[CF-metadata] Integerized Sinusoidal Grid

From: Jonathan Gregory <j.m.gregory>
Date: Sun, 19 Mar 2006 20:15:07 +0000

Dear Julien

> Its characteristics are that on each row of latitude there is an integer
> number of longitude bins. Poles always represented as 3 triangular bins.
> Bins aren't aligned between rows.
> In SEAWiFS/MODIS Level 3 HDF only bins (pixels) with data are stored,
> and the geolocation information for each bin is only its indice in the
> global integerized sinusoidal grid (first bin is on south, last on the
> north).
>
> The only mecanisms I see in CF to do that are:
>
> - "5.3 Reduced horizontal grid": but:

Yes, I think your case is most like this case.

> Are bins always aligned ?
You have to specify the latitude and longitude of each bin (grid point).

> How can I know/compute the coverage of each pixel (its vertex) ?
I am not sure what you mean. Do you mean the area of the grid box? This can
be stored using cell_measures (CF 7.2).

> Is this mechanism largely used ?
> Are there free tools to see this kind of CF files ? (FERRET ?)
I don't know whether Ferret will handle it. The intention of the convention
is that a generic application will be able to interpret the lat and lon
information without understanding the grid itself.

dimensions:
        Data_Bins = 5965 ;
variables:
        short mean(Data_Bins) ;
          mean:long_name = "Arithmetic mean of the geophysical variable for each bin" ;
          mean:units = "mg m-3" ;
          mean:coordinates="lat lon";
          mean:cell_measures="area: bin_area";
        float lat(Data_Bins);
          lat:units="degrees_north";
        float lon(Data_Bins);
          lon:units="degrees_east";
        float bin_area(Data_Bins);
          bin_area:units="m2";

You would have to obtain the values of lat and lon by looking them up in the
general grid by using the bin number, I imagine.

You are right, there is no mechanism for describing your integerised sinusoidal
grid at present. If you wish to include a description of the grid construction
in the file, maybe it could be done by providing a new entry for Appendix F.

Best wishes

Jonathan
Received on Sun Mar 19 2006 - 13:15:07 GMT