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edges

edges(F, return_boundary_indices=False, return_interior_indices=False, return_nonmanifold_indices=False)

Given a triangle mesh with face indices F, returns all unique unoriented edges as indices into the vertex array. There is no particular ordering convention for edges. Boundary edges are guaranteed to be oriented as in F.

Parameters:

Name Type Description Default
F (m,3) numpy int array

face index list of a triangle mesh

 required
return_boundary_indices bool, optional (default False)

whether to return a list of indices into E denoting the boundary edges

 False
return_interior_indices bool, optional (default False)

whether to return a list of indices into E denoting the interior edges

 False
return_nonmanifold_indices bool, optional (default False)

whether to return a list of indices into E denoting the nonmanifold edges

 False

Returns:

Name Type Description
E (e,2) numpy int array

indices of edges into the vertex array
boundary_indices if requested, (b,) numpy int array

list of indices into E of boundary edges
interior_indices if requested, (i,) numpy int array

list of indices into E of interior edges
nonmanifold_indices if requested, (nm,) numpy int array

list of indices into E of nonmanifold edges

Examples:

from gpytoolbox import read_mesh, edges
v,f = read_mesh("test/unit_tests_data/bunny_oded.obj")
e = edges(f)
#Euler's (?) theorem
self.assertTrue(v.shape[0] - e.shape[0] + f.shape[0] == 2)
Source code in src/gpytoolbox/edges.py 
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def edges(F,
    return_boundary_indices=False,
    return_interior_indices=False,
    return_nonmanifold_indices=False):
    """Given a triangle mesh with face indices F, returns all unique unoriented
    edges as indices into the vertex array.
    There is no particular ordering convention for edges.
    Boundary edges are guaranteed to be oriented as in F.

    Parameters
    ----------
    F : (m,3) numpy int array
        face index list of a triangle mesh
    return_boundary_indices : bool, optional (default False)
        whether to return a list of indices into E denoting the boundary edges
    return_interior_indices : bool, optional (default False)
        whether to return a list of indices into E denoting the interior edges
    return_nonmanifold_indices : bool, optional (default False)
        whether to return a list of indices into E denoting the nonmanifold edges

    Returns
    -------
    E : (e,2) numpy int array
        indices of edges into the vertex array
    boundary_indices : if requested, (b,) numpy int array
        list of indices into E of boundary edges
    interior_indices : if requested, (i,) numpy int array
        list of indices into E of interior edges
    nonmanifold_indices : if requested, (nm,) numpy int array
        list of indices into E of nonmanifold edges

    Examples
    --------
    ```python
    from gpytoolbox import read_mesh, edges
    v,f = read_mesh("test/unit_tests_data/bunny_oded.obj")
    e = edges(f)
    #Euler's (?) theorem
    self.assertTrue(v.shape[0] - e.shape[0] + f.shape[0] == 2)
    ```

    """

    assert F.shape[0] > 0
    assert F.shape[1] == 3

    #Sort halfedges. Remove duplicates.
    he = halfedges(F)
    flat_he = np.concatenate([he[:,0,:],he[:,1,:],he[:,2,:]], axis=0)
    sorted_he = np.sort(flat_he, axis=1)
    unique_he, unique_indices, unique_count = np.unique(sorted_he, axis=0,
        return_index=True, return_counts=True)

    #Construct edge arrays by preserving the unique indices of boundary and
    # picking sorted orientation for interior edges.
    #Boundary edges have only one halfedge.
    bdry_edges = flat_he[unique_indices[unique_count==1],:]
    #Interior edges have two ore more halfedges.
    interior_edges = unique_he[unique_count>1,:]
    E = np.concatenate([bdry_edges,interior_edges], axis=0)
    assert E.shape == unique_he.shape

    if return_boundary_indices or return_interior_indices or return_nonmanifold_indices:
        retval = [E]
        if return_boundary_indices:
            retval.append(np.arange(0, bdry_edges.shape[0]))
        if return_interior_indices:
            retval.append(np.where(unique_count>1)[0])
        if return_nonmanifold_indices:
            #Nonmanifold edges have three or more halfedges.
            retval.append(np.where(unique_count>2)[0])
        return retval
    else:
        return E