Basic Information on impos

Task: impos
Purpose: Converts image coordinates between different systems.
Categories: image analysis

IMPOS takes a coordinate in a specified system (such
as "abspix" or "arcsec") and converts it to all appropriate
coordinate systems (absolute world, offset world, pixels, 
offset pixels).   Spectral axes are converted to values in
frequency, radio and optical velocities.

If the input is an image and the specified coordinate represents
a valid pixel, its value is reported as well.

Key: in
The input image or visibility dataset. For a visibility dataset,
the coordinate system is relative to the first visibility
record.

Key: coord
Specify the coordinate for each axis that you are interested 
in; you don't necessarily need one for every axis in the image.
No default.

Key: type
Specify the coordinate system of the input coordinate for each 
axis.  Different axes can be in different systems. Choose from:

   "hms"         HH:MM:SS.S  (e.g. for RA)
   "dms"         DD:MM:SS.S  (e.g. for DEC)
   "arcsec"      Arcseconds relative to the reference pixel
   "absdeg"      Absolute degrees
   "reldeg"      Degrees relative to the reference pixel
   "abspix"      Pixels 
   "relpix"      Pixels relative to the reference pixel
   "absghz"      GHz
   "relghz"      GHz relative to the reference pixel
   "abskms"      km/s
   "relkms"      km/s relative to the reference pixel
   "abslin"      Linear coordinate 
   "rellin"      Linear coordinate relative to the reference pixel

The default is "abspix".

Key: stype
'radio', 'optical', or 'frequency'.  If you specify a spectral axis
coordinate, this indicates what convention it is in.  For example, 
you might give an optical velocity with "type=abskms", but the header 
indicates a frequency axis.  If unset, it is assumed the coordinate
is in the convention defined by the image header.   

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