The output from GT_CENTER can be the location of the center of
the field of view in (a) full resolution IDL (FRE) pixels, (b) heliocentric
coordinates, (c) the angle E/W and N/S from the center of the sun
in arcseconds, or (d) the HXT equivalent pixel coordinates.
The default is to read the ATT S/C pointing database for
the true de-jittered S/C pointing. It is possible to use the commanded
S/C pointing information by using the /CMD option, which is much faster
and only of slightly reduced accuracy.
IDL> pix = gt_center(index)
IDL> helio = gt_center(index, /helio)
IDL> helio = gt_center(index, /helio, /cmd)
IDL> ang = gt_center(roadmap)
where ang(0,*) is arcseconds east/west with east being
negative and ang(1,*) is arcseconds north/south with
north being positive. helio is in degrees, and pix is
in full resolution pixels. It is possible to get the heliocentric
coordinates in a string of the form ``N12W23'' by using the /STRING
option.