Sign error fix in measure.regionprops for orientations of 45 degrees

[jakeMartin1234]

Description

Fixed a sign error in the orientation property in measure.regionprops. The preset values for the orientations PI/4 and -PI/4 needed to be switched. This probably dates from switching regionprops over from xy coordinates to rc coordinates.

Closes #6815

Checklist

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[decorouz]

Nice work man. I was about to create a PR for same.

[jni]

thanks @jakeMartin1234! It looks like a test needs updating:

_______________________________ test_orientation _______________________________

    def test_orientation():
        orient = regionprops(SAMPLE)[0].orientation
        # determined with MATLAB
        target_orient = -1.4663278802756865
        assert_almost_equal(orient, target_orient)

        orient = regionprops(SAMPLE, spacing=(2, 2))[0].orientation
        assert_almost_equal(orient, target_orient)

        # test diagonal regions
        diag = np.eye(10, dtype=int)
        orient_diag = regionprops(diag)[0].orientation
>       assert_almost_equal(orient_diag, -math.pi / 4)

/opt/hostedtoolcache/Python/3.11.2/x64/lib/python3.11/site-packages/skimage/measure/tests/test_regionprops.py:648:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

args = (0.7853981633974483, -0.7853981633974483), kwds = {}

    @wraps(func)
    def inner(*args, **kwds):
        with self._recreate_cm():
>           return func(*args, **kwds)
E           AssertionError:
E           Arrays are not almost equal to 7 decimals
E            ACTUAL: 0.7853981633974483
E            DESIRED: -0.7853981633974483

I'd also like it if you could add an extra test: copy image over from #6815, then do something like:

def test_orientation_continuity():
    props = regionprops(image)
    orientations = [prop.orientation for prop in props]
    np.testing.assert_allclose(orientations, orientations[1], rtol=0, atol=0.08)

[jakeMartin1234]

@jni I just updated the test. Are you saying that I should copy over the image and store it in the repository then load it into the python file or copy over the arrays that that represent the images in #6815? If I need to store the image in the repository, where should I store it? Would be great if you could let me know so that I can add the test to my branch.

[jni]

You can just copy the code from the issue into the test function:

def test_orientation_continuity():
    # nearly diagonal array
    arr1 = np.array([[0, 0, 1, 1],[0, 0, 1, 0],[0, 1, 0, 0],[1, 0, 0, 0]])
    # diagonal array 
    arr2 = np.array([[0, 0, 0, 2],[0, 0, 2, 0],[0, 2, 0, 0],[2, 0, 0, 0]])
    # nearly diagonal array 
    arr3 = np.array([[0, 0, 0, 3],[0, 0, 3, 3],[0, 3, 0, 0],[3, 0, 0, 0]])
    image = np.hstack((arr1,arr2,arr3))
    props = regionprops(image)
    orientations = [prop.orientation for prop in props]
    np.testing.assert_allclose(orientations, orientations[1], rtol=0, atol=0.08)

[jni]

Remember to push any additional commits to your branch so we can see them here! 😅

[jakeMartin1234]

Hi @jni, I just pushed the new changes to the test file. I added a few more checks in the test_orientation_continuity(). Let me know if you think anything else needs changing.

[jni]

Awesome! 😍