vtkSelectPolyData - select portion of polygonal mesh; generate selection scalars

Super Class: vtkPolyDataToPolyDataFilter

Description:

vtkSelectPolyData is a filter that selects polygonal data based on defining a "loop" and indicating the region inside of the loop. The mesh within the loop consists of complete cells (the cells are not cut). Alternatively, this filter can be used to generate scalars. These scalar values, which are a distance measure to the loop, can be used to clip, contour. or extract data (i.e., anything that an implicit function can do). The loop is defined by an array of x-y-z point coordinates. (Coordinates should be in the same coordinate space as the input polygonal data.) The loop can be concave and non-planar, but not self-intersecting. The input to the filter is a polygonal mesh (only surface primitives such as triangle strips and polygons); the output is either a) a portion of the original mesh laying within the selection loop (GenerateSelectionScalarsOff); or b) the same polygonal mesh with the addition of scalar values (GenerateSelectionScalarsOn). The algorithm works as follows. For each point coordinate in the loop, the closest point in the mesh is found. The result is a loop of closest point ids from the mesh. Then, the edges in the mesh connecting the closest points (and laying along the lines forming the loop) are found. A greedy edge tracking procedure is used as follows. At the current point, the mesh edge oriented in the direction of and whose end point is closest to the line is chosen. The edge is followed to the new end point, and the procedure is repeated. This process continues until the entire loop has been created. To determine what portion of the mesh is inside and outside of the loop, three options are possible. 1) the smallest connected region, 2) the largest connected region, and 3) the connected region closest to a user specified point. (Set the ivar SelectionMode.) Once the loop is computed as above, the GenerateSelectionScalars controls the output of the filter. If on, then scalar values are generated based on distance to the loop lines. Otherwise, the cells laying inside the selection loop are output. By default, the mesh lying within the loop is output; however, if InsideOut is on, then the portion of the mesh lying outside of the loop is output. The filter can be configured to generate the unselected portions of the mesh as output by setting GenerateUnselectedOutput. Use the method GetUnselectedOutput to access this output. (Note: this flag is pertinent only when GenerateSelectionScalars is off.)

Caveats:

Make sure that the points you pick are on a connected surface. If not, then the filter will generate an empty or partial result. Also, self-intersecting loops will generate unpredictable results. During processing of the data, non-triangular cells are converted to triangles if GenerateSelectionScalars is off.

See Also:

vtkImplicitSelectionLoop

Methods:

Detailed Method Descriptions: