DM-9111 Add rotator information to HSC VisitInfo

[jmeyers314]

No description provided.

[r-owen]

Looks great, though I asked for one comment to be clarified.

Please also fix the code that computes rotation angle in obs_lsstSim and obs_test, since you have changed the sign convention. (LSST needs careful checking; obs_test is likely already correct for the old standard)

[r-owen]

The above is nice and clean, but wrong for MOUNT. Please try again. I suppose you could back off to something like "The meaning of the angle is defined by rotType, which see.", but if you can find a compact way to say more without misleading for MOUNT that would be nice.

[jmeyers314]

Sure. How about:

    /**
    * Get rotation angle at boresight at middle of exposure
    *
    * The meaning of rotation angle depends on rotType.  If rotType is SKY (HORIZON), then rotation
    * angle is position angle of focal plane +Y with respect to North (+Alt).  If rotType is MOUNT,
    * then rotation angle indicates the position sent to the rotator which depends on the specific
    * rotator.  Finally, if rotType is UNKNOWN, then the meaning of rotation angle is undefined.
    *
    * As an example, if rotType is SKY, rotation angle 0 means North is along focal plane +Y and
    * East is along +X or -X (flipped to match handedness if necessary).  At rotation angle of 90,
    * +Y is along East.
    */

[r-owen]

I worry about the duplication of information with rotType. That can lead to the information going out of date in one place or the other. My first inclination would be to rely on a Doxygen link to the rotation type information and put very little information here. A compromise that might suffice is to provide the most common example (other than UNKNOWN, which is all too common, alas, but self-explanatory) but not complete information, for instance:

* The meaning...depends on @ref RotType "rotType". For example, if `rotType` is SKY,
* the angle is the position angle of the focal plane +Y with respect to North.

[jmeyers314]

Good point. I've switched the doc to your suggestion.