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DM-49268: Avoid NaNs from dividing by zero weights #386

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DM-49268: Avoid NaNs from dividing by zero weights #386

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14 changes: 10 additions & 4 deletions python/lsst/ip/diffim/getTemplate.py
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Original file line number Diff line number Diff line change
Expand Up @@ -398,7 +398,9 @@ def _merge(self, maskedImages, bbox, wcs):
merged = afwImage.ExposureF(bbox, wcs)
weights = afwImage.ImageF(bbox)
for maskedImage in maskedImages:
weight = afwImage.ImageF(maskedImage.variance.array**(-0.5))
goodPix = maskedImage.variance.array > 0
weight = afwImage.ImageF(maskedImage.getBBox())
weight.array[goodPix] = maskedImage.variance.array[goodPix]**(-0.5)
bad = np.isnan(maskedImage.image.array) | ~np.isfinite(maskedImage.variance.array)
# Note that modifying the patch MaskedImage in place is fine;
# we're throwing it away at the end anyway.
Expand All @@ -419,9 +421,13 @@ def _merge(self, maskedImages, bbox, wcs):
# Cannot use `merged.maskedImage /= weights` because that operator
# divides the variance by the weight twice; in this case `weights` are
# the exact values we want to scale by.
merged.image /= weights
merged.variance /= weights
merged.mask.array |= merged.mask.getPlaneBitMask("NO_DATA") * (weights.array == 0)
invWeights = np.zeros_like(weights.array)
goodPix = weights.array > 0
invWeights[goodPix] = 1/weights.array[goodPix]

merged.image.array *= invWeights
merged.variance.array *= invWeights
merged.mask.array |= merged.mask.getPlaneBitMask("NO_DATA") * (invWeights == 0)

return merged

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4 changes: 1 addition & 3 deletions tests/test_getTemplate.py
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Expand Up @@ -282,9 +282,7 @@ def testMissingPatches(self):
dataIds=self.dataIds,
physical_filter="a_test")
no_data = (result.template.mask.array & result.template.mask.getPlaneBitMask("NO_DATA")) != 0
self.assertTrue(all(np.isnan(result.template.image.array[no_data])))
self.assertTrue(all(np.isnan(result.template.variance.array[no_data])))
self.assertEqual(no_data.sum(), 21548)
self.assertEqual(no_data.sum(), 20990)


def setup_module(module):
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