A world coordinate (RA and DEC) system can be defined for a mosaic
image produced with the redimage task by setting the
coord flag. The coordinate system is defined from the base
position of the mosaic stored in the image header entries meanra
and meandec, and the maximum RA offset and the minimum DEC
offset used in combining the mosaic and stored in the mosaic header
entries moffra and moffdec when redimage forms the
mosaic.
If the coord and display flags are set when
redimage is run, an RA and DEC coordinate grid is overlaid on
the mosaic image when it is displayed. This may be helpful for
identifying objects in large mosaics and for determining the scale of
a mosaic.
The images.tv.wcslab task can be used to overlay the world
coordinate grid at any time when the mosaic image is redisplayed.
Note that this does not work with SAOIMAGE under Solaris 2, and the
wcslab command must currently be issued twice when using the
XIMTOOL display under Solaris 2.
Once the world coordinate system grid has been defined, RA and DEC positions of selected objects can be obtained by typing
rimcursor wcs=world
Use the image display cursor to select objects and type any key to print the
coordinates. Exit rimcursor by typing <cntrl>d with the cursor in
the image display.