
examinging pswarp to handle inverse transformations or more general transformations:

pswarp:
  * setup / init functions (psLibInit, psphotInit, etc)
  * pswarpArguments   : parse things like -file (name), -list (name), etc
  * pswarpParseCamera : examine minimal files, define cameras & pmFPAfile + pmFPA
    		        this function reads headers for files

			uses pmFPAfileDefineFromArgs / pmFPAfileBindFromArgs for inputs
			uses pswarpDefineSkycell for outputs

  * pswarpOptions     : check the recipe options, reconcile with cmd-line options

  * pswarpDefine      : create output image pixels, update related concepts, 
    		      	associate output astrometry (skycell) with output pmFPA structures
			


in pswarpParseCamera:
  * pswarpDefineSkycell : this function is based on pmFPAfileDefineFromArgs
    			* reads fileset from config->arguments (a fileset is an array of filenames)
			* select first filename & translate to UNIX namespace
			* open fits file
			* read fits header (PHU)
			* inherit some config elements from input config (user, system, files, arguments)
			* determine format from header
			  (NOTE: currently does not examine or set fileLevel)
			* build the pmFPA structure based on camera & name
			* bind filerule to fpa, generate the pmFPAfile
			* sets file->fileLevel based on format, but slightly out of sync wrt pmFPAfileDefineFromArgs
  			  (NOTE: does not expect / examine any other file)
			  

