[gdal-dev] Gdalwarp is unable to output a geotiff with units = seconds correctly

[Even Rouault]

Le mardi 27 mai 2014 13:10:05, Marcel Korn a écrit :
> We use geotif with units=seconds quite a lot.
> 
> I found that running :
> gdalwarp -t_srs <srs-def> <input path> <output path>
> 
> 1. If target srs_def is a prj file with EPSG code for GCS WGS84 and units=
> degree and my input file is a geotiff with GCS WGS84 and units= Seconds -
> the output file is a "normal" geotiff with GCS WGS84 and units= degree.
> 2. If target srs_def in a prj file with EPSG code for GCS WGS84 and units=
> SECONDS and my input file is a geotiff with GCS WGS84 and units= degree  -
> the output is a geotiff with the units undetected correctly.
> In order to correct the output file I used ArcCatalog and set the units to
> seconds.
> After the correction the file (and the header was ok).
> Note: the prj must include authority = EPSG and the code (in this case
> 4326) otherwise the geotiff is produced as Custom CS and it may or may not
> be identified correctly and fully by apps.
> Also note that with default units you can run gdalwarp with EPSG:4326
> instead of the prj file.
> 
> It seems like there is a functional program bug since GDAL reads
> non-default units OK but cannot produce a geotiff with seconds. Something
> similar will probable happen with UTM PCSs if the target is feet instead of
> meter (the default).
> 
> I would like to know if somebody else found this problem and how he solved
> it.
> Of course, I wait to get confirmation it is a bug or maybe I did something
> wrong.
> If it is a "new bug" I woułd like to know what can I do to advance the
> solution for it.
> 
> This bug reminds me of a very old ArcMap bug that manifests itself when you
> open a polygon or a raster with non-default units like second. If this is
> the first item you open, the units are not read correctly until you reload
> the GCS into the Data Frame. And than you get Degrees...the logic (or the
> lack of it) is similar.
> 
> Best regards,
> Moty

Marcel,

could you open a ticket with all the elements to reproduce ?

From a quick review, it would require some work in proj.4 to add support for 
angular units and in the GDAL interface to proj.4 to use it to/from WKT. 
Perhaps in the GeoTIFF driver too.

I would note, that using EPSG:4326 in WKT with units != degree is something 
that calls for trouble. The equivalent of EPSG:4326 with units = seconds  is 
not EPSG:4326

You can contract a GDAL service provider if you want that topic to go forward.

Best regards,

Even

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