# [ncl-talk] Extract point value + WRF model output

Setareh Rahimi setareh.rahimi at gmail.com
Wed Oct 27 02:01:58 MDT 2021

```Dear Dennies,
so many thanks for your help.
Best wishes,

On Mon, Oct 25, 2021 at 7:48 AM Dennis Shea <shea at ucar.edu> wrote:

> Barry illustrated how to get some answers via wrf_ functions
> ====
> In your screen shot you are using NCL's "*coordinate variable*" syntax:
> {...}
>
> By netCDF definition, a "*coordinate variable*" is a *one* dimensional
> variable.
> Some examples include: time(time), level(level), lat(lat), lon(lon).
>
> WRF geographical coordinates are *multi-dimensional*. Hence, they are not
> "coordinate variables".
> For eample:
>         float XLAT(Time, south_north, west_east)
>         float XLONG(Time, south_north, west_east)
> They are variables that contain coordinates.
>
> By rule, NCL's coordinate variable notation [ {...} ] can not be used on
> multi-dimensional arrays that contain coordinates..
>
> --------------
> You can interpolate to a specific locations using: *rcm2points
> <http://www.ncl.ucar.edu/Document/Functions/Built-in/rcm2points.shtml> *or
> *rcm2points_Wrap*
> <http://www.ncl.ucar.edu/Document/Functions/Contributed/rcm2points_Wrap.shtml>
> (Possibly, these could be slow.)
>
>    lon_pts = (/-104.867, -102.0/)
>    lat_pts  = (/   39.75,      38.0/)
>
>    f     = addfile ("some_WRF_file.nc", "r")
>    lat2d  = f->XLAT(0,:,:)                  ; size = (nlat,nlon)
>    lon2d = f->XLONG(0,:,:)              ; size = (nlat,nlon)
>    x     = f->X
>
>    x_pts  = *rcm2points_Wrap *(lat2d, lon2d, x, lat_pts, lon_pts, 0)
>    print(x_pts)
>
> ---------------
> The following will return the indices (subscripts) of the spatial
> coordinates closest to a location.
>
> *getind_latlon2d*
> <http://www.ncl.ucar.edu/Document/Functions/Contributed/getind_latlon2d.shtml>
>
>    lon_pts = (/-104.867, -102.0/)
>    lat_pts  = (/ 39.75,     38.0/)
>
>    f     = addfile ("some_WRF_file.nc", "r")
>    lat2d  = f->XLAT(0,:,:)                  ; size = (nlat,nlon)
>    lon2d = f->XLONG(0,:,:)              ; size = (nlat,nlon)
>    x     = f->X
>
>   nm = *getind_latlon2d* (lat2d,lon2d, lat_pts, lon_pts)
>
>   *print* <http://www.ncl.ucar.edu/Document/Functions/Built-in/print.shtml>(nm)
>
>   do k=0,*dimsizes* <http://www.ncl.ucar.edu/Document/Functions/Built-in/dimsizes.shtml>(lat_pts)-1    ; loop over locations
>      n = nm(k,0)
>      m = nm(k,1)
>
>      x_nm = x(:,n,m)     ;  x(:,:,n,m)
>
>      print("---")
>      *print* <http://www.ncl.ucar.edu/Document/Functions/Built-in/print.shtml>(lat2d(n,m)+"   "+lon2d(n,m))
>      print(x_nm)
>
>   end do
>
>
>
> On Sun, Oct 24, 2021 at 2:15 PM Setareh Rahimi via ncl-talk <
> ncl-talk at mailman.ucar.edu> wrote:
>
>> Dear all,
>> Regarding my question, I tried below codes to extract point values.But I
>> noticed there is no associated coordinate variable for latitude( have look
>> at the attached image).
>>
>> begin
>> lat = a->XLAT
>> printVarSummary(lat)
>> t = a->T2(:,{35.6},{51})      ;T2 refers to temperature at 2m
>> printVarSummary(t)
>> asciiwrite("outfile.txt",t)
>> end
>>
>> Therefore I can not choose my desire lat/lon to extract point value for a
>> specific variable.
>> Best wishes
>>
>> On Sat, Oct 23, 2021 at 8:20 PM Setareh Rahimi <setareh.rahimi at gmail.com>
>> wrote:
>>
>>> Dear NCL users,
>>> I have a WRF output file in nc format. I need to have point values of
>>> wind, temperature,and humidity  at specific lat/lon and specific times. I
>>> do not need a map plot or time series. I just want point values for each
>>> variable at specific times ( 00,03,06,09,12,15,18,21 UTC) in ascii format
>>> .For example, for wind variable at lat:y and lon:x
>>> Time:             00   ,  03   , 06   , 09   ,12
>>> wind value :   x1   ,  x2   , x3   , x4   , x5,
>>> Would  you please kindly help me in this regard?
>>> Best wishes,
>>>
>>> --
>>> S.Rahimi
>>>
>>>
>>
>> --
>> S.Rahimi
>>
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>
>

--
S.Rahimi
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