20030407: reading a multi-dimensional variable

[Steve Emmerson <steve@xxxxxxxxxxxxxxxx>]

Tom,

> To: support-netcdf-perl@xxxxxxxxxxxxxxxx
> From: tom cook <cook@xxxxxxxxxxxxxxx>
> Subject: varinq not reporting correct varid?
> Organization: U Miami/RSMAS

The above message contained the following:

> Hi, I'm trying to read in some NCEP reanalysis data which is in netcdf 
> format. The data consists of 4 variables, 3 1-d arrays and 1 3-d array. 
> Here is the curtailed info from ncdump:
> -------------------------------------------
> ~>ncdump uwnd.10m.gauss.2000.nc |more
> netcdf uwnd.10m.gauss.2000 {
> dimensions:
> 	lon = 192 ;
> 	lat = 94 ;
> 	time = UNLIMITED ; // (1464 currently)
> variables:
> 	float lat(lat) ;
> 		lat:units = "degrees_north" ;
> 		lat:actual_range = 88.542f, -88.542f ;
> 		lat:long_name = "Latitude" ;
> 	float lon(lon) ;
> 		lon:units = "degrees_east" ;
> 		lon:long_name = "Longitude" ;
> 		lon:actual_range = 0.f, 358.125f ;
> 	double time(time) ;
> 		time:units = "hours since 1-1-1 00:00:0.0" ;
> 		time:long_name = "Time" ;
> 		time:actual_range = 17522904., 17531682. ;
> 		time:delta_t = "0000-00-00 06:00:00" ;
> 	short uwnd(time, lat, lon) ;
> 		uwnd:long_name = "4xDaily u-wind at 10 m" ;
> 		uwnd:valid_range = -102.2f, 102.2f ;
> 		uwnd:actual_range = -26.7f, 32.5f ;
> 		uwnd:units = "m/s" ;
> 		uwnd:add_offset = 225.45f ;
> 		uwnd:scale_factor = 0.01f ;
> 		uwnd:missing_value = 32766s ;
> 		uwnd:precision = 2s ;
> 		uwnd:least_significant_digit = 1s ;
> 		uwnd:GRIB_id = 33s ;
> 		uwnd:GRIB_name = "U GRD" ;
> 		uwnd:var_desc = "u-wind\n",
>     "U" ;
> 		uwnd:dataset = "NMC Reanalysis\n",
>     "L" ;
> 		uwnd:level_desc = "10 m\n",
>     "P" ;
> 		uwnd:statistic = "Individual Obs\n",
>     "I" ;
> 		uwnd:parent_stat = "Other\n",
>     "-" ;
> 
> // global attributes:
> 		:Conventions = "COARDS" ;
> 		:title = "4x daily NMC reanalysis (2000)" ;
> 		:base_date = 2000s, 1s, 1s ;
> 		:history = "created 00/01/30 by Hoop (netCDF2.3)" ;
> 		:description = "Data is from NMC initialized 
> reanalysis\n",
>     "(4x/day).  It consists of T62 variables interpolated to\n",
>     "pressure surfaces from model (sigma) surfaces." ;
> 		:platform = "Model" ;
> data:
> etc...
> --------------------------------
> 
> I'm using the following to read the data:
> 
> ------------
> #!/usr/bin/perl
> use NetCDF;
> $ncid=NetCDF::open("uwnd.10m.gauss.2000.nc", NetCDF::READ);
> NetCDF::inquire($ncid, $ndims, $nvars, $natts, $recdir);
> for ($i=0;$i<=$nvars-1;$i++){
>     NetCDF::varinq($ncid,$i, $name, $datatype, $ndims, \@dimids, $natts);
>     NetCDF::varget($ncid,$i,0,2,\@data);

The "start" and "count" arguments in the "varget()" call above are
incorrect.  They must be references to arrays.

An example of reading a multi-dimensional netCDF variable can be
found in the perl script "perl/test.pl" of the netcdf-perl
distribution.  Search for the string "Vet fixed variable values".

Let me know if you don't have access to this perl script.

Please let me know if this helps.

>     etc ...
> }
> ----------
> 
> Anyway, when I run this variable 0-2 read ok with varget, but when it gets 
> to variable 3 ($i=3) I get the following error message:
> 
> ncvarget: ncid 3: Index exceeds dimension bound
> 
> So I'm thinking, either this isn't the correct way to read a 3-dim 
> variable, or the varid is somehow off. Any thoughts or help would be very 
> appreciated.
> 
> Thanks,
> Tom

Regards,
Steve Emmerson