RA and Dec values should reflect actual array pointing

[david-macmahon]

When performing a pair of ON/OFF scans, the location of the OFF scan is typically specified as the location of the ON scan plus an offset (typically 3 degrees in our recent MeerKAT test scans). The RA and Dec values published must include this offset so that the RA and Dec values the metadata will refer to the actual RA and Dec location (in J2000 epoch) that the array was pointing towards.

The ON/OFF scans from the 2020-05-21 test session had equal values for RA and Dec. The offset was not included in the RA/Dec values for the OFF scan.

[david-macmahon]

Part of the problem is that these (and other?) sensors values seem to suffer from latency or other issues that prevent us from getting timely updates.

[danielczech]

This is the case for at least cbf_<number>_target and subarray_<number>_observation_activity. As confirmed yesterday, these sensor values are updated correctly in the KATPortal GUI but are occasionally not delivered via the websocket subscription.
I'm inclined to think that the per-antenna versions of the target sensor do not suffer from this problem - although we would then suffer from the (albeit comparatively short) delay when fetching sensor values from every antenna in the whole subarray. Perhaps that's an acceptable compromise for the moment.