PK_ERROR_code_t      PK_EDGE_find_end_tangents
(
--- received arguments ---
PK_EDGE_t            edge,               --- edge

--- returned arguments ---
PK_VECTOR_t   *const start,              --- start position of edge
PK_VECTOR_t   *const start_tangent,      --- tangent at start position
PK_VECTOR_t   *const end,                --- end position of edge
PK_VECTOR_t   *const end_tangent         --- tangent at end position
)


This function finds the end positions of an edge and the edge tangents at
those positions.


Specific Errors:
PK_ERROR_wrong_entity     (MILD) The edge is a ring without a vertex
PK_ERROR_at_singularity   (MILD) Failed to evaluate the tangent at singularity
PK_ERROR_missing_geom     (MILD) Edge has no curve geometry


Given an edge, this function will find its start and end positions
and also the tangents at each end. The start and end positions correspond
to the start and end vertices as given by PK_EDGE_ask_vertices.  The end
tangents are directed along the edge from the start position to the end
position.  Note that for an edge for which PK_EDGE_ask_oriented_curve
returns an orientation of PK_LOGICAL_false, these tangents will be
anti-parallel to the curve tangents at these positions.