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The programs in this section are used to mosaic individual observations (processed by the software in § 3) into larger area maps. They require that the names for the fits files produced by the software in § 3 remain unchanged and that they are found in separate directories. Specifically, they use the b_n.fits, expose_n.fits, back_n.fits, and mask_m.fits files where n is the band number and m is a band or band range (e.g., b_5.fits, expose_5.fits, back_5.fits, and mask_47.fits). As an example of the utility of these programs, see Snowden & Petre (1994) for the mosaic image of the LMC.
The output files for the mosaic programs are in the zenith equal-area
projection (ZEA). For small regions, there is little difference between
the ZEA projection and the tangential projection ( 
% at a radius of
). If your favorite image display package doesn't support ZEA,
the header information can be changed from ZEA to TAN. Appendix 3 gives an
example of the FITS header for mosaicked data.