plane?

Any suggestions that you have would be most appreciated.

--Rick

Date: Thu, 2 Dec 93 12:56:06 PST
From: greg (Gregory J. Ward)
To: RGMARC@engri.psu.edu
Subject: Re:  Radiance questions

Hi Rick,

To answer your questions:

1.  The RGB values for glow, light, spotlight are all spectral radiance values
in watts/sr/m^2.  To compute appropriate values use the interactive program
"lampcolor".

2.  I agree it would be nice to have such a tool.  I wrote something like this
a long time ago for X10, but never ported it to X11 or anything else.  Maybe
it's time to do it, if I can just find the time.

3.  To compute irradiance outdoors, you must use -ab 1 at least with rtrace.
This value is available directly from gensky, though, in a comment in the
output.  When it says "Ground ambient level:" you can just take that number
and multiply it by pi and you'll have the diffuse irradiance at the
groundplane.  The global irradiance needs the solar component as well,
which may be computed from the solar radiance and altitude.  For a vertical
plane, you'll just have to rely on rtrace.

-Greg

Date: Wed, 19 Jan 1994 17:49:46 +0000 (GMT)
From: "Dr R.C. Everett" <rce1001@cus.cam.ac.uk>
Subject: RADIANCE QUESTIONS
To: GJWARD@lbl.gov

Dear Mr.Ward,
      Here at the Martin Centre in Cambridge University, we've just started 
using RADIANCE on a number of Silicon Graphics Indigo machines. The department 
is involved in various form of 3-D visual computer programming, including 
walk-throughs using a space-ball. We're finding RADIANCE very interesting 
and the new RSHOW routine is excellent and helps the slightly ponderous
task of data input.

I am mainly concerned on two European Community funded daylighting 
research projects, mainly so far about a Greek hospital.
The ability of RADIANCE to model different sky conditions makes 
it a useful alternative to testing cardboard models in an artificial
sky chamber, (especially when our sky chamber doesn't quite do Greek 
conditions). 

I have been trying to marry up daylight factor contours for a simple room 
as produced with the DAYFACT routine with measurements on our cardboard 
model rooms and mundane simple theory. I'm not getting good agreements, 
so I'm probably not pressing the right buttons and I haven't read the 
instructions properly.

Since the DAYFACT routine was sponsored by LESO in Switzerland, is there 
any formal documentation of the theory? If so how can I get a copy?

I am also puzzled by a number of things:

Do windows have to have two sides to get the proper transmission 
coefficients?

The illum process appears to replace a diffuse window light source with 
an equivalent point source. What are the geometric maths of this?

What is the format of the illum.dat files? Presumeably they all add up to 
the total light passing through the window. Can I use this file to 
cross-check this with my own calculations, or even insert my own numbers?

The -as parameter appears to be some sort of spatial smoothing filter. 
When I use it on DAYFACT daylight factor contour maps, is there a danger 
of getting wrong answers by using too much smoothing?

I also feel that the only way I'm really going to get things to work 
properly is to sit down with someone who is already using RADIANCE for 
daylighting work. Any suggestions of people I can pester on this side of 
the Atlantic?

Best Wishes,


Bob Everett - alias  RCE1001@cus.cam.ac.uk

The Martin Centre
Cambridge University Dept.of Architecture,
6, Chaucer Rd.,
Cambridge .U.K.
TEL +44-223-332981   FAX +44-223-332983

Date: Wed, 19 Jan 94 10:32:03 PST
From: greg (Gregory J. Ward)
To: rce1001@cus.cam.ac.uk
Subject: Re:  RADIANCE QUESTIONS

Hi Bob,

It just so happens that one of the best experts on using Radiance for daylight
calculations works at Aberdeen University there in G.B.  His name is John
Mardaljevic, and his e-mail is "j.mardaljevic@aberdeen.ac.uk".

Just offhand, I'm not sure what is going wrong in your calculations.
To answer your questions, though, you don't need to use two surfaces for
your window as long as you use the type "glass", but you do need to make
it's surface normal face inwards if you want to use mkillum with it.
Mkillum does not make the window into a point source, though it may look
that way in rview, which approximates large sources as points to save
calculation time.  You may change this and other behaviors using the
various rview options -- -ds .3 will get it to treat area sources as
area sources.  You should familiarize yourself with the "rad" program
for rendering -- it sets a lot of these options for you.

The format of the illum.dat files is mysterious.  I can't even tell you
which values correspond to which points, as it is a rather strange
coordinate mapping.  (Uneven increments of the polar angle.)

The -as option associated with the renderers merely improves the accuracy
of the indirect calculation in spaces with a lot of light variability.
It is not a smoothing option.

-Greg

Date: Mon, 24 Jan 1994 16:05:02 +0000 (GMT)
From: "Dr R.C. Everett" <rce1001@cus.cam.ac.uk>
Subject: RADIANCE QUESTIONS
To: Greg@hobbes.lbl.gov

Dear Greg,
    Thanks for coming back on my questions. 

I've already talked to John Mardelevic. Unfortunately his new job in 
Aberdeen is not involved with Radiance, so he's not really in a position 
to help with the kind of detailed questions I want to ask.

His main advice to me was to learn by experiment, which I can see taking 
a long time. This is difficult for me because I have project deadlines 
and other such administrative nonsense to meet.

Can you send me the e-mail address of the people in Switzerland?

Perhaps I can press you again on the format of the illum.dat files, 
because that would allow me to isolate my problems to either the inside 
of the room or the sky model. I shouldn't worry about it being in obscure 
coordinates - we have people here who have to teach this sort of thing.

I have tried the Rad script. In many ways it is very useful, but in other 
ways it obscures the processes going on underneath and it is these that I am 
trying to understand. My first attempts at using it just set off some 54-hour
 renderings, whereas I just wanted something that would run overnight. 
The most useful information has been the tables 
of settings that you sent out in answer to other e-mail questions. This 
has enabled me to make my own best pick of values to give reasonable 
quality.

It would help if there was a layman's guide to what the various rpict 
options do.

Since we are involved in producing daylighting teaching material and 
daylighting design competitions, we really are interested in finding out 
about daylighting software. We would also like to be in a position to help 
develop it for simple design applications. 

If there is any descriptive material, on paper, rather than in 
electronic form, that might help us, we will happily pay for photocopying 
and postage,

I look forward to hearing from you,

Best Wishes,

Bob Everett  alias  rce1001@bootes.cus.cam.ac.uk
 
Date: Mon, 24 Jan 94 09:44:53 PST
From: greg (Gregory J. Ward)
To: rce1001@cus.cam.ac.uk
Subject: Re:  RADIANCE QUESTIONS

Hi Bob,

Alas, there is nothing written in layman's terms, or any terms for that
matter, on the options to rpict.  The only available documentation is
what you have.  My best advice is to read the rpict manual page very
carefully, and ask me to clear up the points or topics giving you trouble.
The ultimate reference of course is the C code (yuck).

[Just an aside, I have since updated the notes on setting rpict options
in the ray/doc/notes/rpict.options file in release 2.4.]

I have been wanting to write a better description of rpict for years
now, but have found no source of funding that would allow me the time
to do so.  If it's any consolation, even I can't guess how long a
rendering's going to take without some experimentation.

The file src/gen/illum.cal contains the definitions for the mkillum
data file's coordinate system.  Unless you are using mkillum on a sphere,
the one's you need to decypher are il_alth and il_azih:

	il_alth = sq(-Dx*A7-Dy*A8-Dz*A9);
	il_azih = norm_rad(Atan2(-Dx*A4-Dy*A5-Dz*A6, -Dx*A1-Dy*A2-Dz*A3));

	norm_rad(r) = if( r, r, r+2*PI );

These expressions look worse than they really are.  For example, il_azih
simply gives the azimuthal angle (in radians) using the argument unit
vectors [A1 A2 A3] and [A4 A5 A6].  The altitude coordinate is more
unusual.  It says that the coordinate index is equal to the square of the
dot product between the ray direction and the local surface normal
(which is given by [A7 A8 A9] in this case).  What's even stranger, you
will notice that the range of this coordinate is 0 and 1, but in the
data file the range is somewhat different.  This is to provide proper
interpolation and extrapolation for data values in the normal direction
and on the "horizon".

The actual data in the mkillum files are radiance values in watts/sr/m^2.
Multiply the values by 179 to obtain luminance in cd/m^2.  Note that the
actual output of a flat illum surface is the radiance or luminance
multiplied by the projected area, that is, the surface area times the cosine
to the normal.  The answer is in watts/sr or cd (depending on your choice
of units).

Hope this helps.
-Greg

P.S.  The address of Raphael Compagnon in Switzerland is
	"compagnon@eldp.epfl.ch".

From: Stuart Lewis <stuart@archsun.arch.gatech.edu>
Subject: RADIANCE Question
To: gjward@lbl.gov
Date: Thu, 31 Mar 1994 16:38:22 -0500 (EST)

Dr. Ward,

I am using Radiance2.3 to investigate elements of daylight design.
I am most interested in extracting illuminance information from 
Radiance scenes, and as such would appreciate any pointers you might 
have to documentation beyond that found in the Radiance distribution 
and the tutorial that would help me to make better use of RTRACE to 
write scripts, etc. in which I (and more importantly, my advisor!) 
can have some confidence.
Any other leads in this area would be greatly appreciated.

Thanks for your assistance.  I would have posted this request to 
the Radiance mailing list instead, but have not yet received any 
confirmation of my enrollment (via newuser.)

Stuart Lewis
stuart@archsun.arch.gatech.edu

Georgia Tech

Date: Thu, 31 Mar 94 14:19:05 PST
From: greg (Gregory J. Ward)
To: stuart@archsun.arch.gatech.edu
Subject: Re:  RADIANCE Question

Hi Stuart,

You are on the mailing list.  Normally, I do not send out confirmation to
new users.  Also, the mailing list is for my postings of user mail only,
not for general questions (which you should send to me directly).  If you
want to see back issues of the "Radiance Digest," they may be found in
the /pub/digest directory on the anonymous ftp account of hobbes.lbl.gov.

Using rtrace is a bit tricky, since it is a fairly general interface to
the Radiance calculation.  You can see an example of how it might be
applied in the file ray/src/util/dayfact.csh.

Together with cnt, rcalc and total, rtrace may be used to calculate almost
any lighting metric.  A very simple application where illuminance (in lux)
is calculated may be found in the file ray/src/util/rlux.csh.  The way this
script works is like so:

	% ximage picture_file | rlux [rtrace options] octree

Typing 't' (or hitting the middle mouse button) at a point on the image
will cause the illuminance at that point to be printed on the standard
output.

If you want more help, I'd be glad to assist you in a specific example, or
check the work that you've done.

-Greg

==========================================================================
SPECULAR APPROXIMATION

Date: Mon, 22 Nov 93 10:28:38 MST
From: jmchugh@carbon.lance.colostate.edu (Jon McHugh)
To: GJWard@lbl.gov
Subject: Fresnel's relations

Hi Greg,

In your discussion of Radiance 2.3 you say that 
"Removed Fresnel approximation to specular reflection from Radiance materials,
since the direct component was not being computed correctly.  This
may have a slight affect on the appearance of surfaces, but it can't be
helped."


How are the Fresnel relations approximations? I thought they are a direct
application of Maxwell's Equations. Is there some problem with using
the Fresnel relations to calculate angular properties of dielectrics
such as glass and many specular building materials?

______________________________________
|         Jonathan R. McHugh          |
|   Dept. of Mechanical Engineering   |
|      Colorado State University      |
|       Fort Collins, CO 80523        |
|          (303) 491-7479             |
|          (303) 491-1055 FAX         |
| jmchugh@carbon.lance.colostate.edu  |
---------------------------------------

Date: Mon, 22 Nov 93 09:42:48 PST
From: greg (Gregory J. Ward)
To: jmchugh@carbon.lance.colostate.edu
Subject: Re:  Fresnel's relations

Hi Jon,

There is nothing wrong with the Fresnel relations!  I still do use them
(in one form or another) for the types dielectric, interface and glass.
(Glass uses an exact solution to the infinite series resulting from
internal reflections in a pane of glass, and includes polarization as it
affects transmittance and reflectance.)

I used to use an approximation to the "unpolarized" Fresnel reflectivity
function in my normal materials that used an exponential fit I
discovered (and probably not for the first time).  This formula was an
approximation, and was used only because it provided a faster
calculation with little loss in accuracy.  I don't use any Fresnel term
in these materials anymore, which is a shame, but it caused a measurable
inconsistency in the calculated results.

-Greg

==========================================================================
MEMORY USAGE

From: apian@ise.fhg.de
Subject: rpict memory statistics ?
To: gjward@lbl.gov (Greg Ward)
Date: Wed, 24 Nov 1993 06:30:05 +0100 (MEZ)

Hi Greg,

just curious: you ever wondered where the memory goes in rpict ?
This sounds like an offensive question, which it isn't. I also see
that rpict is probably one of the best optimized raytracers around.

Just wondering where the 40MB size of my running rpicts come from,
there's an 8MB picture, some redicolous amount of books and 25 or so
function files for windows generated by mkillum.

Not that 40MB is something to really worry about, just that 32MB machines
do choke a bit...

(not a high prio request)
TIA
Peter
-- 

----------------------------------------------------------------------
 Peter Apian-Bennewitz				apian@ise.fhg.de
 Fraunhofer Institute for Solar Energy Systems	   Tel +49-761-4588-123
 (Germany) D-79100 Freiburg, Oltmannsstrasse 5,    Fax +49-761-4588-302
----------------------------------------------------------------------

Date: Tue, 23 Nov 93 22:43:31 PST
From: greg (Gregory J. Ward)
To: apian@ise.fhg.de
Subject: Re:  rpict memory statistics ?

Hi Peter,

A large picture will definitely occupy a lot of memory, since the data
routines treat it the same as any data file and each pixel gets put into
three floats, thus takes up at least (width*height*4*3) bytes of memory.
Best to work with small images for this reason...  Also, my malloc()
routines are not as efficient space-wise as they could be, using up
to twice as much core as is actually required (typically 25% waste).
This is usually compensated by my use of bmalloc() which is 100%
space-efficient for most of my allocations.  Not used for data
arrays, though (sorry).  Unless you are using some outrageous options
for mkillum, it's doubtful that the data files it produces use a
significant amount of memory.

For large, complicated models, the surface identifiers can end up taking
a fair bit of core, then are almost never accessed!  For this reason,
I put them into their own large blocks of memory that are the first
to get swapped out when the going gets rough.  (See common/savqstr.c.)

An rpict process can grow quite large with the interreflection calculation,
especially if -ab is 2 or higher and the scene has a lot of detail
geometry.  Excluding trees and stuff from the calculation is a good idea
using the -ae and/or -aE options.

The rest of the memory is used to store the geometry and the octree, and
is about as efficient as I can make it.  You can try recompiling everything
with the -DSMLFLT option, which reduces scene storage space by around 30%,
but this has many drawbacks in rendering accuracy as cracks may appear in
scenes with large ranges of dimensions.

Hope this helps.  I wrote Radiance on an 8M machine, so I remember
what it's like to have limited memory.  (An oxymoron?)

-Greg

From: apian@ise.fhg.de
Subject: Re: rpict memory statistics ?
To: greg@hobbes.lbl.gov (Gregory J. Ward)
Date: Wed, 24 Nov 1993 08:16:20 +0100 (MEZ)

Hi Greg and a yawnful good morning,
astonishingly its getting light outside...

thanks for the fast reply, I fancy its the scene complexity (ab=1,
768x576 pixel).  The machine doesn't come to a complete standstill, so
some fairly large amount gets swapped out and stays out most of the
time.  I'll look into this before doing the next attempt for a movie.
thanks again,

have a nice evening,
Peter

From: "Mr. A. Morris" <jabt282@liverpool.ac.uk>
Subject: oconv query part 2
To: greg@hobbes.lbl.gov
Date: Fri, 3 Dec 1993 09:40:20 +0000 (GMT)

Dear Greg

Thanks very much for your reply, 1st Dec to my initial query about the
"out of octree space" system error I've been encountering.
Unfortunately I haven't resolved it yet.  I've tried running the
command as a batch job on one of the larger machines when I did
encounter the message "out of octree space- out of memory" However once
I ran it again as a unlimited memory and filesize job the error
reverted to the usual "out of octree space" again.

I have just installed the lasest version of radiance and included in
the installation the option for scenes with a large no. of objects, but
this doesn't seem to have had any effect on the problem.

In your reply you stated,

"If not, then you may be running up against the internal limits to the
octree size.  To change them, you need to rerun makeall install,
changing the rmake command to include -DBIGMEM as one of the MACH=
options.

At any rate, you shouldn't start having this sort of problem until your
scene has 10,000+ polygons"

I am unsure how to estimate the no. of polygons that my scene may have could
you explain roughly how to estimate it, ie does a cube have 6 polygons at its
simplest and how many will a cylinder have? My current scene description has
about 600 objects, am I right in thinking that with that no. of objects it could
be possible to exceed the internal limit of 10,000 polygons?

Could you also explain more simply the process of "changing the rmake command
to include -DBIGMEM as one of the MACH= options" I'm a novice at this sort of
thing!

With respect to the "artificial sky" question, mine are being generated by the
"torad" autocad to radiance converter which I've been using. I presume that it
is generated using the gensky command as I am prompted to give the time, date,
lat. and long. etc.

I hope you can explain the procedure for changing the rmake command, I'm getting
desperate to complete this work! 

yours faithfully

Alex Morris.

Date: Fri, 3 Dec 93 09:21:39 PST
From: greg (Gregory J. Ward)
To: jabt282@liverpool.ac.uk
Subject: Re:  oconv query part 2

Hi Alex,

If you are using AutoCAD, it may create many surfaces per cylinder when only
one is actually required (a Radiance cylinder).  Unfortunately, AutoCAD only
produces polygons.  There should be a parameter somewhere that would allow
you to change the number of facets a given volume is broken into.  Cubes
and other polyhedral objects shouldn't be affected, but it's a good idea to
break small curved objects into the smallest number of polygons you can live
with.

To change the compile parameters, run "makeall install" again, this time say
"yes" when asked if you want to change the rmake command.  Then, change the
MACH= line by adding -DBIGMEM and change the OPT= line by removing -DSMLFLT.
(This is probably what's causing your results to look speckled.)  Makeall will
do the rest.

With -DBIGMEM defined, it is unlikely that you will run into internal limits
before you run out of swap space.

I'm not sure what kind of artificial sky torad generates since I've never used
it, but it sounds as though it's running gensky all right.  The sky shouldn't
affect your octree size, therefore.

-Greg

==========================================================================
SGI GAMMA

Date: Thu, 9 Dec 93 16:44:52 GMT
From: ann@graf10.jsc.nasa.gov (ann aldridge)
Apparently-To: greg@hobbes.lbl.gov

Hi Greg,

We have been collecting beautiful pictures from the HST repair mission.
I will send you a three pictures which we hope to work on.

...
   2. Image of HST.  This picture appears to be lit only by payload bay lights.
      Hopefully, without sun we can reproduce lighing.  Have just begun work
      on this picture.  See pic2real.pic. This picture looks terrible as a pic
      file.  See pic2real.rgb for better image if you can display this format!
...

Do you want the radiance files to work on getting better images?  We would
welcome any suggestions you have.

Thanks, Ann


Date: Thu, 9 Dec 93 10:08:31 PST
From: greg (Gregory J. Ward)
To: ann@graf10.jsc.nasa.gov
Subject: pictures

Hi Ann,

The .rgb version looks the same as the .pic version on my display.  The fact
that yours doesn't means either that the gamma value associated with the
original file is not the default 2.2 that ra_tiff expected, or that you have
not set your GAMMA environment variable properly for ximage to work.

SGI's are weird because they have something called the system gamma (stored
in /etc/config/system.glGammaVal and set by the gamma program) that is a
partial correction factor for the natural gamma of the monitor.  This value
is not the gamma that you get, which is:

	Gf = Gm/Gs	where:	Gf = final gamma,
				Gm = natural monitor gamma,
				Gs = system gamma set by "gamma" program

The final gamma, Gf, is what you should set your GAMMA environment variable
to.  Most monitors have a natural gamma around 2.0, and most SGI systems
set the gamma value to 1.7, so the Gf number is around 1.2.  Personally, I
don't like all this fussing with the natural gamma of the monitor because
I believe it introduces quantization errors, so I set the system gamma
to 1, like it is on non-SGI systems.

Anyway, you can find out what the final gamma of your display is directly
by using the picture ray/lib/lib/gamma.pic, like so:

	ximage -b -g 1 gamma.pic

Just back up and make the closest match between the brightness on the left
and the one on the right, and take the corresponding number as the combined
gamma.  Then, put a line like:

	setenv GAMMA 1.2

in your .login or .cshrc file.  In the next release, you should be able
to use the radiance.gamma resource on your X11 server to accomplish the
same thing.  In my opinion, the powers that be should have worked out
these problems ages ago.  It's a bit sticky, though, since monitor gamma
changes with brightness and contrast settings...

-Greg

==========================================================================
PROGRAM NAMING

From: Kurt.Jaeger@rus.uni-stuttgart.de (Kurt Jaeger aka PI)
Subject: Radiance 2.3 and the calc binary
To: GJWard@lbl.gov
Date: Fri, 24 Dec 1993 11:55:27 +0100 (MEZ)

Hi!

During the installation of the radiance 2.3 software, a binary
called calc was installed as well. While it is a very useful tool,
I'd like to know where it is used by other radiance binaries.

We have established a common software installation scheme
and the name for the calc binary collides with the recently posted
calc-2.92.

So I'd like to know whether calc is a required binary for
radiance. Otherwise it would lighten Your burden of administrating
the distribution by not including calc with radiance because there
is a different calc out there 8-)

		So short, PI

-- 
PI at the User Help Desk Comp.Center U of Stuttgart, FRG      27 years to go ! 
EMail: pi@rus.uni-stuttgart.de
Phone: +49 711 685-4828                (aka Kurt Jaeger)


Date: Fri, 24 Dec 93 06:55:11 PST
From: greg (Gregory J. Ward)
To: Kurt.Jaeger@rus.uni-stuttgart.de
Subject: Re:  Radiance 2.3 and the calc binary

Hi Kurt,

You're right that calc is not an essential part of the distribution, but
then there are a lot of non-essential things in the distribution.  What
is this calc-2.92 you mention?  The name "calc" also collides with a program
on the PC under Windows, so it may be time to come up with a new name.
Any suggestions?

-Greg

Subject: Re: Radiance 2.3 and the calc binary
To: greg@hobbes.lbl.gov (Gregory J. Ward)
Date: Fri, 24 Dec 1993 16:31:30 +0100 (MEZ)

Hi!

> You're right that calc is not an essential part of the distribution, but
> then there are a lot of non-essential things in the distribution.
> What is this calc-2.92 you mention?
I'll attach the intro file of the software below (its calc-2.9.0, actually,
I remembered the wrong version). It was posted a few days ago in
some of the sources groups.

> The name "calc" also collides with a program
> on the PC under Windows, so it may be time to come up with a new name.

I would suggest that You try to limit the radiance distribution
to the essential stuff. You can factor out the additional stuff
and maybe even distribute it seperatly. I think cnt, total etc
are good programs, its just that I'd prefer to keep things
seperate, if possible. Are these programs in any way
essential, because they are called by the core radiance binaries ?

Otherwise the namespace of the programs that can live in $PATH
will be cluttered sometime in the future. Ok, this is no problem
for You as maintainer of radiance, but I already begin to sense
the problems we have locally with the name space of $PATH.

You can ask the authors of calc-2.9.0 if he wants to merge
the two calc's (and their additional tools) into one package ?

Their EMail adress is:
    dbell@canb.auug.org.au
    chongo@toad.com

I'd be interested in hearing about Your decision on this aspect.

	Thanks, PI

---intro-calc-2.9.0---

Quick introduction

	This is an interactive calculator which provides for easy large
	numeric calculations, but which also can be easily programmed
	for difficult or long calculations.  It can accept a command line
	argument, in which case it executes that single command and exits.
	Otherwise, it enters interactive mode.  In this mode, it accepts
	commands one at a time, processes them, and displays the answers.
	In the simplest case, commands are simply expressions which are
	evaluated.

[Stuff deleted.]

Kurt Jaeger

Date: Fri, 24 Dec 93 08:12:09 PST
From: greg (Gregory J. Ward)
To: Kurt.Jaeger@rus.uni-stuttgart.de
Subject: Re: Radiance 2.3 and the calc binary

Just one other question.  Since the user community for Radiance on any
given machine is probably small, why not put all the binaries in a 
separate directory and only include that in the path of those who
really need it?  That's the usual way of handling large software
packages, after all.

From: Kurt.Jaeger@rus.uni-stuttgart.de (Kurt Jaeger aka PI)
Subject: Re: Radiance 2.3 and the calc binary
To: greg@hobbes.lbl.gov (Gregory J. Ward)
Date: Fri, 24 Dec 1993 23:04:42 +0100 (MEZ)

Hi!

The binaries for different packages *are* in seperate directories.

But we provide a common directory called /client/, where the
subdirectories bin/, lib/ etc are accessed by the users through $PATH.

> That's the usual way of handling large software packages, after all.
Yes, You're right. We are working on a scheme where the end users, the
biggest part of a community, have nothing special to call or do
to access as many packages as possible.

So, providing something like a getpub procedure can be done, but is
not preferred.

		So short, PI (aka Kurt Jaeger)

==========================================================================
RVIEW SURFACE NORMALS

Date: Thu, 6 Jan 94 17:55:07 -0500
From: phils@boullee.mit.edu (Philip Thompson)
To: greg@hobbes.lbl.gov
Subject: Rview suggestion

Greg,
Here's one for the suggestion box.

It would be nice if in rview the user could somehow get the orientation
of a surface surface.  A quick way would be to just have a dot product
of the incident ray and surface normal.  This would give a indication of
whether or not a surface was facing the viewer or not.

It's not easy, if not impossible, to have control of how polygons are
written  from a cad modeler.  This option would make life easier in
those cases where it matters.
Thanks,
Philip


Date: Thu, 6 Jan 94 15:02:05 PST
From: greg (Gregory J. Ward)
To: phils@boullee.mit.edu
Subject: Re:  Rview suggestion

Hi Philip,

Sure, that sounds easy enough.  All the information is available within
the trace routine, but I never thought the surface normal was much use
since it's such a confusing quantity.  How would it be if I gave both
the surface normal and the angle to the incoming ray (computed from the
dot product)?  I think this might be the most meaningful combination.

-Greg

Date: Thu, 6 Jan 94 18:17:43 -0500
From: phils@boullee.mit.edu (Philip Thompson)
To: greg@hobbes.lbl.gov (Gregory J. Ward)
Subject: Re:  Rview suggestion

Yes, I was thinking of something along those lines.  The problem I
and other people run into is when we make windows in a cad model.
When we want to turn windows into illum sources then orientation
matters.  So to simplify this its seems the easiest solution
would be to stand inside a room and point at the windows and get
some feedback as to their orientations. You could call it "n" or
"o".

- Philip

Date: Thu, 6 Jan 94 15:47:29 PST
From: greg (Gregory J. Ward)
To: phils@boullee.mit.edu
Subject: Re: rview suggestion

As a final compromise, I added a check so if the ray hit the back side
of the material, the trace command mentions that fact, without going
into detail about the intersected angle and surface normal.

-G

==========================================================================
WATER

From: phils@MIT.EDU
Date: Tue, 11 Jan 1994 14:54:19 -0500
To: greg@hobbes.lbl.gov
Subject: Material for water

Greg,

What is the best material for water when modeling a pool?
It seems when I use a dielectric I can't see the bottom.
What is the difference between the two materials in this case?

I'll send you a sample pool.rad below.

Thanks,
Philip

# pool.rad

void plastic white_paint
0
0
5 .5 .45 .4 0 0

# pool water
void texfunc wavy
6 wave_x wave_y wave_z wave.cal -s .25
0
1 .05

wavy dielectric wavy_water
0
0
5 .9 .9 .91 1.33 0

# wavy glass wavy_water
# 0
# 0
# 4 .9 .9 .91 1.33

# genbox white_paint pool 3 5 1

[etc...]

Date: Wed, 12 Jan 94 10:03:20 PST
From: greg (Gregory J. Ward)
To: phils@MIT.EDU
Subject: Re:  Material for water

Hi Philip,

The difference between dielectric and glass is that glass imitates a thin
pane (or whatever) made of glass, and dielectric represents an interface
between air and some dielectric material.  Glass is only appropriate for
windows or other thin glass surfaces, and more efficient in those cases
than two opposite-facing surfaces of type dielectric.  Dielectric is the
only type to use for thick bodies of transparent media, such as a crystal
ball or a swimming pool.  (There is also the type 'interface', which is
appropriate for a boundary between two dielectric media, neither of which
is air.)

Unfortunately, lighting inside a dielectric medium is none too easy.
The chief problem within Radiance is the difficulty of finding the
light source (e.g. the sun) from the bottom of the pool.  The only person
I am aware of who's tackled this problem successfully is Mark Watt, and
he wrote a paper about it in the 1990 Siggraph proceedings.

You might be able to get Radiance to find the sun for a still body of
water using the 'prism2' type, but you have to know what you're doing.

How important is this to you?  If you're just going for looks and not
very interested in physical accuracy, go ahead and use 'glass'.  At
least you will be able to see the bottom of your pool that way.

-Greg

==========================================================================
STAR FILTER

Return-Path: <srouten@rubidium.service.indiana.edu>
Date: Sat, 12 Feb 1994 14:24:30 -0500
From: srouten@rubidium.service.indiana.edu
To: greg@hobbes.lbl.gov

Hi Greg, 

Reuben and I are working on a short animation which consists of some lights
simply flying by an object.  The trouble is, we'd like to use the star
filter, which seems to rule out an absolute exposure for every frame.  I
read digest v2n4 where you mention, in the VIDEO section, that you could 
provide some information on dynamic exposure, so that is what i'm asking
for.

Thanks in advance,
Scott

Date: Mon, 14 Feb 94 10:42:45 PST
From: greg (Gregory J. Ward)
To: srouten@rubidium.service.indiana.edu
Subject: exposure

Hi Scott,

Well, I guess we need ANOTHER option for pfilt!  Actually, you can just do
a two-pass filtering, and follow it up with a one-pass run to bring the
exposure back to where you want it.  Unfortunately, this is the only easy
solution right now.  To find out what exposure pfilt actually used, run
getinfo on the filtered image and look at the EXPOSURE= line.  You can
use the following command to go from the exposure you got to the value "1.7".
Of course, you may substitute whatever you like for the '1.7' value:

	% pfilt -2 [options] orig.pic > filtered.pic
	% pfilt -1 \
	-e `getinfo<filtered.pic|rcalc -i 'EXPOSURE=${ex}' -e '$1=1.7/ex'` \
	filtered.pic > corrected.pic

Be sure to pay attention to back-quotes vs. regular quotes!

-Greg

==========================================================================
GLOW

Date: Wed, 16 Feb 1994 01:41:43 -0800
From: COURRET@sc2a.unige.ch
To: greg@hobbes.lbl.gov
Subject: glow material

Hi greg,

I am having some difficulties to understand the definition of the glow
material.  From manuel Ray.1 yoou wrote the 8/12/93, i can see that the
difference between the light and the glow materials is that the glow
one is limited in its effect.  Could you, please, quantify this
limitation ?

In the tutorial named tutorial.1, you describ a  standard sky and ground
to follow a gensky sun and sky distribution. Why is the sky modelized with
a glaw material and not a light one as it is the case for the sun?

Gilles.

Date: Wed, 16 Feb 94 10:21:32 PST
From: greg (Gregory J. Ward)
To: COURRET@sc2a.unige.ch
Subject: Re:  glow material

Hi Gilles,

The limitation of the glow type is determined by the setting of the distance
(fourth) parameter.  Any calculation point further than this distance from
a glow source will not look to the source for direct illumination.  The
glow source will, however, contribute in the interreflection calculation
if -ab is 1 or greater.  If a distance of 0 is used, or the source is at
infinity (such as the sky), then a glow can only contribute indirectly.

If we used a light type for the sky, Radiance would not be able to sample
it adequately, because it is much too large.  Light sources must be
reasonably well localized in order to act properly in the direct calculation.
The indirect calculation, on the other hand, works very well for widely
distributed illumination sources.

I hope this clears things up for you a little.

-Greg

==========================================================================
TMESH2RAD

[The following discussion relates to the creation of the new tmesh2rad
translator.]

Date: Fri, 18 Feb 94 20:19:59 GMT
From: ann@graf10.jsc.nasa.gov (ann aldridge)
Apparently-To: greg@hobbes.lbl.gov

Hi again,

We do not usually use WaveFront format.  We have an internal format,
but can convert to various other output formats. Below is a short
sample of the file I currently use (included for you
entertainment):DEFAULT is material name. first 3 numbers are vertex,
last three are normal.

triangle DEFAULT -14.673 -3.119 50 -0.95677 -0.203374 1.17936e-10
-14.673 3.118 50 -0.94236 0.271166 -1.6951e-10
-14.673 3.118 -50 -0.97118 0.135583 -8.47551e-11
triangle DEFAULT -14.673 3.118 -50 -0.97118 0.135583 -8.47551e-11
-14.673 -3.119 -50 -0.95677 -0.203374 1.17936e-10
-14.673 -3.119 50 -0.95677 -0.203374 1.17936e-10
triangle DEFAULT -14.673 -3.119 50 -0.95677 -0.203374 1.17936e-10
-14.673 -3.119 -50 -0.95677 -0.203374 1.17936e-10
-12.136 -8.817 -50 -0.791363 -0.574922 4.84915e-10
     .....etc.

I was being lazy using WaveFront because it was so similar to your
format.  To get the vertex normals I will have to convert format
above.  Most WaveFront objects we use are not triangles, so you
probably should keep your format.  I can work with it.  (We do have a
routine to triangularize a WaveFront file.)

I am still working on recompiling.  Then I will make a new cylinder file
with normals.

Thanks again, Ann.

Date: Thu, 17 Feb 94 12:41:35 PST
From: greg (Gregory J. Ward)
To: ann@graf10.jsc.nasa.gov
Subject: suggestion

Instead of putting all the vertices before the triangles, it would be easier
to convert your format as follows.  The original:

	triangle DEFAULT -14.673 -3.119 50 -0.95677 -0.203374 1.17936e-10
	-14.673 3.118 50 -0.94236 0.271166 -1.6951e-10
	-14.673 3.118 -50 -0.97118 0.135583 -8.47551e-11
	triangle DEFAULT -14.673 3.118 -50 -0.97118 0.135583 -8.47551e-11
	-14.673 -3.119 -50 -0.95677 -0.203374 1.17936e-10
	-14.673 -3.119 50 -0.95677 -0.203374 1.17936e-10

would become:

	m DEFAULT
	v 1 -14.673 -3.119 50 n -0.95677 -0.203374 1.17936e-10
	v 2 -14.673 3.118 50 n -0.94236 0.271166 -1.6951e-10
	v 3 -14.673 3.118 -50 n -0.97118 0.135583 -8.47551e-11
	t 1 2 3

	m DEFAULT
	v 1 -14.673 3.118 -50 n -0.97118 0.135583 -8.47551e-11
	v 2 -14.673 -3.119 -50 n -0.95677 -0.203374 1.17936e-10
	v 3 -14.673 -3.119 50 n -0.95677 -0.203374 1.17936e-10
	t 1 2 3

Notice that the same vertex id's are reused.  This is an advantage of
my format -- you can save memory and confusion by grouping
your triangles and vertices however you like.  The 'm' command of
course did not need to be repeated in this case, but that way your
translator can be a little simpler.  The final output of tmesh2rad
is the same.

If you want, you can use rcalc instead of writing a translator, like so:

	% rcalc -i inp.fmt -o out.fmt orig_file | tmesh2rad > rad_file

Where inp.fmt contains:

triangle $(mat) $(x1) $(y1) $(z1) $(nx1) $(ny1) $(nz1)
$(x2) $(y2) $(z2) $(nx2) $(ny2) $(nz2)
$(x3) $(y3) $(z3) $(nx3) $(ny3) $(nz3)

And out.fmt contains:

m $(mat)
v 1 $(x1) $(y1) $(z1) n $(nx1) $(ny1) $(nz1)
v 2 $(x2) $(y2) $(z2) n $(nx2) $(ny2) $(nz2)
v 3 $(x3) $(y3) $(z3) n $(nx3) $(ny3) $(nz3)
t 1 2 3

If I understand your format correctly, this should do it.

-Greg

==========================================================================
LUMINAIRE MODELING

Date: 18 Feb 1994 17:24:32 -0400 (EDT)
From: "Richard G. Mistrick" <RGMARC@ENGR.PSU.EDU>
Subject: Tubular luminaires in radiance
To: greg@hobbes.lbl.gov

Greg:
    We are getting some good use out of Radiance.  I have a simple question as
to how to best model tubular luminaires.  Below are a few questions:

1. The photometry is general performed relative to the center of the
luminare.  As I understand it, you generate a luminous rectangle or two
(horizontal plane) that emit light upward and downward.  How can I put
these at the luminous center of a tubular luminaire?  All that I've
found to date is that I can use an illum source, but must put it
outside the luminaire.

2. How can I make the luminous element of the luminaire (which may be curved)
appear bright without contributing additional light to the space?

I would appreciate any tips related to the above that you can pass along.

Thanks, Rick Mistrick

Date: Fri, 18 Feb 94 14:50:53 PST
From: greg (Gregory J. Ward)
To: RGMARC@ENGR.PSU.EDU
Subject: Re:  Tubular luminaires in radiance

Hi Rick,

I was reading your e-mail and thinking to myself, "Gee, this guy really
knows his stuff."  I didn't notice your name until I got to the end...

Yes, you have hit on a sticking point.  The solution of putting a rectangle
above and below the luminaire is a marginal one, and is used by ies2rad
mostly because the IES format doesn't give much of a clue as to the true
fixture geometry.

1.  When you say you have a "tubular luminaire," do you mean a cylinder?
If in fact you had a cylinder whose entire area emitted light, you could
model this as a cylindrical light source directly in Radiance (with or
without an associated intensity distribution).  If, as I suspect, only
part of your tube is luminous, you may need to use an illum that
is outside the actual luminaire.  This illum may composed of one or
more polygons, or you could use a cylinder larger than the actual fixture.
The computed emission will be from the whole illum surface, so you shouldn't
make it too much larger than the actual radiating area.

2. Use the material type "glow".  If you give a small positive value as
the influence distance (fourth real parameter), then the assigned surfaces
will illuminate local objects (ie. other parts of the luminaire).  If the
value is zero, the assigned surfaces will be visually bright without having
any direct contributions.  In any case, the (invisible) illum surface will
block any rays from reaching the glow surface, so the luminaire can't be
overcounted.

Luminaire modeling is definitely an art, and a rather painful one at that.
I wish the IES computer committee was a little more focused on the future
of full geometric models and near-field photometry and a little less
focused on database issues, but I shouldn't complain if I won't volunteer...

-Greg

==========================================================================
GENSKY

Date: Fri, 4 Mar 94 08:01:34 EST
From: TCVC@ucs.indiana.edu
Subject: Re:  water swells
To: greg@hobbes.lbl.gov

Fractals can be fun.. yes it will take a while to "hone" in on the
right effect, but thanks for opening the door for me!

This might sound awefully naive from a "long time explorer " of 
Radiance, but I need to run a daylight image (first one!!!!)..
I feel like a vampire that has come out into the sun.

All of our geometry is based on :

		+z	= north
                +x       = west
  		+y     is up

Say its at your location or Hong Kong for that matter,
How do I twist gensky to line up with my coordinate system?
And where is the suggested "ambient" value found?

-Rob
(I will have a series of images that I think you will enjoy. Some are
highly theatrical from my Graduate Design Students in THeatre, and
I am working on a building top that should be quite interesting!!
Will post when all are complete)

From greg Fri Mar  4 09:16:15 1994
Return-Path: <greg>
Date: Fri, 4 Mar 94 09:15:50 PST
From: greg (Gregory J. Ward)
To: TCVC@ucs.indiana.edu
Subject: Re:  water swells
Status: R

Hi Rob,

To change gensky's output from its default coordinates (+Y = North, +X = East,
+Z = up), use xform.

The easiest way for me to think about it is to imagine what the sky looks
like in my coordinate system when first output by gensky, then move it where
it ought to go.  When gensky is run, it produces a sky whose North direction
is pointing straight up instead of in the +Z direction like we want it, and
whose other directions are wrong as well.  To rotate gensky's North from our
up (+Y) to our North (+Z), we need to rotate about our X-axis by +90 degrees
(using the right-hand rule to determine the sign).  Once we have done this,
the original gensky X orientation will still be wrong, pointing East instead
of West.  We therefore rotate about the Z-axis by 180 degrees (sign doesn't
matter for this particular rotation).  So, the command is:

	gensky Month Day Time [options] | xform -rx 90 -rz 180

Note that the order of rotations is important.  There are many
other equivalent rotations, also.

I look forward to seeing more examples of your work and your students'.

-Greg

Date: Fri, 4 Mar 94 09:37:23 PST
From: greg (Gregory J. Ward)
To: TCVC@ucs.indiana.edu
Subject: P.S.

I forgot to answer the part about Southern latitudes.  Simply apply the -a
option to gensky, giving a negative latitude to indicate the number of
degrees below the equator.


From: apian@ise.fhg.de
Subject: gensky (take #645)
To: gjward@lbl.gov (Greg Ward)
Date: Thu, 24 Feb 1994 21:03:15 +0100 (MEZ)

Dear Greg,

Anne Kovach and myself are wondering for the nth time what the
hack genksy is producing.

....

Hi Greg,

Im sitting here with Peter and we were discussing some
of my calculation results in figuring out what gensky
is doing.

I was/am testing how well Radiance is suited (ie. gensky) in
determining the Irradiation (rtrace -I option I used for this case) on
an area.  To test the values from gensky , I simulated the global
irradiation on the horizontal with gensky over an entire year for the
Freiburg location.  The values that I got were verz very low.  Then I
thought maybe the 3 values out from rtrace should be summed since these
are the 3 channels.  SO I summed them and got a value 3 times larger.
(oh... [P. editorial remark])

When I compared these values of +s, -s, +c, -c (4 simulations each with
a different distribution) with the TRY data from Freiburg, the data IN
ALL CASES was still too low -- although I multiplied by 3!!
(Thismultiplication by 3 I learned is not correct -- via Peter.)
("Each channel can be thought of in terms of
watts/m2/steradian/"bandwidth".  In other words, going from a
three-color measure of radiance to a monochromatic measure, we wouldn't
add up the three channels to compute the total radiance, we would take
some average.  This simplifies computations quite a bit." [ from your
mail 1 month ago, P.] )

THe main points of this simulation which were puzzling are
asfollows:

1. Why are the Irradiation values (units + W/m2 I am assuming
so low?)  eg. June in Freiburg is 38 kWh/m2/month and in the
TRY year it is around 169 kWh/m2/month. (THis was calculated
with the +s option in this case.)

2. What can be done to make these values higher??  ie. WHat parameters
could be changed? in sky_glow ? bandwidth values?  (not just
the RGB??)
( I guess your answer is adjusting the zenith brightness, just why ??
Adjusting CIE to local climate ??? P.)

3.  FOr SF data, does the monthly measured data correspond to
gensky?

4. Is multiplying by 3 such a bad idea??

P.S.  THe only other option I used is -ab 1 for gensky,  with 
, of course the skyfunc glow values as given in the 
Radiance tutorial . (Cindy Larson)i as follows:

skyfunc glow sky_glow
0
0
4 .9 .9 1 0

sky_glow source sky
0
0
4 0 0 1 180

( Yes, the glow problems, requiring ab=1, are known here - P.)

As far as I (P.) understand, the basic problem we have is:
	a) we don't use the options correctly (unlikely)
	b) we don't understand some basic principles (well...)
	c) CIE is stuffed and/or requires local adjustments

cheers
Anne , Peter

-- 
 Peter Apian-Bennewitz	apian@ise.fhg.de  +49-761-4588-[123|302] 
 Fraunhofer Institute for Solar Energy Systems, D-79100 Freiburg


Date: Thu, 24 Feb 94 12:13:44 PST
From: greg (Gregory J. Ward)
To: apian@ise.fhg.de, kovach@ise.fhg.de
Subject: Re:  gensky (take #645)

Hi Peter and Anne,

The problems you are experiencing with gensky are probably due to the
absolute difference between the zenith and solar radiances computed by
the program and those of your TRY data.

Daylight is a highly variable quantity, as you must know.  Even if the CIE
sky distributions were good approximations of realy skies (which they are
not), the variation in absolute brightnesses is going to make for very
poor agreement between measurements and simulations.

The best thing to do is to use the -r (or -R) and -b (or -B) options of
gensky to calibrate the absolute levels to match your weather data.
Otherwise, gensky is going to use some default assumptions about atmospheric
turbidity and mean solar brightness to come up with highly approximate
brightness values.

Note that a new option has been added to gensky in version 2.3 for the
modeling of so-called "intermediate" skies.  This may be more appropriate
for many of your daylight conditions in Germany than either the default
clear or overcast model.

In the process of implementing this option, I also managed to wreck the
calculation of ground plane brightness, and you should pick up the repaired
version of gensky.c from hobbes.lbl.gov in the /pub/patch directory.
However, from the description of your problem, the ground plane brightness
is probably not the source of your disagreement.

I hope this helps!

-Greg

From: apian@ise.fhg.de
Subject: Re: RGB nm values ?
To: greg@hobbes.lbl.gov (Gregory J. Ward)
Date: Fri, 25 Feb 1994 15:33:53 +0100 (MEZ)

Hi Greg,

about gensky/CIE:

(before you say "read my lips", I read your last mail... )

after a cross-check with x11image.c and falsecolor.csh,
everyone here is convinced that the average (il)luminance has to be 
the weighted average of the RGB channels (and NOT the sum).
(we had this discussion already)

Ok, - so the CIE are aprox. a factor 3-6 too low. 
Question: Do you know from other chaps who checked gensky against
reality and what's the factor between these too ?
If gensky is good enough for Berkeley weather, a factor of 6
for Freiburg seems to be far out.
6 is for average monthly radiance, 3 is for daily luminance, both
global radiation on a horizontal surface.

as always, many TIA
Peter

-- 
 Peter Apian-Bennewitz	apian@ise.fhg.de  +49-761-4588-[123|302] 
 Fraunhofer Institute for Solar Energy Systems, D-79100 Freiburg


From: apian@ise.fhg.de
Subject: anne's factor
To: gjward@lbl.gov (Greg Ward)
Date: Fri, 25 Feb 1994 17:49:30 +0100 (MEZ)

seems to be more on the 1.5 - 2.0 side, not so much a factor 6.
user error gone unchecked. crunch.

-- 
 Peter Apian-Bennewitz	apian@ise.fhg.de  +49-761-4588-[123|302] 
 Fraunhofer Institute for Solar Energy Systems, D-79100 Freiburg


Date: Fri, 25 Feb 94 08:58:19 PST
From: greg (Gregory J. Ward)
To: apian@ise.fhg.de
Subject: Re:  anne's factor

I recently compared gensky's values to San Diego weather averages, and
the gensky values seemed to be lower than measured averages by about 30%.

The low values from gensky are probably due to a too-high turbidity value.
You can lower it to correspond better with your weather, but the best
way to proceed (as I said before) is to plug in your own values for
zenith and solar radiance.  There is no other way to get good correspondence
with measurements.

-G

From: kovach@ise.fhg.de
Subject: Radiance
To: greg@hobbes.lbl.gov
Date: Fri, 4 Mar 1994 11:50:18 +0100 (MEZ)

Hi Greg,

Thanks for your help and comments with gensky.  I am presently 
investigating the effect of the individual parameters -R, -b and
-t on the output of gensky in comparison with a Freiburg climate.

In comparing the monthly values of Freiburg TRY weather data,
the highest discrepancy between gensky +s and Freiburg TRY
using the default values was 34 %, where TRY global horiz. was 34 %
higher than gensky's values.  The lowest amount of discrepancy occurred 
in Dec where TRY was only 8% higher than gensky.  For the 
other options with no direct source, the TRY values were approx.
70-80 percent higher than those values generated by gensky.

Since  I dont want to blindly plug in different parameters that
dont make any physical sense, I took a look in the source code
for gensky.   I also
took a look at Superlite since it also uses a CIE sky distribution.
There was a list of turbidity factors in the Superlite manual
and the factors all seemed to
be lower than 1.   Therefore I only have 2 questions.

1) Did you use a specific turbidity model to estimate
the turbidity factor? (eg. Linke Turbidity Factors?) What are
the units in this case? (or are there no units?)

2) Could you recommend a reference where I could take a look
at to get a better understanding of the  meaning of the different
values of these parameters and to help explain the role of these
factors in the gensky model?
Unfortunately Freiburg is not as full of bookstores as Berkeley!
-- a great disadvantage!

Your helpfulness is really appreciated.

Ciao,
Anne

Date: Fri, 4 Mar 94 09:51:41 PST
From: greg (Gregory J. Ward)
To: kovach@ise.fhg.de
Subject: Re:  Radiance

Hi Anne,

I am disappointed to hear that your sky measurements are in disagreement
with gensky's output.  The default turbidity factor (reported by
"gensky -defaults") is 2.75.  This is Linke's turbidity factor, which by
its place in our equation should have units of kcd/m^2.  It is quite
probable that a higher turbidity factor is called for in your climate.

The formulas I use in gensky can be found around line 200 in gensky.c:

                if (overcast)
                        zenithbr = 8.6*sundir[2] + .123;
                else
                        zenithbr = (1.376*turbidity-1.81)*tan(altitude)+0.38;
                if (skytype == S_INTER)
                        zenithbr = (zenithbr + 8.6*sundir[2] + .123)/2.0;

For an overcast sky, I think I use the same formula used in SUPERLITE.  I
wish I knew where it came from, especially since it's so far off from your
measurements.  Perhaps this is not too surprising, though, since cloud
cover varies considerably and one overcast day can be MUCH darker than another.

For the clear sky luminance, I use the formula reported in a 1984 paper by
Karayel, Navvab, Ne'eman and Selkowitz (Energy and Buildings, 6, pp. 283-291).
This formula is apparently a simplified version of one proposed by Dogniaux
relating turbidity to zenith luminance, and the factors were determined
empirically from measurements of clear skies over San Francisco.  Again, it
may not be the most appropriate formula for your area.

For intermediate skies, a recent addition to the program, I had no idea
what to use for the zenith luminance so I just averaged the clear and
overcast brightnesses together.

Let me just emphasize once more that sky conditions and luminance patterns
are highly variable, and predicting them is not an exact science.  Obviously,
the formulas used in gensky could use updating, and I've been trying to find
an opportunity to do that.  A lot of good data has been gathered by your group
and others as part of the IEA International Daylight Measurement Year, and
some of this data has even been digested and fitted to more advanced sky
models.

As I said before, the best you can do is to use your own values for
zenith luminance (or the equivalent ground plane illuminance) and go
from there.  Even doing this, I think the standard CIE clear sky formula
is starting to show its age.  I should really be replaced by something
that correlates better to real skies.

If you want to use gensky's calculation of clear sky luminance for some
reason, just adjust the turbidity factor up by 30% or so until the zenith
luminances more closely match your measurements.  There is nothing you
can do other than override the default luminance value for overcast
skies.  Again, this is what I recommend you do for all sky types, anyway.

-Greg

==========================================================================
COMPILE PROBLEMS

Date: Thu, 3 Mar 94 15:14:38 +0100
From: Education <lucius@arch.ethz.ch>
To: greg@hobbes.lbl.gov
Subject: fun with a compiler

Hi Greg !

Don't know if you still remember me, but I'm still working hard bringing
Radiance to different plattforms. I don't know, if I told you, but at
the moment I trying to compile it on a Intel Paragon, a 100 processor
machine, that is supposed to be really fast. I finally got the accont,
but now I have several problems with the compiler.  For example, the
Paragon doesn't know the call of CLK_TCK (it occors in rpict.c: 155, so
I have to solve this problem). What happens, if I set to a fixed value,
does the programm still work propably.
Another question is, why do you define
	 -DDCL_ATOF -DALIGN=double
Is that really nessesary for every compiler or just for a specific one.

And a last one: Since I only want to use the Paragon as a number
cruncher, I only need to run rpiece ( and so I guess rpict ). Do you
have any makefile, that is creating only the basic parts of Radiance,
that would save me a lot of time. My problem is, that I don't know
enough about your programm structure to remove single parts of the
Rmakefiles

			thanks a lot, 	Daniel
					c\o Prof. Schmitt
					Architektur & CAAD
					HIL D 74.3, CH- 8093 ETH Zuerich					E-Mail 	lucius@arch.ethz.ch
				phone	+41 1  633 29 20

Date: Thu, 3 Mar 94 16:03:51 +0100
From: Education <lucius@arch.ethz.ch>
To: greg@hobbes.lbl.gov
Subject: a few more questions

Hi greg !

Here are a few more questions  

1. Very often I get the following message. Do I have to take care of it ?

PGC-W-0118-Function ebotch does not contain a return statement (calexpr.c: 274)
PGC/Paragon Paragon Rel 4.1.1: compilation completed with warnings

2. Why do you redefine fabs:

PGC-W-0221-Redefinition of symbol fabs (./defs.h: 346)
PGC/Paragon Paragon Rel 4.1.1: compilation completed with warnings

3. Even more often I get :

PGC-W-0095-Type cast required for this conversion 

Is that a special problem with the Paragon compiler or is it because of
the complier options I told you about within the other E-Mail

						Thanks, Daniel

Date: Thu, 3 Mar 94 11:12:16 PST
From: greg (Gregory J. Ward)
To: lucius@arch.ethz.ch
Subject: Re:  fun with a compiler

Hi Daniel,

The problem with CLK_TCK being undefined has been repaired, and the new
version of rpict.c is in the /pub/patch directory on hobbes.lbl.gov.
I found out after I wrote this code at the insistence of Peter Apian
that there are many different ways that so-called System-V compatible
and POSIX-compatibe UNIX implementations handle this stupid problem.

The -DDCL_ATOF definition is usual for systems that declare atof()
as double but don't necessarily put it in math.h.  If atof() is declared
as something strange or is a macro, then this option is left off.
The -DALIGN=double is needed for proper compilation of the memory
allocation routines (common/*alloc.c) on RISC architectures.  Older
CISC machines usually use int as the alignment type, which is the default.

The warnings you are getting can probably be safely ignored.  You no doubt
have an ANSI-standard C compiler on the Paragon.  Radiance predates ANSI
C, so you should find a way to switch off function prototypes if you want
the warnings to go away.  Some ANSI compilers offer a -cckr option for
"Kernighan and Ritchie" standard, which is the original standard and the
one to which Radiance adheres best.

Hope this helps.
-Greg

==========================================================================
GLASS BRICKS

Date: Fri, 4 Mar 94 11:20:25 WST
From: crones@puffin.curtin.edu.au (Simon "fish" Crone)
To: greg@hobbes.lbl.gov
Subject: Re:  Street Scapes

Hi Greg,

	Thanks for the information.  Don't worry about the Ove Arup slide or
the San Francisco images, but I would like to see your nighttime roadway 
simulation.  Would you mind putting it up on your ftp server?

Also ( I forgot to mention it yesterday ), have you, or do you know of
anyone else, who has tried to model a glass block wall?

I have basically been modeling each brick individually using a rippled
glass texture for the front and back sides of each block and then a white
mortar in between.  The problem with this is that the inside 'walls' of
the glass block, ( ie. the mortar ), appear quite dark ( as they are in
shadow ).  I don't particulary want to make the far side glass block a
light source ( ie illum ) as there are so many glass blocks.
Any clues?

Simon.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|                                                                              |
|                       Simon Crone - Masters Student                          |
|                                                                              |
|          School of Architecture, Curtin University of Technology,            |
|                GPO Box U1987, Perth, Western Australia 6001                  |
|         Phone:+61-9-351-7310 Internet:crones@puffin.curtin.edu.au            |
|                                                                              |
|                   "He who dies with the most toys wins!"                     |
|                                                                              |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Date: Fri, 4 Mar 94 08:59:12 PST
From: greg (Gregory J. Ward)
To: crones@puffin.curtin.edu.au
Subject: Re:  Street Scapes

Hi Simon,

I just happened to have the roadway simulation in an 8-bit Sun rasterfile
(your favorite format), which I compressed and put on my ftp server in
the /xfer directory.  The file is called "road.ras.Z".

As for your glass blocks, what material are you applying to the surfaces?
Are you really using the type "glass", or are you using "dielectric" or
something else.  I would recommend that you use either "glass" or "trans",
since these materials have a special property which allows light to pass
through them directly even if they have a texture also.  Dielectric, though
it may be more realistic, does not allow light to pass through without being
refracted, and this refraction usually messes up the direct calculation in
the way you described.

A single glass or trans surface at the front and back (and sides if you like,
though you should make sure to leave a small gap between your bricks and your
mortar if you do this) should work.

-Greg

==========================================================================
AMBIENT VALUES

Date: Fri, 25 Mar 94 09:23:57 GMT
From: jon@esru.strathclyde.ac.uk (jon)
To: mdonn@arch.vuw.ac.nz, greg <greg@hobbes.lbl.gov>
Subject: ambient values query

Mike Donn and/or Greg Ward,

We are having a debate here over the use of ambient values.  The sky
file includes a ground ambient and with outside views the inclusion of
these values in the "-av" option of rpict seems to work quit nicely.

Question is - in an inside view which has ONLY daylighting and direct
sun penetration I am assuming that I should include the same -av
values.  Some of the students complain that this gives high lux
values.  No, I have not gotten around to pulling across the new release
but it is on my todo list.

Our desktop/converter e2r scans the sky file and picks up the ground
ambient values and uses them in rpict calls unless the user overrides
it.  Any opinions?

Regards,

Jon Hand

Date: Fri, 25 Mar 94 08:37:25 PST
From: greg (Gregory J. Ward)
To: jon@esru.strathclyde.ac.uk
Subject: Re:  ambient values query
Cc: mdonn@arch.vuw.ac.nz

Hi John,

You are correct in using the ambient value suggested by gensky for exterior
views, but your students are correct that it is too high for interiors.
In fact, setting this parameter correctly is not easy to do automatically.
You would have to perform some sort of zonal cavity approximation to find
out how much average light (excluding sources) you have bouncing around
your interior.

The method I've found to be most effective is the one incorporated in the
new "rad" program distributed with release 2.3.  It takes an exposure value
as determined by the user, and computes the ambient value from that.  The
user is still charged with finding the right exposure, but once that's done,
the rest is automatic.

(The computation of ambient value from exposure is simply 0.5/exp_mult.)

-Greg

==========================================================================
LOCK MANAGER

From: sjain@arch2.engin.umich.edu
Date: Fri, 1 Apr 94 09:24:58 -0500
To: greg@hobbes.lbl.gov
Subject: Storing Indirect Illuminance Values in a File

Thanks for the advice with the "RAD" program.  I am trying to write the
indirect illuminance values to a file by using the "-af" option in RPICT.
Even though RPICT opens the file with read/write permissions there is the
following error:
  rpict: system - cannot (un)lock ambient file: Invalid argument

I am using the following RPICT options
  rpict -vtv -vp 33 -16 1.76 -vd -11 3 0 -vu 0 0 1 -vh 60 -vv 60
  -x 300 -y 300 -pa 1 -ab 1 -af rokko_ab -t 0 rokko2.oct | pfilt >
  /users/sjain/rokko2.pic

Please advice.

- Shailesh

Date: Fri, 1 Apr 94 09:03:24 PST
From: greg (Gregory J. Ward)
To: sjain@arch2.engin.umich.edu
Subject: Re:  Storing Indirect Illuminance Values in a File

Dear Shailesh,

Sounds like your on a machine with a completely broken lock manager.  I
noticed this behavior before.  There is a file called BUGS in the top
directory on the anonymous ftp account of hobbes.lbl.gov.  Here's what
it has to say:

			KNOWN BUGS AND WORKAROUNDS

Silicon Graphics:

	The network lock manager seems to be broken on release 5.1.1.1
	of IRIX, and therefore rpict, rtrace and rview will not be able
	to share ambient files while running simultaneously.  Also,
	rpiece will not work.

System V derivative UNIX's:

	The network lock manager in general seems to be unreliable on
	most SGI's, so rpiece may abort with strange results.  I haven't
	a clue how to fix this, as it appears to be an operating system
	defect.  Please take the time to complain to your vendor if you
	run into this problem.  It's going to take a lot of people
	coming to them before they're likely to do anything about it.

	If the renderers give you some message about not being able
	to lock or unlock a file, you can add the following line
	to the end of src/common/standard.h as a last resort:

	#undef F_SETLKW

	This should remove all the dependent code, killing
	rpiece in the process.


I can only hope they will fix this problem in coming releases.  I do
encourage you to register a complaint.

-Greg

==========================================================================
SPECKLE

From: "Mr. A. Morris" <jabt282@liverpool.ac.uk>
Subject: radiance query
To: greg@hobbes.lbl.gov
Date: Mon, 11 Apr 1994 15:32:51 +0100 (BST)

Greg

I don't know if you remember answering my queries last autumn I've been
using radiance for several months now and have found it very useful 
especially since the addition of the rad function in the latest version.

Receintly however I've been having difficulties producing clean images
which I know it is capeable. I've enlarged a model which previously 
produced very good images, increasing the complexity of the model. the 
model now has several thousand objects and renders well except that
round objects inthe scene (which previously rendered giving smooth shading)
now have a speckled appearance which is very pronounced. the flat elements
all seem to be rendering as normal although as the columns and other round
elements are created on autocad they are actually faceted. I've tried rendering
these round elements alone and they work fine.
Have you got any suggestions?

Alex Morris Liverpool Uni.

Date: Mon, 11 Apr 94 10:02:58 PDT
From: greg (Gregory J. Ward)
To: jabt282@liverpool.ac.uk
Subject: Re:  radiance query

Hello Alex,

There are three possible sources of the artifacts you are seeing:

1. You are using an outdated release of Radiance where I was using an
inaccurate calculation for sphere intersections.  This bug has existed
since the dawn of Radiance, but only recently became noticeable as people
started working on very large models with very small spheres.  It was
fixed last November, well in time for release 2.3.

2. You are seeing the result of Monte Carlo sampling for the rough specular
(i.e. directional-diffuse) component, which can show up as speckles under
certain circumstances.  You can mitigate this effect using the new -m option
of pfilt, or by increasing -st above the specularity of your surface or
decreasing the -sj parameter.  The latter two approaches diminish image
accuracy, however.

3. You have answered "yes" to the question about rendering huge models during
the Radiance makeall build, thus causing -DSMLFLT to appear in the rmake
script used to compile the programs.  As it warned you, there are sometimes
errors in the intersection calculations that result from using this option,
and as a general rule I don't recommend it.  I have since taken out this
question, so the next release will have to be hacked to compile with short
(4-byte) floats.  To go back to double-precision data values, run
"makeall clean" followed by removing the rmake command from your Radiance
executable directory (/usr/local/bin by default), followed by "makeall install".
This time, answer "no" when it asks you if you plan to render huge models.

Hope this works.
-Greg

==========================================================================
OBJVIEW

Date: Fri, 15 Apr 1994 09:40:04 -0600 (MDT)
From: Ric Wilson <rwilson@boi.hp.com>
Subject: Radiance question
To: GJWard@lbl.gov

This is probably a stupid question, but how do render the sample .oct
scenes in the radiance package?  I get the warning that there is no light
source and then a black picture.  Any help would be greatly appreciated.

Ric Wilson
rwilson@boi.hp.com

Date: Fri, 15 Apr 94 09:16:50 PDT
From: greg (Gregory J. Ward)
To: rwilson@boi.hp.com
Subject: Re:  Radiance question

Hi Ric,

The sample octrees are meant to be included in other scenes as instances
using the "instance" primitive type.  If you want to render them by
themselves, I suggest you use the following rather tortured command line:

	% objview '\!echo void instance example 1 example.oct 0 0'

You may do this from any directory and it should work so long as your
RAYPATH variable is set to search the location containing the actual
octree ("example.oct" in this example).

Objview is a generaly useful script that adds a few light sources and
a background to a scene or object, puts it in an octree and starts rview
on it.  The source to this script may be found in ray/src/util/objview.csh.
There is a manual page, also, but it doesn't say much.

-Greg

P.S.  A question is only as stupid as its answer.

==========================================================================
CSG

From: cloister bell <cloister@u.washington.edu>
Sender: cloister bell <cloister@u.washington.edu>
Reply-To: cloister bell <cloister@u.washington.edu>
Subject: complex objects in radiance.
To: greg@pink.lbl.gov

hi there.  i've been using radiance for a month or so now, and thought i'd
offer some comments and ask a question.  overall, i'm terribly impressed
with radiance.  it does lighting so well that i'm not seriously tempted to
switch back to anything like povray or rayshade.  but there are some 
things which were a lot easier in pov and rayshade that are giving me 
fits in radiance:

1. there doesn't seem to be any comprehensive documentation source for 
   all the math that radiance seems capable of.  for example, i'm 
   constantly seeing hermite(....) being used in scene description files, 
   but it took forever to find out (by looking in rayinit.cal) that it 
   was a library function.  and i wasn't able to find out anything more 
   than that.

2. the documentation for surface property definition/declaration is 
   pretty sparse.  most of what i've been able to do i had to learn by 
   looking at other people's sample files.  while this works, no one ever 
   bothers to comment their example files it, which means i'm left with a 
   lot to guesswork and hocus pocus in my files.

3. not being able to group objects into larger objects for composite 
   solid geometry is making life hard.  it wouldn't be a problem except 
   that intersecting antimatter volumes create problems.  for 
   example, short of using heightfields (which i really want to avoid for 
   performance reasons), i can't think of a way of making the 90 degree 
   fillets at an inside corner of a cube meet smoothly.  the obvious 
   thing to is to use 3 mutually orthogonal antimatter cylinders and a 
   sphere such that the center of the sphere is also one of the endpoints 
   of each cylinder.  of course, the overlapping antimatter makes big 
   black spots on my image.  i tried just using an antimatter rounded 
   box from genbox, but of course that didn't do what i wanted at all. am i
   missing something really obvious?

i hope that the problems i'm having have simple solutions that have 
already been explained in some document that i managed not to get.  but 
if that isn't the case, could you give me some hints?  i anticipate doing 
a lot more work with radiance, and any advice you could give that would 
make my life easier would be greatly appreciated.  thanks,

jason.


Date: Fri, 15 Apr 94 19:43:25 PDT
From: greg (Gregory J. Ward)
To: cloister@u.washington.edu
Subject: Re:  complex objects in radiance.

Hi Jason,

The only other documentation you might be missing is the User's Manual in
the mac.sit.hqx file in the ray/doc directory.  You'll need a Macintosh
with StuffIt and Microsoft Word to print it out, but there's a lot of
good examples and information in there.  It's a bit out of date, and not
100% error-free, but it's all we have at the moment.  I've been trying
to interest a publisher in sponsoring a book on Radiance, but so far I've
had no luck.  The documentation is lamentable, but there's been consistently
zero funding from the Department of Energy to do anything about it.

The problems with antimatter are numerous, and I generally don't use it
myself.  Complicated surfaces are best represented as (smoothed) polygons,
which can be produced nicely by the gensurf(1) or genrev(1) programs.
The additional cost in rendering time is much less than you'd expect,
thanks to the octree acceleration techniques employed in Radiance.

In fact, the only reason I created antimatter was to cut windows out of
walls and the like for CAD programs that work that way.  Also, if you
absolutely must have an accurate sphere with a section missing, antimatter
is the only way in Radiance.

I can't say for certain, but I have a hunch that the additional intersections
and overhead associated with CSG would outweigh any advantage you might
get from simplifying the geometric model in this way.  Also, for the scenes
Radiance is usually used to represent (architectural lighting), CSG is
not really necessary.

Are you really doing all this nasty geometry in the scene file itself?
I thought I was the only one stubborn enough to do that...

On the bright side, I've almost finished a Wavefront .obj to Radiance
file translator, which might make a few things easier.

-Greg

Date: Fri, 15 Apr 1994 22:44:07 -0700 (PDT)
From: cloister bell <cloister@u.washington.edu>
Subject: Re: complex objects in radiance.
To: "Gregory J. Ward" <greg@hobbes.lbl.gov>

> The only other documentation you might be missing is the User's Manual in
> the mac.sit.hqx file in the ray/doc directory.

ok.  i'll check it out.

> Are you really doing all this nasty geometry in the scene file itself?
> I thought I was the only one stubborn enough to do that...

yep.  i do better with doing the geometry in my head and on paper than in 
trying to use front end modelers
 
> On the bright side, I've almost finished a Wavefront .obj to Radiance
> file translator, which might make a few things easier.

cool.  thanks.
jason.

==========================================================================
RAD PROBLEMS

[The conversation starts with my thanking Veronika Summeraur for her
work on the HTML manual pages.  Her questions on rad follow in her response.]

Date: Wed, 13 Apr 94 11:49:23 PDT
From: greg (Gregory J. Ward)
To: summer@arch.ethz.ch
Subject: man pages

Hi Veronika,

Thank you so much for translating the Radiance 2.3 manual pages to HTML
format.  They look GREAT!

Raphael told me about them, and I just loaded them on our WWW server
(ftp://hobbes.lbl.gov/www/radiance/radiance.html).

How did you do it?  There was obviously a fair amount of work just in
specifying the links and everything, but you surely must have a program
of some sort to convert nroff-formatted text into HTML.  Anyway, the
results are terrific!

Thanks a million!
-Greg

Date: Sun, 17 Apr 94 06:06:13 +0200
From: summerauer veronika <summer@arch.ethz.ch>
To: greg@hobbes.lbl.gov
Subject: Re: man pages

hi Greg,

thanks for your mail - it's really good to hear that you liked this 
html-stuff i did.

> How did you do it?  There was obviously a fair amount of work just in
> specifying the links and everything, but you surely must have a program
> of some sort to convert nroff-formatted text into HTML.  

the tutorial and the reference manual i did 'by hand' i.e. using a vi i 
have customized with a lot of macros, which make the insertion of html-
tags quite comfortable and fast (though very cryptic ;-). for the manual 
pages i modified one of the man2html Perl scripts that are availabe on 
the Net, but still had to do some editing by hand (since i have no 
experience in programming perl, and the scripts did not meet all my needs 
regarding formatting).

as we do not have a www server at our site (i cannot use <ISINDEX> search), 
i worked on your digests as well - inserting named anchors for each 
topic, and created a 'list of keywords' document (currrently it is sorted 
alphabetically, maybe i'll add one sorted by topics...), which allows you
to access the digests by topic, not 'by date/version'. if you are interested,
i can upload those files to hobbes.



i'd like to add some questions on Radiance to this mail - i had planned to
ask you before but never got to actually write an e-mail.

maybe you remember - i am (still) working on an AutoCAD extension program,
which is used as a graphical interface to Radiance. currently i'm updating
the first version which has been used by students here during the last two
months. i think the results were pretty good (though the interface is
not yet very stable and has lots of bugs) - you might ask Florian 
(wenz@arch.ethz.ch) in case you would like to see some of the final images.
everyone who started to work with Radiance here is very enthusiastic about
your software and the possibilites it offers to examine and visualize
architectural projects.

my questions are related to the 'rad' program, which i use to start the
rendering process after the AutoCAD user has selected the preferred
settings for sun, sky, ambient light, viewpoint, quality ...

1) oconv:
   i have noticed that most of the times the rad-program executes the 
   oconv command twice.
   i think that this relates to the way the sun-definition is specified
   (using !gensky [options] in a seperate scene file, with one of the +s, 
   -s, -c and -u options besides the specification of location and 
   date+time.)
   (playing around with !gensurf i watched 'rad' rebuiling the octree 
   three (!) times before starting rpict or rview - that's why i think 
   it is related to !gen[something].)
   when the size of the octree is rather big (2 to 5 Mbyte), this slows 
   down the process a lot, especially if the user chooses the option for 
   'preview' (-> rview). 
   can you give me any clues on when and why the oconv program is applied 
   more then once?
   
2) scene= /object=
   the translation of an AutoCAD drawing/scene is organized according to
   entity color or layer structure. This may result in many different
   scene files (one per color/layer), which 'rad' takes as arguments for
   the oconv command. i repeatedly had the problem that the length of the 
   oconv command exceeded a limit of maximal string length (?), i guess that 
   comes from the bourne shell or csh (i use both).
   i tried to work around the problem by maintaining a scene master file, 
   (!cat filename.rad for each seperate scene file), and specifiying the
   scene files as objects, but i still have the same problem if i use
   'rad' to create a complete rif-file (-n and -e option), as 'rad' places
   all objects on one line, which again exceeds a builtin limit. the result
   is that the rif-file is incomplete and cannot be used again with 'rad'.
   currently i no longer specify the scene files as scene= or objects= for
   'rad', but try from inside AutoCAD to keep the scene master file as 
   up-to-date as possible. 
   i know that i could use 'make' as an intermediate step to create/rebuild
   the octree but i am still looking for a solution with 'rad'. 
   
   ( BTW - we am working with Sun sparc2 / SunOS 4.1.3 
                          and SGI Indigo / IRIX 4.0.5H )

3) ambientfiles
   what exactly are the parameters which are considered by 'rad' whether
   to remove an already existing ambientfile or to re-use it? 
   (material definitions are kept in a seperate file, specified as 
    materials= project.mat in project.rif)
   
   
thanks in advance for any advice you can give.
veronika. 


Date: Sun, 17 Apr 94 10:15:15 PDT
From: greg (Gregory J. Ward)
To: summer@arch.ethz.ch
Subject: Re: man pages

Hi Veronika,

Yes, I would like very much to get the index you made for the Radiance Digests.
I will add it to my WWW server's digest page.  Please drop it off in the /xfer
directory on hobbes.lbl.gov.  Thanks!

Regarding your interface work, I would be very interested to see it at some
point.  We may be embarking on a project with the U.S. Federal Aviation
Administration (which controls air traffic in our country), writing a
graphical user interface for Radiance, possibly linking it to AutoCAD.

Anyway, I will try my best to answer your three questions:

1) In fact, rad does call the oconv() routine in two or three places, and
only the first call should cause the octree to be rebuilt.  The reason is
that oconv() checks the file modification times, and only rebuilds the
octree if the current one is out of date with respect to one or more of
the scene= or objects= files.  What I suspect is happening in your case
is that you are on a network of machines that disagree about what time
it is, and NFS doesn't resolve these differences.  Rad runs oconv() the
first time, creating an up-to-date octree, then calls it a little
while later and somehow the the system still says the octree is old.
The best way to solve this problem is to run the network time daemon on
your networked machines, so they can all agree about what time it is.
A secondary option is to manually synchronize your machines' clocks and
do this periodically as inaccuracies cause them to drift.  I will check
my code again to see if there is something I can do to circumvent the
problem within rad.

2) This is a problem I noticed as well, and I have put in a fix for the
next release.  In the meantime, the solution you have come up with seems
adequate.  There is a limit built into oconv as to the maximum number of
object files as well (63 according to my version of oconv.c), so fixing
the -e option of rad as I have done isn't a complete solution to the problem.
Beyond that, there is a limit to the length of a UNIX command line, though
I believe it is quite generous (on the order of 10k).

3) Ambient files are removed by rad whenever there is a change to any scene
or object file that causes the octree to be rebuilt, or if there is a change
to a materials file.  Basically, if anything about a scene changes, the
ambient file is no longer reliably valid.

Thank you again for all the great work you have done!

-Greg

