[Radiance-general] Cutting a cylinder, or modeling smooth geometry...

[giulio]

may be this can help, hope so.
http://web.mac.com/geotrupes/iWeb/Main%20site/RadBlog/ 
19993E4C-9633-4930-9D7F-72C4115D2E62.html
ciao
G.


On 6 Feb 2009, at 17:02, Greg Ward wrote:

> Hi Lars,
>
> Your idea of applying a mixfunc is clever, and I believe it should  
> work, at least in Radiance "classic".  I have no idea if material  
> mixing is supported in the photon mapping extension, however.
>
> Best,
> -Greg
>
>> From: "Lars O. Grobe" <akilog at nus.edu.sg>
>> Date: February 5, 2009 11:21:26 PM PST
>>
>> Hi,
>>
>> I am running into problems due to the lack of csg in radiance. I  
>> need to accurately model a tube with a very specular material,  
>> which is bent. The real tube is produced by cutting a cylinder  
>> under 22.5 degree and assembling it, leading to a nice 45degree  
>> angle with one ellyptical edge. As I am not able to cut a cylinder  
>> geometry in radiance, I have modeled it as a mesh, but the  
>> specularity leads to visible edges.
>>
>> I have been sonsidering several solutions so far:
>>
>> 1) Using antimatter to cut away parts of the cylinder would  
>> probably not work, as the second cylinder, which also has to be  
>> cut, would lead to two overlapping antimatter volumes.
>>
>> 2) Refining the mesh would result in huge geometry, as the  
>> segments would become thinner while keeping their length, this  
>> would lead to a real worst case for oconv. Also to make the edges  
>> disappear, I would have to get into dimensions where one facet  
>> should not take much more then one pixel in the final rendering.
>>
>> 3) Using "smooth" surface normals would lead to an visual  
>> improvement. But I have my doubts if these would be considered for  
>> photon mapping and especially caustics? In my setup, the pipe ends  
>> with a diffusor (currently modeled as a box modified by a rather  
>> generic trans material). I would expect caustic effects to become  
>> visible caused by a round tube geometry with very high specularity.
>>
>> 4) The last option I see is using a cylinder object with a mixfunc  
>> modifier and a simple cal file containing just the line
>>
>> condition=if(Pz-Px,1,0);
>>
>> to cut my geometry in 45 degrees, using void to get parts of the  
>> geometry invisible. Would that work with overlapping geometries  
>> (which would still exist, even if invisible), and would it be  
>> relieable with the pmap extension? The main disadvantage here is  
>> that I would have to maintain an extra set of geometry for  
>> radiance, while I could use converters to import from other  
>> programs so far.
>>
>> CU Lars.
>
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