[GRASS-user] GRIB2 r.in.gdal problem

[Hamish]

(sorry for top posting, no time to deal with yahoo mail today)

Hi,

note for GRIB you need gdal 1.10 or newer, there were
edge coordinate bugs in earlier versions.


---> see:  http://grasswiki.osgeo.org/wiki/GRIB


note grass uses the cell-center for data value convention,
not the data values at grid line confluences (nodes) convention for raster arrays.


and so in grass the region's e,w,s,n values are at the outer edge of the raster cells, while gridline-centered arrays* would give coords overhanging the edges of the region by half a cell.

sometimes when loading in gridline-centered data you need to crop away the data row at 90N,S and one of the two at 0,360 or +-180 longitude. See the MODIS page in the wiki perhaps.
the way there is to use 'r.in.gdal -l' to force it to fit into 90N,S, then carefully use g.region + r.mapcalc to crop away the two rows, then use r.region to fix the map bounds back to where they should.

resolution ends up with bounds at e.g. 25,75m with a cell size of 50m, you have to be careful that d.zoom or 'g.region -a' doesn't realign the bounds to 0,50,100m instead of 25,75 (so silently shifted by 1/2 a cell). 



* (usually can spot them as they have like 501x1001 cells not 500x1000)



http://grasswiki.osgeo.org/wiki/GRASS_raster_semantics#Cell_Locations

http://grasswiki.osgeo.org/wiki/GRASS_FAQ#Errors


but the first thing to verify for the GRIB format is that your gdal version is 1.10 or newer.


regards,

Hamish


On Wednesday, February 12, 2014 6:21 PM, Lee Eddington <lee.w.eddington at gmail.com> wrote:

I’m trying to import some GRIB2 data into GRASS (6.4.3 on a Mac) and am having a problem with the range of the latitude coordinates.  I’m working with the following file:
>
>    http://www.ftp.ncep.noaa.gov/data/nccf/com/gfs/prod/gfs.2014021112/gfs.t12z.master.grbf72.10m.uv.grib2
>
>I used gdal_translate to create a GeoTiff file, but when I try to import it into a lat/lon location I get the following:
>
>GRASS 6.4.3 (GFS_from_grib):~ > r.in.gdal input=gfs.t12z.master.grbf72.10m.uv.tif output=gfs
>WARNING: Datum <unknown> not recognised by GRASS and no parameters found
>Projection of input dataset and current location appear to match
>WARNING: G_set_window(): Illegal latitude for North
>
>Here is the output from gdalinfo:
>
>lees-mbp:GFS Lee$ gdalinfo gfs.t12z.master.grbf72.10m.uv.tif
>Driver: GTiff/GeoTIFF
>Files: gfs.t12z.master.grbf72.10m.uv.tif
>       gfs.t12z.master.grbf72.10m.uv.tif.aux.xml
>Size is 720, 361
>Coordinate System
is:
>GEOGCS["Coordinate System imported from GRIB file",
>    DATUM["unknown",
>        SPHEROID["Sphere",6371229,0]],
>    PRIMEM["Greenwich",0],
>    UNIT["degree",0.0174532925199433]]
>Origin = (-0.250000000000000,90.250000000000000)
>Pixel Size = (0.500000000000000,-0.500000000000000)
>Metadata:
>  AREA_OR_POINT=Area
>Image Structure Metadata:
>  INTERLEAVE=PIXEL
>Corner Coordinates:
>Upper Left  (  -0.2500000,  90.2500000) (  0d15' 0.00"W, 90d15' 0.00"N)
>Lower Left  (  -0.2500000, -90.2500000) (  0d15' 0.00"W, 90d15' 0.00"S)
>Upper Right (     359.750,      90.250) (359d45' 0.00"E, 90d15' 0.00"N)
>Lower Right (     359.750,     -90.250) (359d45' 0.00"E, 90d15' 0.00"S)
>Center      ( 179.7500000,   0.0000000) (179d45' 0.00"E,  0d 0' 0.01"N)
>Band 1
Block=720x1 Type=Float64, ColorInterp=Gray
>  Description = 10[m] HTGL="Specified height level above ground"
>  Metadata:
>    GRIB_COMMENT=u-component of wind [m/s]
>    GRIB_ELEMENT=UGRD
>    GRIB_FORECAST_SECONDS=259200 sec
>    GRIB_PDS_PDTN=0
>    GRIB_PDS_TEMPLATE_NUMBERS=2 2 2 0 96 0 0 0 1 0 0 0 72 103 0 0 0 0 10 255 0 0 0 0 0
>    GRIB_REF_TIME=1392120000 sec UTC
>    GRIB_SHORT_NAME=10-HTGL
>    GRIB_UNIT=[m/s]
>    GRIB_VALID_TIME=1392379200 sec UTC
>Band 2 Block=720x1 Type=Float64, ColorInterp=Undefined
>  Description = 10[m] HTGL="Specified height level above ground"
>  Metadata:
>    GRIB_COMMENT=v-component of wind [m/s]
>    GRIB_ELEMENT=VGRD
>    GRIB_FORECAST_SECONDS=259200 sec
>    GRIB_REF_TIME=1392120000 sec UTC
>   
GRIB_SHORT_NAME=10-HTGL
>    GRIB_UNIT=[m/s]
>    GRIB_VALID_TIME=1392379200 sec UTC
>
>So it’s showing the north and south bounds of 90.25 N and -90.25 S.  I’m almost positive that this would be the values of the edges of the cells and that the cells are centered at 90 N and 90 S.
>
>Is there a way to import this data?
>
>Thanks,
>Lee
>
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