[gdal-dev] RFC 22: RPC Georeferencing

[Frank Warmerdam]

Folks,

It is proposed that GDAL support an additional mechanism for geolocation of 
imagery based on rational polynomial coefficients (RPCs) represented as metadata.

Many modern raw satellite products are distributed with RPCs, including 
products from GeoEye, and DigitalGlobe. RPCs provide a higher systematic 
description of georeferencing over an image, and also contain information on 
the viewing geometry that in theory makes orthocorrection (given a DEM) and 
some 3D operations like building height computation possible.

To some extent RPCs were already supported in GDAL but the support was
incomplete and not well documented.  This RFC revises the approach somewhat
and is intended to make this a "fully supported" geolocation method in GDAL.

   http://trac.osgeo.org/gdal/wiki/rfc22_rpc

Pretty much everything is already implemented and committed, but I'm willing
to make changes as needed.  One aspect that I consider very unsettled (and
which I have not yet committed) is the SWIG bindings for the GDAL transformer
API.  I'd especially appreciate if the SWIG gods could review and propose a
better binding approach.  The current bindings result in code like this:

     ds = gdal.Open('data/gcps.vrt')
     tr = gdal.Transformer( ds, None, [ 'METHOD=GCP_POLYNOMIAL' ] )

     (success,pnt) = tr.TransformPoint( 0, 20, 10, 0 )

With "pnt" being a 3-tuple.  I don't even see how the TransformPoints
function in the proposal (transform an array of points in place) will
map in Python.

This email is a call for feedback, but I'm hoping to put forward a motion
to adopt on Monday sometime, so prompt feedback for revisions is
encouraged!

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org