Index of /swift/om/docs/xmm-om/mssl/tc/0049

	Name	Last modified	Size	Description

	Parent Directory		-

OM Coordinate systems

Unfortunately this doc is only on paper, so see APD.

Useful note from Bob Shirey

XMM-OM/MSSL/TC/0049.01 is indeed wrong. For whatever reason, it appears that the coord system of Science window data (and the corrected, X/Y-swapped ENG4) is NOT the same as the redundant CCD coords as defined in that document. So, I would not rely on that document to go from the FITS files to spacecraft coords. Comparing relative offsets on the sky (for a common observation) unambiguously shows that all instruments are pointing within about 0.5' of a common offset location about 2' from the nominal pointing.

In the axis summary table, if we replace TC/0049.01 CCD coords, which don't correspond to any of our FITS images, with Sci-win file coords, comparison with PN-derived spacecraft coords drawn on the sky shows us that the Sci-win and ENG-4 FITS files as we currently receive them are oriented as follows relative to the spacecraft (and to celestial coords under zero position angle): Sci-win FITS -Z +Y +Z -Y

Spacecraft Celestial coords for zero PosAng ENG-4 FITS (uncorrected)
N +X +Y

E +Y +X

S -X -Y

W -Y -X

Spacecraft	Celestial coords for zero PosAng	ENG-4 FITS (uncorrected)
N	+X	+Y
E	+Y	+X
S	-X	-Y
W	-Y	-X

To view an image in sky coords oriented with N up and E left, rotate Sci Win images (and correctly X/Y swapped ENG-4 images) counter-clockwise 90 degrees and then further rotate counter-clockwise by the position angle.

The last column will become obsolete as soon as ENG-4 FITS production is corrected to use the same coords as Sci Wins, but the rest should be a useful permanent reference.