clipka <ano### [at] anonymousorg> wrote:
> Am 04.08.2016 um 17:44 schrieb And:
> > Why?
> > here is a union version. It's ok.
>
> Union is special among the CSG operations in that it works fine with
> non-solid objects. All other CSG operations need solid objects to work
> properly.
>
> To POV-Ray, "solid" means that there is a method to test whether any
> given point is inside or outside a shape. The normal ray tracing
> algorithm does not need such a test, since the only thing it cares about
> is surfaces. Likewise, unions do not need such a test, since they do not
> change what surfaces are rendered. Merge, difference, intersection and
> clipped_by, on the other hand, work by selectively suppressing portions
> of an object's surface depending on which other objects they're inside
> -- and that's where the insideness test is crucial.
>
> For meshes, the insideness test is implemented by tracing a ray from the
> point in question in an arbitrary direction, and counting how many times
> that ray intersects the object's surface. An odd number of intersections
> indicates that the point in question is inside, while an even number
> indicates that it is outside. For this algorithm to work properly, two
> conditions must be met:
>
> - The mesh must be properly closed (i.e. each and every triangle must
> precisely share each of its edges with an odd number of other triangles).
>
> - The "arbitrary direction" needs to be chosen. This is not done
> automatically, but instead requires the use of the `inside_vector`
> keyword, with a non-zero vector. (The actual direction does not normally
> matter; however, if the vector happens to be almost but not quite
> parallel to one of the triangles, there is a slight chance that
> artifacts may occur, especially if that triangle is particularly large.)


Mmm... ok. Sounds that I need do this in another way.
Heee

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