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DM-16208: Add position-dependent magnitudeToInstFlux() #412

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Nov 2, 2018
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9 changes: 8 additions & 1 deletion include/lsst/afw/image/PhotoCalib.h
Original file line number Diff line number Diff line change
Expand Up @@ -341,12 +341,19 @@ class PhotoCalib : public table::io::PersistableFacade<PhotoCalib>, public table
MaskedImage<float> calibrateImage(MaskedImage<float> const &maskedImage) const;

/**
* Convert AB magnitude to instFlux (ADU), using the mean instFlux/magnitude scaling factor.
* Convert AB magnitude to instFlux (ADU).
*
* If passed point, use the exact calculation at that point, otherwise, use the mean scaling factor.
*
* Useful for inserting fake sources into an image.
*
* @param[in] magnitude The AB magnitude to convert.
* @param[in] point The position that magnitude is to be converted at.
*
* @returns Source instFlux in ADU.
*/
double magnitudeToInstFlux(double magnitude, lsst::geom::Point<double, 2> const &point) const;
/// @overload magnitudeToInstFlux(double, lsst::geom::Point<double, 2> const &) const;
double magnitudeToInstFlux(double magnitude) const;

/**
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11 changes: 8 additions & 3 deletions python/lsst/afw/image/photoCalib.cc
Original file line number Diff line number Diff line change
Expand Up @@ -133,14 +133,19 @@ PYBIND11_MODULE(photoCalib, mod) {
PhotoCalib::instFluxToMagnitude,
"sourceCatalog"_a, "instFluxField"_a, "outField"_a);

/* from magnitude. */
cls.def("magnitudeToInstFlux",
py::overload_cast<double, lsst::geom::Point<double, 2> const &>(&PhotoCalib::magnitudeToInstFlux,
py::const_),
"instFlux"_a, "point"_a);
cls.def("magnitudeToInstFlux", py::overload_cast<double>(&PhotoCalib::magnitudeToInstFlux, py::const_),
"instFlux"_a);

/* utilities */
cls.def("getCalibrationMean", &PhotoCalib::getCalibrationMean);
cls.def("getCalibrationErr", &PhotoCalib::getCalibrationErr);
cls.def("getInstFluxMag0", &PhotoCalib::getInstFluxMag0);

cls.def("magnitudeToInstFlux", (double (PhotoCalib::*)(double) const) & PhotoCalib::magnitudeToInstFlux,
"magnitude"_a);

cls.def("computeScaledCalibration", &PhotoCalib::computeScaledCalibration);
cls.def("computeScalingTo", &PhotoCalib::computeScalingTo);

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8 changes: 7 additions & 1 deletion src/image/PhotoCalib.cc
Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,8 @@ double toMaggies(double instFlux, double scale) { return instFlux * scale; }

double toMagnitude(double instFlux, double scale) { return -2.5 * log10(instFlux * scale); }

double fromMagnitude(double magnitude, double scale) { return pow(10, magnitude / -2.5) / scale; }

double toMaggiesErr(double instFlux, double instFluxErr, double scale, double scaleErr, double maggies) {
return maggies * hypot(instFluxErr / instFlux, scaleErr / scale);
}
Expand Down Expand Up @@ -193,7 +195,11 @@ void PhotoCalib::instFluxToMagnitude(afw::table::SourceCatalog &sourceCatalog,
// ------------------- other utility methods -------------------

double PhotoCalib::magnitudeToInstFlux(double magnitude) const {
return pow(10, magnitude / -2.5) / _calibrationMean;
return fromMagnitude(magnitude, _calibrationMean);
}

double PhotoCalib::magnitudeToInstFlux(double magnitude, lsst::geom::Point<double, 2> const &point) const {
return fromMagnitude(magnitude, evaluate(point));
}

std::shared_ptr<math::BoundedField> PhotoCalib::computeScaledCalibration() const {
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7 changes: 7 additions & 0 deletions tests/test_photoCalib.py
Original file line number Diff line number Diff line change
Expand Up @@ -187,6 +187,13 @@ def _testPhotoCalibCenter(self, photoCalib, calibrationErr):
self.assertFloatsAlmostEqual(self.instFlux, photoCalib.magnitudeToInstFlux(0))
self.assertFloatsAlmostEqual(self.instFlux*1e-9, photoCalib.magnitudeToInstFlux(22.5))

# test round-tripping
mag = photoCalib.instFluxToMagnitude(self.instFlux, self.pointXShift)
self.assertFloatsAlmostEqual(self.instFlux, photoCalib.magnitudeToInstFlux(mag, self.pointXShift))
mag = photoCalib.instFluxToMagnitude(self.instFlux*1e-9, self.pointXShift)
self.assertFloatsAlmostEqual(self.instFlux*1e-9,
photoCalib.magnitudeToInstFlux(mag, self.pointXShift))

def _testSourceCatalog(self, photoCalib, catalog, expectMaggies, expectMag):
"""Test passing in a sourceCatalog."""

Expand Down