Reference position

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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.