[Gdal-dev] NITF and RPCs

[Frank Warmerdam]

Simon Perkins wrote:
> Hi,
> 
> I have a Quickbird NITF file which I'm having georeferencing problems
> with under GDAL. The Geotransform numbers that I get back from GDAL seem
> very wrong. However, other applications such as ENVI (with the NITF
> module) are able to read the geocoordinates just fine. On closer
> investigation it seems that the file contains RPC values, and I wonder
> if ENVI is using these coefficients in preference to the geotransform
> data. Is this what should happen?
> 
> I found an e-mail from Frank from 2003, which talks about recently added
> support for RCP in NITF. However, all I can find is the
> GDALExtractRPCInfo() method which extracts the raw RPC numbers. Are
> there any GDAL methods for converting row/column coords to geocoords
> using this RPC data? How does one do this?

Simon,

A gdalinfo report should include RPC information in the metadata if
RPCs are aailable.  The RPC info should include a lat/long bounding
box with approximate region.

eg.
   RPC_MIN_LONG=-117.16045
   RPC_MAX_LONG=-117.09095
   RPC_MIN_LAT=32.59485
   RPC_MAX_LAT=32.61995

Just how off is the geotransform information?  The geotransform is
normally derived from the low accuracy IGEOLO fields.

> Any idea why GDALGetGeotransform() is returning such strange numbers?
> For various reasons it's a little tricky for me to obtain the ouput of,
> say, gdalinfo applied to the file, but I could try to do this if it
> would be helpful.

I'm not sure.  If you can build the nitfdump utility in gdal/frmts/nitf
you may find it provides useful information on the file as well.

Best regards,
-- 
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