On Wed, Mar 11, 2015 at 1:20 PM, Roy Stogner <royst...@ices.utexas.edu>
wrote:
>
> On Wed, 11 Mar 2015, Roy Stogner wrote:
>
> On Wed, 11 Mar 2015, David Knezevic wrote:
>>
>> On Wed, Mar 11, 2015 at 12:29 PM, Roy Stogner <royst...@ices.utexas.edu>
>>> wrote:
>>>
>>> We need some kind of fully general intersection test for cartesian
>>> boxes with libMesh elements...
>>>
>>
>> Hmm, OK. Do you have an idea about how to implement that? I'll be happy
>>> to help out, if needed.
>>>
>>
>> No great ideas. I've only seen intersection tests for cases involving
>> polyhedra, spheres, and cones, not arbitrary quadratic parametric
>> volumes.
>>
>> We could probably handle the (tri,bi,)linear non-axis-aligned
>> anisotropic cases with standard algorithms, though: orthogonalize the
>> vectors given by dx/dxi to get a more appropriate coordinate system,
>> find the "axis-aligned bounding box" by translating the nodes into
>> those coordinates, and do the intersection test for that bounding box
>> with the coordinate-aligned BB that our trees use. The trilinear case
>> has curved faces, but I believe each face is still always bounded by
>> any bounding box of its four nodes.
>>
>> http://www.realtimerendering.com/intersections.html
>>
>> We'll need to figure out something smarter before we get to play
>> safely with point locators for general quadratic geometry or NURBS,
>> though.
>>
>
> To clarify: although an exact intersection test would be *great*, all
> we need for now is something like the above: a test that doesn't give
> us any false negatives or *too* many false positives.
>
OK.
Also, I'd also like to provide a quick for this current test mesh.
Changing "200" to "250" in:
if (!is_planar_xy)
_tree = new Trees::OctTree (this->_mesh, 250, _build_type);
works for me. Would you be happy with a "hacky" fix like that in the short
term? Or would you prefer to keep the code as-is until we have a more
thorough fix?
David
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