Documentation on impos

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

        IMPOS takes an image 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 (VELO) and optical (FELO) velocities.

        If the specified coordinate represents a pixel actually on the
        image, its value is reported as well.

Key: in
        The input image.

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

        Default is "abspix", or value of previous coordinate.

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.