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eregionanalyse (especget-1.54) [xmmsas_20230412_1735-21.0.0]

Source and background regions

Spatial regions may be entered in detector, sky (X/Y) or celestial (RA, DEC, FK4 2000) coordinates. If the coordinates of the region are not the same as those of the image, e.g. a sky pixel region on a detector coordinate image, then the task will still function but will run more slowly. An error will result if the spatial region is not within the image. Any shape conforming to the selectlib rules may be used but see section 3.2.9

In celestial coordinates a circular or annular region is actually elliptical due to the sperical geometry. To avoid conceptual problems related to this, in these special cases the region is converted internally into sky (X/Y) coordinates so that it remains circular and maintains the same size on the tangential image projection as the user might expect.

XMM-Newton SOC -- 2023-04-16