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pythonpytorchrotationtorch

Direction of rotation of torch.rot90

In the documentation for torch.rot90 it is stated that

Rotation direction is from the first towards the second axis if k > 0, and from the second towards the first for k < 0.

However say that we are rotating from axis 0 to axis 1, is axis 0 rotating to axis 1 in the clockwise or anti-clockwise direction? (since they are both 90 degree rotations as per the image below)

enter image description here

Solution

  • axis=0 is the dimension that points downwards, while axis=1 points to the right. Visualize the axes like this:

    ---------> axis=1
|
|
|
\/
axis=0

    Now, k>0 means counter-clockwise direction, k<0 is clockwise.

    Thus,

    >>> x = torch.arange(6).view(3, 2)
>>> x
tensor([[0, 1],
        [2, 3],
        [4, 5]])

>>> torch.rot90(x, 1, [0,1])
tensor([[1, 3, 5],
        [0, 2, 4]])

>>> torch.rot90(x, 1, [1,0])
tensor([[4, 2, 0],
        [5, 3, 1]])

    The torch.rot90() is similar to numpy.rot90()

    e.g.

    numpy.rot90(m, k=3, axes=(0, 1))

    would graphically be represented as per the image below:

    enter image description here