Compute sift at custom key points

Question

I want to find the sift descriptors at custom Keypoint locations in matlab. Is there any function in vlfeat library to do so ?

Answer 1

Yes. See the custom frames section of VLFeat tutorial:

[...] vl_sift [...] can bypass the detector and compute the descriptor on custom frames using the Frames option.

For instance, we can compute the descriptor of a SIFT frame centered at position (100,100), of scale 10 and orientation -pi/8 by:

fc = [100;100;10;-pi/8] ;
[f,d] = vl_sift(I,'frames',fc) ;