setMatchDistance.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/>.
#

__all__ = ["setMatchDistance"]

import lsst.afw.table as afwTable


def setMatchDistance(matches):
    """Set the distance field of the matches in a match list to the distance in
    radians on the sky.

    Parameters
    ----------
    matches : `list` of `lsst.afw.table.ReferenceMatch`
        a list of matches, reads the coord field of the source and reference
        object of each match writes the distance field of each match

    Notes
    -----
    .. warning::
       the coord field of the source in each match must be correct
    """
    if len(matches) < 1:
        return

    sourceCoordKey = afwTable.CoordKey(matches[0].first.schema["coord"])
    refObjCoordKey = afwTable.CoordKey(matches[0].second.schema["coord"])
    for match in matches:
        sourceCoord = match.first.get(sourceCoordKey)
        refObjCoord = match.second.get(refObjCoordKey)
        match.distance = refObjCoord.separation(sourceCoord).asRadians()