find intersected cells of a mesh

Question

Hi all,

I had a question when i do something about updating the mesh function. I found that for some case, I can not find the intersection cell for some given point with the intersected_cell call. I used my own mesh and for some point inside the mesh domain,

a=Point(0.8023355,0.931834,0.7110645)
mesh.intersected_cell(a)

this return -1, which mean there is no intersected cell found for that point. I did not understand why it would happen? Meanwhile, truncate the number a little bit,

a=Point(0.8,0.93,0.711)
mesh.intersected_cell(a)

then a index of cell is returned. Any suggestion about what is going on here? Further, is there a way to guarantee to find the intersected cell? Thanks a lot.

Comments

What dolfin version are you using? Could you provide a mesh to replicate the error?

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Did you move/smooth mesh before searching an intersection? If yes, you need to call

 mesh.intersection_operator().clear()

before intersection queries.

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I used fenics1.2 and I did nothing else before seaching an intersection. I would like to provide the mesh I used. How to do that since I did not find how to attach a file to the web? Actually, it did not produce any error and just cannot find an intersected cell.

Ok, I upload the mesh file already. You can download at http://www.fileswap.com/dl/R1QVh3tZ9/
and then try it. Thanks

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You could initialize IntersectionOperator with kernel_type='ExactPredicates'. Note that collision algorithms have been implemented directly into DOLFIN in current development version to get rid of dependency on CGAL library. Currently it suffers from similar issue.

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Still cannot find the intersected cell. can you show how to do that?Thanks

Answer 1

Use 'ExactPredicates' CGAL geometry kernel.

from dolfin import *
mesh = Mesh('ion.pqr.xml')
mesh.intersection_operator().reset_kernel('ExactPredicates')

print mesh.intersected_cell(Point(0.8023355,0.931834,0.7110645))
print mesh.intersected_cell(Point(0.8,0.93,0.711))

Output:

15197
0