For individual obs packages, we are using "translators" to convert metadata from raw files into internally consistent conventions (as many telescopes have different sets of conventions and header naming).  Our convention for boresight rotation angle is:

At boresightRotAngle = 0, the focal plane pixels are aligned:

+x: E->W (-ve RA), +y: S->N (+ve Dec)

(and see the documentation).

Accordingly, the imsim translator in obs_lsst should reflect that:

boresightRotAngle = 90 deg - ROTANGLE

(where the ROTANGLE is the FITS card in the raw data).

The reason data is currently being processed properly is due to a compensation (prior to the translator functionality) for this 90 deg shift in the lsstCamMapper here. This latter "correction" should be removed from there and accommodated in the imsim translator.

This change will be validated by running a visit of DC2 data before and after and checking that we get consistent results.