prepare_roidb does not precompute the maximum overlap between each ROI and each ground-truth box

[alexwongdl]

Hi: The prepare_roidb method in roidb.py claimed to precompute the maximum overlap between each ROI and each ground-truth box. However, I didn't see any information about ROI calculation. And the code

# max overlap with gt over classes (columns)
 max_overlaps = gt_overlaps.max(axis=1)
 # gt class that had the max overlap
max_classes = gt_overlaps.argmax(axis=1)

is strange. As gt_overlaps is calculated in pascal_voc.py overlaps[ix, cls] = 1.0 in line 233.

gt_overlaps.max(axis=1)
gt_overlaps.argmax(axis=1)

doesn't make sense.