lwt_GetFaceByPoint()

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

Find the face-id of a face containing 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 a containing face

Returns

a face identifier if one is found (0 if universe), -1 on error (multiple faces within distance or point on node or edge). The liblwgeom error handler will be invoked in case of error.

Definition at line 4738 of file lwgeom_topo.c.

{
  LWT_ELEMID id = 0;
  LWT_ISO_EDGE *elem;
  int num, i;
  int flds = LWT_COL_EDGE_EDGE_ID |
             LWT_COL_EDGE_GEOM |
             LWT_COL_EDGE_FACE_LEFT |
             LWT_COL_EDGE_FACE_RIGHT;
  LWGEOM *qp = lwpoint_as_lwgeom(pt);
 
  id = lwt_be_getFaceContainingPoint(topo, pt);
  if ( id == -2 ) {
    lwerror("Backend error: %s", lwt_be_lastErrorMessage(topo->be_iface));
    return -1;
  }
 
  if ( id > 0 )
  {
    return id;
  }
  id = 0; /* or it'll be -1 for not found */
 
  LWDEBUG(1, "No face properly contains query point,"
             " looking for edges");
 
  /* Not in a face, may be in universe or on edge, let's check
   * for distance */
  /* NOTE: we never pass a tolerance of 0 to avoid ever using
   * ST_Within, which doesn't include endpoints matches */
  elem = lwt_be_getEdgeWithinDistance2D(topo, pt, tol?tol:1e-5, &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]);
    LWT_ELEMID eface = 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;
    }
 
    /* don't consider dangling edges */
    if ( e->face_left == e->face_right )
    {
      LWDEBUGF(1, "Edge %" LWTFMT_ELEMID
                  " is dangling, won't consider it", e->edge_id);
      continue;
    }
 
    geom = lwline_as_lwgeom(e->geom);
    dist = lwgeom_mindistance2d_tolerance(geom, qp, tol);
 
    LWDEBUGF(1, "Distance from edge %" LWTFMT_ELEMID
                " is %g (tol=%g)", e->edge_id, dist, tol);
 
    /* we won't consider edges too far */
    if ( dist > tol ) continue;
    if ( e->face_left == 0 ) {
      eface = e->face_right;
    }
    else if ( e->face_right == 0 ) {
      eface = e->face_left;
    }
    else {
      _lwt_release_edges(elem, num);
      lwerror("Two or more faces found");
      return -1;
    }
 
    if ( id && id != eface )
    {
      _lwt_release_edges(elem, num);
      lwerror("Two or more faces found"
#if 0 /* debugging */
              " (%" LWTFMT_ELEMID
              " and %" LWTFMT_ELEMID ")", id, eface
#endif
             );
      return -1;
    }
    else id = eface;
  }
  if ( num ) _lwt_release_edges(elem, num);
 
  return id;
}

References _lwt_release_edges(), LWT_TOPOLOGY_T::be_iface, LWT_ISO_EDGE::edge_id, LWT_ISO_EDGE::face_left, LWT_ISO_EDGE::face_right, LWT_ISO_EDGE::geom, LWDEBUG, LWDEBUGF, lwerror(), lwgeom_mindistance2d_tolerance(), lwline_as_lwgeom(), lwnotice(), lwpoint_as_lwgeom(), lwt_be_getEdgeWithinDistance2D(), lwt_be_getFaceContainingPoint(), lwt_be_lastErrorMessage(), LWT_COL_EDGE_EDGE_ID, LWT_COL_EDGE_FACE_LEFT, LWT_COL_EDGE_FACE_RIGHT, LWT_COL_EDGE_GEOM, and LWTFMT_ELEMID.

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