[ncl-talk] dsgrid interpolation problem station data)

[Dennis Shea]

Ricks approach should work. However, for some unuknown rease (?bug?) the
coordinates had to be reversed to attain the correct plot. A JIRA-2621
(bug) ticket has been created.

The attached uses x11 and creates the gridded data via several methods. Of
course, these could be tuned for better results but I'll let that up to you.

%> ncl noa_test.ncl_stavros

Good luck

On Mon, May 22, 2017 at 11:15 AM, Rick Brownrigg <brownrig at ucar.edu> wrote:

> Hi Stavros,
>
> I don't see where the array zo returned from dsgrid2() has any coordinate
> information (?)
>
> I'm not expert at this, but if I correctly understand what's going on, I
> think you need to do something like:
>
> ; make coordinate variables; i.e, varname == dimension name
> xo!0 = "xo"
> yo!0 = "yo"
>
> ; associate coord vars to data variable
> zo!0 = "xo"
> zo!1 = "yo"
> zo&xo = xo
> zo&yo = yo
>
> and then of course, to reorder for plotting you'd write  zo(yo|:, xo|:)
>
> I hope that helps.
>
> On Mon, May 22, 2017 at 6:07 AM, Stavros Dafis <sdafis at cc.uoi.gr> wrote:
>
>> Dear NCL users,
>>
>> I am facing a problem when interpolating unstructured station data. I
>> read an
>> ascii file with lat/lon and rainfall data. The problem is that the
>> interpolated
>> values with dsgrid2 do not match with the real data, for example in the
>> map
>> attached 69mm of rainfall (North Greece) is printed on the map but the
>> shaded
>> rainfall is far away from the actual position of the station. Moreover,
>> near
>> Athens, we have some stations with up to 20mm of accumulated rainfall but
>> interpolation gives 0-5mm.
>>
>> I have to mention that with temperature data, from the same ascii, using
>> the
>> same method with dsgrid2, the result is almost flawless (attached png with
>> Attica).
>>
>> I have also tried ESMF method (attached), obj_anal_ic, triple2grid,
>> natgrid but
>> the problem is the same. Here is the part of the code doing calculations:
>>
>>
>> x = stations(:,2)  ; Column 3 of file contains LONGITUDE values.
>> y = stations(:,1)  ; Column 2 of file contains LATITUDE values.
>> z = stations(:,15)  ; Column 11 of file contains RAINFALL values.
>>
>>
>>   numxout = 100  ; Define output grid for call to "dsgrid2".
>>   numyout = 100
>>   xmin    = min(x)
>>   ymin    = min(y)
>>   xmax    = max(x)
>>   ymax    = max(y)
>>   zmin    = min(z)
>>   zmax    = max(z)
>>
>>   xc      = (xmax-xmin)/(numxout-1)
>>   yc      = (ymax-ymin)/(numyout-1)
>>   xo      = xmin + ispan(0,numxout-1,1)*xc
>>   yo      = ymin + ispan(0,numyout-1,1)*yc
>>
>>   ;zo = natgrid(x, y, z, xo, yo)  ; Interpolate.
>>   ;zo = natgrids(x, y, z, xo, yo) ; Interpolate.
>>    rscan = (/0.25, 0.1, 0.01/)
>>   ;zo = obj_anal_ic(x,y,z, xo,yo, rscan, False)
>> opt  = True
>> opt at distmx = 30      ; kilometers
>> ;zo = triple2grid(x, y, z, xo, yo, opt)
>>
>>
>> zo = dsgrid2(x, y, z, xo, yo)  ; Interpolate.
>>
>> zo!0 = "i"  ; Name the dimensions of "zo".
>> zo!1 = "j"
>>
>>
>> contour = gsn_csm_contour_map(wks,zo(j|:,i|:),res)
>>
>>
>> ;--------
>> ;ESMF
>>   Opt                 = True
>>   Opt at SrcGridLat      = y
>>   Opt at SrcGridLon      = x
>>   Opt at DstLLCorner     = (/floor(min(y)),floor(min(x))/)
>>   Opt at DstURCorner     = (/ ceil(max(y)), ceil(max(x))/)
>>   Opt at DstGridType     = "0.1deg"
>>   Opt at ForceOverwrite  = True
>>   Opt at Debug           = True
>>   Opt at InterpMethod    = "patch"
>>   ;zo = ESMF_regrid(z,Opt)
>>
>>
>> Any help would be appreciated.
>>
>>
>>
>> --
>> Stavros NTAFIS (DAFIS)
>> -----------------------------------------------
>> Physicist - Meteorologist, M.Sc.
>> Research Associate, National Observatory of Athens
>> Tel. : (+33)9 81 94 22 12
>> Mobile: (+33) 066 030 0147
>> (+30) 697 04 20 242
>> ---------------
>> Weather charts:
>> http://www.meteo.gr
>> http://www.meteo.gr/meteomaps/
>>
>>
>>
>>
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>
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