code: public void describe(double x, double y, double angle, double scale, BrightFeature ret)
  	{
  		describe(x, y, angle, scale, (TupleDesc_F64) ret);
  
  		// normalize feature vector to have an Euclidean length of 1
  		// adds light invariance
  		UtilFeature.normalizeL2(ret);
  
  		// Laplacian's sign
  		ret.white = computeLaplaceSign((int)(x+0.5),(int)(y+0.5), scale);
  	}
docs: <p>
  Computes the SURF descriptor for the specified interest point.  If the feature
  goes outside of the image border (including convolution kernels) then null is returned.
  </p>
  
  @param x Location of interest point.
  @param y Location of interest point.
  @param angle The angle the feature is pointing at in radians.
  @param scale Scale of the interest point. Null is returned if the feature goes outside the image border.
  @param ret storage for the feature. Must have 64 values.