During processing a dataset with multiBandDriver.py in hscPipe 5.0-beta1, I ran into an error:

Traceback (most recent call last):

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/ctrl_pool/13.0-1-g0a48345/python/lsst/ctrl/pool/pool.py", line 113, in wrapper

    return func(*args, **kwargs)

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/ctrl_pool/13.0-1-g0a48345/python/lsst/ctrl/pool/pool.py", line 1067, in run

    while not menu[command]():

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/ctrl_pool/13.0-1-g0a48345/python/lsst/ctrl/pool/pool.py", line 237, in wrapper

    return func(*args, **kwargs)

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/ctrl_pool/13.0-1-g0a48345/python/lsst/ctrl/pool/pool.py", line 1085, in reduce

    result = self._processQueue(context, func, [(index, data)], *args, **kwargs)[0]

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/ctrl_pool/13.0-1-g0a48345/python/lsst/ctrl/pool/pool.py", line 544, in _processQueue

    return self._reduceQueue(context, None, func, queue, *args, **kwargs)

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/ctrl_pool/13.0-1-g0a48345/python/lsst/ctrl/pool/pool.py", line 570, in _reduceQueue

    resultList = [func(self._getCache(context, i), data, *args, **kwargs) for i, data in queue]

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/pipe_drivers/13.0-1-g07ace30+4/python/lsst/pipe/drivers/multiBandDriver.py", line 388, in runForcedPhot

    self.forcedPhotCoadd.run(dataRef)

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/meas_base/13.0-3-gc489882+1/python/lsst/meas/base/forcedPhotImage.py", line 147, in run

    self.measurement.run(measCat, exposure, refCat, refWcs, exposureId=self.getExposureId(dataRef))

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/meas_base/13.0-3-gc489882+1/python/lsst/meas/base/forcedMeasurement.py", line 330, in run

    beginOrder=beginOrder, endOrder=endOrder)

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/meas_base/13.0-3-gc489882+1/python/lsst/meas/base/baseMeasurement.py", line 268, in callMeasure

    self.doMeasurement(plugin, measRecord, *args, **kwds)

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/meas_base/13.0-3-gc489882+1/python/lsst/meas/base/baseMeasurement.py", line 287, in doMeasurement

    plugin.measure(measRecord, *args, **kwds)

  File "/data/mineo/opt/hscpipe/5/stack_5.0-beta1/Linux64/meas_modelfit/13.0-3-g177c5a2+1/python/lsst/meas/modelfit/cmodel.py", line 98, in measure

    "CModel forced measurement currently requires the measurement image to have the same"

FatalAlgorithmError: CModel forced measurement currently requires the measurement image to have the same Wcs as the reference catalog (this is a temporary limitation).

application called MPI_Abort(MPI_COMM_WORLD, 1) - process 10

The exception was thrown from

meas_modelfit/13.0-3-g177c5a2+1/python/lsst/meas/modelfit/cmodel.py:

    def measure(self, measRecord, exposure, refRecord, refWcs):

        if refWcs != exposure.getWcs(): ### Condition (A) ###

            raise lsst.meas.base.FatalAlgorithmError(

                "CModel forced measurement currently requires the measurement image to have the same"

                " Wcs as the reference catalog (this is a temporary limitation)."

            )

`refWcs` and `exposure` in Condition (A) was from

meas_base/13.0-3-gc489882+1/python/lsst/meas/base/forcedPhotImage.py:139

        refWcs = self.references.getWcs(dataRef)

        exposure = self.getExposure(dataRef)

`self.references.getWcs` was probably defined in

meas_base/13.0-3-gc489882+1/python/lsst/meas/base/references.py:202:

    def getWcs(self, dataRef):

        """Return the WCS for reference sources.  The given dataRef must include the tract in its dataId.

        """

        skyMap = dataRef.get(self.config.coaddName + "Coadd_skyMap", immediate=True)

        return skyMap[dataRef.dataId["tract"]].getWcs()

Therefore, in Condition (A), one of the compared WCS was from skyMap,

and the other was from a FITS file.

I suspected that WCS had been changed when saved in the FITS file,

due to limited number of digits written in FITS headers.

To prove it, I wrote the following script. It actually proved

that there are some tracts where Condition (A) is violated.

======================

import lsst.afw.image as afwImage

import cPickle as pickle

def main():

    skyMap = pickle.load(open("skyMap.pickle", "rb"))

    for tract, tractInfo in enumerate(skyMap):

        testWcs(tract, tractInfo.getWcs())

def testWcs(tract, wcs):

    exp = afwImage.ExposureF(0, 0)

    exp.setWcs(wcs)

    exp.writeFits("/dev/shm/foo.fits")

    exp = afwImage.ExposureF("/dev/shm/foo.fits")

    # This message must always be "{tract}, True"

    print tract, exp.getWcs() == wcs

main()