[GRASS-user] seeking advice on importing "unprojected" data

[Michel Wortmann]

Hi Ken,
I see. This way you will have to resample your data into the other 
coordinate system tho. That might indeed be a bit tricky with a Polar 
projection.
Hit me up if you need any info on the workaround.
Michel

On 17.08.2017 23:11, Ken Mankoff wrote:
> Hi Michel, list,
>
> I've come across a different method - using the CDO tools to remap the 
> rotated pole data set.
>
> See thread here: https://code.mpimet.mpg.de/boards/2/topics/96
> The answer there uses a simple ASCII "mygrid" as the target grid, but 
> the command can be "cdo remapbil,file.nc <http://file.nc> ifile ofile" 
> where "file.nc <http://file.nc>" is a netcdf file that represents the 
> target grid. It has specific format requirements discussed here: 
> https://earthscience.stackexchange.com/questions/8086/interpolate-gaussian-grids-to-regular-fixed-grids-using-bilinear-interpolation
>
> I'm trying to figure out this CDO method, and having trouble 
> converting my GRASS GIS projection information (and the longitude and 
> latitude coordinates for each grid cell) to the correct NetCDF file... 
> work is in progress.
>
> If I can't do it this way I'll hand-code it as you suggested in your 
> reply. I'm not totally clear on your method yet, so I may write and 
> ask for more details.
>
> Thanks,
>
>   -k.
>
>
> On Thu, Aug 17, 2017 at 12:49 PM, Michel Wortmann 
> <wortmann at pik-potsdam.de <mailto:wortmann at pik-potsdam.de>> wrote:
>
>     Hi Ken,
>     I have had to compare lonlat data with ncdf rotated pole data
>     before and also chose to import the centroids of the rotated grid
>     into a vector. To fill the cells I actually converted the points
>     to much smaller resolution (e.g. you could use the 30m of your
>     other dataset) raster cells with an ID and used r.grow.distance to
>     create an ID grid. I could then just reclass this ID grid for each
>     timestep, meaning no excess data in the grass db. At the time it
>     seemed like a bit of a workaround, but reading the thread below
>     makes me think this is the way to go.
>
>     Regards,
>     Michel
>
>
>
>
>     On 15.08.2017 14:38, Ken Mankoff wrote:
>>     It seems that my suggested approach might be the right one based
>>     on this thread from 2012:
>>     https://lists.osgeo.org/pipermail/grass-dev/2012-March/058179.html
>>     <https://lists.osgeo.org/pipermail/grass-dev/2012-March/058179.html>
>>
>>       -k.
>>
>>     On Tue, Aug 15, 2017 at 1:59 PM, Ken Mankoff <mankoff at gmail.com
>>     <mailto:mankoff at gmail.com>> wrote:
>>
>>         Hi GRASS list,
>>
>>         I'm trying to compare two data sets and need to import them
>>         into the same location. One is a GeoTIFF in WGS84 lon,lat
>>         coordinates. When I create a new GRASS location using "-c
>>         file.tif" everything appears to work, and
>>
>>         $ g.region -p
>>         projection: 99 (unnamed)
>>         zone:       0
>>         datum:      wgs84
>>         ellipsoid:  wgs84
>>         etc...
>>
>>         And from gdalinfo:
>>
>>         Coordinate System is:
>>         PROJCS["unnamed",
>>             GEOGCS["WGS 84",
>>                 DATUM["WGS_1984",
>>                     SPHEROID["WGS 84",6378137,298.257223563,
>>                         AUTHORITY["EPSG","7030"]],
>>                     AUTHORITY["EPSG","6326"]],
>>                 PRIMEM["Greenwich",0],
>>                 UNIT["degree",0.0174532925199433],
>>                 AUTHORITY["EPSG","4326"]],
>>             PROJECTION["Polar_Stereographic"],
>>             PARAMETER["latitude_of_origin",70],
>>             PARAMETER["central_meridian",-45],
>>             PARAMETER["scale_factor",1],
>>             PARAMETER["false_easting",1],
>>             PARAMETER["false_northing",1],
>>             UNIT["metre",1,
>>                 AUTHORITY["EPSG","9001"]]]
>>         Origin = (107900.000000000000000,-655550.000000000000000)
>>         Pixel Size = (30.000000000000000,-30.000000000000000)
>>
>>
>>         I have a second data set that I would like to co-locate with
>>         this one. That data comes in a NetCDF file but the projection
>>         is a custom rotated-pole projection. I have three variables
>>         in the NetCDF file: lon, lat, and the data.
>>
>>         What is the best method to convert on data set to the other?
>>         My first approach might be to convert the NetCDF to
>>         lon,lat,data ASCII file, import as points with m.proj, then
>>         convert to raster. I'm wondering if this is what the experts
>>         on this list would do. Note that I have one TIF, and 50,000
>>         NetCDF time steps, so it may be more efficient to convert the
>>         TIF to the custom NetCDF projection, but it is not a requirement.
>>
>>         Thanks for any advice you may have,
>>
>>           -k.
>>
>>
>>
>>
>>
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