Hi Sebastien:
I have to tell you that "Reduced Horizontal Grid" and "compression by
gathering" will probably be deprecated in CF. In any case, CDM/ncWMS cannot read those kinds
of files. I would definietly use netcdf-4 if possible as Rich suggests, the space savings will be
at least as good, and the compression is transparent to applications.
John
Jonathan Blower wrote:
Hi Sebastien,
Good to hear from you, thanks for getting in touch. I think you are the
first person to ask me this question! ncWMS does not make any special
provision for reduced horizontal grids or compression by gathering.
However, I don’t know if there’s any support for this in the NetCDF-Java
libraries, so I’m copying this message to their list.
If NetCDF-Java doesn’t support this kind of grid it may be possible to
implement it in ncWMS. However, I’m travelling at the moment so I can’t
give this much attention now I’m afraid. I’ll wait to hear from
Unidata, then I’ll have a think about how to handle this.
Best wishes,
Jon
*From:* Mancini Sebastien [mailto:Sebastien.Mancini@xxxxxxxxxxx]
*Sent:* 31 March 2010 06:41
*To:* jdb@xxxxxxxxxxxxxxxxxxxx
*Subject:* ncWMS question
Hi Jon,
I do not know if you remember me. My name is Sebastien. I worked at eMII
(IMOS) in Hobart.
We met last year at the Ocean Obs conference in Venice.
We are using at the moment ncWMS to visualise some of IMOS satellite
data (gridded netcdf file).
I am doing some tests on displaying some radar data in ncWMS.
The radar data is not created on a filled grid but on a sparse grid in
order to save space in the NetCDF file.
I am trying to modify those NetCDF files and make them compliant with
the CF convention using paragraph 5.3 on the « Reduced Horizontal Grid »
and paragraph 8.2 on the « compression by gathering ».
I created a NetCDF file example.
I used ncdump to extract the following lines.
dimensions:
TIME = 1;
POSITION = 1650;
latdim = 80;
londim = 80;
variables:
double TIME(TIME) ;
TIME:standard_name = "time" ;
TIME:long_name = "analysis_time" ;
TIME:units = "days since 1950-01-01 00:00:00" ;
TIME:axis = "T" ;
TIME:_FillValue = -9999. ;
double LATITUDE(POSITION) ;
LATITUDE:standard_name = "latitude" ;
LATITUDE:long_name = "latitude" ;
LATITUDE:units = "degrees_north" ;
LATITUDE:axis = "Y" ;
LATITUDE:_FillValue = 9999. ;
double LONGITUDE(POSITION) ;
LONGITUDE:standard_name = "longitude" ;
LONGITUDE:long_name = "longitude" ;
LONGITUDE:units = "degrees_east" ;
LONGITUDE:axis = "X" ;
LONGITUDE:_FillValue = 9999. ;
double POSITION(POSITION) ;
POSITION:long_name = "grid position index" ;
POSITION:compress = "latdim londim" ;
double SPEED(TIME, POSITION) ;
SPEED:standard_name = "sea_water_speed" ;
SPEED:long_name = "sea water speed" ;
SPEED:units = "m s-1" ;
SPEED:_FillValue = 9999. ;
SPEED:coordinates = "LONGITUDE LATITUDE" ;
I tried to visualise this file with ncWMS but it did not work.
Is it possible to visualise this kind of NetCDF file using the actual
version of ncWMS?
If yes, I certainly made a mistake in the NetCDF file in the declaration
of the different variables. Will you be able to send me an example of
this kind of NetCDF file?
Thanks for your help.
Regards
Sebastien
Sebastien Mancini
Project Officer
eMII Project
University of Tasmania
Private Bag 21
Hobart TAS 7001
Ph: (03) 6226 8571
Fax: (03) 6226 2997
sebastien.mancini@xxxxxxxxxxx <mailto:sebastien.mancini@xxxxxxxxxxx>
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