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Fix line-segment intersection for scaled homogeneous endpoints #282

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Fix line-segment intersection for scaled homogeneous endpoints #282

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5 changes: 5 additions & 0 deletions spatialmath/geom2d.py
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Original file line number Diff line number Diff line change
Expand Up @@ -178,12 +178,17 @@ def intersect_segment(
Tests whether the line intersects the line segment defined by endpoints
``p1`` and ``p2`` which are given in Euclidean or homogeneous form.
"""
# Use unit weight for finite endpoints in the sign and tolerance tests.
p1 = smb.getvector(p1)
if len(p1) == 2:
p1 = np.r_[p1, 1]
elif p1[2] != 0:
p1 = p1 / p1[2]
p2 = smb.getvector(p2)
if len(p2) == 2:
p2 = np.r_[p2, 1]
elif p2[2] != 0:
p2 = p2 / p2[2]

z1 = np.dot(self.line, p1)
z2 = np.dot(self.line, p2)
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12 changes: 12 additions & 0 deletions tests/test_geom2d.py
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Expand Up @@ -140,6 +140,18 @@ def test_intersect_segment(self):
self.assertFalse(l1.intersect_segment((2, 1), (2, 3)))
self.assertTrue(l1.intersect_segment((2, 1), (2, -1)))

def test_intersect_segment_homogeneous_endpoints(self):
line = Line2([0, 1, 0]) # y = 0
above = np.array([1, 2, 1])
below = np.array([1, -2, 1])
for p1, p2, expected in (
((0, 1), -above, False),
(-below, (0, 1), True),
(1e-16 * above, (0, 1), False),
):
with self.subTest(p1=p1, p2=p2):
self.assertEqual(line.intersect_segment(p1, p2), expected)


class EllipseTest(unittest.TestCase):
def test_constructor(self):
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