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Purpose: To merge count, background, and exposure data (images) from separate observations of different pointings into a large-area mosaic.
1) Fixed input - after the band, component, and mask have been selected, the program reads in the appropriate cast array and mask for each observation.
2) Directory list - the file dir.dat must contain an ascii list of the path names to the directories containing the observation arrays to be cast. MERGE will use these path names to create the file names to be cast. For instance, if the component being cast is the exposure, the band being cast is R5, the mask is mask_47.fits, and the directory (VMS) is [SNOWDEN.DATA.OBS1], the program will input the two files: [SNOWDEN.DATA.OBS1]expose_5.fits and [SNOWDEN.DATA.OBS1]mask_47.fits.
1) Coordinate control - determines the coordinate system for the mosaic image. 1 for ecliptic, 2 for equatorial, or 3 for galactic coordinates.
2) Central coordinates - the center of the mosaic image in decimal degrees in the coordinate system selected in 1).
3) Scale factor for mosaic - arc minutes per pixel for the mosaic.
4) Radius limit - the radius of the region in the individual pointings, in arc minutes, to be cast into the mosaic (applied to the sky image rather than in detector coordinates). A limit of 53' serves reasonably well to exclude the worst problems caused by the large point response function at large off-axis angles.
5) Band to be cast - the program will cast only one band at a time. Enter 0 for HRI data.
6) Component to be cast - the program will cast only one component at a time. 1 for counts, 2 for exposure, or 3 for background. The program FINAL_IMAGE must be run on the individual bands to create the back_n.fits files for the background counts. All files to be cast must have the same names as they were labelled when generated, i.e., b_n.fits, expose_n.fits, and back_n.fits. counts.fits, expose.fits, and back.fits for HRI data.
7) Mask file name for masking of the data - the data will be masked using files with the input file name. The mask files must be in the same directories as the data files. If no additional masking is desired, enter ``none''.
8) Add to an existing array - data can be added to an existing array.
Fits file counts_n.fits, expose_n.fits, or back_n.fits depending on the chosen component. Note that expose_n.fits and back_n.fits have the same names as the files for the individual observations. counts.fits, expose.fits, and back.fits for HRI data.