[vtkusers] Scalar value minima in PolyData

[Kevin H. Hobbs]

On Wed, 2007-11-21 at 08:40 -0500, Kevin H. Hobbs wrote:
> Is there a better way to find all of the positions of the scalar value
> minima in a PolyData than to :
> 	loop over all of the points
> 		loop over all of the cells the point is in
> 			loop over all of the other points in the cell
> 				compare the values of the other points to the first points value
> 		save the points location if it is value is less than all of its neighbor's values.
> 


For example the code below is rather confusing because it is so loopy.

	// Find minima in sphere cut
	vtkPolyData * sphere_poly = sphere_cutter->GetOutput();
	sphere_poly->BuildLinks();
	vtkPoints * sphere_points = sphere_poly->GetPoints();
	vtkIdType num_points = sphere_points->GetNumberOfPoints();
	vtkDataArray * point_scalars 
		= sphere_poly->GetPointData()->GetScalars();
	vtkIdType point;
	vtkIdList * point_cells = vtkIdList::New();
	vtkIdList * cell_points = vtkIdList::New();
	for (point = 0; point < num_points; ++point )
	{
		// What is the points value?
		double value;
		point_scalars->GetTuple(point, &value);

		// Assume the point is a minima.
		int minima = 1;

		// What cells is this point in.
		sphere_poly->GetPointCells( point, point_cells );
		vtkIdType num_cells 
			= point_cells->GetNumberOfIds();
		vtkIdType cell;
		for ( cell = 0; cell < num_cells; ++cell )
		{
			vtkIdType neighbor_cell;
			neighbor_cell = point_cells->GetId( cell );
			sphere_poly->GetCellPoints( 
					neighbor_cell, 
					cell_points );
			vtkIdType num_cell_points 
				= cell_points->GetNumberOfIds();
			vtkIdType neighbor_point;
			for ( 
					neighbor_point = 0; 
					neighbor_point < num_cell_points; 
					++neighbor_point )
			{
				vtkIdType neighbor_point_id 
					= cell_points->GetId(neighbor_point);
				double neighbor_value;
				point_scalars->GetTuple(neighbor_point_id, &neighbor_value);
				if ( neighbor_value < value )
					minima = 0;

			}
		}
		// Is the point actually a minima?
		if ((value < stop_time) && ( minima == 1 ))
		{
			// What is the point's location?
			double * pcoord;
			pcoord = sphere_poly->GetPoint( point );
			std::cout 
				<< pcoord[0] << " "
				<< pcoord[1] << " "
				<< pcoord[2] << std::endl;

		}
		
	}

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