Sorry I haven't send what I promise yet -- I've been home sick.
On 12/2/11 1:37 AM, Jonathan Gregory wrote:
I agree, this is a case for a ragged array, with two unlimited dimensions, logically speaking. However such a thing can be accommodated in the new discrete geometry conventions http://www.unidata.ucar.edu/staff/caron/public/CFch9-may10.pdf This describes two ragged array representations, which are intended for this purpose. Only one netCDF unlimited dimension is used; the two logical axes are combined into one netCDF axis.
int row_size(time) ; row_size:long_name = "number of particles for this time"; row_size:sample_dimension = "obs" ; double time(obs) ; time:standard_name = "time"; time:units = "days since 1970-01-01 00:00:00" ; int particle(obs) particle:long_name="particle number"; float quantity(obs) ; quantity:long_name="one of the physical properties of the particle" quantity:coordinates = "lat lon alt particle" ;
I'm sorry, I wasn't quite clear -- what you give below is pretty much what we've arrived at, but I had already considered combining the "two logical axis" into one unlimited dimension.
The conflict Ute presented what that he doesn't know at the start of the model run the number of time steps that are required. So he'd like the time dimension to be unlimited as well -- thus two unlimited dimensions.
The only place the time dimension is used is for the time and row_size variables, so I can't help thinking there could be a work around. Rich Signell suggested you could just use a as-big-as-you-might-need time coordinate -- which is one option.
If I ever feel better -- more later, but I think we are close.
If there is also invariant information for each particle, a large enough particle dimension would also be needed and various auxiliary coord vars of this dimension.
That would be a trick if you don't know how many particles you're starting with -- another nice use for an unlimited dimension...
Thanks, -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception [email protected] _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
