utils.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.
# 
# You should have received a copy of the LSST License Statement and 
# the GNU General Public License along with this program.  If not, 
# see <http://www.lsstcorp.org/LegalNotices/>.
#
import numpy

import lsst.afw.coord as afwCoord
import lsst.afw.geom as afwGeom

__all__ = ["coordFromVec"]

_TinyFloat = numpy.finfo(float).tiny

def coordFromVec(vec, defRA=None):
    """Convert an ICRS cartesian vector to an ICRS Coord
    
    @param[in] vec: an ICRS catesian vector as a sequence of three floats
    @param[in] defRA: the RA to use if the vector is too near a pole (an afwGeom Angle);
                ignored if not near a pole
    
    @throw RuntimeError if vec too near a pole and defRA is None
    """
    if abs(vec[0]) < _TinyFloat and abs(vec[1]) < _TinyFloat:
        if defRA is None:
            raise RuntimeError("At pole and defRA==None")
        if vec[2] > 0:
            dec = 90.0
        else:
            dec = -90.0
        return afwCoord.makeCoord(afwCoord.ICRS, defRA, afwGeom.Angle(dec, afwGeom.degrees))
    return afwCoord.makeCoord(afwCoord.ICRS, afwGeom.Point3D(*vec))