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DM-16650: Update to nanojansky photocalib definition #5

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Dec 27, 2018
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DM-16650: Update to nanojansky photocalib definition #5

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e78e4f3
Update to nanojansky photocalib definition
parejkoj Dec 14, 2018
b716b74
post review fix
parejkoj Dec 21, 2018
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5 changes: 3 additions & 2 deletions python/lsst/fgcmcal/fgcmOutputProducts.py
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@
import numpy as np
import healpy as hp
import esutil
from astropy import units

import lsst.pex.config as pexConfig
import lsst.pipe.base as pipeBase
Expand Down Expand Up @@ -743,7 +744,7 @@ def _getChebyshevPhotoCalib(self, coefficients, err, xyMax, offset, scaling):
# Take the zeropoint, apply the absolute relative calibration offset,
# and whatever flat-field scaling was applied
pars[:, :] = (coefficients.reshape(orderPlus1, orderPlus1) *
10.**(offset / (-2.5)) * scaling)
(offset*units.ABmag).to_value(units.nJy) * scaling)
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The offset here is delta-mag, not ABmag. So an offset of say delta_mag = 0.1 should be applying a factor of 0.91 (original code), and now will apply an offset of 3311311214825.901.
Basically, the key is that the code will match whatever the units of the reference catalog are.

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Okay, I finally figured out for myself what's going on here, and it's correct, but it works because the units of the original returned coefficients from fgcm. I'll have to document that better on the fgcm side, or change that.

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Methods like this are perfect use cases for simple unittests. I can help you write one, if you want.

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I guess this is DM-16525


field = afwMath.ChebyshevBoundedField(bbox, pars)
calibMean = field.mean()
Expand Down Expand Up @@ -777,7 +778,7 @@ def _getConstantPhotoCalib(self, zeropoint, err, offset, scaling):
# Take the zeropoint, apply the absolute relative calibration offset,
# and whatever flat-field scaling was applied

calibMean = 10.**(zeropoint / (-2.5)) * 10.**(offset / (-2.5)) * scaling
calibMean = ((zeropoint + offset)*units.ABmag).to_value(units.nJy) * scaling
calibErr = (np.log(10.) / 2.5) * calibMean * err
photoCalib = afwImage.PhotoCalib(calibMean, calibErr)

Expand Down