/*=========================================================================

  Program:   Visualization Toolkit
  Module:    $RCSfile: vtkFiniteDifferenceGradientEstimator.h,v $
  Language:  C++
  Date:      $Date: 2001/10/11 13:38:08 $
  Version:   $Revision: 1.16 $


Copyright (c) 1993-2001 Ken Martin, Will Schroeder, Bill Lorensen 
All rights reserved.

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 * Neither name of Ken Martin, Will Schroeder, or Bill Lorensen nor the names
   of any contributors may be used to endorse or promote products derived
   from this software without specific prior written permission.

 * Modified source versions must be plainly marked as such, and must not be
   misrepresented as being the original software.

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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

=========================================================================*/

// .NAME vtkFiniteDifferenceGradientEstimator - Use finite differences to estimate gradient.
//
// .SECTION Description
//  vtkFiniteDifferenceGradientEstimator is a concrete subclass of 
//  vtkEncodedGradientEstimator that uses a central differences technique to
//  estimate the gradient. The gradient at some sample location (x,y,z)
//  would be estimated by:
//      
//       nx = (f(x-dx,y,z) - f(x+dx,y,z)) / 2*dx;
//       ny = (f(x,y-dy,z) - f(x,y+dy,z)) / 2*dy;
//       nz = (f(x,y,z-dz) - f(x,y,z+dz)) / 2*dz;
//
//  This value is normalized to determine a unit direction vector and a
//  magnitude. The normal is computed in voxel space, and 
//  dx = dy = dz = SampleSpacingInVoxels. A scaling factor is applied to
//  convert this normal from voxel space to world coordinates.
//
// .SECTION see also
// vtkEncodedGradientEstimator

#ifndef __vtkFiniteDifferenceGradientEstimator_h
#define __vtkFiniteDifferenceGradientEstimator_h

#include "vtkEncodedGradientEstimator.h"

class VTK_RENDERING_EXPORT vtkFiniteDifferenceGradientEstimator : public vtkEncodedGradientEstimator
{
public:
  vtkTypeMacro(vtkFiniteDifferenceGradientEstimator,vtkEncodedGradientEstimator);
  void PrintSelf( ostream& os, vtkIndent index );

  // Description:
  // Construct a vtkFiniteDifferenceGradientEstimator with
  // a SampleSpacingInVoxels of 1.
  static vtkFiniteDifferenceGradientEstimator *New();

  // Description:
  // Set/Get the spacing between samples for the finite differences
  // method used to compute the normal. This spacing is in voxel units.
  vtkSetMacro( SampleSpacingInVoxels, int );
  vtkGetMacro( SampleSpacingInVoxels, int );

  // The sample spacing between samples taken for the normal estimation
  int SampleSpacingInVoxels;

protected:
  vtkFiniteDifferenceGradientEstimator();
  ~vtkFiniteDifferenceGradientEstimator();


  // Description:
  // Recompute the encoded normals and gradient magnitudes.
  void UpdateNormals( void );
private:
  vtkFiniteDifferenceGradientEstimator(const vtkFiniteDifferenceGradientEstimator&);  // Not implemented.
  void operator=(const vtkFiniteDifferenceGradientEstimator&);  // Not implemented.
}; 


#endif
