[Numpy-discussion] Help req: IDL --> Numeric/numarray

RJ rays at san.rr.com
Tue Aug 31 06:51:04 CDT 2004


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


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