Am 17.08.2017 um 21:01 schrieb Kenneth:

>> But the information that I need to do that is:
>> POV-ray shoots a ray in the direction specified by `inside_vector` _FROM_ ---
>> where?
> 
> That's something I've wondered about as well.
> 
> From newsgroup comments years ago, my own understanding about inside_vector is
> currently this (and I could be wrong):
> 
> 1) it isn't used until the mesh is CSG'd with some other object.

More precisely, it is only used in non-`union` CSGs.

> 2) Perhaps the 'shoot-from point' (or from *multiple* points) is actually the
> surface of the other intersecting object.

Exactly that.

As a raytracer, POV-Ray's main schtick to render any objects in the
scene is to compute intersection points between rays (usually
originating at the camera location) and object surfaces.

For geometric primitives, ray-surface intersections are computed via
more or less complicated mathematical formulae.

For `union` CSGs, ray-surface intersections are computed simply by
computing the ray-surface intersections with all child objects.

For all other CSGs, the ray-surface intersection points of all the child
objects are filtered according to whether they are /inside/ sibling objects.

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