Hi,
I m planning to create an interactive walkthrough model of a building.
To improve the visual appearance I thought it might be a good idea to
generate illuminated textures.
I know people have done this using radiosity solutions getting quite good
results for example in games engines....
I was wondering if anyone has done this using radiance ???
My idea was to use orthogonal cameras in front of every flat surface, render
the whole scene in radiance from that viewpoint
and then apply the rendered image as a texture back to the surface.
I know this would work only properly on view independent reflectance
materials but anyway has anyone tried ?
Bernhard
···
--
Bernhard Spanlang,
Department of Computer Science,
University College London,
Gower Street,
London WC1E 6BT,
email: b.spanlang at cs.ucl.ac.uk
url: http://www.cs.ucl.ac.uk/staff/b.spanlang
tel: +44 (0)20 7679 3673
fax: +44 (0)20 7387 1397
Bernhard
I have done something similar although it was only a simple model as a test.
I started as yourself with parallel images of each surface. The model was a
12' cube with one window in the south wall. Once I had those six images I
then used the .jpg's and positioned them in a VRML environment such that I
could walk around the model. I appreciate that does not solve the
illuminated surfaces question but may offer an alternative.
I plan to produce a more complex model but the issue is one of the time to
set up each camera. For example if you have drawn 6 columns, each made up
of 8 facets then for the columns alone you would need 48 cameras. Also
another problem although I have not yet put any thought to the solution
would be if you had say a sloped roof and therefore none rectangular
surfaces. I think the ideal would be a C++ program which examined a .dxf
file and read in each surface and outputed a view file of all of the cameras
needed. I think this is possible unfortunatly time is limited.
An alternative may be a quicktime or similar panoramic. There are some good
examples available but alas I do not have access to my favourites at the
moment.
I hope that is of some help.
Andrew
···
-----Original Message-----
From: Bernhard Spanlang [SMTP:[email protected]]
Sent: 20 March 2002 10:26
To: radiance-general
Subject: [Radiance-general] light maps in radiance
Hi,
I m planning to create an interactive walkthrough model of a building.
To improve the visual appearance I thought it might be a good idea to
generate illuminated textures.
I know people have done this using radiosity solutions getting quite good
results for example in games engines....
I was wondering if anyone has done this using radiance ???
My idea was to use orthogonal cameras in front of every flat surface,
render
the whole scene in radiance from that viewpoint
and then apply the rendered image as a texture back to the surface.
I know this would work only properly on view independent reflectance
materials but anyway has anyone tried ?
Bernhard
--
Bernhard Spanlang,
Department of Computer Science,
University College London,
Gower Street,
London WC1E 6BT,
email: b.spanlang at cs.ucl.ac.uk
url: http://www.cs.ucl.ac.uk/staff/b.spanlang
tel: +44 (0)20 7679 3673
fax: +44 (0)20 7387 1397
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http://www.radiance-online.org/mailman/listinfo/radiance-general
Hi Bernhard !
I don't know if I get your question right, so my answer may be to
simple: Do you want to have luminous images or surfaces ( like e.g.
modern billboards which are illuminated from the back) ? For these
you may apply a "colorpict" to a glow material and set the fourth glow
parameter to -1. You then can place e.g. polygons out of this material
in the room and adjust their brightness as you like (of course, they
won't illumante things nearby, but they're shining.)
-cb
Hi Carsten,
I don't think you got my question right .
I know how to use colorpict to apply 2D images to surfaces.
But what I really want to do is alomost the opposite. I want the texture of
the surface back after it was lit.
I then want to apply these lit textures back onto geometry in a fileformat
for interactive rendering such as VRML, ... and then view it in a graphics
hardware accelerated browser.
Bernhard
Hi Bernhard !
Ok, now I got it, you want to use the raytracer for a specific way of
image generation. In fact, I did this already, and it really works
fine, by "playing " around with cal-files and e.g semitransparent
layers you can get nice effects out of it, useable for 2D-Graphics and
Art and the like. But there is no other way than the one you already
have in mind. By the way, (I dare to mention this here 
) you
certainly have heard of POVRay already ? Its texture modelling
facilities are a lot more intuitive to handle, so perhaps for these
sorts of visual effects it may better suit your needs.
- cb
Carsten Bauer wrote:
Hi Bernhard !
I don't know if I get your question right, so my answer may be to
simple: Do you want to have luminous images or surfaces ( like e.g.
modern billboards which are illuminated from the back) ? For these
you may apply a "colorpict" to a glow material and set the fourth glow
parameter to -1. You then can place e.g. polygons out of this material
in the room and adjust their brightness as you like (of course, they
won't illumante things nearby, but they're shining.)
my two cent comment for the archives:
they won't illuminate things by 'direct calculation' - with ambient
calculations they do
-Peter
···
-cb
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pab-opto, Freiburg, Germany, www.pab-opto.de
Hi Peter !
you're right but let's spend my last cent on this -- not if the fourth
parameter is -1 ?
There is of course a personal interest behind it. The reason, why I'm
hacking on this is, that I spent some time thinking of other ways to
deal with broad area sources (for some design-case studies) . If you use
glow sources in direct mode, you will see the effects of
source-subdivision on nearby objects illuminated by them (e.g. semi-
transparent layers. ) If you use glows in ambient mode, things are
better, but for a nice look you need very high parameter settings,
(although personally I'm still not satisfied ..). I got the assumption
that the hemisphere-sampling method works better in the "far field
range" than for near field illumination. (sorry, but it seems that I
always try to use tools for tasks they weren't intentionally made for...
)
so long
-cb
Carsten Bauer wrote:
Hi Peter !
you're right but let's spend my last cent on this -- not if the fourth
parameter is -1 ?
oops.- right. (never used it myself, so.)
There is of course a personal interest behind it. The reason, why I'm
hacking on this is, that I spent some time thinking of other ways to
deal with broad area sources (for some design-case studies) . If you use
glow sources in direct mode, you will see the effects of
source-subdivision on nearby objects illuminated by them (e.g. semi-
transparent layers. ) If you use glows in ambient mode, things are
better, but for a nice look you need very high parameter settings,
(although personally I'm still not satisfied ..). I got the assumption
that the hemisphere-sampling method works better in the "far field
range" than for near field illumination. (sorry, but it seems that I
always try to use tools for tasks they weren't intentionally made for...
What do you mean by "far field" ? -
Quick thoughts from the back of my head: The Monte Carlo integration in
ambient calcs cause noise when the integrand in the integral over the
hemisphere of incident radiance (times BRTF) fluctuates a lot. Typically
this is a problem in indirect illumination scenes with bright spots of
direct illumination on ceilings etc.
For large area sources whose radiance is nearly constant over its surface,
the MC integration should work well. Unless one maps a brightfunc/brightpic
onto the large area undulating radiance output dependent on surface
position and thereby causing fluctuations in the integrand of nearby
ambient calcs which mean noisy ambient values there.
The MC integration is brute force (e.g. it doesn't reuse any information
from one integral to the next [would be tricky anyway], there's no real
adaptive subdivison, and with varying area sources it "under-samples" the
source at points leading to alias [maybe level-of-detail handing in
colorpicts would help there]), plus MC is slow in general, with the
positive aspects being that it's simple (which is very helpful during
validation), general and bias free. Greg's razor to Radiance had been that
it's gotta be simple and effective.
What were your conclusions and suggestions on this ?
-Peter
···
--
pab-opto, Freiburg, Germany, www.pab-opto.de
Hi Peter !
A short answer due to lack of time:
..Unless one maps a brightfunc/brightpic onto the large area
undulating radiance > output ...
This - or similar arrangements- are exactly the crucial topics ...
near field/far field - ? a somewhat "blown up" terminology, I
admit, far field is in fact the room, near field is e.g. the good old
lampshade. (and there's of course Garfield 
...
My interest often lies in the point where luminaire and lighting design
meet, that may explain my special demands.
suggestions ?
I put them on halt still within a very vague state, I thought about a
combination of raytracing and radiosity approaches or forward
raytracing, resulting in the end in a further light source primitive.
But before I really should have a closer look at the activities form
other contributors.
so long
-cb
) you