The first thing we need to do is to get rid of the shift and possibly of the small rotation between the images. To do that we need to chose one reference for this astrometric procedure. This reference can be specified in configuration file process_config, the relevant keyword is REFERENCE. You must also choose a degree for the 2 dimensional polynomial of the astrometric re-mapping to the reference, the relevant keyword is DEGREE.  The correct set-up for the data-set of this example is already done in process_config , but you may find useful to have a look at this file anyway...
 

To run the registration and interpolation script just type:

./interp.csh

 It should take about 1 min. on most computer, may be a little more if you use an old machine...

 Once this process is completed, you can have a look at the log file: ../images2/log_interp2
 
 

   sigmax: 0.083038 sigmay: 0.079344 ndata: 211 nrest: 184 nfile1.fits
   sigmax: 0.094743 sigmay: 0.104723 ndata: 201 nrest: 183 nfile2.fits

   sigmax is the residual relevant to the astrometric transform along the X direction
   sigmay is the residual relevant to the astrometric transform along the Y direction
   nrest    is the effective number of stars used to compute this astrometric transform