BoundingBoxTree.compute_closest_entity gives wrong distance in 2D

[Tuomas Airaksinen]

BoundingBoxTree.compute_closest_entity gives wrong distances in 2D. In 3D (at least for UnitCubeMesh) it seems to be OK.

Example:

from dolfin import *

mesh = UnitSquareMesh(4,4)
bmesh = BoundaryMesh(mesh, "exterior")

bbtree = BoundingBoxTree()
bbtree.build(bmesh)

vertex_distance_to_boundary = MeshFunction("double", mesh, 0)

for v_idx in xrange(mesh.num_vertices()):
    v = Vertex(mesh, v_idx)
    _, distance = bbtree.compute_closest_entity(v.point())
    vertex_distance_to_boundary[v_idx] = distance

plot(vertex_distance_to_boundary)
interactive()

In this example, distance to the boundary should be plotted.

see also http://fenicsproject.org/qa/1446/distance-to-boundary .

[Prof Garth Wells]

Please modify your report to be explicit in what you expect the output to be, and what it actually is.

[Tuomas Airaksinen]

I expect the value plotted to be distance to the boundary of the domain. I get the following:

[Prof Garth Wells]

Please have your report print numbers for comparison.

[Tuomas Airaksinen]

Ok, here.

from dolfin import *

mesh = UnitSquareMesh(4,4)
bmesh = BoundaryMesh(mesh, "exterior")

bbtree = BoundingBoxTree()
bbtree.build(bmesh)

vertex_distance_to_boundary = MeshFunction("double", mesh, 0)

for v_idx in xrange(mesh.num_vertices()):
    v = Vertex(mesh, v_idx)
    p = [v.point()[i] for i in range(3)]
    _, distance = bbtree.compute_closest_entity(v.point())
    vertex_distance_to_boundary[v_idx] = distance
    print p, distance

and result:

[0.0, 0.0, 0.0] 0.0
[0.25, 0.0, 0.0] 0.0
[0.5, 0.0, 0.0] 0.0
[0.75, 0.0, 0.0] 0.0
[1.0, 0.0, 0.0] 0.0
[0.0, 0.25, 0.0] 0.0
[0.25, 0.25, 0.0] 0.0
[0.5, 0.25, 0.0] 0.0
[0.75, 0.25, 0.0] 0.0
[1.0, 0.25, 0.0] 0.0
[0.0, 0.5, 0.0] 0.0
[0.25, 0.5, 0.0] 0.25
[0.5, 0.5, 0.0] 0.0
[0.75, 0.5, 0.0] 0.25
[1.0, 0.5, 0.0] 0.0
[0.0, 0.75, 0.0] 0.0
[0.25, 0.75, 0.0] 0.0
[0.5, 0.75, 0.0] 0.0
[0.75, 0.75, 0.0] 0.0
[1.0, 0.75, 0.0] 0.0
[0.0, 1.0, 0.0] 0.0
[0.25, 1.0, 0.0] 0.0
[0.5, 1.0, 0.0] 0.0
[0.75, 1.0, 0.0] 0.0
[1.0, 1.0, 0.0] 0.0

[Anders Logg (Chalmers)]

Thanks. I'll look into this but let me just comment that this has not been tested at all (bounding box tree for surface embedded in higher dimensions), so it's not surprising that it breaks.

[Anders Logg (Chalmers)]

Fix issue 139: BoundingBoxTree.compute_closest_entity gives wrong distance in 2D

→ <<cset 91bad31c2228>>

[Anders Logg (Chalmers)]

This should be fixed now (fix merged into next).

[Prof Garth Wells]

Removing milestone: 1.3 (automated comment)