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fix intersection out of bounds point #4046

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fix intersection out of bounds point #4046

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4 changes: 4 additions & 0 deletions docs/src/whatsnew/latest.rst
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Expand Up @@ -62,6 +62,10 @@ This document explains the changes made to Iris for this release
#. `@gcaria`_ fixed :meth:`~iris.cube.Cube.ancillary_variable_dims` to also accept
the string name of a :class:`~iris.coords.AncillaryVariable`. (:pull:`3931`)

#. `@rcomer`_ fixed :meth:`~iris.cube.Cube.intersection` for special cases
where one cell's bounds align with the requested maximum and minimum, as
reported in :issue:`3391`. (:pull:`4046`)


💣 Incompatible Changes
=======================
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21 changes: 11 additions & 10 deletions lib/iris/cube.py
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Expand Up @@ -3186,18 +3186,19 @@ def _intersect_modulus(
pre_wrap_delta != post_wrap_delta
)

# Recalculate the extended minimum.
indices = inside_indices[split_cell_indices]
cells = bounds[indices]
cells_delta = np.diff(coord.bounds[indices])

# Watch out for ascending/descending bounds
if cells_delta[0, 0] > 0:
cells[:, 0] = cells[:, 1] - cells_delta[:, 0]
minimum = np.min(cells[:, 0])
else:
cells[:, 1] = cells[:, 0] + cells_delta[:, 0]
minimum = np.min(cells[:, 1])
if maximum % modulus not in cells:
# Recalculate the extended minimum.
cells_delta = np.diff(coord.bounds[indices])

# Watch out for ascending/descending bounds.
if cells_delta[0, 0] > 0:
cells[:, 0] = cells[:, 1] - cells_delta[:, 0]
minimum = np.min(cells[:, 0])
else:
cells[:, 1] = cells[:, 0] + cells_delta[:, 0]
minimum = np.min(cells[:, 1])

points = wrap_lons(coord.points, minimum, modulus)

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8 changes: 8 additions & 0 deletions lib/iris/tests/unit/cube/test_Cube.py
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Expand Up @@ -1731,6 +1731,14 @@ def test_aligned_exclusive(self):
self.assertEqual(result.data[0, 0, 0], 171)
self.assertEqual(result.data[0, 0, -1], 189)

def test_aligned_bounds_at_modulus(self):
cube = create_cube(-179.5, 180.5, bounds=True)
result = cube.intersection(longitude=(0, 360))
self.assertArrayEqual(result.coord("longitude").bounds[0], [0, 1])
self.assertArrayEqual(result.coord("longitude").bounds[-1], [359, 360])
self.assertEqual(result.data[0, 0, 0], 180)
self.assertEqual(result.data[0, 0, -1], 179)

def test_negative_misaligned_points_inside(self):
cube = create_cube(0, 360, bounds=True)
result = cube.intersection(longitude=(-10.25, 10.25))
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