Write data in a netcdf file

Question

Julien on 15 May 2012

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https://uk.mathworks.com/matlabcentral/answers/38457-write-data-in-a-netcdf-file

Hey,

First and foremost, I'm french, so sorry if my english is bad.

I'm a student and for a project I have to manipulate a netcdf file.

I have a matlab file with data from a sea experiment, during which researchers have followed a container. As a consequence, I have in this matlab file the speed data of the container for each latitude and longitude of a located zone and for each timestep for two days.

My aim is to create a grib file, but first I have to create from this data a netcdf file (and then convert netcdf to grib with a tool found on the internet).

I have spent quite a day on creating an empty netcdf file with matlab with the "structure" wanted.

What I did:

ncid = netcdf.create('iroise.nc','CLASSIC_MODEL');
dim_lon = netcdf.defDim(ncid,'lon',50);
dim_lat = netcdf.defDim(ncid,'lat',50);
dim_depth = netcdf.defDim(ncid,'depth',50);
dim_time= netcdf.defDim(ncid,'time',50);
var_lon = netcdf.defVar(ncid,'lon','double',dim_lon);
var_lat = netcdf.defVar(ncid,'lat','double',dim_lat);
var_dep = netcdf.defVar(ncid,'depth','double',dim_depth);
var_ti = netcdf.defVar(ncid,'time','double',dim_time);
var_49 = netcdf.defVar(ncid,'var49','float', [dim_time dim_depth dim_lat dim_lon]);
var_50 = netcdf.defVar(ncid,'var50','float', [dim_time dim_depth dim_lat dim_lon]);
netcdf.putAtt(ncid,var_lon,'standard_name','longitude');
netcdf.putAtt(ncid,var_lon,'long_name','longitude');
netcdf.putAtt(ncid,var_lon,'units','degrees_east');
netcdf.putAtt(ncid,var_lon,'axis','X');
netcdf.putAtt(ncid,var_lat,'standard_name','latitude');
netcdf.putAtt(ncid,var_lat,'long_name','latitude');
netcdf.putAtt(ncid,var_lat,'units','degrees_north');
netcdf.putAtt(ncid,var_lat,'axis','Y');
netcdf.putAtt(ncid,var_dep,'standard_name','depth');
netcdf.putAtt(ncid,var_dep,'long_name','depth_below_sea');
netcdf.putAtt(ncid,var_dep,'units','m');
netcdf.putAtt(ncid,var_dep,'positive','down');
netcdf.putAtt(ncid,var_dep,'axis','Z');
netcdf.putAtt(ncid,var_ti,'standard_name','time');
netcdf.putAtt(ncid,var_ti,'units','hours since 2008-09-22 00:00:00');
netcdf.putAtt(ncid,var_ti,'calendar','proleptic_gregorian');
netcdf.putAtt(ncid,var_49,'table','3');
netcdf.putAtt(ncid,var_50,'table','3');

It works well and "ncdump -h iroise.nc" gives me

netcdf iroise {
dimensions:
  lon = 50 ;
  lat = 50 ;
  depth = 50 ;
  time = 50 ;
variables:
  double lon(lon) ;
    lon:standard_name = "longitude" ;
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
    lon:axis = "X" ;
  double lat(lat) ;
    lat:standard_name = "latitude" ;
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;
    lat:axis = "Y" ;
  double depth(depth) ;
    depth:standard_name = "depth" ;
    depth:long_name = "depth_below_sea" ;
    depth:units = "m" ;
    depth:positive = "down" ;
    depth:axis = "Z" ;
  double time(time) ;
    time:standard_name = "time" ;
    time:units = "hours since 2008-09-22 00:00:00" ;
    time:calendar = "proleptic_gregorian" ;
  float var49(lon, lat, depth, time) ;
    var49:table = "3" ;
  float var50(lon, lat, depth, time) ;
    var50:table = "3" ;
}

(I arbitrarily put the dimension length to 50, with no particular reason)

But now I would like to "insert" the data from the matlab file to this netcdf file. As I don't know if I'm allowed to give you the data file, I prefer just show you the "structure" of the matlab file:

X - <6x9 double>   (corresponding to the longitude)
Y - <6x9 double>   (corresponding to the latitude)
mtime - <1x48 double>     (corresponding to the time, 48 hours)
U - <6x432 double>           (corresponding to the first component of the speed)
V - <6x432 double>           (corresponding to the other component of the speed)