[RFC] Different menaning of angle parameter in affine and rotate ops

[vfdev-5]

In Torchvision stable API, there are 2 ops: affine and rotate that has angle as parameter.

However, positive angle parameter in F.affine op performs clockwise rotation.

vision/torchvision/transforms/functional.py

Line 1092 in 8aadef5

angle (number): rotation angle in degrees between -180 and 180, clockwise direction.

while in F.rotate it is an opposite meaning, it does counter clockwise rotation:

vision/torchvision/transforms/functional.py

Line 1004 in 8aadef5

angle (number): rotation angle value in degrees, counter-clockwise.

For Detectron2, Pillow or albumentations, they do counter clockwise rotation for positive angle value.

Question: Should we align F.affine op to perform counter clockwise rotation for positive angle value ?

cc @vfdev-5 @datumbox

[datumbox]

This is ugly. As we discussed offline, we could take the approach of aligning the two AND on the layer that will ensures BC between new and old API, we could add a method that does the conversion and a deprecation warning. I would probably leave this for after the API is completed.

@pmeier any thoughts on this?

[pmeier]

I agree that we should align. Just to make sure that we are on the same page: you want positive angles on the affine_image kernel to mean CCW rotation, and switch the sign for F.affine, correct?