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315 lines
9.8 KiB
315 lines
9.8 KiB
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 auxiliary 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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: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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: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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: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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: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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: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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: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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: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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:param subdiv: Delaunay or another subdivision. |
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:param pt: Point to locate. |
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:param edge: Output edge that the point belongs to or is located to the right of it. |
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:param vertex: Optional output vertex double pointer the input point coincides 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 subdivision 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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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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: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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: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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