Re: [netcdfgroup] ncdump (snapshot2009102000) missing some coordinate variables for OPeNDAP data set

  • To: Jennifer Adams <jma@xxxxxxxxxxxxx>
  • Subject: Re: [netcdfgroup] ncdump (snapshot2009102000) missing some coordinate variables for OPeNDAP data set
  • From: Dennis Heimbigner <dmh@xxxxxxxxxxxxxxxx>
  • Date: Mon, 26 Oct 2009 12:29:27 -0600
Jennifer-

As you discovered, some servers (including GrADS)
will not serve up a whole dataset, which is what you
may get if you ask for, for example,
http://monsoondata.org:9090/dods/model

Other servers do not require constraints as
part of the DAP request.

[James- is the GrADS behavior (requiring a constraint)
proper or improper behavior for an OPeNDAP server?]

=Dennis Heimbigner

Jennifer Adams wrote:
Dear Experts -- I am new to this group but not to NetCDF or OPeNDAP. I have been testing netcdf-4.1 for use with GrADS. I had noticed some problems ncdump was having in getting the attribute metadata for the coordinate axes of an OPeNDAP data set. I tried it with the latest snapshot (dated 2009102000) and ncdump is working much better, but it is not yet getting it right. The data set in question is behind a GrADS Data Server, a 4-dimensional low-resolution demo data set used for the tutorial and testing. Before running ncdump, I followed the recommendation from an earlier post and set the environment variable OCLOGFILE to <blank>. Here is the output:
 ncdump -c http://monsoondata.org:9090/dods/model

 # ./ncdump -c http://cola51x:9090/dods/model
Warning::USE_CACHE: not currently supported
Warning::MAX_CACHE_SIZE: not currently supported
Warning::MAX_CACHED_OBJ: not currently supported
Warning::IGNORE_EXPIRES: not currently supported
Warning::CACHE_ROOT: not currently supported
Warning::DEFAULT_EXPIRES: not currently supported
Warning::ALWAYS_VALIDATE: not currently supported
netcdf model {
dimensions:
        lat = 46 ;
        lev = 7 ;
        lon = 72 ;
        time = 5 ;
variables:
        double lat(lat) ;
                lat:grads_dim = "y" ;
                lat:grads_mapping = "linear" ;
                lat:grads_size = "46" ;
                lat:units = "degrees_north" ;
                lat:long_name = "latitude" ;
                lat:minimum = -90. ;
                lat:maximum = 90. ;
                lat:resolution = 4.f ;
        float ua(time, lev, lat, lon) ;
                ua:_FillValue = 1.e+20f ;
                ua:missing_value = 1.e+20f ;
                ua:long_name = "eastward wind [m/s] " ;
        float ps(time, lat, lon) ;
                ps:_FillValue = 1.e+20f ;
                ps:missing_value = 1.e+20f ;
                ps:long_name = "surface pressure [hpa] " ;
        float va(time, lev, lat, lon) ;
                va:_FillValue = 1.e+20f ;
                va:missing_value = 1.e+20f ;
                va:long_name = "northward wind [m/s] " ;
        float zg(time, lev, lat, lon) ;
                zg:_FillValue = 1.e+20f ;
                zg:missing_value = 1.e+20f ;
                zg:long_name = "geopotential height [m] " ;
        float ta(time, lev, lat, lon) ;
                ta:_FillValue = 1.e+20f ;
                ta:missing_value = 1.e+20f ;
                ta:long_name = "air temperature [k] " ;
        float hus(time, lev, lat, lon) ;
                hus:_FillValue = 1.e+20f ;
                hus:missing_value = 1.e+20f ;
                hus:long_name = "specific humidity [kg/kg] " ;
        float ts(time, lat, lon) ;
                ts:_FillValue = 1.e+20f ;
                ts:missing_value = 1.e+20f ;
                ts:long_name = "surface (2m) air temperature [k] " ;
        float pr(time, lat, lon) ;
                pr:_FillValue = 1.e+20f ;
                pr:missing_value = 1.e+20f ;
                pr:long_name = "total precipitation rate [kg/(m^2*s)] " ;

// global attributes:
                :title = "Sample Model Data" ;
                :Conventions = "COARDSGrADS" ;
                :dataType = "Grid" ;
:history = "Mon Oct 26 12:59:29 EDT 2009 : imported by GrADS Data Server 2.0" ;
data:

Error: :oc_open: server error retrieving url: code=0 message="subset requests must include a constraint expression"
./ncdump: NetCDF: DAP server side error
lat =

Since I am the administrator of the server, I can look in the logs and see what went wrong. The request that failed and led to the error message above was: ...GET /model.dods

The request from the client (ncdump) should have the ?varname[constraints] syntax following ".dods" , like this: ...GET /model.dods?time[0:1:4] ...GET /model.dods?lev[0:1:6] ...GET /model.dods?lat[0:1:45] ...GET /model.dods?lon[0:1:71] I also note that only 1 out of the 4 coordinate axes (lat) shows up as a data variable. I hope this is helpful information. The DAP interface in netcdf-4.1 is vital to GrADS, I am eager to adopt it as soon as it is working properly. --Jennifer


--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma@xxxxxxxxxxxxx <mailto:jma@xxxxxxxxxxxxx>




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