326 lines
10 KiB
ReStructuredText
326 lines
10 KiB
ReStructuredText
Planar Subdivisions (C API)
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============================
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.. highlight:: c
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CvSubdiv2D
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----------
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.. ocv:struct:: CvSubdiv2D
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Planar subdivision.
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::
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#define CV_SUBDIV2D_FIELDS() \
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CV_GRAPH_FIELDS() \
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int quad_edges; \
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int is_geometry_valid; \
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CvSubdiv2DEdge recent_edge; \
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CvPoint2D32f topleft; \
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CvPoint2D32f bottomright;
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typedef struct CvSubdiv2D
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{
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CV_SUBDIV2D_FIELDS()
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}
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CvSubdiv2D;
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..
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Planar subdivision is the subdivision of a plane into a set of
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non-overlapped regions (facets) that cover the whole plane. The above
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structure describes a subdivision built on a 2D point set, where the points
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are linked together and form a planar graph, which, together with a few
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edges connecting the exterior subdivision points (namely, convex hull points)
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with infinity, subdivides a plane into facets by its edges.
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For every subdivision, there is a dual subdivision in which facets and
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points (subdivision vertices) swap their roles. This means that a facet is
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treated as a vertex (called a virtual point below) of the dual subdivision and
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the original subdivision vertices become facets. In the figure below, the
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original subdivision is marked with solid lines and dual subdivision -
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with dotted lines.
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.. image:: pics/subdiv.png
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OpenCV subdivides a plane into triangles using the Delaunay's
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algorithm. Subdivision is built iteratively starting from a dummy
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triangle that includes all the subdivision points for sure. In this
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case, the dual subdivision is a Voronoi diagram of the input 2D point set. The
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subdivisions can be used for the 3D piece-wise transformation of a plane,
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morphing, fast location of points on the plane, building special graphs
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(such as NNG,RNG), and so forth.
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CvQuadEdge2D
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------------
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.. ocv:struct:: CvQuadEdge2D
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Quad-edge of a planar subdivision.
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::
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/* one of edges within quad-edge, lower 2 bits is index (0..3)
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and upper bits are quad-edge pointer */
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typedef long CvSubdiv2DEdge;
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/* quad-edge structure fields */
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#define CV_QUADEDGE2D_FIELDS() \
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int flags; \
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struct CvSubdiv2DPoint* pt[4]; \
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CvSubdiv2DEdge next[4];
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typedef struct CvQuadEdge2D
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{
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CV_QUADEDGE2D_FIELDS()
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}
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CvQuadEdge2D;
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..
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Quad-edge is a basic element of a subdivision containing four edges (e, eRot, reversed e, and reversed eRot):
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.. image:: pics/quadedge.png
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CvSubdiv2DPoint
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---------------
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.. ocv:struct:: CvSubdiv2DPoint
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Point of an original or dual subdivision.
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::
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#define CV_SUBDIV2D_POINT_FIELDS()\
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int flags; \
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CvSubdiv2DEdge first; \
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CvPoint2D32f pt; \
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int id;
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#define CV_SUBDIV2D_VIRTUAL_POINT_FLAG (1 << 30)
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typedef struct CvSubdiv2DPoint
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{
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CV_SUBDIV2D_POINT_FIELDS()
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}
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CvSubdiv2DPoint;
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..
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* id
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This integer can be used to index auxillary data associated with each vertex of the planar subdivision.
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CalcSubdivVoronoi2D
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-------------------
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Calculates the coordinates of the Voronoi diagram cells.
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.. ocv:cfunction:: void cvCalcSubdivVoronoi2D( CvSubdiv2D* subdiv )
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.. ocv:pyoldfunction:: cv.CalcSubdivVoronoi2D(subdiv)-> None
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:param subdiv: Delaunay subdivision, in which all the points are already added.
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The function calculates the coordinates
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of virtual points. All virtual points corresponding to a vertex of the
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original subdivision form (when connected together) a boundary of the Voronoi
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cell at that point.
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ClearSubdivVoronoi2D
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--------------------
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Removes all virtual points.
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.. ocv:cfunction:: void cvClearSubdivVoronoi2D( CvSubdiv2D* subdiv )
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.. ocv:pyoldfunction:: cv.ClearSubdivVoronoi2D(subdiv)-> None
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:param subdiv: Delaunay subdivision.
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The function removes all of the virtual points. It
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is called internally in
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:ocv:cfunc:`CalcSubdivVoronoi2D`
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if the subdivision
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was modified after the previous call to the function.
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CreateSubdivDelaunay2D
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----------------------
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Creates an empty Delaunay triangulation.
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.. ocv:cfunction:: CvSubdiv2D* cvCreateSubdivDelaunay2D( CvRect rect, CvMemStorage* storage )
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.. ocv:pyoldfunction:: cv.CreateSubdivDelaunay2D(rect, storage)-> emptyDelaunayTriangulation
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:param rect: Rectangle that includes all of the 2D points that are to be added to the subdivision.
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:param storage: Container for the subdivision.
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The function creates an empty Delaunay
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subdivision where 2D points can be added using the function
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:ocv:cfunc:`SubdivDelaunay2DInsert`
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. All of the points to be added must be within
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the specified rectangle, otherwise a runtime error is raised.
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Note that the triangulation is a single large triangle that covers the given rectangle. Hence the three vertices of this triangle are outside the rectangle
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``rect``
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.
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FindNearestPoint2D
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------------------
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Finds the subdivision vertex closest to the given point.
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.. ocv:cfunction:: CvSubdiv2DPoint* cvFindNearestPoint2D( CvSubdiv2D* subdiv, CvPoint2D32f pt )
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.. ocv:pyoldfunction:: cv.FindNearestPoint2D(subdiv, pt)-> point
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:param subdiv: Delaunay or another subdivision.
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:param pt: Input point.
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The function is another function that
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locates the input point within the subdivision. It finds the subdivision vertex that
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is the closest to the input point. It is not necessarily one of vertices
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of the facet containing the input point, though the facet (located using
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:ocv:cfunc:`Subdiv2DLocate`
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) is used as a starting
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point. The function returns a pointer to the found subdivision vertex.
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Subdiv2DEdgeDst
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---------------
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Returns the edge destination.
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.. ocv:cfunction:: CvSubdiv2DPoint* cvSubdiv2DEdgeDst( CvSubdiv2DEdge edge )
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.. ocv:pyoldfunction:: cv.Subdiv2DEdgeDst(edge)-> point
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:param edge: Subdivision edge (not a quad-edge).
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The function returns the edge destination. The
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returned pointer may be NULL if the edge is from a dual subdivision and
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the virtual point coordinates are not calculated yet. The virtual points
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can be calculated using the function
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:ocv:cfunc:`CalcSubdivVoronoi2D`.
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Subdiv2DGetEdge
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---------------
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Returns one of the edges related to the given edge.
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.. ocv:cfunction:: CvSubdiv2DEdge cvSubdiv2DGetEdge( CvSubdiv2DEdge edge, CvNextEdgeType type )
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.. ocv:pyoldfunction:: cv.Subdiv2DGetEdge(edge, type)-> CvSubdiv2DEdge
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:param edge: Subdivision edge (not a quad-edge).
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:param type: Parameter specifying which of the related edges to return. The following values are possible:
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* **CV_NEXT_AROUND_ORG** next around the edge origin ( ``eOnext`` on the picture below if ``e`` is the input edge)
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* **CV_NEXT_AROUND_DST** next around the edge vertex ( ``eDnext`` )
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* **CV_PREV_AROUND_ORG** previous around the edge origin (reversed ``eRnext`` )
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* **CV_PREV_AROUND_DST** previous around the edge destination (reversed ``eLnext`` )
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* **CV_NEXT_AROUND_LEFT** next around the left facet ( ``eLnext`` )
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* **CV_NEXT_AROUND_RIGHT** next around the right facet ( ``eRnext`` )
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* **CV_PREV_AROUND_LEFT** previous around the left facet (reversed ``eOnext`` )
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* **CV_PREV_AROUND_RIGHT** previous around the right facet (reversed ``eDnext`` )
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.. image:: pics/quadedge.png
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The function returns one of the edges related to the input edge.
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Subdiv2DNextEdge
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----------------
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Returns next edge around the edge origin.
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.. ocv:cfunction:: CvSubdiv2DEdge cvSubdiv2DNextEdge( CvSubdiv2DEdge edge )
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.. ocv:pyoldfunction:: cv.Subdiv2DNextEdge(edge)-> CvSubdiv2DEdge
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:param edge: Subdivision edge (not a quad-edge).
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The function returns the next edge around the edge origin:
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``eOnext``
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on the picture above if
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``e``
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is the input edge).
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Subdiv2DLocate
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--------------
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Returns the location of a point within a Delaunay triangulation.
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.. ocv:cfunction:: CvSubdiv2DPointLocation cvSubdiv2DLocate( CvSubdiv2D* subdiv, CvPoint2D32f pt, CvSubdiv2DEdge* edge, CvSubdiv2DPoint** vertex=NULL )
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.. ocv:pyoldfunction:: cv.Subdiv2DLocate(subdiv, pt) -> (loc, where)
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:param subdiv: Delaunay or another subdivision.
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:param pt: Point to locate.
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:param edge: Output edge the point falls onto or right to.
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:param vertex: Optional output vertex double pointer the input point coinsides with.
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The function locates the input point within the subdivision. There are five cases:
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*
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The point falls into some facet. The function returns
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``CV_PTLOC_INSIDE``
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and
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``*edge``
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will contain one of edges of the facet.
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*
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The point falls onto the edge. The function returns
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``CV_PTLOC_ON_EDGE``
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and
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``*edge``
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will contain this edge.
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*
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The point coincides with one of the subdivision vertices. The function returns
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``CV_PTLOC_VERTEX``
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and
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``*vertex``
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will contain a pointer to the vertex.
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*
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The point is outside the subdivsion reference rectangle. The function returns
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``CV_PTLOC_OUTSIDE_RECT``
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and no pointers are filled.
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*
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One of input arguments is invalid. A runtime error is raised or, if silent or "parent" error processing mode is selected,
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``CV_PTLOC_ERROR``
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is returnd.
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Subdiv2DRotateEdge
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------------------
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Returns another edge of the same quad-edge.
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.. ocv:cfunction:: CvSubdiv2DEdge cvSubdiv2DRotateEdge( CvSubdiv2DEdge edge, int rotate )
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.. ocv:pyoldfunction:: cv.Subdiv2DRotateEdge(edge, rotate)-> CvSubdiv2DEdge
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:param edge: Subdivision edge (not a quad-edge).
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:param rotate: Parameter specifying which of the edges of the same quad-edge as the input one to return. The following values are possible:
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* **0** the input edge ( ``e`` on the picture below if ``e`` is the input edge)
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* **1** the rotated edge ( ``eRot`` )
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* **2** the reversed edge (reversed ``e`` (in green))
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* **3** the reversed rotated edge (reversed ``eRot`` (in green))
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The function returns one of the edges of the same quad-edge as the input edge.
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SubdivDelaunay2DInsert
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----------------------
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Inserts a single point into a Delaunay triangulation.
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.. ocv:cfunction:: CvSubdiv2DPoint* cvSubdivDelaunay2DInsert( CvSubdiv2D* subdiv, CvPoint2D32f pt)
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.. ocv:pyoldfunction:: cv.SubdivDelaunay2DInsert(subdiv, pt)-> point
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:param subdiv: Delaunay subdivision created by the function :ocv:cfunc:`CreateSubdivDelaunay2D`.
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:param pt: Inserted point.
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The function inserts a single point into a subdivision and modifies the subdivision topology appropriately. If a point with the same coordinates exists already, no new point is added. The function returns a pointer to the allocated point. No virtual point coordinates are calculated at this stage.
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