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https://issues.apache.org/jira/browse/MATH-1211?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14484606#comment-14484606
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Mike Zimmerman commented on MATH-1211:
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It might be enough to incorporate a direction check just after line 365 in the
recurseFirstIntersection method of PolyhedronsSet, something like:
final Vector3D hit3D = plane.intersection(line);
if (hit3D != null && hit3D.subtract(point).dotProduct(line.getDirection()>0) {
...
}
The problem is that the Plane.intersection method does not check for
directionality of the line, thus the PolyhedronsSet.firstIntersection method
simply returns the first face that intersects the "whole" line rather than the
first face intersecting the semi-infinite "front" of the line.
> PolyhedronsSet.firstIntersection(Vector3D point, Line line) sometimes reports
> intersections on wrong end of line
> ----------------------------------------------------------------------------------------------------------------
>
> Key: MATH-1211
> URL: https://issues.apache.org/jira/browse/MATH-1211
> Project: Commons Math
> Issue Type: Bug
> Reporter: Mike Zimmerman
>
> I constructed a PolyhedronsSet from a list of triangular faces representing
> an icosphere (using the instructions found at
> https://mail-archives.apache.org/mod_mbox/commons-user/201208.mbox/<5039fe35.2090...@free.fr>).
> This seems to produce correct INSIDE/OUTSIDE results for randomly chosen
> points. I think my mesh triangles are defined appropriately.
> However, using PolyhedronsSet.firstIntersection(Vector3D point, Line line) to
> shoot randomly oriented rays from the origin sometimes gives a wrong mesh
> intersection point "behind" the origin. The intersection algorithm is
> sometimes picking up faces of the sphere-shaped mesh on the wrong
> semi-infinite portion of the line, i.e.
> meshIntersectionPoint.subtract(point).dotProduct(line.getDirection())<0 where
> point is the Vector3D at center of the sphere and line extends outward
> through the mesh.
> I think the dot product above should always be positive. If multiple
> intersections exist along a "whole" line then the first one in "front" of the
> line's origin should be returned. This makes ray tracing with a
> PolyhedronsSet possible.
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