DM-13891: matchRaDec: fix imprecision at small distance #335
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r-owen
requested changes
Mar 27, 2018
tests/test_sourceMatch.py
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| Based on DM-13891. | ||
| """ | ||
| rng = np.random.RandomState(12345) # I have the same combination on my luggage |
tests/test_sourceMatch.py
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| radius = 0.5*afwGeom.arcseconds | ||
| num = 1000 | ||
| raKey = afwTable.SourceTable.getCoordKey().getRa() | ||
| decKey = afwTable.SourceTable.getCoordKey().getDec() |
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These aren't used below, are they? (Please always run a flake8 linter)
tests/test_sourceMatch.py
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| coord = src1.getCoord().offset(rng.uniform(high=360)*afwGeom.degrees, | ||
| rng.uniform(high=radius.asArcseconds())*afwGeom.arcseconds) | ||
| src2.set(afwTable.SourceTable.getCoordKey().getRa(), coord.getLongitude()) | ||
| src2.set(afwTable.SourceTable.getCoordKey().getDec(), coord.getLatitude()) |
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Couldn't this be written as src2.set(coordKey, coord) where you get the coordKey outside the loop?
I had no idea that getCoordKey().getRa() would return a key for the RA field. Interesting.
| matches = afwTable.matchRaDec(self.ss1, self.ss2, radius) | ||
| dist1 = np.array([(mm.distance*afwGeom.radians).asArcseconds() for mm in matches]) | ||
| dist2 = np.array([mm.first.getCoord().separation(mm.second.getCoord()).asArcseconds() for mm in matches]) | ||
| diff = dist1 - dist2 |
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Instead of comparing a summary statistic I strongly suggest comparing values individually, e.g. by calling self.assertFloatsAlmostEqual or numpy.testing.assert_allclose
PaulPrice
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The formula used for converting unit sphere distance^2 to an Angle isn't precise for small distance. Using an alternative formula that (unfortunately) includes a sqrt is more precise. Bug identified by Dominique Boutigny.
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The formula used for converting unit sphere distance^2 to an Angle
isn't precise for small distance. Using an alternative formula that
(unfortunately) includes a sqrt is more precise.
Bug identified by Dominique Boutigny.