Hi, Dennis, James, et al. --
I didn't know before today that a GDS request with only the ".dods"
extension is automatically rejected by the server, but it makes
sense ... it would mean delivering the entire data set -- coordinate
and data variables in their entirety -- to the client. For large data
sets this would be doomed to fail. But in order to fulfill the 'ncdump
-c' request, the entire data set is not required, only the .das and
the .dds and the data values for the coordinate variables need to be
retrieved.
One other detail ... when I try 'ncdump -h', the server delivers
the .das and .dds without errors, but ncdump only shows 1 out of 4
coordinate variables.
--Jennifer
On Oct 26, 2009, at 2:29 PM, Dennis Heimbigner wrote:
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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