- NAME
XYXY
- PURPOSE
To use a pair of headers to convert X/Y positions from one frame
to another.
- CALLING SEQUENCE
XYXY, hdra, hdrb, xa, ya, [ xb, yb ]
- INPUTS
hdra - The header containing the plate solution describing the
frame of reference being converted FROM.
hdra - The header containing the plate solution describing the
frame of reference being converted TO.
xa - A scalar or vector containing the x coordinate(s) to convert.
ya - A scalar or vector containing the y coordinate(s) to convert.
Must have the same number of elements as 'xa'.
- OUTPUTS
xb - The converted x coordinate(s). If this parameter is not
specified, it is returned through 'xa'.
yb - The converted y coordinate(s). If this parameter is not
specified, it is returned through 'ya'.
- PROCEDURE
The procedures 'xyad' and 'adxy' are used to perform the
onversion. The equinoxes of each header are checked with
get_equinox" to make sure that they are identical, and "precess"
s used if they are not. HEULER used if the headers have a different
oordinate system (e.g. Celestial, Galactic, Ecliptic)
ote that all X,Y coordinates are in the IDL convention (starting with
,0) and not the FITS convention (first pixel is 1,1)
- PROCEDURES USED
GET_EQUINOX(), EXTAST, XYAD, ADXY, PRECESS, HEULER
- MODIFICATION HISTORY
Written by Michael R. Greason, Hughes-STX, 13 April 1992.
Updated to use ASTROMETRY structures. J.D.Offenberg, HSTX, Jan 1993
coordinate system J. Ballet/ W. Landsman April 2004
sure output arrays supplied W. Landsman Feb 2017