[gdal-dev] JPEG file with ESRI world file .jpgw but geotransform not established

[Markus Neteler]

Hi Even,

On Mon, Jan 27, 2020 at 1:45 AM Even Rouault <even.rouault at spatialys.com> wrote:
> Hi Markus,
>
> I've found some doc about this .jgwx in
> http://resources.arcgis.com/en/help/main/10.1/index.html#//009t00000028000000
> So this is a ESRI specific thing
> """Starting at ArcGIS 9.2 SP2, if the transformation cannot be expressed as a
> world file, the Update Georeferencing command on the Georeferencing toolbar
> writes the transformation into the .aux.xml file and also writes an
> approximate affine transformation into a text file or a world file with an x
> on the end of the extension name. [...]. Keep in mind that this is not an
> exact transformation; it is only an approximation."""
>
> So it might not be always relevant to report the content of the .jgwx as a
> geotransform. Or if we did, we should probably add some metadata like
> APPROXIMATE_GEOTRANSFORM=YES

I see, thanks for investigating.

> > Using the graphical GPC tool of GRASS GIS
> > (https://grass.osgeo.org/grass78/manuals/wxGUI.gcp.html)
> > and exporting the map to GeoTIFF + gdal_translate to JPG with World
> > file I obtained a quite similar result with working geotransform:
>
> How does this tool manage to create a geotransform frmo this file ?

What it does is that it writes a POINTS file which is specific to
https://grass.osgeo.org/grass78/manuals/i.rectify.html

> The .aux.xml file does contain a GeodataXform ESRI specific element. GDAL just
> extract this in the xml:ESRI metadata domain, but doesn't do further use of
> this. Here it could potentially report the GCPs in it as GDAL GCPs. I've
> grepped in GRASS source code to see if it has specific code to extract GCPs
> from GeodataXform, but I can't find anything. So this is quite mysterious to
> me.

Sorry for the misunderstanding: I used to GRASS GIS' g.gui.gcp to
generate GPCs from scratch, interactively.
This graphical tool let's you assign X,Y to E,N, then it uses
i.rectify (https://grass.osgeo.org/grass78/manuals/i.rectify.html) to
georectify all images in the source imagery group.
Eventually I exported to file using r.out.gdal.

Best,
Markus