[Radiance-general] modeling trees in Radiance

[Greg Ward]

Hi Joe,

The setting of trans parameters is a bit tricky and an oft-visited question that should be the first in a FAQ, if indeed such a thing will happen if it hasn't yet after 25 years....  If you do a search on the Radiance mailing list for "trans parameters" or similar, I'm sure you'll find some choice entries.  Maybe someone can recommend a calculator for you, but the basic formulae are given in Section 5.2 on p. 325-6 of "Rendering with Radiance," attached below.

I like the concept of using a mixfunc with void and plastic on the outside and mist on the inside.  Working out the appropriate parameters to get a reasonable look would be a challenge, but the results might be worth it.

Best,
-Greg


> From: Joe Smith <the.oat.cracker at gmail.com>
> Subject: Re: [Radiance-general] modeling trees in Radiance
> Date: February 6, 2015 12:55:47 AM PST
> 
> Dear all, thank you very much!
> 
> To Greg: May I ask, if I also want to consider reflection or scattering of the sphere surface, how should I specify the parameters for the trans type of material? and what does the "trans" parameter for trans material means? 
> 
> To German: Thank you for the tip of using a mixfunc! Can you advise on how to specify the funcfile to define the pattern and proportion of mixing of void and plastic materials?
> 
> To Compagnon: Thank you for the square-root reminder!
> 
> To Christopher and Greg: Thanks for the tip on mist! Can we imagine the tree object modeled in this way as a hollowed sphere whose surface is composed of a texture with an "alternating void and plastic" pattern, and the inside of the sphere is filled with a lump of "mysterious" fog ...?
> 
> 
> On Fri, Feb 6, 2015 at 8:14 AM, Greg Ward <gregoryjward at gmail.com> wrote:
> Yes, I should have thought about the square root -- good catch!
> 
> The trans type doesn't change with incident angle (unlike glass or dielectric), which is part of why I suggested it.  I don't know what's happening in Germán's case, but using a mixfunc with void and plastic is a perfectly acceptable approach.
> 
> As for varying the absorption using mist, a ball of mist might indeed have the desired behavior, as the absorption is an exponential function of the volume traversed using the mist material.
> 
> Cheers,
> -Greg
> 
>> From: Christopher Rush <Christopher.Rush at arup.com>
>> Subject: Re: [Radiance-general] modeling trees in Radiance
>> Date: February 5, 2015 7:05:02 AM PST
>> 
>> I see Raphaël just pointed out what I was in the middle of typing about the square root transmittance correction. Also, keep in mind this will only be a very rough approximation for any measurements very near the tree, where rays passing through all parts of the tree get the same reduction even if they just glance the fringe of the sphere or other shape. In reality, rays passing through the outer fringes of a tree canopy would intersect with fewer leaves than those passing through the more substantial core of the tree (also depending on tree species).
>> 
>> I would love to here if anyone has a more ideal solution for modeling trees that is relatively accurate, and reasonable in terms of rendering time and use of RAM – in other words without modeling every single leaf. If it looked nice that would be a bonus. Is this a possible application for something exotic like mist? I’ve never even investigated mist so apologies if that’s a ridiculous suggestion.
>> 
> 
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
> http://www.radiance-online.org/mailman/listinfo/radiance-general
> 
> 
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
> http://www.radiance-online.org/mailman/listinfo/radiance-general
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.radiance-online.org/pipermail/radiance-general/attachments/20150206/651a0e93/attachment-0002.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: TransMaterial.pdf
Type: application/pdf
Size: 81901 bytes
Desc: not available
URL: <http://www.radiance-online.org/pipermail/radiance-general/attachments/20150206/651a0e93/attachment-0001.pdf>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.radiance-online.org/pipermail/radiance-general/attachments/20150206/651a0e93/attachment-0003.html>