Christopher James Huff wrote:
> In article <h32gavo8csv7vcgefdsi0fl3ei8orr0cdq@4ax.com>,
>  ABX <abx### [at] abxartpl> wrote:
> 
> 
>>That's me who suggested that macro. When I refered to it I wasn't sure if he 
>>is interested in METHOD or RESULT of his description.
> 
> 
> Oh, sorry about that then.
> 
> 
> 
>>I'm still not sure if he is rather interested in RESULT of specific 
>>case of his sum or in general METHOD. I hope my hints helped him and 
>>I hope you are not angry that I answered instead of licensed TAG 
>>member ;-)
> 
> 
> The TAG does not have any exclusive rights on giving help. ;-)
> 
> Anyway, I've been assuming he wants a general "sum" object similar to 
> the CSG union object. In this case, a way of finding an intersection 
> between a ray and the sum of the objects is necessary. The given 
> descriptions involve adding points on the objects together to get new 
> points, but POV doesn't have those points in the first place, it finds 
> them as necessary using object-specific methods. The original poster 
> asked about insideness testing...each object has a function that can 
> determine if a given point is inside it, which doesn't seem at all 
> helpful for this.
> 
> It might be possible to find a large enough number of points do get fair 
> approximations of the surfaces by randomly tracing rays at the objects. 
> You could then operate on these point fields and either patch POV to 
> render them directly (there are algorithms for directly raytracing point 
> fields) or convert them into a mesh. 

Converting arbitrary point sets into meshes or surfaces is a difficult 
task (known as "surface reconstruction"). Are there algorithms for this 
task used with (or in) povray?



> I'm not sure how good the results 
> will look, and you will need to handle a *lot* of points. The original 
> poster seems to be expecting something more like a CSG operation, which 
> is just impossible as far as I can tell. The macro mentioned can do it, 
> but it was created by hand...I see no way of telling a program to 
> combine arbitrary shapes and get a composite of several objects of 
> different types (spheres, boxes, and cylinders in this case) as a result.
> 

I agree... :-)

Achill

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