[gdal-dev] georeferenced but not georeferenced?

[Matt.Wilkie at yukon.ca]

Thank you Even, especially for highlighting a DEM should be used. I 'knew' that but hadn't taken the time to fully ingest the meaning. It's drastically changed how I'm approaching this project.

-Matt

From: Even Rouault <even.rouault at spatialys.com>
Sent: November 10, 2021 2:16 PM
To: Matt.Wilkie <Matt.Wilkie at yukon.ca>; gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] georeferenced but not georeferenced?

Le 10/11/2021 à 22:03, Matt.Wilkie at yukon.ca<mailto:Matt.Wilkie at yukon.ca> a écrit :

Hi all,



I'm creating images from SPOT6/7 archive DIMAP format. The resulting images display in the correct position in the world when combined with other sources, however all the usual tools say the images have no georeferencing.



* If the images have no georeferencing how do ArcMap/Pro and Qgis know to put them in the right place?

Those images have RPC. You can see RPC information with gdalinfo in the "RPC Metadata" section

listeo/geotiffcp and a number of utilities are not RPC aware. But gdalwarp is.



* How can I convert whatever-this-is into proper georeferencing so that other tools know how to handle them too?
You can use gdalwarp to orthorectify them.  You should generally specify -to RPC_DEM=some_dem_with_elevation_as_ellipsoidal_heights or -to RPC_HEIGHT=ellipsoidal_height. See https://gdal.org/api/gdal_alg.html?highlight=rpc_dem




Attached is a sample image.  It was created with (on one line):



    gdal_translate  -outsize 100 0

    -co compress=zstd -co predictor=yes -co level=17 -co bigtiff=yes -of cog

    .\path\to\IMG_SPOT6_MS_001_A\DIM_SPOT6_MS_201609082010410_SEN_1.XML

    source_tiny.tif



The biggest problem this causes me at the moment is that gdal_pansharpen.py output does not have any kind of goereferencing, and I can't use old faithfuls like listgeo, geotiffcp, or gdalcopyproj.py to copy the coordinate system across.



thanks in advance for your thoughts,



Matt Wilkie

Geomatics Developer & Administrator

Environment | Technology, Innovation and Mapping

T 867-667-8133 | Yukon.ca

Hours: 08:30-16:30, Mon-Wed: Office, Thu: Remote, Fri: Away.



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