Jonathan,
I just had a long talk with Tom Gross, and we have the following proposal
for handling unstructured grids:
(1) Add the following standard_names to CF:
Horizontal_Triangular_Element_Incidence_List
Boundary_Segment_Node_List
(2) remove units attributes from the variables that correspond to
these names.
(3) Define the upcoming CF Convention "parameters" attribute
as "index_start_0" or "index_start_1"
The resulting unstructured CDL would thus look like:
netcdf umesh_cf {
dimensions:
node = 9700 ;
nele = 17925 ;
nbnd = 1476 ;
nface = 3 ;
nbi = 4 ;
sigma = 1 ;
time = UNLIMITED ; // (0 currently)
variables:
int ele(nele, nface) ;
ele:standard_name =
"Horizontal_Triangular_Element_Incidence_List" ;
ele:parameters = "index_start_1" ;
int bnd(nbnd, nbi) ;
bnd:standard_name = "Boundary_Segment_Node_List" ;
bnd:parameters = "index_start_1" ;
float time(time) ;
time:long_name = "Time" ;
time:units = "days since 2003-01-01 0:00:00 00:00" ;
time:base_date = 2003, 1, 1, 0 ;
time:standard_name = "time" ;
float lon(node) ;
lon:long_name = "Longitude" ;
lon:units = "degrees_east" ;
lon:standard_name = "longitude" ;
float lat(node) ;
lat:long_name = "Latitude" ;
lat:units = "degrees_north" ;
lat:standard_name = "latitude" ;
float depth(node) ;
depth:long_name = "Bathymetry" ;
depth:units = "meters" ;
depth:positive = "down" ;
depth:standard_name = "depth" ;
// global attributes:
:file_type = "FEM" ;
:Conventions = "CF-1.0" ;
:grid_type = "Triangular" ;
:z_type = "sigma" ;
:model = "quoddyv511" ;
:title = "Chesapeake Bay FEM" ;
:comment = "zzrtquoddylinux Twice Daily Runs" ;
:source = "bassmmap" ;
:institution = "NOAA/NOS/OCS/CSDL/MMAP" ;
:history = "original" ;
:references = "tom.gross at noaa.gov" ;
:creation_date = "2004-05-06 9:18:23 04:00" ;
}
Jonathan Gregory wrote:
>Dear Tom
>
>I think we didn't finish the earlier discussion, back in February.
>
>We need to have standard names for the various quantities that define your
>mesh, such as your "Horizontal Triangular Element Incidence List" and "Boundary
>Segment Node List". We agreed that the convention for whether it numbers from
>0 or 1 needs to be stated. You've suggested doing this with the units
>attribute e.g. units="index_start_1". I think that it would be better to put
>the "start 0" or "start 1" information into the standard name itself because
>
>(a) units="index_start_1" or similar is not a legal udunit. Hence it would
>cause a problem to anything which uses udunits to interpret the attribute.
>
>(b) we do not use units to indicate sign conventions, and this strikes me as
>a similar kind of issue.
>
>(c) it is absolutely essential that this information is specified. With
>physical quantities you could often make an intelligent guess if the units
>weren't specified, but in this case a guess would be hard to make. Since it is
>essential, putting it in the standard name is good because it's unavoidable.
>
>However a compromise might be to consider putting this into a standard_name_
>parameter which has to be specified as well as the standard name, such as we
>have been discussing in another thread.
>
>Any comments?
>
>Best wishes
>
>Jonathan
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>CF-metadata at cgd.ucar.edu
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>
>
--
Richard P. Signell rsignell at usgs.gov
U.S. Geological Survey Phone: (508) 457-2229
384 Woods Hole Road Fax: (508) 457-2310
Woods Hole, MA 02543-1598
Received on Mon Nov 15 2004 - 15:35:41 GMT
