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Make sure a discrete data type is preserved through resampling #510

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Nov 23, 2018
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15 changes: 12 additions & 3 deletions satpy/resample.py
Original file line number Diff line number Diff line change
Expand Up @@ -851,8 +851,15 @@ def resample(source_area, data, destination_area,
return res


def get_fill_value(dataset):
"""Get the fill value of the *dataset*, defaulting to np.nan."""
if np.issubdtype(dataset.dtype, np.integer):
return dataset.attrs.get('_FillValue', np.nan)
return np.nan


def resample_dataset(dataset, destination_area, **kwargs):
"""Resample the current projectable and return the resampled one.
"""Resample *dataset* and return the resampled version.

Args:
dataset (xarray.DataArray): Data to be resampled.
Expand All @@ -862,7 +869,8 @@ def resample_dataset(dataset, destination_area, **kwargs):
**kwargs: The extra parameters to pass to the resampler objects.

Returns:
A resampled DataArray with updated ``.attrs["area"]`` field.
A resampled DataArray with updated ``.attrs["area"]`` field. The dtype
of the array is preserved.

"""
# call the projection stuff here
Expand All @@ -874,7 +882,8 @@ def resample_dataset(dataset, destination_area, **kwargs):

return dataset

new_data = resample(source_area, dataset, destination_area, **kwargs)
fill_value = kwargs.pop('fill_value', get_fill_value(dataset))
new_data = resample(source_area, dataset, destination_area, fill_value=fill_value, **kwargs)
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new_attrs = new_data.attrs
new_data.attrs = dataset.attrs.copy()
new_data.attrs.update(new_attrs)
Expand Down
24 changes: 24 additions & 0 deletions satpy/tests/test_resample.py
Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,29 @@
import mock


class TestHLResample(unittest.TestCase):
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"""Test the higher level resampling functions."""

def test_type_preserve(self):
"""Check that the type of resampled datasets is preserved."""
from satpy.resample import resample_dataset
import xarray as xr
import dask.array as da
import numpy as np
from pyresample.geometry import SwathDefinition
source_area = SwathDefinition(xr.DataArray(da.arange(4, chunks=5).reshape((2, 2)), dims=['y', 'x']),
xr.DataArray(da.arange(4, chunks=5).reshape((2, 2)), dims=['y', 'x']))
dest_area = SwathDefinition(xr.DataArray(da.arange(4, chunks=5).reshape((2, 2)) + .0001, dims=['y', 'x']),
xr.DataArray(da.arange(4, chunks=5).reshape((2, 2)) + .0001, dims=['y', 'x']))
expected = np.array([[1, 2], [3, 255]])
data = xr.DataArray(da.from_array(expected, chunks=5), dims=['y', 'x'])
data.attrs['_FillValue'] = 255
data.attrs['area'] = source_area
res = resample_dataset(data, dest_area)
self.assertEqual(res.dtype, data.dtype)
self.assertTrue(np.all(res.values == expected))


class TestKDTreeResampler(unittest.TestCase):
"""Test the kd-tree resampler."""

Expand Down Expand Up @@ -369,6 +392,7 @@ def suite():
mysuite.addTest(loader.loadTestsFromTestCase(TestNativeResampler))
mysuite.addTest(loader.loadTestsFromTestCase(TestKDTreeResampler))
mysuite.addTest(loader.loadTestsFromTestCase(TestEWAResampler))
mysuite.addTest(loader.loadTestsFromTestCase(TestHLResample))

return mysuite

Expand Down
2 changes: 1 addition & 1 deletion setup.py
Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@

from setuptools import find_packages, setup

requires = ['numpy >=1.12', 'pillow', 'pyresample >=1.10.0', 'trollsift',
requires = ['numpy >=1.12', 'pillow', 'pyresample >=1.10.3', 'trollsift',
'trollimage >=1.5.1', 'pykdtree', 'six', 'pyyaml', 'xarray >=0.10.1',
'dask[array] >=0.17.1']

Expand Down