scikit-image

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import numpy as np
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from skimage.measure import approximate_polygon, subdivide_polygon
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from skimage.measure._polygon import _SUBDIVISION_MASKS
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from skimage._shared import testing
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from skimage._shared.testing import assert_array_equal, assert_equal
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square = np.array(
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    [
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        [0, 0],
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        [0, 1],
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        [0, 2],
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        [0, 3],
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        [1, 3],
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        [2, 3],
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        [3, 3],
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        [3, 2],
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        [3, 1],
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        [3, 0],
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        [2, 0],
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        [1, 0],
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        [0, 0],
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    ]
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)
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def test_approximate_polygon():
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    out = approximate_polygon(square, 0.1)
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    assert_array_equal(out, square[(0, 3, 6, 9, 12), :])
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    out = approximate_polygon(square, 2.2)
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    assert_array_equal(out, square[(0, 6, 12), :])
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    out = approximate_polygon(square[(0, 1, 3, 4, 5, 6, 7, 9, 11, 12), :], 0.1)
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    assert_array_equal(out, square[(0, 3, 6, 9, 12), :])
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    out = approximate_polygon(square, -1)
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    assert_array_equal(out, square)
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    out = approximate_polygon(square, 0)
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    assert_array_equal(out, square)
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def test_subdivide_polygon():
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    new_square1 = square
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    new_square2 = square[:-1]
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    new_square3 = square[:-1]
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    # test iterative subdvision
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    for _ in range(10):
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        square1, square2, square3 = new_square1, new_square2, new_square3
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        # test different B-Spline degrees
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        for degree in range(1, 7):
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            mask_len = len(_SUBDIVISION_MASKS[degree][0])
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            # test circular
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            new_square1 = subdivide_polygon(square1, degree)
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            assert_array_equal(new_square1[-1], new_square1[0])
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            assert_equal(new_square1.shape[0], 2 * square1.shape[0] - 1)
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            # test non-circular
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            new_square2 = subdivide_polygon(square2, degree)
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            assert_equal(new_square2.shape[0], 2 * (square2.shape[0] - mask_len + 1))
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            # test non-circular, preserve_ends
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            new_square3 = subdivide_polygon(square3, degree, True)
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            assert_equal(new_square3[0], square3[0])
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            assert_equal(new_square3[-1], square3[-1])
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            assert_equal(new_square3.shape[0], 2 * (square3.shape[0] - mask_len + 2))
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    # not supported B-Spline degree
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    with testing.raises(ValueError):
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        subdivide_polygon(square, 0)
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    with testing.raises(ValueError):
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        subdivide_polygon(square, 8)
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