[Qgis-developer] reading GRIB data

[Paolo Cavallini]

Il 05/01/2017 16:31, Even Rouault ha scritto:
> This is a bit vague as a description of issues ;-) gdalinfo reports on
> datasets would be a start. GRIB support is generally a pain due to the
> diversity of the format.

Hi Even,
sorry for being vague - I hoped I was just missing something obvious,
and an howto was already available. Life is mostly more complicated :)
So, symptoms:
* the grib is loaded with a custom CRS:
 * Generated CRS (+proj=longlat +a=6371200 +b=6371200 +no_defs)
* it occupies a thin vertical stretch, from about 1.86884,-1418.31515 to
about 18.142,67.489
* colours are obviously not understandable
* the bands are superimposed, as if it was an RGB file, not
understanding the multiband structure of GRIB
* a series of warning is issued, of the type:
Warning 1: Band 895 of GRIB dataset is 33x23, while the first band and
dataset is 65x45.  Georeferencing of band 895 may be incorrect, and data
access may be incomplete.
* gdalinfo reports:
Driver: GRIB/GRIdded Binary (.grb)
Files: data
       data.aux.xml
Size is 65, 45
Coordinate System is:
GEOGCS["Coordinate System imported from GRIB file",
    DATUM["unknown",
        SPHEROID["Sphere",6371200,0]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433]]
Origin = (1.875000000000000,67.509000000000000)
Pixel Size = (0.250000000000000,-33.018000000000001)
Corner Coordinates:
Upper Left  (   1.8750000,  67.5090000) (  1d52'30.00"E, 67d30'32.40"N)
Lower Left  (       1.875,   -1418.301) (  1d52'30.00"E,Invalid angle)
Upper Right (  18.1250000,  67.5090000) ( 18d 7'30.00"E, 67d30'32.40"N)
Lower Right (      18.125,   -1418.301) ( 18d 7'30.00"E,Invalid angle)
Center      (      10.000,    -675.396) ( 10d 0' 0.00"E,Invalid angle)
Band 1 Block=65x1 Type=Float64, ColorInterp=Undefined
  Description = 0[-] var10 (reserved)
  Min=0.000 Max=100.000
  Minimum=0.000, Maximum=100.000, Mean=37.745, StdDev=41.769
  Metadata:
    GRIB_COMMENT=Total cloud cover [%]
    GRIB_ELEMENT=TCDC
    GRIB_FORECAST_SECONDS=10800 sec
    GRIB_REF_TIME=1440050400 sec UTC
    GRIB_SHORT_NAME=0-var10
    GRIB_UNIT=[%]
    GRIB_VALID_TIME=1440061200 sec UTC
    STATISTICS_MAXIMUM=100
    STATISTICS_MEAN=37.745299145299
    STATISTICS_MINIMUM=0
    STATISTICS_STDDEV=41.768590202144
Band 2 Block=65x1 Type=Float64, ColorInterp=Undefined
...
* zyGrib opens and displays the same file just fine.
All the best, and thanks.
-- 
Paolo Cavallini - www.faunalia.eu
QGIS & PostGIS courses: http://www.faunalia.eu/training.html
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