On Wed, Sep 19, 2018 at 9:43 AM Tim Adowski <trado...@buffalo.edu> wrote:
> Hello everyone: > > I am having an issue with the `Elem::contains_point()` function where it > returns a false negative when the point tested is near the boundary of an > element when using tol=libMesh::TOLERANCE. > > I modified introduction_ex1 on this branch > <https://github.com/tradowsk/libmesh/blob/rayfire-issue/examples/introduction/introduction_ex1/introduction_ex1.C> > to > show this behavior. I've manually plotted the element nodes and the point > to confirm that the point is indeed on the element, though right on an edge. > > tl;dr > how can I best handle this behavior to avoid a false negative? Arbitrarily > raising the tolerance until the failure goes away seems more like tuning > the code to a specific mesh rather than trying to fix the underlying > problem. > > ====== > longer version > > This issue arose in development of the GRINS::RayfireMesh class. In short, > the user supplies an origin point on a mesh boundary, and the class will > walk in a straight line across the mesh in a given direction. On each > element along the line, the class will calculate the points where it enters > and leaves that element to create an EDGE2 element that gets stored > internally. The problem with that calculation is verifying whether or not a > calculated point is actually on the side/face of the given element (SECOND > order elements use a newton solver due to the potential nonlinearity on the > element sides/faces). > > The test case above is from a larger mesh where the rayfire traverses the > z=0 mesh boundary. I found that using 10.0*libMesh::TOLERANCE for > `contains_point()` allows the rayfire to complete successfully for this > particular mesh, but I don't know if that tolerance value would work for an > arbitrary mesh. > > Does anyone have a suggestion for how I can best handle these cases? In > the test case above, I imagine the failure is due to the difference in > z-components, even though they are all essentially zero. > > Any help is greatly appreciated! > Would it be more correct for you to use Elem::close_to_point() instead of Elem::contains_point() in your application? I haven't had a chance to try your example yet, but thanks for providing it. I'm curious if you know whether the initial bounding box test is what returns false, or the subsequent FEInterface::inverse_map() and FEInterface::on_reference_element() checks? -- John
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