[GRASS-user] Import and reproject COSMO REA6 data set

[Markus Metz]

On Mon, Nov 6, 2017 at 2:05 PM, Helmut Kudrnovsky <hellik at web.de> wrote:
>
> Pietro Zambelli wrote
> > Dear Helmut,
> >
> > On 06/11/17 08:22, Helmut Kudrnovsky wrote:
> >> not really an answer, but the data documentation says:
> >>
> >> "Output format:      GRIB 1, rotated spherical"
> >>
> >> a quick web search shows some hints to handle such data.
> >
> > Looking at the reference model manual:
> >
> >
http://www.cosmo-model.org/content/model/documentation/core/cosmoDyncsNumcs.pdf
> >
> > at page 25, there are some equation to transform the rotated spherical
> > coordinates back and forward, see the attached image.
> >
> > Are these the hints that you mentioned in your previous reply?
> >
> > Should I convert the raster in to a x_s, y_s, z list of points and write
> > a function to convert the spherical coordinates (x_s, y_s) values
> > defining my own python script to apply the transformation function and
> > generate the lat, lon, z triplet of values, to be imported into a WGS84
> > location?
> > Any better approach/idea?
> >
> > Thank you for the support.
>
> never used such kind of data for myself; maybe it would be worth to ask on
> the GDAL ML how to used this kind of data.

GDAL and GRASS use proj4 for reprojection, but proj4 does not support these
rotated spheres where the latitude origin for a longlat projection is not
0. The easiest solution is to use a different data source. Otherwise you
would have to write a reprojection routine for such rotated spheres. The
source code of gdalwarp or r.proj could be used as a template.

Markus M
>
> some other things I've found in the web, e.g.
>
>
https://gis.stackexchange.com/questions/10808/manually-transforming-rotated-lat-lon-to-regular-lat-lon
>
https://gis.stackexchange.com/questions/64210/transforming-regular-lat-lon-to-rotated-lat-lon
> http://jgrib.sourceforge.net/docs/rotLatLon.pdf
> [...]
>
> they looks similar you've found.
>
>
>
>
> -----
> best regards
> Helmut
> --
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