2009/12/3 Fred Smith <osgfo...@tevs.eu> > Hi, > > On one occasion I don't get two intersections, only one. That's the > problem. > > I expect two intersections. One for the first triangle, one for the second. > I get only one, for the second triangle, even though I picked the left > triangle. > > You can easily reproduce this with the OSG file I listed. > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=20825#20825 > > This bug is due to the geometry being 2D and the actual intersection being calculated w/ floats.
If you need a quick and dirty fix, you can change the code in void TriangleIntersector::operator () (...) [[ src\osgUtil\LineSegmentIntersector.cpp ]] To use doubles instead. I was going to make a submission for that, but I've been busy and this issue may benefit from a bit of discussion, rather than just changing the code to use doubles. Basically it boils down the fact that when the geometry is entirely 2d, there is some code in bool LineSegmentIntersector::intersectAndClip(...) which expands the bounding box, leaving it just 1e-4 across in the thin direction. When you have vertices out at larger coordinates (> ~4000) the intersection code starts hitting numeric precision problems. So you can either go with doubles, change the size of the expansion of the bounding box (and then hit precision issues again at some point in the future), add some sort of approximate floating point compare code or maybe don't clip the pick ray to the bounding box when there is 2D geometry. -- http://www.ssTk.co.uk
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