[CF-metadata] Cell bounds associated with coordinate variable rather than data variable

From: Ethan Davis <edavis>
Date: Wed, 21 Oct 2009 22:56:11 -0600

Hi all,

We're looking at some GRIB-2 model data that contains 3, 6, 12, and 24
hour accumulated precipitation. I had been thinking we could represent
it through the netCDF-Java library as follows:

> dimensions:
> time=30;
> x=185;
> y=129;
> nv=2;
>
> variables:
> float time(time), x(x), y(y);
>
> float 3hr_accumulated_precip(time,y,x);
> 3hr_accumulated_precip:bounds="3hr_bounds";
> 3hr_accumulated_precip:cell_methods = "time: sum";
> float 6hr_accumulated_precip(time,y,x);
> 6hr_accumulated_precip:bounds="6hr_bounds";
> 6hr_accumulated_precip:cell_methods = "time: sum";
> float 12hr_accumulated_precip(time,y,x);
> 12hr_accumulated_precip:bounds="12hr_bounds";
> 12hr_accumulated_precip:cell_methods = "time: sum";
> float 24hr_accumulated_precip(time,y,x);
> 24hr_accumulated_precip:bounds="24hr_bounds";
> 24hr_accumulated_precip:cell_methods = "time: sum";
>
> float 3hr_bounds(time,nv);
> float 6hr_bounds(time,nv);
> float 12hr_bounds(time,nv);
> float 24hr_bounds(time,nv);
>
> data:
> 3hr_bounds = _, _, 0, 3, 3, 6, 6, 9, 9, 12, ...;
> 6hr_bounds = _, _, _, _, 0, 6, 3, 9, 6, 12, 9, 15, ...;
> 12hr_bounds = _, _, _, _, _, _, _, _, 0, 12, 3, 15, 6, 18, ...;
> 24hr_bounds = _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, 0, 24, 3, 27, 6, 30, ...;

But after re-reading section 7.1 "Cell Boundaries" it seems that a
boundary variable should be associated with a coordinate variable rather
than a data variable.

I would prefer not to create duplicate time coordinate variables with
different bounds as that would put each data variable on a different
time coordinate. Which doesn't seem optimal.

Am I missing another way to represent this? If not, why are boundary
variables associated with coordinate variables rather than data
variables? Is it just that this type of use case hasn't come up before
or is there something more fundamental I'm missing?

Thanks,

Ethan
Received on Wed Oct 21 2009 - 22:56:11 BST