I'm doing motion capturing of facial expressions, having an empty (constrained to a track in the movie clip editor) "sliding" on a facial surface mesh (depth object). However, for some large facial movements, the empty "drops off" the depth object. I don't want to enlarge the depth object.

Here the empty "slides" on the depth object (facial mesh): enter image description here

Here the empty can not be projected on the depth object and "falls off" to some standard distance: enter image description here

Is there a way to test for each frame whether the empty "touches" the mesh/depth object (or not) in bpy?

  • $\begingroup$ Hard to understand your question. Can you add a scene or some images to show what you are trying to accomplish? $\endgroup$
    – brockmann
    Jan 17 '18 at 15:18
  • $\begingroup$ Sorry for beeing imprecise. I added some screen shots. $\endgroup$
    – emil
    Jan 17 '18 at 15:53
  • 1
    $\begingroup$ Could use distance from empty to its Closest point on mesh in a frame change handler or somesuch. $\endgroup$
    – batFINGER
    Jan 17 '18 at 16:07

Thanks to the link of batFINGER to the function closest_point_on_mesh() I wrote a function which does the trick:

def is_empty_on_mesh (empty,mesh,maxDist = .000001):

    empty = bpy.data.objects[empty]
    mesh = bpy.data.objects[mesh]    

    # to compute distance via closest_point_on_mesh() the
    # objects have to be translated from global to local space
    emw = empty.matrix_world.to_translation()
    mmwi = mesh.matrix_world.inverted()

    local_pos = mmwi * emw
    (hit, loc, norm, face_index) = mesh.closest_point_on_mesh(local_pos)
    vec = mesh.matrix_world * loc

    dist = (vec - emw).length
    #print("Function Dist:",dist) # Debugging
    return(dist < maxDist)

is_empty_on_mesh(NameOfEmpty, NameOfMesh)

The function returns TRUE or FALSE, depending on the distance being smaller than .000001 (this value is somehow arbitrary).


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