[Radiance-general] Ambient mess

Wed, 12 Nov 2003 14:53:22 -0000

This is a multi-part message in MIME format.

------_=_NextPart_001_01C3A92C.B7AF3938
Content-Type: text/plain;
	charset="US-ASCII"
Content-Transfer-Encoding: quoted-printable

What I thought would be a straightforward night-time scene has turned
out not to be. The first two images at the link below shows a
conventional scene with the lights replmarks-ed in. All the lights are
based the same fitting, a Thorn Contrast C (33000lm).=20

http://uk.f1.pg.photos.yahoo.com/ph/bsounes/lst?.dir=3D/ambient_mess&.vie=
w
=3Dt

After doing a few test renders with just one light, a wall and a ground
plane I realized the splotchy areas beyond the site where the result of
the ambient calculation picking up the bright wall areas just below the
fittings. No extra ab's, ad's ,as's, extra ar or setting aa to 0 solved
the problem. The lamp is modeled as a 10mm sphere therefore source
sub-structuring didn't seem to be the issue either.=20

This suggested to me using mkillum to eliminate the gamble of the first
ambient bounce finding the bright surfaces: feed the brightest surfaces
to mkillum while retaining the original surface modifiers for the final
render. This involved switching to AutoCAD to 'radout' the polygons
(previously I was using .obj files), a degree of re-modelling , checking
the surface normals and splitting the model in two. The result (third
image: 'AlternativeA_pcond') is still less than satisfactory.

I experimented putting a void illum polygon a few millimeters in front
of the wall. A single bright splotch still appeared. There also seemed
to be a slightly different light distribution, which made me question
using opaque surfaces as illum sources.

An illum 'fence' could be spaced a distance from each building to try
and catch the splotches before they appear, but I haven't tried that
yet.

I am interested primarily in the final appearance of the image. The
illuminance beyond the site boundary is quite low - below 3 lux.=20

Does anyone have any suggestions?=20

Bruce Sounes

------_=_NextPart_001_01C3A92C.B7AF3938
Content-Type: text/html;
	charset="US-ASCII"
Content-Transfer-Encoding: quoted-printable

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =
charset=3Dus-ascii">
<META NAME=3D"Generator" CONTENT=3D"MS Exchange Server version =
6.0.6249.1">
<TITLE>Ambient mess</TITLE>
</HEAD>
<BODY>
<!-- Converted from text/rtf format -->

What I thought would be a straightforward night-time scene has =
turned out not to be. The first two images at the link below shows a =
conventional scene with the lights replmarks-ed in. All the lights are =
based the same fitting, a Thorn Contrast C (33000lm).

<P ALIGN=3DLEFT><SPAN LANG=3D"en-us"></SPAN><A =
HREF=3D"http://uk.f1.pg.photos.yahoo.com/ph/bsounes/lst?.dir=3D/ambient_m=
ess&amp;.view=3Dt"><SPAN LANG=3D"en-us"><U><FONT COLOR=3D"#0000FF" =
SIZE=3D2 FACE=3D"Courier =
New">http://uk.f1.pg.photos.yahoo.com/ph/bsounes/lst?.dir=3D/ambient_mess=
&amp;.view=3Dt</FONT></U></SPAN><SPAN LANG=3D"en-us"></SPAN></A><SPAN =
LANG=3D"en-us"></SPAN></P>
<BR>

After doing a few test renders with just one light, a wall and a =
ground plane I realized the splotchy areas beyond the site where the =
result of the ambient calculation picking up the bright wall areas just =
below the fittings. No extra ab&#8217;s, ad&#8217;s ,as&#8217;s, extra =
ar or setting aa to 0 solved the problem. The lamp is modeled as a 10mm =
sphere therefore source sub-structuring didn&#8217;t seem to be the issue either. =

This suggested to me using mkillum to eliminate the gamble of the =
first ambient bounce finding the bright surfaces: feed the brightest =
surfaces to mkillum while retaining the original surface modifiers for =
the final render. This involved switching to AutoCAD to =
&#8216;radout&#8217; the polygons (previously I was =
using .obj files), a degree of re-modelling , checking the surface =
normals and splitting the model in two. The result (third image: =
&#8216;AlternativeA_pcond&#8217;) is still less than =
satisfactory.

I experimented putting a void illum polygon a few millimeters in =
front of the wall. A single bright splotch still appeared. There also =
seemed to be a slightly different light distribution, which made me =
question using opaque surfaces as illum sources.

<P ALIGN=3DLEFT><SPAN LANG=3D"en-us"><FONT SIZE=3D2 FACE=3D"Courier =
New">An illum &#8216;fence&#8217; could be spaced a distance from each =
building to try and catch the splotches before they appear, but I =
haven&#8217;t tried that yet.</FONT></SPAN></P>

I am interested primarily in the final appearance of the image. The =
illuminance beyond the site boundary is quite low - below 3 lux. =

<P ALIGN=3DLEFT><SPAN LANG=3D"en-us"><FONT SIZE=3D2 FACE=3D"Courier =
New">Does anyone have any suggestions?</FONT></SPAN><SPAN =
LANG=3D"en-us"> </SPAN></P>

<P ALIGN=3DLEFT><SPAN LANG=3D"en-us"><FONT SIZE=3D2 FACE=3D"Courier =
New">Bruce Sounes</FONT></SPAN></P>
<BR>

</BODY>
</HTML>
------_=_NextPart_001_01C3A92C.B7AF3938--