Jose,
If you were used to using Matlab but no longer have it, you might try
Python, which you can use in a similar fashion. This example shows how
to extract and plot a time series of wave heights from a remote
OPeNDAP dataset, but would work the same with a local NetCDF file:
http://nbviewer.ipython.org/4113653/
This code uses the NetCDF4-Python module, which reads NetCDF and
OPeNDAP datasets using the same syntax. It can be a pain to install,
but I didn't have to build it because I have the Enthought Python
Distribution, which includes NetCDF4-Python with OPeNDAP support. (I
think the full version of the EPD is free for folks with .edu
addressses, and of course there are many other options for free
scientific distributions as well).
Good luck,
-Rich
On Mon, Nov 19, 2012 at 12:59 PM, Jose Borrero <jborrero@xxxxxxx> wrote:
>
>
> Hi All,
>
> I have a program that produces netCDF files of water levels over a geographic
> region fro different times.
>
> the header looks like this:
>
> ===============================================
> lon = 720 ;
> lat = 330 ;
> grid_lon = 720 ;
> grid_lat = 330 ;
> rows = 3 ;
> clms = 3 ;
> time = UNLIMITED ; // (226 currently)
> variables:
> double lon(lon) ;
> lon:long_name = "longitude" ;
> lon:units = "degrees_east" ;
> lon:point_spacing = "even" ;
> double lat(lat) ;
> lat:long_name = "latitude" ;
> lat:units = "degrees_north" ;
> lat:point_spacing = "uneven" ;
> double grid_lon(grid_lon) ;
> grid_lon:long_name = "longitude" ;
> grid_lon:units = "degrees_east" ;
> grid_lon:point_spacing = "even" ;
> double grid_lat(grid_lat) ;
> grid_lat:long_name = "latitude" ;
> grid_lat:units = "degrees_north" ;
> grid_lat:point_spacing = "uneven" ;
> double O2Geo(clms, rows) ;
> O2Geo:long_name = "rotation matrix" ;
> float max_amp(grid_lat, grid_lon) ;
> max_amp:long_name = "Maximum Wave Amplitude" ;
> max_amp:units = "centimeters" ;
> max_amp:_FillValue = -1.e+34f ;
> max_amp:missing_value = -1.e+34f ;
> double time(time) ;
> time:long_name = "time" ;
> time:units = "seconds" ;
> time:calendar = "gregorian" ;
> float ha(time, lat, lon) ;
> ha:long_name = "Wave Amplitude" ;
> ha:units = "centimeters" ;
> ha:missing_value = -1.e+34f ;
> ha:_FillValue = -1.e+34f ;
> ===============================================
>
> i would like to extract a time series of data at a specific location.
>
> I have been looking at the ncdump command and thinking there would be a way
> do it at the command line, i.e. something like:
>
> ncdump -v ha(lat,lon, time[1=>t]) datafile.nc > timeseries.cdl
>
> (I realize the syntax is totally wrong, i am just trying to express how I
> would specify a lat/lon and ask for the data over the entire time)
>
> then using ncgen to make a new binary netCDF that can be read by GMT's nc2xy
> and output a simple 2 column time series.
>
> but I don't think I can specify things that way with ncdump.
>
> I then looked in to using the ncBrowse software. I have managed to use that
> to specify a time series of data at a point, and even write that data out to
> a CDL file. However, the file generated by ncBrowse (pasted below in an
> edited form) cannot be read by nc2xy and has characters that are not
> compatible with ncgen
>
> nc2xy tells me: nc2xy: NetCDF: Unknown file format [ha.cdl]
>
> and ncgen tells me:
>
> ncgen: ha.cdl line 7: syntax error, unexpected '=', expecting ',' or ')'
>
> ===================================================
> netcdf ha.cdl {
> dimensions:
> time = UNLIMITED ; // (226 currently)
> lat = 1 ;
> lon = 1 ;
> variables:
> double time(time=226);
> time:long_name = "time";
> time:units = "seconds";
> time:calendar = "gregorian";
> double lat(lat=330);
> lat:long_name = "latitude";
> lat:units = "degrees_north";
> lat:point_spacing = "uneven";
> double lon(lon=720);
> lon:long_name = "longitude";
> lon:units = "degrees_east";
> lon:point_spacing = "even";
> float ha(time=226, lat=330, lon=720);
> ha:long_name = "Wave Amplitude";
> ha:units = "centimeters";
> ha:missing_value = -1.0E34f; // float
> ha:_FillValue = -1.0E34f; // float
> data:
>
> time = 0.0, <ALL THE TIMES>, 14400.0 ;
>
> lat = 24.00833 ;
>
> lon = 60.00833 ;
>
> ha = 1.0723767, <ALL THE ha VALUES>1.6242466 ;
>
> }
> ===================================================
>
> so then, I go in to the ha.cdl file and edit the header in a text editor to
> remove the =226, =330 and =720 bits and change the line:
>
> float ha(time=226, lat=330, lon=720);
>
> to
>
> float ha(time);
>
> I then run run:
>
> ncgen -b -o ha.nc ha.cdl
>
> and make a file ha.nc which then can be accessed by nc2xy through the command:
>
> nc2xy ha.nc -Ftime/ha > ha.txt
>
> to create the file ha.txt which looks like:
>
> ===========================
> 0.000 17.423
> 64.000 61.289
> 128.000 36.575
> <...SNIP...>
> 14336.000 -2.210
> 14400.000 -2.147
> ===========================
>
> and is exactly what i want! Two columns, time and ha at that particular
> lat/lon So I know it is possible...
>
> So, if you are still with me, how can i do this more simply, through the
> command line preferably, or even a small script that goes:
>
> ncdump (args)
> ncgen (args)
> nc2xy (args)
>
> would be fine, but I just need to know the right arguments to make it all
> talk to each other.
>
> if you can help me, MANY, MANY, THANKS!!!!
>
> -jose
>
> (p.s. i used to do this with MATLAB, but I recently had my computer with
> MATLAB die, and i can't get it up and running again, so i am trying to do
> this an alternative way...)
>
>
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--
Dr. Richard P. Signell (508) 457-2229
USGS, 384 Woods Hole Rd.
Woods Hole, MA 02543-1598
