wcsFactory.py

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#
# LSST Data Management System
# Copyright 2008, 2009, 2010 LSST Corporation.
#
# This product includes software developed by the
# LSST Project (http://www.lsst.org/).
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
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# see <http://www.lsstcorp.org/LegalNotices/>.
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__all__ = ['WcsFactory']

import lsst.geom as geom
import lsst.afw.geom as afwGeom


class WcsFactory:
    """A factory for creating Wcs objects for the sky tiles.

    Parameters
    ----------
    pixelScale : `lsst.geom.Angle`
        Desired scale, as sky/pixel.
    projection : `str`
        FITS-standard 3-letter name of projection, e.g.: TAN (tangent),
        STG (stereographic), MOL (Mollweide's), AIT (Hammer-Aitoff)
        see Representations of celestial coordinates in FITS
        (Calabretta and Greisen, 2002).
    rotation : `lsst.geom.Angle`
        Rotation relative to cardinal.
    flipX : `bool`
        Flip the X axis?
    """

    def __init__(self, pixelScale, projection, rotation=0*geom.radians, flipX=False):
        if len(projection) != 3:
            raise RuntimeError("projection=%r; must have length 3" % (projection,))
        self._projection = projection
        self._cdMatrix = afwGeom.makeCdMatrix(scale=pixelScale, orientation=rotation, flipX=flipX)

    def makeWcs(self, crPixPos, crValCoord):
        """Make a Wcs.

        Parameters
        ----------
        crPixPos : `lsst.geom.Point2D`
            crPix for WCS, using the LSST standard.
        crValCoord : `lsst.geom.SpherePoint`
            ICRS crVal for WCS.

        Returns
        -------
        results : `lsst.afw.geom.SkyWcs`
            The new SkyWcs object.
        """
        return afwGeom.makeSkyWcs(crpix=crPixPos, crval=crValCoord,
                                  cdMatrix=self._cdMatrix, projection=self._projection)