lsst.afw.geom.testUtils Namespace Reference

Classes
class	BoxGrid
class	FrameSetInfo
class	PermutedFrameSet
class	TransformTestBaseClass

Functions
	makeSipPolyMapCoeffs (metadata, name)
	makeSipIwcToPixel (metadata)
	makeSipPixelToIwc (metadata)

Function Documentation

makeSipIwcToPixel()

lsst.afw.geom.testUtils.makeSipIwcToPixel

(

metadata

)

Make an IWC to pixel transform with SIP distortion from FITS-WCS metadata

This function is primarily intended for unit tests.
IWC is intermediate world coordinates, as described in the FITS papers.

Parameters
----------
metadata : lsst.daf.base.PropertySet
    FITS metadata describing a WCS with inverse SIP coefficients

Returns
-------
lsst.afw.geom.TransformPoint2ToPoint2
    Transform from IWC position to pixel position (zero-based)
    in the forward direction. The inverse direction is not defined.

Notes
-----

The inverse SIP terms APn_m, BPn_m are polynomial coefficients x^n y^m
for computing transformed x, y respectively. If we call the resulting
polynomial inverseSipPolynomial, the returned transformation is:

    pixelPosition = pixel origin + uv + inverseSipPolynomial(uv)
    where uv = inverseCdMatrix * iwcPosition

Definition at line 196 of file testUtils.py.

def makeSipIwcToPixel(metadata):
    """Make an IWC to pixel transform with SIP distortion from FITS-WCS metadata
 
    This function is primarily intended for unit tests.
    IWC is intermediate world coordinates, as described in the FITS papers.
 
    Parameters
    ----------
    metadata : lsst.daf.base.PropertySet
        FITS metadata describing a WCS with inverse SIP coefficients
 
    Returns
    -------
    lsst.afw.geom.TransformPoint2ToPoint2
        Transform from IWC position to pixel position (zero-based)
        in the forward direction. The inverse direction is not defined.
 
    Notes
    -----
 
    The inverse SIP terms APn_m, BPn_m are polynomial coefficients x^n y^m
    for computing transformed x, y respectively. If we call the resulting
    polynomial inverseSipPolynomial, the returned transformation is:
 
        pixelPosition = pixel origin + uv + inverseSipPolynomial(uv)
        where uv = inverseCdMatrix * iwcPosition
    """
    crpix = (metadata.getScalar("CRPIX1") - 1, metadata.getScalar("CRPIX2") - 1)
    pixelRelativeToAbsoluteMap = ast.ShiftMap(crpix)
    cdMatrix = getCdMatrixFromMetadata(metadata)
    cdMatrixMap = ast.MatrixMap(cdMatrix.copy())
    coeffList = makeSipPolyMapCoeffs(metadata, "AP") + makeSipPolyMapCoeffs(metadata, "BP")
    coeffArr = np.array(coeffList, dtype=float)
    sipPolyMap = ast.PolyMap(coeffArr, 2, "IterInverse=0")
 
    iwcToPixelMap = cdMatrixMap.inverted().then(sipPolyMap).then(pixelRelativeToAbsoluteMap)
    return afwGeom.TransformPoint2ToPoint2(iwcToPixelMap)
 
 

makeSipPixelToIwc()

lsst.afw.geom.testUtils.makeSipPixelToIwc

(

metadata

)

Make a pixel to IWC transform with SIP distortion from FITS-WCS metadata

This function is primarily intended for unit tests.
IWC is intermediate world coordinates, as described in the FITS papers.

Parameters
----------
metadata : lsst.daf.base.PropertySet
    FITS metadata describing a WCS with forward SIP coefficients

Returns
-------
lsst.afw.geom.TransformPoint2ToPoint2
    Transform from pixel position (zero-based) to IWC position
    in the forward direction. The inverse direction is not defined.

Notes
-----

The forward SIP terms An_m, Bn_m are polynomial coefficients x^n y^m
for computing transformed x, y respectively. If we call the resulting
polynomial sipPolynomial, the returned transformation is:

    iwcPosition = cdMatrix * (dxy + sipPolynomial(dxy))
    where dxy = pixelPosition - pixelOrigin

Definition at line 235 of file testUtils.py.

def makeSipPixelToIwc(metadata):
    """Make a pixel to IWC transform with SIP distortion from FITS-WCS metadata
 
    This function is primarily intended for unit tests.
    IWC is intermediate world coordinates, as described in the FITS papers.
 
    Parameters
    ----------
    metadata : lsst.daf.base.PropertySet
        FITS metadata describing a WCS with forward SIP coefficients
 
    Returns
    -------
    lsst.afw.geom.TransformPoint2ToPoint2
        Transform from pixel position (zero-based) to IWC position
        in the forward direction. The inverse direction is not defined.
 
    Notes
    -----
 
    The forward SIP terms An_m, Bn_m are polynomial coefficients x^n y^m
    for computing transformed x, y respectively. If we call the resulting
    polynomial sipPolynomial, the returned transformation is:
 
        iwcPosition = cdMatrix * (dxy + sipPolynomial(dxy))
        where dxy = pixelPosition - pixelOrigin
    """
    crpix = (metadata.getScalar("CRPIX1") - 1, metadata.getScalar("CRPIX2") - 1)
    pixelAbsoluteToRelativeMap = ast.ShiftMap(crpix).inverted()
    cdMatrix = getCdMatrixFromMetadata(metadata)
    cdMatrixMap = ast.MatrixMap(cdMatrix.copy())
    coeffList = makeSipPolyMapCoeffs(metadata, "A") + makeSipPolyMapCoeffs(metadata, "B")
    coeffArr = np.array(coeffList, dtype=float)
    sipPolyMap = ast.PolyMap(coeffArr, 2, "IterInverse=0")
    pixelToIwcMap = pixelAbsoluteToRelativeMap.then(sipPolyMap).then(cdMatrixMap)
    return afwGeom.TransformPoint2ToPoint2(pixelToIwcMap)
 
 

makeSipPolyMapCoeffs()

lsst.afw.geom.testUtils.makeSipPolyMapCoeffs	(		metadata,
			name )

Return a list of ast.PolyMap coefficients for the specified SIP matrix

The returned list of coefficients for an ast.PolyMap
that computes the following function:

    f(dxy) = dxy + sipPolynomial(dxy))
    where dxy = pixelPosition - pixelOrigin
    and sipPolynomial is a polynomial with terms `<name>n_m for x^n y^m`
        (e.g. A2_0 is the coefficient for x^2 y^0)

Parameters
----------
metadata : lsst.daf.base.PropertySet
    FITS metadata describing a WCS with the specified SIP coefficients
name : str
    The desired SIP terms: one of A, B, AP, BP

Returns
-------
list
    A list of coefficients for an ast.PolyMap that computes
    the specified SIP polynomial, including a term for out = in

Note
----
This is an internal function for use by makeSipIwcToPixel
and makeSipPixelToIwc

Definition at line 141 of file testUtils.py.

def makeSipPolyMapCoeffs(metadata, name):
    """Return a list of ast.PolyMap coefficients for the specified SIP matrix
 
    The returned list of coefficients for an ast.PolyMap
    that computes the following function:
 
        f(dxy) = dxy + sipPolynomial(dxy))
        where dxy = pixelPosition - pixelOrigin
        and sipPolynomial is a polynomial with terms `<name>n_m for x^n y^m`
            (e.g. A2_0 is the coefficient for x^2 y^0)
 
    Parameters
    ----------
    metadata : lsst.daf.base.PropertySet
        FITS metadata describing a WCS with the specified SIP coefficients
    name : str
        The desired SIP terms: one of A, B, AP, BP
 
    Returns
    -------
    list
        A list of coefficients for an ast.PolyMap that computes
        the specified SIP polynomial, including a term for out = in
 
    Note
    ----
    This is an internal function for use by makeSipIwcToPixel
    and makeSipPixelToIwc
    """
    outAxisDict = dict(A=1, B=2, AP=1, BP=2)
    outAxis = outAxisDict.get(name)
    if outAxis is None:
        raise RuntimeError(f"{name} not a supported SIP name")
    width = metadata.getAsInt(f"{name}_ORDER") + 1
    found = False
    # start with a term for out = in
    coeffs = []
    if outAxis == 1:
        coeffs.append([1.0, outAxis, 1, 0])
    else:
        coeffs.append([1.0, outAxis, 0, 1])
    # add SIP distortion terms
    for xPower in range(width):
        for yPower in range(width):
            coeffName = f"{name}_{xPower}_{yPower}"
            if not metadata.exists(coeffName):
                continue
            found = True
            coeff = metadata.getAsDouble(coeffName)
            coeffs.append([coeff, outAxis, xPower, yPower])
    if not found:
        raise RuntimeError(f"No {name} coefficients found")
    return coeffs