# [ncl-talk] Assign lat lon cordinates to polar stereographic coordinate

Guido Cioni guidocioni at gmail.com
Tue Sep 13 02:19:12 MDT 2016

```Also make sure to perform the short to float conversion before working with your data!!!

http://www.ncl.ucar.edu/Document/Functions/Contributed/short2flt.shtml <http://www.ncl.ucar.edu/Document/Functions/Contributed/short2flt.shtml>

Guido Cioni
http://guidocioni.altervista <http://guidocioni.altervista/>.org

> On 13 Sep 2016, at 10:15, Guido Cioni <guidocioni at gmail.com> wrote:
>
> Assuming from your filedump you do have coordinate variables associated, so the following should easily work.
>
> temp_avg=dim_avg_n_Wrap(temp(:,:,{40:50},{-30:-10}),(/2,3/))
>
> Otherwise you would have to convert the latitude/longitude variables from 2D to 1D, use the ind function to find all the indices that map into your box, convert again into 2D indices with ind_resolve, subset temp with these indices, do the average.
>
> Guido Cioni
> http://guidocioni.altervista <http://guidocioni.altervista/>.org
>
>> On 13 Sep 2016, at 09:10, Sourav Chatterjee <srvsxc at outlook.com <mailto:srvsxc at outlook.com>> wrote:
>>
>> Thanks alot Mary for the explanation.
>>
>> Actually I need to do some area averaging for which I have the lat lon information e.g say, surface temperature averaged over 40-50N and -30:-10E. How to perform this spatial averaging with this temperature(time,depth,y,x) variable?
>>
>> Thanks
>> Sourav
>> From: Mary Haley <mailto:haley at ucar.edu>
>> Sent: ‎12-‎09-‎2016 23:38
>> To: Sourav Chatterjee <mailto:srvsxc at outlook.com>
>> Cc: ncl-talk at ucar.edu <mailto:ncl-talk at ucar.edu>
>> Subject: Re: [ncl-talk] Assign lat lon cordinates to polar stereographic coordinate
>>
>> Sourav,
>>
>> I'm not sure what you mean by "converting my variable".
>>
>> Since your latitude and longitude arrays are two-dimensional, you cannot associate them with "temperature" in the same way that "y" and "x" are currently associated with "temperature" as coordinate variables. This is a NetCDF limitation that requires that coordinate variables be one-dimensional and the same length as the dimension they represent.
>>
>> You already have a "coordinates" *attribute* associated with "temperature", that indicates which variables represent the lat/lon arrays for your data:
>>
>>         temperature:coordinates = "longitude latitude" ;
>>
>> This is how we would normally suggest that you "associate" 2D lat/lon arrays with a variable on a NetCDF file, so really, your "temperature" variable looks pretty good as it is.
>>
>> --Mary
>>
>>
>> On Fri, Sep 9, 2016 at 4:19 AM, Sourav Chatterjee <srvsxc at outlook.com <mailto:srvsxc at outlook.com>> wrote:
>> Hi all
>>
>>
>> I want convert my variable (temperature) to temperature (time,depth,lat,lon) from temperature(time,depth,x,y)
>>
>>
>> here is how it looks like now.
>>
>>
>> Any help!
>>
>>
>> Thanks
>>
>>
>> dimensions:
>>     depth = 12 ;
>>     time = UNLIMITED ; // (288 currently)
>>     x = 428 ;
>>     y = 403 ;
>> variables:
>>     int stereographic ;
>>         stereographic:grid_mapping_name = "polar_stereographic" ;
>>         stereographic:latitude_of_projection_origin = 90. ;
>>         stereographic:longitude_of_projection_origin = -45. ;
>>         stereographic:scale_factor_at_projection_origin = 1. ;
>>         stereographic:straight_vertical_longitude_from_pole = -45. ;
>>         stereographic:false_easting = 0. ;
>>         stereographic:false_northing = 0. ;
>>     float x(x) ;
>>         x:axis = "X" ;
>>         x:standard_name = "projection_x_coordinate" ;
>>         x:units = "100  km" ;
>>     float y(y) ;
>>         y:standard_name = "projection_y_coordinate" ;
>>         y:axis = "Y" ;
>>         y:units = "100  km" ;
>>     float depth(depth) ;
>>         depth:long_name = "depth" ;
>>         depth:units = "m" ;
>>         depth:standard_name = "depth" ;
>>         depth:positive = "down" ;
>>         depth:axis = "Z" ;
>>     double time(time) ;
>>         time:units = "hour since 1950-1-1T00:00:00Z" ;
>>         time:long_name = "forecast time" ;
>>     float longitude(y, x) ;
>>         longitude:standard_name = "longitude" ;
>>         longitude:units = "degrees_east" ;
>>     float latitude(y, x) ;
>>         latitude:standard_name = "latitude" ;
>>         latitude:units = "degrees_north" ;
>>     short temperature(time, depth, y, x) ;
>>         temperature:_FillValue = -32767s ;
>>         temperature:missing_value = -32767s ;
>>         temperature:scale_factor = 0.000808839239385893 ;
>>         temperature:units = "Celsius" ;
>>         temperature:standard_name = "sea_water_potential_temperature" ;
>>         temperature:grid_mapping = "stereographic" ;
>>         temperature:coordinates = "longitude latitude" ;
>>         temperature:cell_methods = "area: mean" ;
>>
>> // global attributes:
>>         :title = "Arctic Ocean Physics Reanalysis (1991-2014), 12.5km monthly mean (dataset-ran-arc-myoceanv2-be)" ;
>>         :institution = "NERSC, Thormoehlens gate 47, N-5006 Bergen, Norway" ;
>>         :history = "20160112:Created by program hyc2proj, version V0.3" ;
>>         :source = "NERSC-HYCOM model fields" ;
>>         :references = "http://topaz.nersc.no <http://topaz.nersc.no/>" ;
>>         :field_type = "Files based on file type nersc_weekly" ;
>>         :Conventions = "CF-1.4" ;
>>         :field_date = "2014-11-15" ;
>>         :bulletin_date = "2014-11-15" ;
>> }
>>
>>
>>
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