[GRASS-user] Issue with netcdf import into GRASS 7

Tue Jun 9 21:17:50 PDT 2015

Micha,

It looks like your first suggestion worked. I did, however, have to add -b
1 to the end of your line:

 gdal_translate -of AAIGrid NETCDF:"geo_em.d02.nc":GREENFRAC greenfrac.asc
-b 1

because I was getting the error:

Warning 1: No UNIDATA NC_GLOBAL:Conventions attribute
Input file size is 420, 320
ERROR 6: AAIG driver doesn't support 12 bands.  Must be 1 band.

There are 12 bands (1 for each month) in the file 'geo_em.d02.nc', so I had
to specify which band number. Then I just needed to change the dx=dy from
1.0 to 1000. in the greenfrac.asc file. The imported file seems to be
placed correctly with the right resolution.

Thank you so much for your help!

Cheers!
Tom

On Tue, Jun 9, 2015 at 5:22 PM, Micha Silver <micha at arava.co.il> wrote:

>  Hi Tom:
>
> These geo_em* netcdf files do not have any "proper" CRS information in the
> headers. So you indeed get a simple X-Y matrix with cellsize 1 when you try
> to import directly using GDAL.
>
> One of the ways to work around this (explained in NCAR's user manual,
> chapter 4, about p. 59) is to export to an ARCInfo ASCII file, then
> manually edit the ASCII file header rows and change the xllcorner,
> yllcorner, and cellsize to the correct values.
>
> So first:
> gdal_translate -of AAIGrid NETCDF:"geo_em.d02.nc":GREENFRAC greenfrac.asc
> Now do:
> ncdump geo_em.d02.nc | grep corner
>         :corner_lats = 36.19099f, 39.06561f, 39.08329f, 36.20801f,
> 36.19086f, 39.06547f, 39.08319f, 36.20791f, 36.18649f, 39.07011f, 39.0878f,
> 36.20351f, 36.18636f, 39.06997f, 39.0877f, 36.2034f ;
>         :corner_lons = -108.7585f, -108.8684f, -104.0023f, -104.0788f,
> -108.7641f, -108.8742f, -103.9965f, -104.0732f, -108.7584f, -108.8686f,
> -104.0021f, -104.0789f, -108.7639f, -108.8744f, -103.9963f, -104.0733f ;
>
> The above "corner_lats" and "corner_lons" are the correct Lon/Lat for the
> corners and center for each of the four corner pixels in the domain 2. The
> lower left corner of the lower left pixel is at -108.7585,36.19099. You
> enter these into the AAI header rows, and set the cellsize to 1000, then
> import that altered AAIGrid into GRASS *in a WGS84 location* .
>
> One caveat: this method assumes that the whole geo_em.d03 is projected in
> a Lon/Lat WGS84 coordinate system, which is wrong, as you know. The way I
> know of to get an accurate raster is to parse out the XLAT and XLONG
> variables, together with the GREENFRAC variable you are interested in as a
> CSV list of lon,lat,greenfac values, import the values as vector points,
> and do an interpolation.
>
> Another possibility comes to mind, but I've never tried it: You should be
> able to convert the above xllcorner and yllcorner values to your Lambert
> Conformal Conic projection in advance, and use the converted values in the
> AAI header rows. Then import the AAI file directly into the correct LCC
> location. You would do this by:
>
>    1. create a point vector of a single point (v.in.ascii) from the
>    Long/Lat values above in an WGS84 location
>    2. project that point to your LCC location (v.proj)
>    3. get the LCC X-Y coordinates (v.out.ascii)
>    4. Edit the header rows with the LCC xllcorner and yllcorner values
>    5. Import into an LCC location (with r.in.gdal -o as you did)
>
> I'd be interested to know if this works :-)
>
> Regards,
> Micha
>
>
>
>
> On 06/09/2015 05:47 AM, Thomas Adams wrote:
>
> All:
>
>  Using the help found here: http://grasswiki.osgeo.org/wiki/NetCDF I have
> been able to import a netcdf file into GRASS 7, but the data is not scaled
> correctly.
>
>  My file is found here:
>
> https://drive.google.com/file/d/0B-Dmtz0DFEiubG5aYTk4TDZERXc/view?usp=sharing
>
>  I created a GRASS LOCATION based on this:
>
>  char Lambert;
>   :grid_mapping_name = "lambert_conformal_conic";
>   :latitude_of_projection_origin = 37.99999237060547; // double
>   :longitude_of_central_meridian = -106.0; // double
>   :standard_parallel = 34.0, 42.0; // double
>   :earth_radius = 6371229.0; // double
>   :_CoordinateTransformType = "Projection";
>   :_CoordinateAxisTypes = "GeoX GeoY";
>
>  which I obtained using panoply from here: http://www.giss.nasa.gov/tools/panoply/
>
> Looking at the file netcdf header information, it's clear the dx=dy=1000m; but, what imports is x=dy=1m resolution even though I set the x & y resolution to 1000m
>
> This is my import command:
>
> r.in.gdal input=NETCDF:"geo_em.d02.nc":GREENFRAC output=greenfrac -o -e --overwrite
>
> which produces..
>
> Warning 1: No UNIDATA NC_GLOBAL:Conventions attribute
> WARNING: Over-riding projection check
>  100%
> Raster map <greenfrac.1> created.
>  100%
> Raster map <greenfrac.2> created.
>  100%
> Raster map <greenfrac.3> created.
>  100%
> Raster map <greenfrac.4> created.
>  100%
> Raster map <greenfrac.5> created.
>  100%
> Raster map <greenfrac.6> created.
>  100%
> Raster map <greenfrac.7> created.
>  100%
> Raster map <greenfrac.8> created.
>  100%
> Raster map <greenfrac.9> created.
>  100%
> Raster map <greenfrac.10> created.
>  100%
> Raster map <greenfrac.11> created.
>  100%
> Raster map <greenfrac.12> created.
> Region for the current mapset updated
> r.in.gdal complete.
>
> I am virtually certain the lower left corner is placed correctly, because
> I can zoom to the lower-left location and it falls about where it should --
> however the spatial extent of the data is not what it should be, but when
> zoomed-in looks correct.
>
> Any thoughts?
>
>  Thank you,
>
> Tom
>
>
>  --
>
>
>
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-- 
Thomas E Adams, III
718 McBurney Drive
Lebanon, OH 45036

1 (513) 739-9512 (cell)
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