I need to understand how SIFT calculates the descriptors for the keypoints.
Intuitively, i understand that it takes each keypoint, calculates the gradients for each pixel in a circular neighborhood of the keypoint.
The paper mentions a coordination system rotation in the keypoint.
My questions:
- is my intuitive understanding correct?
- im following this implementation of SIFT, and in the part of the calculation function there is this cos/sin calculation:
OpenCV's SIFT implementation · GitHub
i think this is related to the coord system rotation, can you explain how?
p.s. This is my first post here!