Sorting keypoints and descriptors on GPU

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Hello,

When calculating keypoints/descriptors with SURF on GPU, in the each run (with same parameters and image) they are stored in a different order, but with the same content. Because of that, some algorithms that I am using produce slightly different results each time.

What would be the easiest way to sort them after calculation? Downloading them and sorting seems hard, since descriptors on CPU contain 64/128x more elements. Is it possible to detect keypoints, download them to CPU, sort them and put them back on GPU to calculate descriptors? I know it is possible to do the calculations separately on CPU version. Also, would it produce same results each time?

Thanks!