[gdal-dev] RPC orthorectification accuracy issues.

[Frank Warmerdam]

Even,

I feel that the RPC coefficients have well establish meanings from the
NITF spec, and file formats like _rpc.txt.  I assume they are
center-of-pixel oriented.  I would *not* want the RPC metadata we keep
(ie https://trac.osgeo.org/gdal/wiki/rfc22_rpc) to have a different
meaning for the pixel/line locations.  So I would suggest we should
not need to transform the RPC coefficients when they are imported -
instead it is the evaluator which needs to adapt between the RPC
pixel/line model and the usual GDAL interpretation.

I'll note this opinion in the ticket as well.

This is going to be moderately distruptive. :-(

Pablo - thank you for bringing this to light!

Best regards,
Frank

On Fri, Jun 19, 2015 at 7:35 AM, Even Rouault
<even.rouault at spatialys.com> wrote:
> Le vendredi 19 juin 2015 15:47:54, Pablo d'Angelo a écrit :
>> Dear GDAL Developers,
>>
>> i have recently compared the results of our internal RPC based
>> orthorectification software and have found several difference, which I
>> think are due to various "corner" vs "center" of pixel issues in the RPC
>> transform code. This lead to significant shifts when using lower
>> resolution DEMs, such as SRTM, particularly in hilly and mountainous
>> regions.
>>
>> I have prepared an analysis and patches to fix these issues at:
>> https://trac.osgeo.org/gdal/ticket/5993
>
> Hi Pablo,
>
> I had seen your well documented ticket and wanted to give feedback. Thanks for
> the reminder.
> To my opinion, adjustments between "vendor"/formats conventions and the GDAL
> convention (0,0=upper-left corner of upper-lef pixel) should be done during
> the reading of the RPC parameters from their source (similarly to what is done
> when reading a geotransform with pixel-is-center convention), so as to make
> the
> https://trac.osgeo.org/gdal/attachment/ticket/5993/fix_RPCTransformPoint.patch
> patch unnecessary.
> Apart .rpb and .rpc_txt, we can also read RPC from GeoTIFF, NITF, ENVI,
> Oracle, PCIDSK... so I'm wondering what our situation is related to them.
> Of course this also leaves the embarassing question of which convention to
> adopt when writing RPC values in .rpb or _rpc.txt files... Probably DG
> convention for .rpb ?
>
> fix_rpc_dem_interpolation.patch looks good to me.
>
> Even
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev



-- 
---------------------------------------+--------------------------------------
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    | Geospatial Software Developer