+mosastro takes a collection of data from mosaic CCD images, all +individually astrometrized, and determines a single global astrometric +solution for the complete system. In this process, it determines a +distortion model for the telescope arising from the optical system, as +well as mapping solutions relating the coordinate systems of the +individual chip pixels to the focal plane. Both of these +transformations may involve up to 3rd order polynomials. + +
+The suggested operation is to use gastro (or gastro2) to determine +linear astrometric solutions for the individual chips before running +mosastro. Mosastro requires the individual chip astrometry have an +accuracy of roughly 1 arcsec or better in order to select the match +between the observed stars and the astrometric reference catalog. +This two stage approach allows a more robust linear solution for the +individual chips, which may have too few reference star matches to +define reliable high-order solution. The mosaic analysis determines a +single distortion model representing the physical contribution of the +telescope optics. + +Mosastro is run assuming the user has a collection of Elixir-style +astrometry / photometry files in one of the CMP/SMP/SMF set of +formats. Mosastro will auto-detect the data format and load the +stellar astrometric and photometric measurements. The collection of +data is assumed to consist of one file per chip, with names which are +sufficiently consistent that they can be identified with a single +filename including wild-cards. + +
+The user command looks like:
+mosastro (glob) (ext) (phu) +- mosastro () +The first argument is an expression containing wild-cards which +expands into the collection of files containing the astrometric data. +The mosastro program must receive the wild-card expression +without expansion by the shell. The user call needs to +protect the wild-card against expansion, which can usually be done by +placing the expression within double-quote marks. The second argument +is the new output extension. The stellar photometry will be written +out to files using the same names as the input, replacing the final +filename extension with the provided extension. The standard input +extensions are one of the following: 'cmp', 'smp' (used for dophot or +sextractor output files in raw text format), 'cmf, 'smf' (used for +dophot or sextractor output files in fits table format). The +recommended output extensions replace the 'c' or 's' with 'x': 'xmp' +for raw text format, or 'xmf' for FITS table format. The final +argument is the name of the output 'primary header unit' file. The +standard usage here is to use the filename root (without chip +identifiers) with the extension 'phu'. The output telescope boresite +and optical distortion terms are written to this primary header entry, +which is constructed from the first of the chip files (true?). - perform mosaic astrometry on a collection of FITS images. The input - consists of SMP files (see gastro) which have valid astrometric - solutions. Mosastro determines a complete mosaic astrometry - solution, including a polynomial term for the telescope optical - distortion and individual polynomials for each chip. + future expansions: allow input list of files from a file, allow +input MEF collection of chip astrom/photom +
+In the following discussion, we refer to conversions between +several coordinate frames. We use the term 'project' to describe the +projection of the celestial coordinates to the linear (focal plane or +chip) coordinates; we use the term 'deproject' to describe the +conversion from the linear chip or focal-plane coordinates to the +spherical celestial coordinates. + +
+mosastro performs the following steps in the analysis. +