[fitswcs] SIP scheme

[rhook at eso.org]

Dear Colleagues, 

As some of you may be aware the Spitzer Science Center (SSC) has adopted the 
"SIP" scheme for the representation of non-linear geometric distortion in 
their FITS image products (http://ssc.spitzer.caltech.edu/documents/ 
distortion_v1.4.pdf).  This is inspired by, and based on, preliminary Paper IV 
FITS work, but is distinct from it.  (Note that the latest draft of Paper IV, 
posted in  April 2004, has changed significantly from the early draft 
referenced in the January 2004 SSC memo.) 

Here at STScI we are also considering the possible adoption of this convention 
for HST - although discussions are at a very early stage and this certainly 
may not ultimately happen. This raises the question of the status and 
evolution of this convenient, de facto, standard  within the FITS world. SIP 
is already quite widely implemented in data handling tools (WCSTools/libwcs, 
SAOImage, DS9, GAIA/Starlink AST, IDLAstro, and recently drizzle too, in 
addition to Spitzer-specific software). 

I have been discussing this with David Shupe, who is lead author of the above 
memo, and we are planning to hold a brief discussion of this work at the 
forthcoming FITS BoF at ADASS in Pasadena at the end of October. 

This message is just an invitation for comments, both to this list and 
possibly by coming along to the BoF at ADASS. 

Best Regards, Richard Hook (ST-ECF/STScI) & David Shupe (IPAC/SSC)