[Radiance-general] gensky question

[Bleicher, Thomas]

Hi Chris.
 
I never checked the angles gensky prints but I remember that Radiance
understands "+" as west and "-" as east. (Remember that it was written
in and for America and it's always good for your ego to have a "+"
associated
with you ;) So the output should be fine. You can check the output of an
hourly
cycle to see how the value changes.
 
Your main problem can be solved by using a file with the diffuser as a
vertical
plane at a position "south" of the origin and "!xform" it into place
with the altitude
and azimuth as arguments for the "-ry" and "-rz" options:
 
!xform -ry <altitude*-1> -rz <azimuth*-1> diffuser.rad
 
The order of -ry and -rz is important!  
 
To model the "perfect diffuser" have a look at Schorsch excelent
explanation
of the trans material at
 
http://www.schorsch.com/rayfront/manual/transdef.html
 
If I understand you right you want a material with 100 % diffuse
transmittance.
I'm not sure Radiance does this correctly as it is physically imposible
but it's
worth a try.
 
Have fun,
Thomas
 



  _____  

From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Chris
Foster
Sent: 24 July 2006 13:39
To: Radiance general discussion; Radiance general
Subject: [Radiance-general] gensky question



Hi Everybody,

I have an aim to find out the luminance of the sun after it hits a
perfect diffuser. I'm sure i have done this the very long way round, but
at least this step by step way i understand what is going on.

I have used gensky to create a sun, and have created a sky and a ground
(see bottom).

Aside question- the default for meridian using gensky is -120, and as im
in london i have put my meridian to 0. this seems to give me a negative
azimuth angle for my early morning sun and a positive for my afternoon
sun. this means that the sun is rising in the west and setting in the
east....im sure its the other way round?????????? the first four lines
of the 10am automatically generated gensky file can be seen below
# gensky 07 24 10 -a 52 -o 2 -m 0 +s
# Local solar time: 9.76
# Solar altitude and azimuth: 48.8 -52.0
# Ground ambient level: 18.3

I have created different files for the sun throughout one day, started
and finishing at 7, so that i have 13 different sun's.
I have then oconv each file to my material file, found a nice view
directly at the sun for each time in rview and then rendering the image
in rpict and finally pcond each image with a -h- option to get a good
exposure level. So i have 13 images all looking directly at the sun.
When i then click on a point and press l it gives me a value for (i
think????) luminance.

I now want to place a perfect diffuser with a normal pointed directly at
the sun in each of these 13 positions and measure the illuminance
reflecting off of the diffuser. My big question is, how do i orientate
the diffuser so that it is normal to the sun each time, and any
recommendations as to what material/values i should make the diffuser
from??

My sky.mat file just for completion

skyfunc glow sky_glow
0
0
4 1 1 1 0

sky_glow source sky
0
0
4 0 0 1 180

skyfunc glow ground_glow
0
0
4 1 1 1 0

ground_glow source ground
0
0
4 0 0 -1 180

# ground plane

void plastic ground_mat
0
0
5 .28 .18 .12 0 0

ground_mat ring groundplane
0
0
8 0 0 -.01
  0 0 1
  0 30

Thanks

Chris




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