[gradsusr] Open GRIB Files over THREDDS Opendap Server

[Jennifer M Adams]

Hi, William — 
You need to be using an SSL-enabled build of the curl library, which is used in the opendap protocol in the netcdf library. Rebuild libcurl using the “—with-ssl” option, then relink netcdf, then relink GrADS. (Actually, the middle step may not be required, but I do it anyway just to be sure.) You could also try using my build of the netcdf library. The SSL library is dynamically linked, so you’ll need to have it installed on your system if it is not already there. 

The metadata from a THREDDS server is not particularly GrADS-friendly, so you will need to create a descriptor file.  Use your SSL-enabled ncdump executable to get the metadata from the file that you will need to populate the descriptor. 

I created a sample descriptor with only two variables, one of them is Z-varying:

dset https://www.ncei.noaa.gov/thredds/dodsC/cfs_v2_anl_mm_pgb/2017/201712/pgblnl.gdas.201712.grib2
dtype netcdf
options yrev zrev
undef -9.99e8 missing_value
xdef 144 linear 0 2.5
ydef 73 linear -90 2.5
zdef 37 levels 1000 975 950 925 900 875 850 82500
 800 775 750 700 650 600 550 500 450 40000
 350 300 250 225 200 175 150 125 100 7000
 50 30 20 10 7 5 3 2 1
tdef 1 linear 06z01dec2017 6hr
vars 2
Relative_humidity_isobaric_136_Hour_AverageNanalysis=>rh  37  t,z,y,x  rh at pressure levels
Relative_humidity_entire_atmosphere_single_layer_136_Hour_AverageNanalysis=>rh1  0  t,y,x  rh entire column
endvars

—Jennifer

> On Feb 1, 2018, at 2:15 AM, William Daniel Scheftic <scheftic at email.arizona.edu> wrote:
> 
> Hi,
> 
> Can I open GRIB files over opendap servers.  I realize they are not netcdf files, so that's probably why sdfopen failed.  But how would I open the file I got the following error with?  I frequently use sdfopen for files over GDS servers with success.
> 
> 
> CURL Error: Couldn't connect to server
> curl error details:
> Error: nc_open failed to open file https://<snipped>
> NetCDF: I/O failure
> gadsdf: Couldn't ingest SDF metadata.
> 
> 
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--
Jennifer Miletta Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
George Mason University