Re: Get a value at agiven lat/lon point

Yann,

You can only use the "{" syntax if you have 1D coordinate arrays, which your data does not have:

> Variable: gust
> Type: float
> Total Size: 4428 bytes
> 1107 values
> Number of Dimensions: 2
> Dimensions and sizes: [ygrid_0 | 27] x [xgrid_0 | 41]
> Coordinates:
> Number Of Attributes: 14

Note there is no list of coordinate variables after the word "Coordinates:"

It looks like you have 2D lat/lon arrays, so see the "getind_latlon2d" function:

http://www.ncl.ucar.edu/Document/Functions/Contributed/getind_latlon2d.shtml

Your lat/lon arrays are likely called "gridlat_0" and "gridlon_0", based on the "coordinates" attribute attached to your data.

You will need to read these two arrays, and use them in the getind_latlon2d function:

lat2d = fin->gridlat_0
lon2d = fin->gridlon_0
lat = 45
lon = 29
nm = getind_latlon2d(lat2d,lon2d, lat, lon)

"nm(0,0)" will be the latitude index, and "nm(0,1)" will be the longitude index into the "gust" array:

print(gust(nm(0,0),nm(0,1))

--Mary

On Apr 18, 2014, at 8:44 AM, Yann Bertrand <yann74@yahoo.fr> wrote:

> Hi,
> How can I get a discrete value at a given point,
> which is not necessarily on a grid point ?
> Does NCL interpolate ?
> I've tried this :
>
> ----------------------
> gust = fin->GUST_P0_L1_GLC0
> lat =45
> lon=29
> gust({lat},{lon})
> ----------------------
>
> fatal:Dimension (xgrid_0) of (gust) does not have an associated coordinate variable
> fatal:["Execute.c":7743]:Execute: Error occurred...
>
> Here's details on my var :
>
> Variable: gust
> Type: float
> Total Size: 4428 bytes
> 1107 values
> Number of Dimensions: 2
> Dimensions and sizes: [ygrid_0 | 27] x [xgrid_0 | 41]
> Coordinates:
> Number Of Attributes: 14
> center : US National Weather Service - NCEP (WMC)
> production_status : Operational products
> long_name : Wind speed (gust)
> units : m s-1
> _FillValue : 1e+20
> coordinates : gridlat_0 gridlon_0
> grid_type : Lambert Conformal can be secant or tangent, conical or bipolar
> parameter_discipline_and_category : Meteorological products, Momentum
> parameter_template_discipline_category_number : ( 0, 0, 2, 22 )
> level_type : Ground or water surface
> level : 0
> forecast_time : 1
> forecast_time_units : hours
> initial_time : 04/17/2014 (06:00)
> (0,0) 0
> (0,1) 0
> (0,2) 0
> (0,3) 0.7...
>
> Thanks in advance for a reply,
> Yann.
>
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Received on Mon Apr 21 20:57:38 2014