#### Example (ii)

Observe an OTF map with first OTF subscan from offsets to , in system trueHorizon (and no off-source reference) This is typical for bolometer OTF maps:

    OTFMAP -300 -300 300 -300 /REFERENCE no /SYSTEM trueHorizon

NOTES. Visiting observers have also used ONOFF in trueHorizon combined with OFFSETS ... /SYSTEM projection with TOTAL POWER, apparently with success.

NOTES.

- one should not specify offsets for the same system with the observing mode and OFFSETS (and there is not need to do this!).

  - If the observing mode uses /SYSTEM projection,
    OFFSETS ... /SYSTEM projection is ignored (not used).
  - If the observing mode uses /SYSTEM trueHorizon,
    OFFSETS ... /SYSTEM trueHorizon is ignored (not used).

- in the commands for the observing modes, the offsets for off-source reference positions must be in the same system as those of the on-source or OTF positions, i.e., /REFERENCE ... and /SYSTEM must select the same system (normally, PROJECTION).

Details at a technical level about these and more offsets can be found in the documentation of “NCS Antennna Mount Drive” by Alain Perrigouard.

NOTES. More explanations about coordinate systems, projections, and how to define descriptive coordinate sytems will be added as they become available for general use.

NOTES. SOURCE does not clear offsets set with OFFSETS.