XMM-Newton Science Analysis System
eregionanalyse (especget-1.54) [xmmsas_20211130_0941-20.0.0]
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 -- 2021-11-30