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DM-14275: The distortion in test_wcsUtils.py testDistortion is unreasonable #350

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May 2, 2018
Merged

DM-14275: The distortion in test_wcsUtils.py testDistortion is unreasonable #350

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59a15b5
Increase iterations for distortion models
r-owen May 2, 2018
a96283e
Fix insanities in test_wcsUtils.py
r-owen May 2, 2018
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37 changes: 17 additions & 20 deletions tests/test_wcsUtils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -62,7 +62,7 @@ def setUp(self):
self.scale = 1.0 * arcseconds
# position of 0,0 pixel position in focal plane
self.ccdPositionMm = afwGeom.Point2D(25.0, 10.0)
self.focalPlaneToPixel = self.makeAffineTransform(
self.pixelToFocalPlane = self.makeAffineTransform(
offset=afwGeom.Extent2D(self.ccdPositionMm),
rotation=self.ccdOrientation,
scale=self.pixelSizeMm,
Expand Down Expand Up @@ -99,25 +99,27 @@ def testNoDistortion(self):
focalPlaneToFieldAngle = self.makeAffineTransform(scale=self.radPerMm)
wcs = makeDistortedTanWcs(
tanWcs=self.tanWcs,
pixelToFocalPlane=self.focalPlaneToPixel.getInverse(),
pixelToFocalPlane=self.pixelToFocalPlane,
focalPlaneToFieldAngle=focalPlaneToFieldAngle,
)
self.assertWcsAlmostEqualOverBBox(wcs, self.tanWcs, bbox=self.bbox)

def testDistortion(self):
"""Test makeDistortedTanWcs using a non-affine transform for pixelToFocalPlane
"""
# Compute a distorted wcs that matches self.tanWcs at the center
# of the field
focalPlaneToFieldAngle = afwGeom.makeRadialTransform([0.0, self.radPerMm, 0.0, self.radPerMm])
# Compute a distorted wcs that matches self.tanWcs at the center of the field;
# the amount of distortion is 10s of pixels over the detector
fieldAngleToFocalPlane = afwGeom.makeRadialTransform([0.0, 1/self.radPerMm, 0.0, 1000/self.radPerMm])
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Ah the joys of picking a "reasonable" fake model. This seems like a better choice.

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It gives much more reasonable values, and is very similar to what LSST uses (the factor of 1000 is not in the LSST model, but the LSST model only shows significant distortion at much larger focal plane radius; I tuned it to get the distortion I wanted over the range of values this test uses).

focalPlaneToFieldAngle = fieldAngleToFocalPlane.getInverse()
focalPlaneToTanFieldAngle = self.makeAffineTransform(scale=self.radPerMm)
wcs = makeDistortedTanWcs(
tanWcs=self.tanWcs,
pixelToFocalPlane=self.focalPlaneToPixel.getInverse(),
pixelToFocalPlane=self.pixelToFocalPlane,
focalPlaneToFieldAngle=focalPlaneToFieldAngle,
)

# At the center of the focal plane both WCS should give the same sky position
pixelAtCtr = self.focalPlaneToPixel.applyForward(afwGeom.Point2D(0, 0))
pixelAtCtr = self.pixelToFocalPlane.applyInverse(afwGeom.Point2D(0, 0))
tanSkyAtCtr = self.tanWcs.pixelToSky(pixelAtCtr)
skyAtCtr = wcs.pixelToSky(pixelAtCtr)
self.assertPairsAlmostEqual(tanSkyAtCtr, skyAtCtr)
Expand All @@ -130,29 +132,24 @@ def testDistortion(self):
# since for a given pointing, field angle gives position on the sky
skyPoints = self.tanWcs.pixelToSky(self.pixelPoints)

pixelToFocalPlane = self.focalPlaneToPixel.getInverse()

focalPlaneToTanFieldAngle = self.makeAffineTransform(scale=self.radPerMm)
tanFieldAnglePoints = focalPlaneToTanFieldAngle.applyForward(
pixelToFocalPlane.applyForward(self.tanWcs.skyToPixel(skyPoints)))

self.pixelToFocalPlane.applyForward(self.tanWcs.skyToPixel(skyPoints)))
fieldAnglePoints = focalPlaneToFieldAngle.applyForward(
pixelToFocalPlane.applyForward(wcs.skyToPixel(skyPoints)))

self.pixelToFocalPlane.applyForward(wcs.skyToPixel(skyPoints)))
assert_allclose(tanFieldAnglePoints, fieldAnglePoints)

# The inverse should also be true: for a set of field angle points
# the following sky positions should be almost equal:
# fieldAngle -> fieldAngleToTanFocalPlane -> focalPlaneToPixel -> tanWcs.pixelToSky
# fieldAngle -> fieldAngleToFocalPlane -> focalPlaneToPixel -> wcs.pixelToSky
focalPlaneToPixel = self.pixelToFocalPlane.getInverse()
fieldAngleToTanFocalPlane = focalPlaneToTanFieldAngle.getInverse()
tanSkyPoints2 = self.tanWcs.pixelToSky(
self.focalPlaneToPixel.applyForward(
focalPlaneToPixel.applyForward(
fieldAngleToTanFocalPlane.applyForward(fieldAnglePoints)))

fieldAngleToFocalPlane = focalPlaneToFieldAngle.getInverse()
skyPoints2 = wcs.pixelToSky(
self.focalPlaneToPixel.applyForward(
focalPlaneToPixel.applyForward(
fieldAngleToFocalPlane.applyForward(fieldAnglePoints)))

self.assertSpherePointListsAlmostEqual(tanSkyPoints2, skyPoints2)
Expand All @@ -170,7 +167,7 @@ def testNoDistortion(self):
"""
focalPlaneToFieldAngle = self.makeAffineTransform(scale=self.radPerMm)
pixelToDistortedPixel = computePixelToDistortedPixel(
pixelToFocalPlane=self.focalPlaneToPixel.getInverse(),
pixelToFocalPlane=self.pixelToFocalPlane,
focalPlaneToFieldAngle=focalPlaneToFieldAngle,
)
bboxD = afwGeom.Box2D(self.bbox)
Expand All @@ -188,7 +185,7 @@ def testDistortion(self):
"""
focalPlaneToFieldAngle = afwGeom.makeRadialTransform([0.0, self.radPerMm, 0.0, self.radPerMm])
pixelToDistortedPixel = computePixelToDistortedPixel(
pixelToFocalPlane=self.focalPlaneToPixel.getInverse(),
pixelToFocalPlane=self.pixelToFocalPlane,
focalPlaneToFieldAngle=focalPlaneToFieldAngle,
)
# Do not try to make pixelToDistortedPixel -> self.tanWcs into a WCS
Expand All @@ -198,7 +195,7 @@ def testDistortion(self):

wcs = makeDistortedTanWcs(
tanWcs=self.tanWcs,
pixelToFocalPlane=self.focalPlaneToPixel.getInverse(),
pixelToFocalPlane=self.pixelToFocalPlane,
focalPlaneToFieldAngle=focalPlaneToFieldAngle,
)

Expand Down