lsst.meas.extensions.trailedSources geebf31c2e0+c4c5166889
VeresModel.cc
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1// -*- LSST-C++ -*-
2/*
3 * This file is part of meas_extensions_trailedSources.
4 *
5 * Developed for the LSST Data Management System.
6 * This product includes software developed by the LSST Project
7 * (https://www.lsst.org).
8 * See the COPYRIGHT file at the top-level directory of this distribution
9 * for details of code ownership.
10 *
11 * This program is free software: you can redistribute it and/or modify
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13 * the Free Software Foundation, either version 3 of the License, or
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16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
20 *
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23 */
24
25#include "lsst/geom.h"
26#include "lsst/afw/image.h"
27#include "lsst/afw/detection.h"
29
30namespace lsst {
31namespace meas {
32namespace extensions {
33namespace trailedSources {
34
38
40 ExposureF const& data
41) : _sigma(data.getPsf()->computeShape().getTraceRadius()),
42 _bbox(data.getBBox()),
43 _data(data.getMaskedImage().getImage()->getArray()),
44 _variance(data.getMaskedImage().getVariance()->getArray()) {}
45
46double VeresModel::operator()(std::vector<double> const& params) const {
47
48 double xc = params[0]; // Centroid x
49 double yc = params[1]; // Centroid y
50 double flux = params[2]; // Flux
51 double length = params[3]; // Trail length
52 double theta = params[4]; // Angle from +x-axis
53
54 // Compute model image and chi-squared
55 double chiSq = 0.0;
56 // Loop is adapted from lsst::afw::detection::Psf::computeKernelImage()
57 for (int yIndex = 0, yp = _bbox.getBeginY(); yIndex < _bbox.getHeight(); ++yIndex, ++yp) {
58 ImageF::Array::Reference dataRow = _data[yIndex];
59 ImageF::Array::Reference varRow = _variance[yIndex];
60 for (int xIndex = 0, xp = _bbox.getBeginX(); xIndex < _bbox.getWidth(); ++xIndex, ++xp) {
61 double model = _computeModel(xp,yp,xc,yc,flux,length,theta);
62 double diff = dataRow[xIndex] - model;
63 chiSq += diff*diff/varRow[xIndex];
64 }
65 }
66
67 return chiSq;
68}
69
71
72 double xc = params[0]; // Centroid x
73 double yc = params[1]; // Centroid y
74 double flux = params[2]; // Flux
75 double length = params[3]; // Trail length
76 double theta = params[4]; // Angle from +x-axis
77
78 // Compute gradients of the model and of chi-squared
79 std::vector<double> gradChiSq = {0.0,0.0,0.0,0.0,0.0};
80 for (int yIndex = 0, yp = _bbox.getBeginY(); yIndex < _bbox.getHeight(); ++yIndex, ++yp) {
81 ImageF::Array::Reference dataRow = _data[yIndex];
82 ImageF::Array::Reference varRow = _variance[yIndex];
83 for (int xIndex = 0, xp = _bbox.getBeginX(); xIndex < _bbox.getWidth(); ++xIndex, ++xp) {
84 double model = _computeModel(xp,yp,xc,yc,flux,length,theta);
85 double gradDiff = -2.0 * (dataRow[xIndex] - model) / varRow[xIndex];
86 std::array<double, 5> gradModel = _computeGradient(xp,yp,xc,yc,flux,length,theta);
87 for (int k=0; k<5; ++k) {
88 gradChiSq[k] += gradModel[k] * gradDiff;
89 }
90 }
91 }
92 return gradChiSq;
93}
94
95double VeresModel::_computeModel(double x, double y, double xc, double yc,
96 double flux, double length, double theta) const noexcept {
97 double xp = (x-xc)*cos(theta) + (y-yc)*sin(theta);
98 double yp = (x-xc)*sin(theta) - (y-yc)*cos(theta);
99 double A = exp(-0.5 * yp*yp / (_sigma*_sigma));
100 double B = erf((xp+length/2) / (sqrt(2.0) * _sigma));
101 double C = erf((xp-length/2) / (sqrt(2.0) * _sigma));
102 return flux * A * (B - C) / (length * 2 * sqrt(2.0 * geom::PI) * _sigma);
103}
104
105std::array<double, 5> VeresModel::_computeGradient(double x, double y, double xc, double yc,
106 double flux, double length, double theta) const noexcept {
107 double xp = (x-xc)*cos(theta) + (y-yc)*sin(theta);
108 double yp = (x-xc)*sin(theta) - (y-yc)*cos(theta);
109
110 // Duplicated quantities
111 double flux2L = flux/(2.0*length);
112 double ypSq = yp*yp;
113 double sqrt2 = sqrt(2.0);
114 double sqrt2Pi = sqrt(2.0*geom::PI);
115 double sigmaSq = _sigma*_sigma;
116 double sigmaSq8 = sigmaSq * 8.0;
117 double eypSq = exp(-ypSq/(2.0*sigmaSq));
118 double lengthPlus = length+2.0*xp;
119 double lengthMinus= length-2.0*xp;
120 double erfPlus = erf(lengthPlus/(2.0*sqrt2*_sigma));
121 double erfMinus = erf(lengthMinus/(2.0*sqrt2*_sigma));
122 double expPlus = exp(-lengthPlus*lengthPlus/sigmaSq8);
123
124 // Compute partials wrt the transformed coordinates
125 double dfdxp = flux2L/(geom::PI*sigmaSq)*exp(-4.0*ypSq/sigmaSq8)*expPlus*
126 (1.0 - exp(length*xp/sigmaSq));
127 double dfdyp = -flux2L*yp/(sqrt2Pi*_sigma*sigmaSq)*eypSq*(erfMinus+erfPlus);
128
129 // Use the chain rule to get partials wrt the centroid and rotation angle
130 double dxpdxc = -cos(theta);
131 double dxpdyc = -sin(theta);
132 double dxpdTheta = -yp;
133 double dypdxc = -sin(theta);
134 double dypdyc = cos(theta);
135 double dypdTheta = xp;
136 double dfdxc = dfdxp*dxpdxc + dfdyp*dypdxc;
137 double dfdyc = dfdxp*dxpdyc + dfdyp*dypdyc;
138 double dfdTheta = dfdxp*dxpdTheta + dfdyp*dypdTheta;
139
140 double dfdFlux = _computeModel(x,y,xc,yc,1.0,length,theta); // dfdFlux = f / flux
141
142 double dfdLength = flux2L/(length*sqrt2Pi*_sigma)*eypSq*(length/(sqrt2Pi*_sigma)*
143 (exp(-lengthMinus*lengthMinus/sigmaSq8)+expPlus) - erfMinus - erfPlus);
144
145 std::array<double, 5> gradModel = {dfdxc, dfdyc, dfdFlux, dfdLength, dfdTheta};
146 return gradModel;
147}
148
149}}}} // lsst::meas::extensions::trailedSources
char * data
double x
int y
int getBeginX() const noexcept
int getHeight() const noexcept
int getWidth() const noexcept
int getBeginY() const noexcept
VeresModel(ExposureF const &data)
Constructor for VeresModel.
Definition: VeresModel.cc:39
std::vector< double > gradient(std::vector< double > const &params) const
Compute the gradient of chi-squared of the model given the data.
Definition: VeresModel.cc:70
double operator()(std::vector< double > const &params) const
Compute chi-squared of the model given the data.
Definition: VeresModel.cc:46
T cos(T... args)
T erf(T... args)
T exp(T... args)
def length(self)
constexpr double PI
T sin(T... args)
T sqrt(T... args)