[ncl-talk] grid_area_avg
Mary Haley
haley at ucar.edu
Fri Oct 13 12:54:16 MDT 2017
Kunal,
Please include the code where you are actually taking the average of your
data using the information returned from getind_latlon2d.
It's important to note that getind_latlon2d simply returns the individual
index values that are closest to each of the lat/lon pairs that you gave
it. It doesn't work in such a way that you give it a lat/lon box and it
returns all the values in that box.
That's what I was trying to illustrate with the wrf_gsn_10.ncl I created.
I gave the function two corners of the box, and then using the two pairs of
index values I got back, I was able to get all the values inside the box
area of interest:
lats = (/ min_lat, max_lat /)
lons = (/ min_lon, max_lon /)
nm = getind_latlon2d (lat2d, lon2d, lats, lons)
ilt1 = nm(0,0) ; start lat index
ilt2 = nm(1,0) ; start lon index
iln1 = nm(0,1) ; end lat index
iln2 = nm(1,1) ; end lon index
var_subset = var(ilt1:ilt2,iln1:iln2)
var_subset_avg = avg(var_subset)
--Mary
On Thu, Oct 12, 2017 at 1:19 PM, Kunal Bali <kunal.bali9 at gmail.com> wrote:
> Dear Haley Ma'am,
>
> Thanks for providing the information and example.
> But if I follow the getind_latlon2d function as I did, then it seems like
> I followed the same procedure as given in the example
> http://www.ncl.ucar.edu/Document/Functions/Contributed/getind_latlon2d.
> shtml
>
> But still I am not getting the mean of the grid box on every time step or
> am I reading incorrectly the result ?
>
>
> regards
> Kunal Bali
>
>
>
>
>
>
> On Fri, Oct 13, 2017 at 12:11 AM, Mary Haley <haley at ucar.edu> wrote:
>
>> Kunal,
>>
>> I created an example for you, showing three ways you can subset a WRF
>> grid (since I already had a similar example). It shows how to use the
>> getind_latlon2d function.
>>
>> You have to be careful with subsetting curvilinear data, because
>> specifying a lat/lon box to take an average over can mean two different
>> things. You will be able to see the difference when you look at the graphic.
>>
>> See example wrf_gsn_10.ncl at:
>>
>> http://www.ncl.ucar.edu/Applications/wrfgsn.shtml#ex10
>>
>> --Mary
>>
>>
>>
>> On Wed, Oct 11, 2017 at 12:03 PM, Kunal Bali <kunal.bali9 at gmail.com>
>> wrote:
>>
>>> Dear NCL users,
>>>
>>> Single point coordinates values of 23.0 N and 77.0 E is extracted or
>>> print by using the script below
>>>
>>> ----------------------------------------------------------------------
>>> ; Main code
>>> ;----------------------------------------------------------------------
>>> dir = "./"
>>> fnames = systemfunc("ls " + dir + "maiactaot*.nc")
>>> print(fnames)
>>> a = addfile(fnames,"r")
>>> data = short2flt(a->Optical_Depth_055_grid1km)
>>> nFill = num(ismissing(data))
>>> lat2d = a->GridLat_grid1km
>>> lon2d = a->GridLon_grid1km
>>>
>>> ;---grid points of interest
>>> latv = (/23.0/)
>>> lonv = (/77.0 /)
>>>
>>> nm = getind_latlon2d (lat2d,lon2d, latv, lonv)
>>>
>>> do k=0,dimsizes(latv)-1
>>> n = nm(k,0)
>>> m = nm(k,1)
>>> print(lat2d(n,m)+" "+lon2d(n,m)) ; grid point location
>>> print(" "+data(:,n,m)) ; nearest grid point
>>> at all time steps
>>> print("-----")
>>> end do
>>>
>>>
>>> NOW, I want to extract the square grid box of 100 km around the
>>> coordinates (23N,77E) such as
>>> latv = (/22, 24.0, 24.0, 22.0, 22.0/)
>>> lonv = (/76, 76.0, 78.0, 78.0, 76.0 /)
>>>
>>>
>>> after that I want to do the area mean of the grid box. So that I can
>>> get one single point value of that grid box.
>>> So when I replacing
>>> latv = (/23.0/)
>>> lonv = (/77.0/)
>>>
>>> with
>>>
>>> latv = (/22, 24.0, 24.0, 22.0, 22.0/)
>>> lonv = (/76, 76.0, 78.0, 78.0, 76.0 /)
>>>
>>> then It's not giving mean of the square grid box.
>>>
>>> It shows the something like that (given below), which is incorrect. So
>>> please let me know how can I get the square grid box mean and then extract
>>> as asciiwrite or print?
>>>
>>> (0) 23.76603307545667 75.53995171540016
>>> (0) 0.179
>>> (1) 0.142
>>> (2) -28672
>>> (3) 0.169
>>> (4) -28672
>>> (5) -28672
>>> (6) -28672
>>> (0) -----
>>> (0) 24.00322458681621 75.99551564353467
>>> (0) 0.171
>>> (1) 0.16
>>> (2) -28672
>>> (3) 0.17
>>> (4) -28672
>>> (5) -28672
>>> (6) -28672
>>>
>>> etc..etc..
>>>
>>>
>>>
>>> regards
>>> Kunal Bali
>>>
>>>
>>>
>>>
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>>
>
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