[Radiance-general] Blotching caused by translucent material

[Andrew McNeil]

Did you try setting roughness to zero in your trans definition? That solves
it for me.
Though if the small extra scatter you get from the roughness is important
to your simulation, than Greg has a good point. Photonmap is best.

Andy

On Wed, Jun 24, 2015 at 12:54 AM, Örn Erlendsson <orn.e at live.com> wrote:

> 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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