vlfeat / vlfeat

Dear gurus from VLFeat,

I have found a problem (or I have a problem) in the way the function vl_plotsiftdescriptor represents the patch on the image. This function assumes that the patch size is Z = 4 * m * s, with m=3 and s the scale of the frame. But checking the code, the real size comes from the definition of the constant W in line

vlfeat/vl/sift.c

Lines 1775 to 1776 in 1b9075f

    
           int    const W      = floor 
        
             (sqrt(2.0) * SBP * (NBP + 1) / 2.0 + 0.5) ;

So the real size of the patch is Z = 2 * W = sqrt(2) * 15 * s, (15 = m * (NBP+1) ), with NBP=4 and m=3. This documentation is in line with this, but why this function is plotting almost half its real size?

	int const W = floor
	(sqrt(2.0) * SBP * (NBP + 1) / 2.0 + 0.5) ;

Real SIFT Patch Size