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

Tue Jun 9 14:26:57 PDT 2015

Micha,

Thank you very much for your detailed help; I'll give these approaches a
try and I'll let you know what I get. This is very helpful; thank you! I
hope all is well. BTW, thank you for the book contribution!!

Best,
Tom

On Tue, Jun 9, 2015 at 4:22 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
>
>
>  --
>
>
>
> This mail was received via Mail-SeCure System.
>
>
> _______________________________________________
> grass-user mailing listgrass-user at lists.osgeo.orghttp://lists.osgeo.org/mailman/listinfo/grass-user
> This mail was received via Mail-SeCure System.
>
>
>
>
>

-- 
Thomas E Adams, III
718 McBurney Drive
Lebanon, OH 45036

1 (513) 739-9512 (cell)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20150609/9628b548/attachment.html>