IRAF Newsletter -- Number 14 -- April 1998

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New Image Registration Tasks

The following world coordinate system (WCS) driven image registration tasks have been added to the new IRAF V2.11 immatch package.

skyxymatch

Generate matched pixel lists using the image celestial wcs

skymap

Compute geometric transforms using the image celestial wcs

sregister

Register 1-D or 2-D images using the image celestial wcs

wcsxymatch

Generate matched pixel lists using the image wcs

wcsmap

Compute geometric transforms using the image wcs

wregister

Register 1-D or 2-D images using the image wcs

wcscopy

Copy the wcs from one image to another

The tasks wregister and sregister use the reference and input image coordinate systems to compute a grid of matched pixel coordinates, use the matched grid to compute a coordinate mapping from the reference image to the input images, compute the output image pixel values by interpolating in the input image at the position of the mapped reference image pixels, and update the output image coordinate systems. wregister can register images with any valid coordinate system provided that the reference and input image have the same coordinate system, e.g., both images have J2000.0 equatorial systems. sregister can only register images with celestial coordinate systems, e.g., equatorial J2000.0 or galactic, but can register images with different celestial coordinates systems, e.g., register an image with an FK4 B1950.0 coordinate system to one with an FK5 J2000.0 coordinate system.

Matched coordinate grids or coordinate mappings can be computed without doing the actual image registration by calling the supporting tasks wcsxymatch / wcsmap in the case of wregister , or the skyxymatch / skymap tasks in the case of sregister . These tasks can be used to examine the coordinate mappings interactively.

The tasks wcsmap / skymap , wregister / sregister are script tasks which call wcsxymatch / skyxymatch to compute the respective matched coordinate grids, geomap to compute the required geometric transformations, geotran to do the actual image registration, and wcscopy to update the image coordinate system.

Lindsey Davis

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IRAF Group, National Optical Astronomy Observatories, P.O. Box 26732, Tucson, AZ 85726, Phone: (520) 318-8160, FAX: (520) 318-8360, Email iraf@noao.edu

Posted: 07May1998