How does zyGrib figure out datum of source grib?

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boozedog
Posts: 1
Joined: 10 Feb 2017 00:42

How does zyGrib figure out datum of source grib?

Post by boozedog » 10 Feb 2017 00:46

I'm downloading a subsetted grib from the following location: http://nomads.ncep.noaa.gov/cgi-bin/fil ... 2017020912

This file renders perfectly in zyGrib, and I'm curious how zyGrib is able to correctly figure out the datum for this grib.

When I look at gdalinfo, the datum seems to be invalid (see below).

Can anyone tell me how zyGrib does its magic to resolve this unknown datum?

Code: Select all

gdalinfo gfs.t12z.pgrb2.0p25.f001
Driver: GRIB/GRIdded Binary (.grb)
Files: gfs.t12z.pgrb2.0p25.f001
Size is 241, 105
Coordinate System is:
GEOGCS["Coordinate System imported from GRIB file",
    DATUM["unknown",
        SPHEROID["Sphere",6371229,0]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433]]
Origin = (233.875000000000000,50.125000000000000)
Pixel Size = (0.250000000000000,-0.250000000000000)
Corner Coordinates:
Upper Left  (     233.875,      50.125) (233d52'30.00"E, 50d 7'30.00"N)
Lower Left  (     233.875,      23.875) (233d52'30.00"E, 23d52'30.00"N)
Upper Right (     294.125,      50.125) (294d 7'30.00"E, 50d 7'30.00"N)
Lower Right (     294.125,      23.875) (294d 7'30.00"E, 23d52'30.00"N)
Center      (     264.000,      37.000) (264d 0' 0.00"E, 37d 0' 0.00"N)
Band 1 Block=241x1 Type=Float64, ColorInterp=Undefined
  Description = 92500[Pa] ISBL="Isobaric surface"
  Metadata:
    GRIB_COMMENT=Relative Humidity [%]
    GRIB_ELEMENT=RH
    GRIB_FORECAST_SECONDS=3600 sec
    GRIB_PDS_PDTN=0
    GRIB_PDS_TEMPLATE_NUMBERS=1 1 2 0 96 0 0 0 1 0 0 0 1 100 0 0 1 105 84 255 0 0 0 0 0
    GRIB_REF_TIME=  1486641600 sec UTC
    GRIB_SHORT_NAME=92500-ISBL
    GRIB_UNIT=[%]
    GRIB_VALID_TIME=  1486645200 sec UTC

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