LSSTApplications  21.0.0+1b62c9342b,21.0.0+45a059f35e,21.0.0-1-ga51b5d4+ceb9cf20a3,21.0.0-17-gf9a0284+9e5b25d042,21.0.0-2-g103fe59+513edb8842,21.0.0-2-g1367e85+d9bb5204cb,21.0.0-2-g2909d54+45a059f35e,21.0.0-2-g45278ab+1b62c9342b,21.0.0-2-g4bc9b9f+36532ac5d2,21.0.0-2-g5242d73+d9bb5204cb,21.0.0-2-g54e2caa+0b4b33a26b,21.0.0-2-g66bcc37+0525a04256,21.0.0-2-g7f82c8f+8938dec807,21.0.0-2-g8dde007+7bfb5851c8,21.0.0-2-g8f08a60+73884b2cf5,21.0.0-2-g973f35b+44678ca34c,21.0.0-2-ga326454+8938dec807,21.0.0-2-ga63a54e+682c8ce20e,21.0.0-2-ga885a99+9a92674037,21.0.0-2-gc738bc1+5ce50b2a03,21.0.0-2-gde069b7+5a8f2956b8,21.0.0-2-ge17e5af+d9bb5204cb,21.0.0-2-ge712728+d5c34dc911,21.0.0-2-gecfae73+8bdf007ced,21.0.0-2-gfc62afb+d9bb5204cb,21.0.0-21-g006371a9+5abec3504c,21.0.0-3-g4c5b185+4e2de95c30,21.0.0-3-g6d51c4a+0525a04256,21.0.0-3-gaa929c8+fca53d2b73,21.0.0-3-gd222c45+afc8332dbe,21.0.0-3-gd5de2f2+0525a04256,21.0.0-4-g3300ddd+1b62c9342b,21.0.0-4-g8a80011+23661db33a,21.0.0-5-gb7080ec+ee9551b7be,21.0.0-5-gcff38f6+e51f0852ce,21.0.0-6-gd3283ba+fca53d2b73,21.0.0-8-g19111d86+898b2b281f,21.0.0-8-gd9c33f4a0+b58bb1f4d6,w.2021.03
LSSTDataManagementBasePackage
Classes | Functions
lsst.meas.astrom.approximateWcs Namespace Reference

Classes

class  _MockTestCase
 

Functions

def approximateWcs (wcs, bbox, order=3, nx=20, ny=20, iterations=3, skyTolerance=0.001 *lsst.geom.arcseconds, pixelTolerance=0.02, useTanWcs=False)
 

Function Documentation

◆ approximateWcs()

def lsst.meas.astrom.approximateWcs.approximateWcs (   wcs,
  bbox,
  order = 3,
  nx = 20,
  ny = 20,
  iterations = 3,
  skyTolerance = 0.001*lsst.geom.arcseconds,
  pixelTolerance = 0.02,
  useTanWcs = False 
)
Approximate an existing WCS as a TAN-SIP WCS

The fit is performed by evaluating the WCS at a uniform grid of points
within a bounding box.

Parameters
----------
wcs : `lsst.afw.geom.SkyWcs`
    wcs to approximate
bbox : `lsst.geom.Box2I`
    the region over which the WCS will be fit
order : `int`
    order of SIP fit
nx : `int`
    number of grid points along x
ny : `int`
    number of grid points along y
iterations : `int`
    number of times to iterate over fitting
skyTolerance : `lsst.geom.Angle`
    maximum allowed difference in world coordinates between
    input wcs and approximate wcs (default is 0.001 arcsec)
pixelTolerance : `float`
    maximum allowed difference in pixel coordinates between
    input wcs and approximate wcs (default is 0.02 pixels)
useTanWcs : `bool`
    send a TAN version of wcs to the fitter? It is documented to require that,
    but I don't think the fitter actually cares

Returns
-------
fitWcs : `lsst.afw.geom.SkyWcs`
    the fit TAN-SIP WCS

Definition at line 43 of file approximateWcs.py.

43 def approximateWcs(wcs, bbox, order=3, nx=20, ny=20, iterations=3,
44  skyTolerance=0.001*lsst.geom.arcseconds, pixelTolerance=0.02, useTanWcs=False):
45  """Approximate an existing WCS as a TAN-SIP WCS
46 
47  The fit is performed by evaluating the WCS at a uniform grid of points
48  within a bounding box.
49 
50  Parameters
51  ----------
52  wcs : `lsst.afw.geom.SkyWcs`
53  wcs to approximate
54  bbox : `lsst.geom.Box2I`
55  the region over which the WCS will be fit
56  order : `int`
57  order of SIP fit
58  nx : `int`
59  number of grid points along x
60  ny : `int`
61  number of grid points along y
62  iterations : `int`
63  number of times to iterate over fitting
64  skyTolerance : `lsst.geom.Angle`
65  maximum allowed difference in world coordinates between
66  input wcs and approximate wcs (default is 0.001 arcsec)
67  pixelTolerance : `float`
68  maximum allowed difference in pixel coordinates between
69  input wcs and approximate wcs (default is 0.02 pixels)
70  useTanWcs : `bool`
71  send a TAN version of wcs to the fitter? It is documented to require that,
72  but I don't think the fitter actually cares
73 
74  Returns
75  -------
76  fitWcs : `lsst.afw.geom.SkyWcs`
77  the fit TAN-SIP WCS
78  """
79  if useTanWcs:
80  crpix = wcs.getPixelOrigin()
81  crval = wcs.getSkyOrigin()
82  cdMatrix = wcs.getCdMatrix(crpix)
83  tanWcs = afwGeom.makeSkyWcs(crpix=crpix, crval=crval, cdMatrix=cdMatrix)
84  else:
85  tanWcs = wcs
86 
87  # create a matchList consisting of a grid of points covering the bbox
88  refSchema = afwTable.SimpleTable.makeMinimalSchema()
89  refCoordKey = afwTable.CoordKey(refSchema["coord"])
90  refCat = afwTable.SimpleCatalog(refSchema)
91 
92  sourceSchema = afwTable.SourceTable.makeMinimalSchema()
93  SingleFrameMeasurementTask(schema=sourceSchema) # expand the schema
94  sourceCentroidKey = afwTable.Point2DKey(sourceSchema["slot_Centroid"])
95 
96  sourceCat = afwTable.SourceCatalog(sourceSchema)
97 
98  matchList = []
99 
100  bboxd = lsst.geom.Box2D(bbox)
101  for x in np.linspace(bboxd.getMinX(), bboxd.getMaxX(), nx):
102  for y in np.linspace(bboxd.getMinY(), bboxd.getMaxY(), ny):
103  pixelPos = lsst.geom.Point2D(x, y)
104  skyCoord = wcs.pixelToSky(pixelPos)
105 
106  refObj = refCat.addNew()
107  refObj.set(refCoordKey, skyCoord)
108 
109  source = sourceCat.addNew()
110  source.set(sourceCentroidKey, pixelPos)
111 
112  matchList.append(afwTable.ReferenceMatch(refObj, source, 0.0))
113 
114  # The TAN-SIP fitter is fitting x and y separately, so we have to iterate to make it converge
115  for indx in range(iterations):
116  sipObject = makeCreateWcsWithSip(matchList, tanWcs, order, bbox)
117  tanWcs = sipObject.getNewWcs()
118  fitWcs = sipObject.getNewWcs()
119 
120  mockTest = _MockTestCase()
121  assertWcsAlmostEqualOverBBox(mockTest, wcs, fitWcs, bbox, maxDiffSky=skyTolerance,
122  maxDiffPix=pixelTolerance)
123 
124  return fitWcs
lsst::afw::table::CoordKey
A FunctorKey used to get or set celestial coordinates from a pair of lsst::geom::Angle keys.
Definition: aggregates.h:210
lsst::meas::astrom.approximateWcs.approximateWcs
def approximateWcs(wcs, bbox, order=3, nx=20, ny=20, iterations=3, skyTolerance=0.001 *lsst.geom.arcseconds, pixelTolerance=0.02, useTanWcs=False)
Definition: approximateWcs.py:43
lsst::afw::table::PointKey< double >
lsst::meas::astrom::sip::makeCreateWcsWithSip
CreateWcsWithSip< MatchT > makeCreateWcsWithSip(std::vector< MatchT > const &matches, afw::geom::SkyWcs const &linearWcs, int const order, geom::Box2I const &bbox=geom::Box2I(), int const ngrid=0)
Factory function for CreateWcsWithSip.
Definition: CreateWcsWithSip.h:168
lsst::afw::table._source.SourceCatalog
Definition: _source.py:32
lsst::afw::table::Match
Lightweight representation of a geometric match between two records.
Definition: Match.h:67
lsst::afw::geom::makeSkyWcs
std::shared_ptr< SkyWcs > makeSkyWcs(TransformPoint2ToPoint2 const &pixelsToFieldAngle, lsst::geom::Angle const &orientation, bool flipX, lsst::geom::SpherePoint const &boresight, std::string const &projection="TAN")
Construct a FITS SkyWcs from camera geometry.
Definition: SkyWcs.cc:536
lsst::geom::Point< double, 2 >
lsst::geom::Box2D
A floating-point coordinate rectangle geometry.
Definition: Box.h:413
lsst::afw::table::SortedCatalogT
Custom catalog class for record/table subclasses that are guaranteed to have an ID,...
Definition: SortedCatalog.h:42
lsst::afw::geom.utils.assertWcsAlmostEqualOverBBox
def assertWcsAlmostEqualOverBBox(testCase, wcs0, wcs1, bbox, maxDiffSky=0.01 *lsst.geom.arcseconds, maxDiffPix=0.01, nx=5, ny=5, msg="WCSs differ")
Definition: utils.py:155