Method EvaluateGradient

Common/DataModel/vtkImplicitSelectionLoop.cxx:138–160

------------------------------------------------------------------------------ Evaluate gradient of the implicit function. Use a numerical scheme: evaluate the function at four points (O,O+dx,O+dy,O+dz) and approximate the gradient. It's damn slow.

// the function at four points (O,O+dx,O+dy,O+dz) and approximate the gradient.
// It's damn slow.
void vtkImplicitSelectionLoop::EvaluateGradient(double x[3], double n[3])
{
  double xp[3], yp[3], zp[3], g0, gx, gy, gz;
  int i;

  g0 = this->EvaluateFunction(x); // side-effect is to compute DeltaX, Y, and Z

  for (i = 0; i < 3; i++)
  {
    xp[i] = yp[i] = zp[i] = x[i];
  }
  xp[0] += this->DeltaX;
  yp[1] += this->DeltaY;
  zp[2] += this->DeltaZ;

  gx = this->EvaluateFunction(xp);
  gy = this->EvaluateFunction(yp);
  gz = this->EvaluateFunction(zp);

  n[0] = (gx - g0) / this->DeltaX;
  n[1] = (gy - g0) / this->DeltaY;
  n[2] = (gz - g0) / this->DeltaZ;
}

//------------------------------------------------------------------------------
vtkMTimeType vtkImplicitSelectionLoop::GetMTime()