lwt_GetEdgeByPoint()

LWT_ELEMID lwt_GetEdgeByPoint	(	LWT_TOPOLOGY *	topo,
		LWPOINT *	pt,
		double	tol
	)

Find the edge-id of an edge that intersects a given point.

Parameters

topo	the topology to operate on
point	the point to use for query
tol	max distance around the given point to look for an intersecting edge

Returns

an edge identifier if one is found, 0 if none is found, -1 on error (multiple edges within distance). The liblwgeom error handler will be invoked in case of error.

Definition at line 4824 of file lwgeom_topo.c.

References _lwt_release_edges(), LWT_TOPOLOGY_T::be_iface, LWT_ISO_EDGE::edge_id, LWT_ISO_EDGE::geom, lwerror(), lwgeom_is_empty(), lwgeom_mindistance2d_tolerance(), lwline_as_lwgeom(), lwnotice(), lwpoint_as_lwgeom(), lwt_be_getEdgeWithinDistance2D(), lwt_be_lastErrorMessage(), LWT_COL_EDGE_EDGE_ID, LWT_COL_EDGE_GEOM, and LWTFMT_ELEMID.

{
  LWT_ISO_EDGE *elem;
  int num, i;
  int flds = LWT_COL_EDGE_EDGE_ID|LWT_COL_EDGE_GEOM; /* GEOM is not needed */
  LWT_ELEMID id = 0;
  LWGEOM *qp = lwpoint_as_lwgeom(pt); /* query point */

  if ( lwgeom_is_empty(qp) )
  {
    lwerror("Empty query point");
    return -1;
  }
  elem = lwt_be_getEdgeWithinDistance2D(topo, pt, tol, &num, flds, 0);
  if ( num == -1 )
  {
    lwerror("Backend error: %s", lwt_be_lastErrorMessage(topo->be_iface));
    return -1;
  }
  for (i=0; i<num;++i)
  {
    LWT_ISO_EDGE *e = &(elem[i]);
#if 0
    LWGEOM* geom;
    double dist;

    if ( ! e->geom )
    {
      _lwt_release_edges(elem, num);
      lwnotice("Corrupted topology: edge %" LWTFMT_ELEMID
               " has null geometry", e->edge_id);
      continue;
    }

    /* Should we check for intersection not being on an endpoint
     * as documented ? */
    geom = lwline_as_lwgeom(e->geom);
    dist = lwgeom_mindistance2d_tolerance(geom, qp, tol);
    if ( dist > tol ) continue;
#endif

    if ( id )
    {
      _lwt_release_edges(elem, num);
      lwerror("Two or more edges found");
      return -1;
    }
    else id = e->edge_id;
  }

  if ( num ) _lwt_release_edges(elem, num);

  return id;
}

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