StarMatch.cc

Go to the documentation of this file.

// -*- LSST-C++ -*-
/*
 * This file is part of jointcal.
 *
 * Developed for the LSST Data Management System.
 * This product includes software developed by the LSST Project
 * (https://www.lsst.org).
 * See the COPYRIGHT file at the top-level directory of this distribution
 * for details of code ownership.
 *
 * 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 GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
#include <iostream>
#include <iomanip>
 
#include "lsst/jointcal/AstrometryTransform.h"
#include "lsst/jointcal/StarMatch.h"
#include "lsst/jointcal/BaseStar.h"
#include "algorithm"  // for copy
 
/* TO DO:
   think about imposing a maximum number of matches that may
   be discarded in Cleanup.
*/
 
namespace lsst {
namespace jointcal {
 
static double sq(double x) { return x * x; }
 
double StarMatch::computeChi2(const AstrometryTransform &transform) const {
    FatPoint tr;
    transform.transformPosAndErrors(point1, tr);
    double vxx = tr.vx + point2.vx;
    double vyy = tr.vy + point2.vy;
    double vxy = tr.vxy + point2.vxy;
    double det = vxx * vyy - vxy * vxy;
    return (vyy * sq(tr.x - point2.x) + vxx * sq(tr.y - point2.y) -
            2 * vxy * (tr.x - point2.x) * (tr.y - point2.y)) /
           det;
}
 
std::ostream &operator<<(std::ostream &stream, const StarMatch &match) {
    stream << match.point1.x << ' ' << match.point1.y << ' ' << match.point2.x << ' ' << match.point2.y << ' '
           << match.distance << std::endl;
    return stream;
}
 
std::ostream &operator<<(std::ostream &stream, const StarMatchList &starMatchList) {
    stream << " number of elements " << starMatchList.size() << std::endl;
    copy(starMatchList.begin(), starMatchList.end(), std::ostream_iterator<StarMatch>(stream));
    return stream;
}
 
static std::vector<double> chi2_array(const StarMatchList &starMatchList,
                                            const AstrometryTransform &transform) {
    std::vector<double> result(starMatchList.size());
    unsigned count = 0;
    for (auto const &it : starMatchList) result[count++] = it.computeChi2(transform);
    return result;
}
 
static unsigned chi2_cleanup(StarMatchList &starMatchList, const double chi2Cut,
                             const AstrometryTransform &transform) {
    unsigned erased = starMatchList.removeAmbiguities(transform);
    for (auto smi = starMatchList.begin(); smi != starMatchList.end();) {
        if (smi->chi2 > chi2Cut) {
            smi = starMatchList.erase(smi);
            erased++;
        } else
            ++smi;
    }
    return erased;
}
 
void StarMatchList::refineTransform(double nSigmas) {
    double cut;
    unsigned nremoved;
    if (!_transform) _transform.reset(new AstrometryTransformLinear);
    do {
        int nused = size();
        if (nused <= 2) {
            _chi2 = -1;
            break;
        }
        _chi2 = _transform->fit(*this);
        /* convention of the fitted routines :
           -  chi2 = 0 means zero degrees of freedom
                (this was not enforced in AstrometryTransform{Lin,Quad,Cub} ...)
           -  chi2 = -1 means ndof <0 (and hence no possible fit)
           --> in either case, refinement is over
           The fact that chi2 = 0 was not enforced when necessary means
           that in this (rare) case, we were discarding matches at random....
           With AstrometryTransformPolynomial::fit, this is no longer the case.
        */
        if (_chi2 <= 0) return;
        unsigned npair = int(size());
        if (npair == 0) break;  // should never happen
 
        // compute some chi2 statistics
        std::vector<double> chi2_array(npair);
        unsigned count = 0;
        for (auto &starMatch : *this)
            chi2_array[count++] = starMatch.chi2 = starMatch.computeChi2(*_transform);
 
        std::sort(chi2_array.begin(), chi2_array.end());
        double median = (npair & 1) ? chi2_array[npair / 2]
                                    : (chi2_array[npair / 2 - 1] + chi2_array[npair / 2]) * 0.5;
 
        // discard outliers : the cut is understood as a "distance" cut
        cut = sq(nSigmas) * median;
        nremoved = chi2_cleanup(*this, cut, *_transform);
    } while (nremoved);
    _dist2 = computeDist2(*this, *_transform);
}
 
/* not very robust : assumes that we went through Refine just before... */
double StarMatchList::computeResidual() const {
    int deno = (2. * size() - _transform->getNpar());
    return (deno > 0) ? sqrt(_dist2 / deno) : -1;  // is -1 a good idea?
}
 
void StarMatchList::setDistance(const AstrometryTransform &transform) {
    for (auto &smi : *this) smi.setDistance(transform);  // c'est compact
}
 
unsigned StarMatchList::removeAmbiguities(const AstrometryTransform &transform, int which) {
    if (!which) return 0;
    setDistance(transform);
    int initial_count = size();
    if (which & 1) {
        sort(compareStar1);
        unique(sameStar1);
    }
    if (which & 2) {
        sort(compareStar2);
        unique(sameStar2);
    }
    return (initial_count - size());
}
 
void StarMatchList::setTransformOrder(int order) {
    if (order == 0)
        setTransform(std::make_shared<AstrometryTransformLinearShift>());
    else if (order == 1)
        setTransform(std::make_shared<AstrometryTransformLinear>());
    else
        setTransform(AstrometryTransformPolynomial(order));
    // might consider throwing if order does not make sense (e.g. >10)
    _order = order;
}
 
/* This routine should operate on a copy : refineTransform
   might shorten the list */
/* it is not const although it tries not to change anything  */
std::unique_ptr<AstrometryTransform> StarMatchList::inverseTransform() {
    if (!_transform) return nullptr;
 
    auto old_transform = _transform->clone();
    double old_chi2 = _chi2;
 
    swap();
    setTransformOrder(_order);
    refineTransform(3.);  // keep same order
    auto inverted_transform = _transform->clone();
    setTransform(old_transform.get());
    swap();
    _chi2 = old_chi2;
 
    return inverted_transform;
}
 
void StarMatchList::cutTail(int nKeep) {
    iterator si;
    int count = 0;
    for (si = begin(); si != end() && count < nKeep; ++count, ++si)
        ;
    erase(si, end());
}
 
void StarMatchList::swap() {
    for (auto &starMatch : *this) {
        starMatch.swap();
    }
}
 
int StarMatchList::recoveredNumber(double mindist) const {
    int n = 0;
    AstrometryTransformIdentity identity;
    for (auto const &starMatch : *this) {
        if (starMatch.computeDistance(identity) < mindist) n++;
    }
    return (n);
}
 
void StarMatchList::applyTransform(StarMatchList &transformed, const AstrometryTransform *priorTransform,
                                   const AstrometryTransform *posteriorTransform) const {
    transformed.clear();
    AstrometryTransformIdentity id;
    const AstrometryTransform &T1 = (priorTransform) ? *priorTransform : id;
    const AstrometryTransform &T2 = (posteriorTransform) ? *posteriorTransform : id;
 
    for (auto const &starMatch : *this) {
        FatPoint p1;
        T1.transformPosAndErrors(starMatch.point1, p1);
        FatPoint p2;
        T2.transformPosAndErrors(starMatch.point2, p2);
        transformed.push_back(StarMatch(p1, p2, starMatch.s1, starMatch.s2));
    }
}
 
void StarMatchList::printTransform(std::ostream &stream) const {
    stream << " ================================================================" << std::endl
           << " Transformation between lists of order " << getTransformOrder() << std::endl
           << *_transform  //<< endl
           << " Chi2 = " << getChi2() << "  Residual = " << computeResidual() << std::endl
           << "  Number in the list = " << size() << std::endl
           << " ================================================================" << std::endl;
}
 
double computeDist2(const StarMatchList &starMatchList, const AstrometryTransform &transform) {
    double dist2 = 0;
    for (auto const &starMatch : starMatchList)
        dist2 += transform.apply(starMatch.point1).computeDist2(starMatch.point2);
    return dist2;
}
 
double computeChi2(const StarMatchList &starMatchList, const AstrometryTransform &transform) {
    auto chi2s(chi2_array(starMatchList, transform));
    double chi2 = 0;
    for (auto const &c : chi2s) chi2 += c;
    return chi2;
}
}  // namespace jointcal
}  // namespace lsst