hk_icosahedron_lattice (
        h,
        k,
        radius,
        orientation,
        )

triangle_map ( tri1,  tri2 )

map_triangles ( tmap,  triangles )

hk_triangle ( h,  k )

hk3_to_xyz ( hklist )

cross_product ( u,  v )

cut_point (
        u,
        v,
        tri,
        )

Find intersection of segment u->v with triangle boundary. u and v must be an interior and an exterior point.

mask_edge ( edge_mask,  *edges )

Mask out edges given by pair of vertex indices (0-2). Bits 0, 1, and 2 correspond to edges 0-1, 1-2, and 2-0 respectively.

triangle_intersection (
        t1,
        t2,
        edge_mask,
        )

Triangulate the portion of triangle t1 inside t2. Only the cases that occur in the hk icosahedral grids are handled.

surface_geometry ( triangles,  tolerance=1e-5 )

Take a list of triangles where each triangle is specified by 3 xyz vertex positions and convert to a vertex and triangle array where the triangle array contains indices into the vertex array. Vertices in the original triangle data that are close (within tolerance) are merged into a single vertex.

segment_intersection (
        a,
        b,
        c,
        d,
        )

Find intersection of segment ab with segment cd. Return (x,y) or None if no intersectin.

show_hk_lattice (
        h,
        k,
        radius,
        orientation='222',
        color_rgba=( 1, 1, 1, 1 ),
        mesh_line_thickness=1,
        sphere_factor=0,
        replace=True,
        )

Produce hexagonal lattices on an icosahedron.

These lattices are described at

http://viperdb.scripps.edu/icos_server.php?icspage=paradigm

interpolate_with_sphere (
        varray,
        radius,
        sphere_factor,
        )

vertex_in_triangle ( v,  t )