[gdal-dev] Transforming Raster Points from GeoTIFF with GCPs

[Matt.Wilkie at yukon.ca]

and https://gdal.org/programs/gdaltransform.html

-Matt

From: gdal-dev <gdal-dev-bounces at lists.osgeo.org> On Behalf Of Simon Eves
Sent: December 10, 2021 12:21 PM
To: Yann-Sebastien Tremblay-Johnston <yanns.tremblay at gmail.com>
Cc: gdal dev <gdal-dev at lists.osgeo.org>
Subject: Re: [gdal-dev] Transforming Raster Points from GeoTIFF with GCPs


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Aha! That's the bit I hadn't found. Thank you! :)

On Fri, Dec 10, 2021 at 10:38 AM Yann-Sebastien Tremblay-Johnston <yanns.tremblay at gmail.com<mailto:yanns.tremblay at gmail.com>> wrote:
Simon,

See the Transformer API, in particular https://gdal.org/api/gdal_alg.html?highlight=transformer#_CPPv419GDALTransformerFunc (or gdal.Transformer in Python).

Sebastien

On Fri, Dec 10, 2021 at 10:24 AM Simon Eves <simon.eves at omnisci.com<mailto:simon.eves at omnisci.com>> wrote:
So we have a GeoTiFF of Sentinel-1 imagery which `gdalinfo` reports as having a GCP projection with 210 points, which we'd (perhaps naively?!) like to import directly, transforming to WGS84 on the fly.

Obviously a simple OGRSpatialReference/OGRCoordinateTransformation transform isn't going to do anything, so I assume we have to do the GCP transform manually.

I found the GCPCoordinateTransformation class and other supporting code in ogr2ogr_lib.cpp as used by gdaltransform, which seems to do what we need, but of course it's not in the core GDAL library so we can't "just use it".

Before embarking on lifting out that code to implement an on-the-fly transformer in our system, I just wanted to make sure I wasn't missing any functionality elsewhere that would make it easier.

It may also be more efficient to just kick off a gdalwarp to pre-convert the file so we can just import it with no transformation required, but that seems ugly unless it's gonna be WAY more efficient?

Thanks,

Simon

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Simon Eves

Senior Graphics Engineer, Rendering Group
100 Montgomery St (5th Floor), San Francisco, CA 94104, USA



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Simon Eves

Senior Graphics Engineer, Rendering Group
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