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).
 
        If a rest frequency is stored in the header, then in addition to
        the type specified in the header, spectral axes are converted
        to frequency (FREQ), radio velocity (VRAD), optical velocity
        (VOPT), redshift (ZOPT), and relativistic velocity (VELO).
 
        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 for unspecified axes is the type of the previous
        axis.  The default for the first axis is "relpix".

Key: stype
        'VRAD' (or 'radio'), 'VOPT' (or 'optical'), 'VELO' (or
        'relativistic') - the velocity convention for a spectral
        coordinate.  For example, the header might define a frequency
        axis but you could provide a velocity with "type=abskms", in
        which case you must qualify the velocity convention via stype,
        i.e. VRAD, VOPT, or VELO.

Key: options
        Extra processing options.  Several can be given, separated by
        commas, with minimum-match.
          altprj    Interpret a CAR (plate carée) projection in the
                    input ot template image as a simple linear
                    coordinate system with an additional 1/cos(lat0)
                    scaling factor applied when computing the longitude,
                    e.g.
                       RA = (p1 - CRPIX1)*CDELT1/cos(CRVAL2).
                    This interpretation differs significantly from the
                    FITS standard when lat0 (i.e. CRVAL2) is non-zero.
          altspc    Report FREQ-{HEL,LSR} axes as is, namely
                    topocentric, i.e. don't Doppler shift to barycentric
                    or LSRK (see help for velsw).
 
Revision: 1.16, 2015/07/31 01:20:50 UTC