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Add support for reg 92.1.8 where lon increment not given
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@m1dr
m1dr committed Apr 8, 2021
1 parent 8036e13 commit 01ef303
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Showing 3 changed files with 49 additions and 15 deletions.
19 changes: 11 additions & 8 deletions iris_grib/_load_convert.py
View file
Expand Up @@ -487,12 +487,13 @@ def ellipsoid_geometry(section):
return major, minor, radius


def _calculate_increment(first_grid_point, last_grid_point, num_intervals):
# Calculates the directional increment from the difference between
# the grid point values divided by the total number of intervals.
# Required by template 0 & 40 when no increment values are provided.

return math.fabs(last_grid_point - first_grid_point) / num_intervals
def _calculate_increment(first_point, last_point, n_increments, mod=math.inf):
"""
Calculates the directional increment from the difference between the grid
point values divided by the total number of increments. Required by
template 0 & 40 when no increment values are provided.
"""
return (last_point - first_point) % mod / n_increments


def grid_definition_template_0_and_1(section, metadata, y_name, x_name, cs):
Expand Down Expand Up @@ -538,7 +539,8 @@ def grid_definition_template_0_and_1(section, metadata, y_name, x_name, cs):
if res_flags.i_increments_given
else _calculate_increment(section['longitudeOfFirstGridPoint'],
section['longitudeOfLastGridPoint'],
section['Ni'] - 1))
section['Ni'] - 1,
360.0 / _GRID_ACCURACY_IN_DEGREES))
x_inc *= _GRID_ACCURACY_IN_DEGREES
x_offset = section['longitudeOfFirstGridPoint'] * _GRID_ACCURACY_IN_DEGREES
x_direction = -1 if scan.i_negative else 1
Expand Down Expand Up @@ -1071,7 +1073,8 @@ def grid_definition_template_40_regular(section, metadata, cs):
if res_flags.i_increments_given
else _calculate_increment(section['longitudeOfFirstGridPoint'],
section['longitudeOfLastGridPoint'],
section['Ni'] - 1))
section['Ni'] - 1,
360.0 / _GRID_ACCURACY_IN_DEGREES))
x_inc *= _GRID_ACCURACY_IN_DEGREES
x_offset = section['longitudeOfFirstGridPoint'] * _GRID_ACCURACY_IN_DEGREES
x_direction = -1 if scan.i_negative else 1
Expand Down
4 changes: 4 additions & 0 deletions iris_grib/tests/unit/load_convert/test_calculate_increment.py
View file
Expand Up @@ -24,6 +24,10 @@ def test_positive(self):
result = _calculate_increment(-5, 5, 10)
self.assertEqual(result, 1)

def test_with_mod(self):
result = _calculate_increment(355, 5, 10, 360)
self.assertEqual(result, 1)


if __name__ == '__main__':
tests.main()
41 changes: 34 additions & 7 deletions iris_grib/tests/unit/load_convert/test_grid_definition_template_0_and_1.py
View file
Expand Up @@ -49,18 +49,17 @@ def section_3(self):
})
return section

def expected(self, x_dim, y_dim, x_neg=True, y_neg=True):
def expected(self, x_dim, y_dim, x_points, y_points, x_neg=True,
y_neg=True):
# Prepare the expectation.
expected = empty_metadata()
cs = iris.coord_systems.GeogCS(6367470)
x_points = np.array([0., 1., 2., 3., 4., 5.])
if x_neg:
x_points = x_points[::-1]
x = iris.coords.DimCoord(x_points,
standard_name='longitude',
units='degrees',
coord_system=cs)
y_points = np.array([0., 1., 2., 3., 4., 5.])
if y_neg:
y_points = y_points[::-1]
y = iris.coords.DimCoord(y_points,
Expand All @@ -77,7 +76,10 @@ def test_without_increments(self):
cs = iris.coord_systems.GeogCS(6367470)
grid_definition_template_0_and_1(section, metadata, 'latitude',
'longitude', cs)
expected = self.expected(1, 0, x_neg=False, y_neg=False)
x_points = np.array([0., 1., 2., 3., 4., 5.])
y_points = np.array([0., 1., 2., 3., 4., 5.])
expected = self.expected(1, 0, x_points, y_points, x_neg=False,
y_neg=False)
self.assertEqual(metadata, expected)

def test_with_increments(self):
Expand All @@ -89,7 +91,10 @@ def test_with_increments(self):
cs = iris.coord_systems.GeogCS(6367470)
grid_definition_template_0_and_1(section, metadata, 'latitude',
'longitude', cs)
expected = self.expected(1, 0, x_neg=False, y_neg=False)
x_points = np.array([0., 1., 2., 3., 4., 5.])
y_points = np.array([0., 1., 2., 3., 4., 5.])
expected = self.expected(1, 0, x_points, y_points, x_neg=False,
y_neg=False)
self.assertEqual(metadata, expected)

def test_with_i_not_j_increment(self):
Expand All @@ -100,7 +105,10 @@ def test_with_i_not_j_increment(self):
cs = iris.coord_systems.GeogCS(6367470)
grid_definition_template_0_and_1(section, metadata, 'latitude',
'longitude', cs)
expected = self.expected(1, 0, x_neg=False, y_neg=False)
x_points = np.array([0., 1., 2., 3., 4., 5.])
y_points = np.array([0., 1., 2., 3., 4., 5.])
expected = self.expected(1, 0, x_points, y_points, x_neg=False,
y_neg=False)
self.assertEqual(metadata, expected)

def test_with_j_not_i_increment(self):
Expand All @@ -111,7 +119,26 @@ def test_with_j_not_i_increment(self):
cs = iris.coord_systems.GeogCS(6367470)
grid_definition_template_0_and_1(section, metadata, 'latitude',
'longitude', cs)
expected = self.expected(1, 0, x_neg=False, y_neg=False)
x_points = np.array([0., 1., 2., 3., 4., 5.])
y_points = np.array([0., 1., 2., 3., 4., 5.])
expected = self.expected(1, 0, x_points, y_points, x_neg=False,
y_neg=False)
self.assertEqual(metadata, expected)

def test_without_increments_crossing_0_lon(self):
section = self.section_3()
section['longitudeOfFirstGridPoint'] = 355000000
section['Ni'] = 11
metadata = empty_metadata()
cs = iris.coord_systems.GeogCS(6367470)
grid_definition_template_0_and_1(section, metadata, 'latitude',
'longitude', cs)
x_points = np.array(
[355., 356., 357., 358., 359., 360., 361., 362., 363., 364., 365.]
)
y_points = np.array([0., 1., 2., 3., 4., 5.])
expected = self.expected(1, 0, x_points, y_points, x_neg=False,
y_neg=False)
self.assertEqual(metadata, expected)


Expand Down

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