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bbrister / SIFT3D

Analogue of the scale-invariant feature transform (SIFT) for three-dimensional images. Includes an image processing and linear algebra library with feature matching and RANSAC regression. Also includes IO functions supporting a variety of image formats.
MIT License
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coordinate values is partly different between keypoints file and Descriptor file #22

Closed junqiangchen closed 5 years ago

junqiangchen commented 5 years ago

hi, i run the example featureC.c code,and generate the keypoints file and Descriptor file.both of all contain feature point coordinate,but i find the coordinate values is partly different between those files,there have 454 feature points,1-382 coordinate values are same,but 383-454 coordinate values are different.

bbrister commented 5 years ago

Hello,

Thanks for your interest.

You are probably seeing different coordinates for features which are in higher octaves of the image pyramid. Descriptor coordinates refer to the original image space, whereas keypoint coordinates refer to the image pyramid level in which they are detected. To do this conversion, multiply the keypoint coordinate by 2 ^ (octave index). Does this match with what you're seeing?

junqiangchen commented 5 years ago

thank you bbrister,this is right.