Wasn't it Abe who wrote:
>"Mike the Elder" <zer### [at] wyanorg> wrote:
>> Is there a reasonably simple way in POV-Ray to produce a Boolean value
>> representing whether or no two objects intersect?  As in...
>>
>> #if ("object{Thing1} intersects object{Thing2}")
>>       // STUFF TO DO IF THEY INTERSECT
>> #else
>>       // STUFF TO DO IF THEY DON'T INTERSECT
>> #end
>>
>> I would very much appreciate if some kind soul could point out the section
>> of the documentation and/or available resources that deal with this issue.
>>
>> Thanks in advance.
>>
>> Mike C.
>
>I was interested in your problem and did a couple of quick tests. Testing
>min_extent and max_extent on two spheres known to intersect produced
>predictable results. When the spheres did not intersect, the results for
>the intersection object were as follows.
>
>min_extent = <-10000000000.000000,-10000000000.000000,-10000000000.000000>
>max_extent = <10000000000.000000,10000000000.000000,10000000000.000000>
>
>So it looks like this could be used as a test, although I don't really know
>how robust it is.

POV calculates the intersection of the bounding boxes (because it can
calculate that) and uses that as the bounding box for the intersection
(which would be next to impossible to calculate in the general case). 

If you consider these non-intersecting spheres
intersection {
  sphere {0,1}
  sphere {0,1 translate <1.2,1.2,1.2>}
  pigment {rgb x}
}

Their bounding boxes do intersect at the corner, like this
intersection {
  box{-1,1}
  box {-1,1 translate <1.2,1.2,1.2>}
  pigment {rgb x}
}

So that method would be wrong in suggesting that the spheres
intersected.

-- 
Mike Williams
Gentleman of Leisure

Post a reply to this message