LIBPATH(3)                 Library Functions Manual                 LIBPATH(3)



NAME
       libpathplan - finds and smooths shortest paths

SYNOPSIS
       #include <graphviz/pathplan.h>

       typedef struct Pxy_t {
           double x, y;
       } Pxy_t;

       typedef struct Pxy_t Ppoint_t;
       typedef struct Pxy_t Pvector_t;

       typedef struct Ppoly_t {
           Ppoint_t *ps;
           int pn;
       } Ppoly_t;

       typedef Ppoly_t Ppolyline_t;

       typedef struct Pedge_t {
           Ppoint_t a, b;
       } Pedge_t;

       typedef struct vconfig_s vconfig_t;

       #define POLYID_NONE
       #define POLYID_UNKNOWN

       int Pshortestpath(Ppoly_t *boundary, Ppoint_t endpoints[2], Ppolyline_t *output_route);

       vconfig_t *Pobsopen(Ppoly_t **obstacles, int n_obstacles);
       int Pobspath(vconfig_t *config, Ppoint_t p0, int poly0, Ppoint_t p1, int poly1, Ppolyline_t *output_route);
       void Pobsclose(vconfig_t *config);

       int Proutespline (Pedge_t *barriers, int n_barriers, Ppolyline_t input_route, Pvector_t endpoint_slopes[2],
              Ppolyline_t *output_route);

       int Ppolybarriers(Ppoly_t **polys, int n_polys, Pedge_t **barriers, int *n_barriers);

DESCRIPTION
       libpathplan provides functions for creating spline paths in the plane
       that are constrained by a polygonal boundary or obstacles to avoid.
       All polygons must be simple, but need not be convex.

      int Pshortestpath(Ppoly_t *boundary, Ppoint_t endpoints[2], Ppolyline_t
       *output_route);
       The function Pshortestpath finds a shortest path between two points in
       a simple polygon.  The polygon is specified by a list of its vertices,
       in either clockwise or counterclockwise order.  You pass endpoints
       interior to the polygon boundary.  A shortest path connecting the
       points that remains in the polygon is returned in output_route.  If
       either endpoint does not lie in the polygon, -1 is returned; otherwise,
       0 is returned on success.  The array of points in output_route is
       static to the library. It should not be freed, and should be used
       before another call to Pshortestpath.

       vconfig_t *Pobsopen(Ppoly_t **obstacles, int n_obstacles);
       Pobspath(vconfig_t *config, Ppoint_t p0, int poly0, Ppoint_t p1, int
       poly1, Ppolyline_t *output_route);
       void Pobsclose(vconfig_t *config);
       These functions find a shortest path between two points in the plane
       that contains polygonal obstacles (holes).  Pobsopen creates a
       configuration (an opaque struct of type vconfig_t) on a set of
       obstacles.  The n_obstacles obstacles are given in the array obstacles;
       the points of each polygon should be in clockwise order.  The function
       Pobsclose frees the data allocated in Pobsopen.

       Pobspath finds a shortest path between the endpoints that remains
       outside the obstacles.  If the endpoints are known to lie inside
       obstacles, poly0 or poly1 should be set to the index in the obstacles
       array.  If an endpoint is definitely not inside an obstacle, then
       POLYID_NONE should be passed.  If the caller has not checked, then
       POLYID_UNKNOWN should be passed, and the path library will perform the
       test. The resulting shortest path is returned in output_route. Note
       that this function does not provide for a boundary polygon. The array
       of points stored in output_route are allocated by the library, but
       should be freed by the user.

      int Proutespline (Pedge_t *barriers, int n_barriers, Ppolyline_t
       input_route, Pvector_t endpoint_slopes[2], Ppolyline_t *output_route);
       This function fits a cubic B-spline curve to a polyline path.  The
       curve is constructed to avoid a set of n_barriers barrier line segments
       specified in the array barriers. If you start with polygonal obstacles,
       you can supply each polygon's edges as part of the barrier list.  The
       polyline input_route provides a template for the final path; it is
       usually the output_route of one of the shortest path finders, but it
       can be any simple path that doesn't cross any barrier segment.  The
       input also allows the specification of desired slopes at the endpoints
       via endpoint_slopes. These are specified as vectors.  For example, to
       have an angle of T at an endpoing, one could use (cos(T),sin(T)).  A
       vector (0,0) means unconstrained slope.  The output is returned in
       output_route and consists of the control points of the B-spline. The
       function return 0 on success; a return value of -1 indicates failure.
       The array of points in output_route is static to the library. It should
       not be freed, and should be used before another call to Proutespline.

      int Ppolybarriers(Ppoly_t **polys, int n_polys, Pedge_t **barriers, int
       *n_barriers);
       This is a utility function that converts an input list of polygons into
       an output list of barrier segments.  The array of points in barriers is
       static to the library. It should not be freed, and should be used
       before another call to Ppolybarriers.  The function returns 1 on
       success.

BUGS
       The function Proutespline does not guarantee that it will preserve the
       topology of the input path as regards the boundaries. For example, if
       some of the segments correspond to a small polygon, it may be possible
       that the final path has flipped over the obstacle.

AUTHORS
       David Dobkin (dpd@cs.princeton.edu), Eleftherios Koutsofios
       (ek@research.att.com), Emden Gansner (erg@research.att.com).



OpenBSD                          01 APRIL 1997                      LIBPATH(3)
