Reference position
Keywords: mrtcal-prog-manual

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Reference position

For each spectrum, the Class Data Format expects a reference (usually source) position. In MRTCAL, this reference is taken from the `LONGOBJ` and `LATOBJ` (Source longitude and latitude in basis frame) in the Scan HDU. The coordinate system of these values are taken from header cards `CTYPE1` and `CTYPE2` (`RA` and `DEC` for equatorial system, `GLON` and `GLAT` for galactic system). Note that the trailing characters describing a projection system (e.g. `-SFL`) are useless: they do not apply to any data which can be found in the Scan HDU.