def get_existing_boundary_indices(mesh):
    """
    Returns
    ----------
        list, int.
        The boundary indices (data['boundary']>0) that exist on the mesh vertices.
    """
    indices = []
    for vkey, data in mesh.vertices(data=True):
        if data['boundary'] > 0:
            if data['boundary'] not in indices:
                indices.append(data['boundary'])
    boundary_indices = sorted(indices)
    return boundary_indices