Hi all, The current IDL REBIN() thread reminded me to post this here... I'm trying to port Hongjie Xie's IDL/ENVI Implementation of the FFT Based Algorithm for Automatic Image Registration http://www.nmt.edu/%7Ehjxie/xie-paper.pdf ftp://ftp.iamg.org/VOL29/v29-08-10.zip to Python/numarray/Numeric and running into some subtle problems. For instance, the IDL ROT() requires some additional steps to emulate, and the MAX(array, position) as well. And, I'm not at all familiar with the correspondence of the FFT libraries... even the simple shift-only routine http://rjs.org/astro/1004x/Python/register/shift_idl.py produces different (incorrect) x shift values than the IDL. My current code http://rjs.org/astro/1004x/Python/register/ conforms to Xie's flow as much as possible for now, but should and will be re-factored when functional. His LogPolar function, to convert rectangular coordinate arrays to polar, is particularly slow. I was recently informed that IDL has a usable demo version which I will try this week, but I would love to hear if anyone else has interest in this. I think that the algorithm would make a nice standalone module, or perhaps something for nd_image, as it calculates shift, scale and rotation for 2d arrays. Xie's main examples are registration of satellite Earth imagery, but it should work just as well looking up ;-) Thank you, Ray Secret anti-spam filter-passing text. Include with reply: qwertyuiop