lsst.afw g5c39d4753b+ee3ebaee16
Classes | Functions
lsst.afw.geom.testUtils Namespace Reference

Classes

class  BoxGrid
 
class  FrameSetInfo
 
class  PermutedFrameSet
 
class  TransformTestBaseClass
 

Functions

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

Function Documentation

◆ makeSipIwcToPixel()

def 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.

◆ makeSipPixelToIwc()

def 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.

◆ makeSipPolyMapCoeffs()

def 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.