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Re: [ferret_users] Default order of dimensions



Thanks a lot for the input from Paul and Ansley. Yes, they have addressed my concerns. --- Peng


On Tue, Apr 8, 2014 at 2:04 PM, Ansley Manke <ansley.b.manke@xxxxxxxx> wrote:
Hi,
I think you can get the grid you want using the /ORDER qualifier as already suggested.  Here is the documentation link for the /ORDER qualifier. http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/commands-reference/SET#_VPINDEXENTRY_1594

The order in the grid of the variables,

   float air_temperature(time, longitude, latitude)

is not the standard order which would be (time, latitude, longitude)

Ferret follows the COARDS and CF standards for netCDF files.
http://ferret.pmel.noaa.gov/Ferret/documentation/coards-netcdf-conventions
The CF conventions, http://cf-convention.github.io/1.6.html#dimensions  discusses this as well.  This ordering is not required in CF, and Ferret can open the file and read the data, but the default ordering is required  Ferret to get plots and other operations right.

In addition, if the variables lon, lat, and time are intended as coordinate variables, then their names should share the names of the dimensions. It looks like this is the case with time in your file, but not longitude and latitude. If one were writing the file, and did it this way:

    float longitude(longitude) ;
        lon:long_name = "Longitude" ;
        lon:standard_name = "longitude" ;
        lon:units = "degrees_east" ;
        lon:valid_range = 0.f, 360.f ;

    float latitude(latitude) ;
etc.

then Ferret would be able to automatically label plots with degrees, and do all the other operations it knows how to do with longitude/latitude coordinates.  We can use Ferret to define axes using the 1-D lon, lat variables in the file.
define axis/x/units="`lon,return=units`"/title="`lon,return=title`" longitude = lon
define axis/y/units="`lat,return=units`"/title="`lat,return=title`" latitude = lat
and you should be good to go.

Ansley



On 4/8/2014 6:51 AM, Ge Peng - NOAA Affiliate wrote:
Does ferret assume by default the order of dimensions of input netCDF files as lon, lat, time without height?

I have a file with array dimensions defined as lat, lon, and time (see the attached ncdump file) and the dimensions loaded into ferret are as follows:

sho data
     currently SET data sets:
    1> ./SEAFLUXNN_ATMOS_CDR_V01R00_D19880101.nc  (default)
 name     title                                             I         J         K         L
 AIR_TEMPERATURE
          NOAA CDR of near-surface air temp  1:720     1:1440    ...       1:8
 SPECIFIC_HUMIDITY
          NOAA FCDR of near-surface speci  1:720     1:1440    ...       1:8
 WIND_SPEED
          NOAA FCDR of near-surface wind   1:720     1:1440    ...       1:8
 LON      Longitude                                  1:1440    ...       ...       ...
 LAT      Latitude                                     1:720     ...       ...       ...
 LAND_MASK
          Land mask                                   1:720     1:1440    ...       ...
 ICE_MASK Ice mask                             1:720     1:1440    ...       ...
 COAST_MASK
          Coastal mask                               1:720     1:1440    ...       ...


Do I need to define those array dimension orders as lon, lat, and time in order to load and display in ferret properly without redefining a new grid?

Thanks,

--- Peng

--
Ge Peng, Ph.D
Research Scholar
Cooperative Institute for Climate and Satellites NC
North Carolina State University
NOAA's National Climatic Data Center
151 Patton Ave, Asheville, NC 28801
ge.peng@xxxxxxxx
o: +1 828 257 3009
f:  +1 828 257 3002

Following CICS-NC on Facebook







--
Ge Peng, Ph.D
Research Scholar
Cooperative Institute for Climate and Satellites NC
North Carolina State University
NOAA's National Climatic Data Center
151 Patton Ave, Asheville, NC 28801
ge.peng@xxxxxxxx
o: +1 828 257 3009
f:  +1 828 257 3002

Following CICS-NC on Facebook




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