Handle Swiss coordinate system

[ScottMcMichael]

ASP has some problems when processing data with this projection: "+proj=somerc +lat_0=46.95240555555556 +lon_0=7.439583333333333 +k_0=1 +x_0=600000 +y_0=200000 +ellps=bessel +towgs84=674.4,15.1,405.3,0,0,0,0 +units=m +no_defs "

Sample data is here: lunokhod2:/home/smcmich1/data/swiss_projection

[oleg-alexandrov]

I narrowed this down to the get_wkt and set_wkt functions in the Cartography module in VW. The second function does not write exactly the thing that the first function reads. We read it in, parse it, form some objects, and then extract again the wkt string from that object. Things get lost on the way. I am sure the problem is not in GDAL or other external tools, as if I pass to GDAL the precise wkt string we read in, and not the thing we process, it can write it correctly.

[dpmayerUSGS]

Not a direct solution, but just note that support for this projection across EPSG, WKT, and GeoTIFF has always been a little shaky. Some notes here: http://geotiff.maptools.org/proj_list/swiss_oblique_cylindrical.html

[oleg-alexandrov]

I made some progress here, at least now the PROJCS and GEOGCS fields are good, and +k_0 is parsed (sorry, internal details), but this is not enough. I think we don't capture the AUTHORITY right.

I'd suggest one reproject this DEM to WGS84 and some other projection, say stereographic, using gdalwarp. It may take us time to untangle this as my current work is non-ASP.

[adehecq]

Thanks. Yes that’s fine, I will just use a different projection for the moment.

On Feb 3, 2019, at 20:45, Oleg Alexandrov notifications@github.com<mailto:notifications@github.com> wrote:

I made some progress here, at least now the PROJCS and GEOGCS fields are good, and +k_0 is parsed (sorry, internal details), but this is not enough. I think we don't capture the AUTHORITY right.

I'd suggest one reproject this DEM to WGS84 and some other projection, say stereographic, using gdalwarp. It may take us time to untangle this as my current work is non-ASP.

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[ScottMcMichael]

I made a small change to VW so that the +towgs84 field is now recorded in our output files. Some of the authority fields are still missing but maybe it is good enough now?