[Radiance-general] Antimatter and windows

[Zack Rogers]

Thanks for the insight Lars,

I had originally tried the box approach and moved onto the co-planar
surface approach as I felt like I was getting further.

Back to the box approach, I've been testing this out now on just a very
simple wall model and am seeing strange behavior.  From all viewing
directions, the shadow from my hole in the wall looks correct.  However,
when viewing the wall from one side it seems like I am seeing the inside
surfaces of my antimatter box as grey_0.60 but not the front surface.
At some view angles from the front side, the side of my antimatter box
disappear and I do get a glimpse through the wall.  From the other side
(shadow side), everything looks as I would expect.

http://docs.google.com/Doc?docid=0AcMF73k-1deIZGdkNmhja3BfOTdnejRjbTloaw
&hl=en
http://docs.google.com/Doc?docid=0AcMF73k-1deIZGdkNmhja3BfOTVjamR4YnZkMw
&hl=en
http://docs.google.com/Doc?docid=0AcMF73k-1deIZGdkNmhja3BfOTNmOHF6N2docA
&hl=en

The box was created with genbox and I double checked that all surface
normals are pointing outward.  I also tested other modifiers in my
antimatter definition and "void" and anything other than the wall
material did not do anything (disregard my earlier statement/question
about materials).

So several of my questions have been answered but there is still the
obvious artifacts in the rendering and I am still wondering about the
validity of this approach using rtrace.  Will it see random errors?

The file I am running for this test is:

void plastic grey_0.25
0
0
5            0.25          0.25          0.25
                0             0

void plastic grey_0.60
0
0
5             0.6           0.6           0.6
                0             0

void antimatter opening
1 grey_0.60
0
0

grey_0.60 polygon Space.10_Wall.38
0
0
12
    0.00    0.00    10.00
    0.00    0.00    0.00
    30.00    0.00    0.00
    30.00    0.00    10.00

!genbox opening hole 10 1 6 | xform -t 10 -.5 2

grey_0.25 polygon ground
0
0
12    -100    -100    -0.5
    100    -100    -0.5
    100    100    -0.5
    -100    100    -0.5

!gensky 3 20 10.5 -a 42.8326 -o 106.329 -m 105.0 +s | xform -rz 0.0

skyfunc glow skyglow
0
0
4 0.9 0.9 1.0 0

skyglow source sky
0
0
4 0.0 0.0 1.0 180

skyfunc glow groundglow
0
0
4 1.0 0.8 0.5 0

groundglow source ground
0
0
4 0.0 0.0 -1.0 180


________________________________

  ZACK ROGERS, P.E., LEED AP, IESNA 
 
INTEGRATED DESIGN ASSOCIATES, INC
437 Main Street
Longmont, CO 80501
tel: 303.848.8299, fax: 303.848.8290 
www.ideasi.com 

-----Original Message-----
From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Lars
O. Grobe
Sent: Wednesday, September 09, 2009 6:20 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] Antimatter and windows

Hi Zack,

the problem you experience appears any time when you have coplanar
surfaces with different modifiers. A ray hitting such a surface sees
either material, and as they are coplanar this results in a random noise
/ mixture of both.

To use antimatter, place a box in you wall, so that the front side of it
is in front of the wall (you would see it from your position) while the
back one is behind. Make sure that there is no other geometry in the
volume of this box.

Now what happens is that a ray hitting the antimatter material with the
surface facing it will become blind, go on traveling the same direction
(or modify it according to what you give in the second line of the
antimatter modifier's definition), and start seeing geomertry only once
he passed thru the back of an antimatter surface again. In other words,
it is like if the ray jumps between the antimatter surfaces ignoring
everything in between.

Hope this is correct, but that was the result of looking at that part of
the code once ;-)

Cheers, Lars.