[Radiance-general] Noisy irradiance rendering from glow materials

[Jack de Valpine]

Hi Claus,

I think if you want to get a smoother result from your ground plane you 
will need to be more careful about how it is constructed. Direct 
sampling (subdivision of the source) occurs relative to the "center" of 
the ground plane geometry, which is why you may not be seeing what you 
expect. Additionally if the center of a ground plane object is "under" 
one of the buildings this will contribute to some of the effects that 
you are seeing. As a test I would consider constructing the ground plane 
of multiple polygons (probably should be quads) where the edge of a 
given polygon meets the edge of a building side at the "ground."

I think that another thing to add into your command line is to set 
direct jitter (-dj). I think you could start out with with -dj .7 and 
see what happens.

I would try reconstructing your ground plane first and then run as is 
with your original command line, then you can try setting -dj to further 
adjust things.

Hope this helps.

-Jack

-- 
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction


On 1/3/2011 8:37 AM, Claus Brøndgaard Madsen wrote:
>
> Hi Thomas and Greg,
>
> Thanks a lot for your feedback to my post.
>
> Happy New Year to everybody.
>
> I spent a good part of my holiday evenings messing around with my 
> problem ... very nerdy, but life with RADIANCE is so inspiring that 
> you sometimes cannot wait until the next official work day J.
>
> Status now is that the noise has "gone" and there is now a new 
> artifact that I cannot get rid of. Thanks, Greg, for the revised and 
> streamlined command line, which I am now using. I must admit that I 
> was so proud of "my own" command line that accepting this revised one 
> was like killing a darling.
>
> In fact I have specified a positive radius for the glow materials. The 
> rendering result I am after is the cosine weighted, hemi-spherical 
> integral of the *direct* incident radiance (caused by the glow 
> materials only). That's why I originally had --ab 0 and then positive 
> radius on the materials. Is using --ab 1 in combination with positive 
> radius going to result in any indirect computation?
>
> In any case I have used Greg's command line verbatim for a new 
> rendering attempt ... see result1.jpg.
>
> I results1.jpg there are 3 things "I don't like":
>
> 1)The odd "hot spots" at crease edges
>
> 2)The fact that the pole in the foreground does not receive the same 
> irradiance on all sides (which it should since the pole sides facing 
> the camera only receive illumination from the ground plane)
>
> 3)The vertical end-plane of the house gets brighter the further away 
> from the groundplane you get ... I am sure it should be the other way 
> around
>
> For these reasons I replaced the single genbox groundplane object with 
> a 10x10 tiling of genbox objects (auto-generated with a small matlab 
> script). With the same command line I arrived at result2.jpg.
>
> While pretty (!) there are still several problems:
>
> 1)Weird hot spots at crease edges
>
> 2)Dark (under-illumination) at the foot of walls
>
> In an attempt to combat this I tried adding a --ds 0.02 option. This 
> multiplied rendering time by a factor of 5 but resulted in no visible 
> changes (result3.jpg). All images show visible jpg compression 
> artifacts but are in all essence true to the actual result.
>
> The scene is a scale model of a dairy. The scene is modeled in meters, 
> so for example the width of the dairy end wall is 0.07 meters and is 
> one single 6 vertex polygon. As described the ground plane is a tiling 
> of side-by-side genbox objects ... each genbox object is 0.3 meters 
> square. This scene is merely a test scene. When I get to the proper 
> experiments the geometry of a scene will be a triangle mesh generated 
> from stereo camera scans of (parts of) real building exteriors ... 
> kind of like trimesh.jpg where the triangle sizes will be very 
> homogeneous.
>
> So, what is the proper approach: subdivide the geometry (for the test 
> scene or test with the tri-mesh real scenes), or add some rendering 
> option to force a subdivision of whatever needs to be subdivided for 
> the hot spots to disappear?
>
> Best,
>
> Claus
>
> *From:*Greg Ward [mailto:gregoryjward at gmail.com]
> *Sent:* 31. december 2010 00:37
> *To:* Radiance general discussion
> *Subject:* Re: [Radiance-general] Noisy irradiance rendering from glow 
> materials
>
> Hi Claus,
>
> I am also a little puzzled by your results.  As Thomas mentioned, glow 
> surfaces are included in the indirect calculation, so unless you 
> specified a positive radius value for your glow materials, they should 
> not light your scene at all with -ab 0.  The complexities of your 
> command line are mostly unnecessary.  You should be able to simplify 
> it to:
>
> vwrays -ff -x $XRES -y $YRES -vf $NAME.vp \
>
> |rtrace -h -fff -opN $NAME.oct \
>
> |rtrace -ffc -x $XRES -y $YRES -I -ab 1 -aa 0.1 -ad 4096 -ar 0 
> $NAME.oct > $NAME.irradiance.hdr
>
> Rays with zero normals will be evaluated as (0 0 0) by the second 
> rtrace, and an epsilon is always added to the origin in the direction 
> of the normal when using the -I option, so your rcalc command, while 
> clever, is unnecessary.  I changed your -ab to 1 and got rid of the 
> other unnecessary options.  I set -ar to 0, since you seem to want a 
> very high resolution result.  I added -aa 0.1 for the same reason.
>
> If you are still getting this peculiar noise pattern after these 
> changes, please post your scene description and I'll have a look at it.
>
> Best,
>
> -Greg
>
> P.S.  Regarding mailing list policy on attachments.  In general, I 
> prefer that people not attach large files to e-mails, and people have 
> been very good about this, posting larger images on websites, instead. 
>  Small JPEGs (less than 100K or so) are acceptable; likewise small 
> text attachments are OK.
>
> *From: *Claus Brøndgaard Madsen <cbm at create.aau.dk 
> <mailto:cbm at create.aau.dk>>
>
> *Date: *December 29, 2010 1:59:30 PM PST
>
>     Dear list,
>
>     With a lot of inspiration from Thomas Bleicher's tutorial
>     (http://sites.google.com/site/tbleicher/radiance/stencil) which he
>     pointed me to back in August (yes, it took me a while to gather
>     the courage to go down that path) I have managed to devise a small
>     script (or rather a command line) which allows me to render the
>     irradiances received at any point in a scene with all glow
>     materials (the standard --i irradiance option for rpict does not
>     work for glow materials).
>
>     I attach (not so sure about list rules regarding attachments) the
>     scene rendered where pixel values represent the outgoing radiance
>     of the glow materials (radiance.jpg) and the scene rendered such
>     that every pixel represents the incident irradiance in the same
>     scene (irradiance.jpg). There are no other light sources than the
>     glow materials.
>
>     My question is simply: how to reduce the significant amount of
>     rendering noise for the (near) vertical surfaces? The irradiance
>     on those surfaces is dominated by energy coming from the
>     horizontal ground plane, which is a single box object (genbox).
>
>     I feel I have tried "everything" with the render options (see my
>     setting below) but have seen no improvement in render noise ...
>     hope to get some pointers/ideas from the list.
>
>     I use the following command line command to render the irradiance:
>
>     vwrays -ff -x $XRES -y $YRES -vf $NAME.vp \
>
>     |rtrace -ffa -opN $NAME.oct \
>
>     |sed '1,8d' \
>
>     |rcalc -ia6 -of \
>
>     -e '$1=$1 + 0.001*$4;$2=$2 + 0.001*$5;$3=$3 + 0.001*$6' \
>
>     -e 'out(v)=if(sqrt($4*$4 + $5*$5 + $6*$6) - 0.9,v,-1)' \
>
>     -e '$4=out($4);$5=out($5);$6=out($6)'  \
>
>     |rtrace -ffc -x $XRES -y $YRES -I -ab 0  -aw 1 -ad 4096 -ar 4096
>     -dt 0.0 -dp 8192 -ds 0.01 -dj 0.9 $NAME.oct > $NAME.irradiance.hdr
>
>     In short: use vwrays to generate the primary rays needed to render
>     the scene, pipe into rtrace to get intersection points and
>     normals, pipe into sed to get rid of header generated by rtrace
>     and leave only lines with intersection point and normal, pipe
>     through rcalc to "lift" intersection points 1/1000 of a unit in
>     the direction of the normal (to avoid surface self-intersection
>     problems later when using intersection point and normal as the
>     start point for an incident irradiance computation) ... and rcalc
>     also sets a (-1, -1, -1) direction vector if the original surface
>     normal from rtrace is close to zero length, finally pipe through
>     rtrace, this time with --I option to gather incident irradiance at
>     the "lifted" surface point.
>
>     Best,
>
>     Claus
>
>
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