[Radiance-general] Blotching caused by translucent material

[Greg Ward]

This seems like a poster case for the new photon-mapping routines.  If you are working with the latest alpha version, you should definitely give that a try.  The irradiance cache isn't built to handle specular scattering like this.  You would have to turn it off with -aa 0 and put up with the noise.  Using a caustic photon map avoids the issue.  It's even built into the latest rad program, so you just need to set up your maps using:

	PGMAP= scene_g.pmp 200K 50
	PCMAP= scene_c.pmp 1M 50

Rad will run mkpmap and set the rvu or rpict options appropriately, and you can watch what it does.  It typically spits out things like:

	oconv sky.rad window3b.rad office.rad window_port.rad > test3f.oct
	mkpmap -apo window_port -fo+ -apg test3f_g.pmp 200K -apc test3f_c.pmp 1M test3f.oct
	rpict -vu 0 1 0 -vf fish.vf -dp 512 -ar 185 -ms 1.3 -ds .3 -dt .1 -dc .5 -dr 1 -ss 1 -st .1 -ab 1 -af test3f.amb -aa .1 -ad 1536 -as 392 -av 10 10 10 -lr 8 -lw 1e-4 -ap test3f_g.pmp 50 -ap test3f_c.pmp 50 -av 0.8 0.8 0.8 -x 64 -y 64 -ps 1 test3f.oct > /dev/null
	rpict -vu 0 1 0 -vf fish.vf -x 1024 -y 1024 -dp 512 -ar 185 -ms 1.3 -ds .3 -dt .1 -dc .5 -dr 1 -ss 1 -st .1 -ab 1 -af test3f.amb -aa .1 -ad 1536 -as 392 -av 10 10 10 -lr 8 -lw 1e-4 -ap test3f_g.pmp 50 -ap test3f_c.pmp 50 -av 0.8 0.8 0.8 -ps 6 -pt .08 test3f.oct > test3f_fish.unf
	pfilt -1 -e .05 -r .6 -x /2 -y /2 test3f_fish.unf > test3f_fish.hdr
	rm -f test3f_fish.unf

You can dig through these for hints of how to run everything if you prefer doing it by hand.

Cheers,
-Greg

> From: Örn Erlendsson <orn.e at live.com>
> Subject: Re: [Radiance-general] Blotching caused by translucent material
> Date: June 24, 2015 12:54:38 AM PDT
> 
> Thank you all for your reply. I have now tried several variations with your suggestions and although the blotching issue is not resolved, the images do get slightly better. Could the issue in fact be that the diffuse and specular transmissive properties are so low that in reality very little light would pass into the scene, thus causing a very low light condition closely represented by the blotching case we see from the simulations? 
> 
> Just to clarify the light transmission of translucent glazing is equal to the sum of the diffuse and specular transmission.... right?
> 
> Örn
> 
> From: amcneil at lbl.gov
> Date: Fri, 12 Jun 2015 12:17:55 -0700
> To: radiance-general at radiance-online.org
> Subject: Re: [Radiance-general] Blotching caused by translucent material
> 
> Chris, I think you're suggestion is valid, particularly for reducing the size of the blotches.
> Andy
> 
> 
> On Fri, Jun 12, 2015 at 11:03 AM, Christopher Rush <Christopher.Rush at arup.com> wrote:
> I retract my answer. Andy is right about it being splotches in the direct transmission. I was too quick to jump to conclusions when I read your subject and barely looked at the images.
> 
>  
> 
> From: Christopher Rush [mailto:Christopher.Rush at arup.com] 
> Sent: Friday, June 12, 2015 1:52 PM
> To: Radiance general discussion
> Subject: Re: [Radiance-general] Blotching caused by translucent material
> 
>  
> 
> Orn,
> 
> With clear glass, a very significant contribution is made by the direct sun, so all the ambient bounces (and their calculation parameters) contribute less to the scene, and you see less blotches.
> 
>  
> 
> For the translucent glass, try again with all of your first run parameters, but instead of -ar 64 try -ar 500 or -ar 1000. This probably has the biggest impact on visibility of blotches. This is particularly important if your model includes a room that’s part of a much larger building, or a full building floor with a very large site context modeled around it.
> 
>  
> 
> In the parameters you tested in the second run, when you increased –ad and lowered –aa those should also improve accuracy, but might not be necessary depending on how much importance you put on accuracy versus calculation time.
> 
>  
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