[ncl-talk] About regridding from
Dennis Shea
shea at ucar.edu
Tue Jan 17 11:15:12 MST 2017
[1]
A general rule for regridding is to go from high-resolution to
low-resolution. *If* the variable is 'smoothly varying' virtually any
interpolation method (eg: bilinear) will do. If the data is fractal (eg:
hourly/3hrly/daily precipitation), then other methods may be more
appropriate.
Interpolating from low-resolution to high-resolution, does *not* provide
any additional information. However, depending upon your objective and use,
this may be what you need to do.
[2]
Look at ESMF Regridding: http://www.ncl.ucar.edu/Applications/ESMF.shtml
Look at Example 21
[a] Take the radar data and make one-dimensional
lat_radar/lon_radar/value_radar arrays. These are your input ('Source').
Create a weight file (say)
Opt at WgtFileName= "WGT.Radar_to_WRF.nc" ; default is "weights_file.nc"
[b] The target grid is defined by the WRF: XLAT, XLONG variables. There
are numerous examples on the ESMF page to illustrate how to do this.
[c] Run the script
[d] The weight file can be used subsequently for other regriddings.
=============
NOTE:
It is your responsibility to look at and study the ESMF URL. Read it
carefully before proceeding. Responding to ncl-talk questions, especially,
ESMF can be quite time consuming and we have our own jobs to do.
Good Luck
On Tue, Jan 17, 2017 at 10:41 AM, Barry Lynn <barry.h.lynn at gmail.com> wrote:
> Hi Tao:
>
> I apologize, but I can't answer right now as I am traveling.
>
> However, in order to provide ncl-talkers with enough information/data, you
> can write out the data grid (lat/lon) you are trying to plot on from WRF,
> and upload one time step of it (or two). You should also upload the radar
> data.
>
> ;---Write wrf variables lat/lon to file for ncltalk.nc
>
>
> system("rm -f file_for_ncltalk.nc")
> fout = addfile("file_for_ncltalk.nc","c")
> fout->xlat = xlat
> fout->xlong = xlong
>
> Barry
>
> On Tue, Jan 17, 2017 at 7:14 PM, Tao Lu <hakufu.asano at gmail.com> wrote:
>
>> Hello Barry:
>>
>> Thank you very much for your reply.
>> I am very appreciated that you shared your codes with us.
>>
>> Some editions have been done in my situation.
>> However, I could not get contour after grid =
>> obj_anal_ic(lon_o,lat_o,obs_o,xlon_m,xlat_m,rscan,False).
>> I attached the edited code and run information, please help me check that.
>>
>> I also have some questions about the method for regridding:
>> 1. There is a item named "rightmost dimension or leftmost dimension" in
>> http://www.ncl.ucar.edu/Document/Functions/Built-in/obj_anal_ic.shtml
>> I googled it but have no ideal.
>>
>> 2. Also according to the webpage in 1. obs_o at _FillValue will be ignored.
>> Does it mean that missing value won't be accounted for when
>> interpolation?
>>
>> 3. "cband radar observations: min=0 max=220" before regridding
>> "var_zoom min=0 max=23.5354" after regridding
>> After regridding the radar density is much smaller than original
>> maximum.
>> Is it normal? Maybe as you said rscan is important.
>>
>> 4. When you use
>> grid = obj_anal_ic(lon_o,lat_o,obs_o,xlon_m,xlat_m,rscan,False)
>>
>> You calculate this
>> ;---Get slice of lat/lon data at halfway points.
>> nlat = dims2d(0)
>> nlon = dims2d(1)
>> xlat_m = xlat2d_m(:,nlon/2)
>> xlon_m = xlon2d_m(nlat/2,:)
>>
>> Is it reasonable to calculate lat/lon at a quarter points?
>>
>> 5. If use halfway points to regrid radar data,
>> [image: Inline image 1]
>> We will get a n(xlat_m) x n(xlon_m) regridded array.
>> So, what will the array's lat/lon will be?
>>
>> 6. This method is to interpolate radar data to wrf grid.
>> Is the mean average method more suitable for radar data? Because
>> radar have
>> so many data points unlike rain gauge data?
>>
>>
>> My ascii data converted from radar is too large, if you need it I will
>> send it to you.
>> The data is something like below:
>> # crain_composite_data:rain_density:lat:lon:ndata=2406400:
>> # 2015-09-09_00:00:00
>> -9999 47.32916666666667 137.01874999999998
>> -9999 47.32916666666667 137.03125
>> -9999 47.32916666666667 137.04375
>> -9999 47.32916666666667 137.05625
>> -9999 47.32916666666667 137.06875
>> -9999 47.32916666666667 137.08124999999998
>>
>>
>> Waiting for your reply.
>> Thank you very much.
>>
>> Tao
>>
>>
>> On Tue, Jan 17, 2017 at 4:05 AM, Barry Lynn <barry.h.lynn at gmail.com>
>> wrote:
>>
>>> Hi Tao:
>>>
>>> Here, I gridded the radar data to the WRF grid.
>>>
>>> You will need to adapt what I did to your situation, but the most
>>> important step is to decide on the degree of smoothing (which is set by
>>> rscan).
>>>
>>> grid = obj_anal_ic(lon_o,lat_o,obs_o,xlon_m,xlat_m,rscan,False)
>>>
>>> Please write if you have questions.
>>>
>>> Barry
>>>
>>> On Mon, Jan 16, 2017 at 9:11 AM, Tao Lu <hakufu.asano at gmail.com> wrote:
>>>
>>>> Dear ncl-talk
>>>>
>>>> Hello.
>>>>
>>>> I am new to regridding, if possible please give me some help and advice.
>>>>
>>>> What I am doing?: Compare two kind of grid data
>>>> *I have two kind of data.*
>>>> 1. radar data:
>>>> resolution: 0.5 minute x 0.75 minute, as seen not regular
>>>> grids
>>>> file format: ascii
>>>> [image: Inline image 1]
>>>> 2. output data from WRF:
>>>> dx = 30000,
>>>> dy = 30000,
>>>> map_proj = 'lambert',
>>>> ref_lat = 36.00,
>>>> ref_lon = 140.00,
>>>> truelat1 = 30.0,
>>>> truelat2 = 60.0,
>>>> stand_lon = 140.0,
>>>> file fomat: netcdf
>>>> [image: Inline image 3]
>>>>
>>>> *I have to regrid the two data to each other or to new grid.*
>>>> 1. Regrid wrf data grid to radar data grid?
>>>> 2. Regrid radar data to wrf data?
>>>> 3. Regrid both to another data?
>>>> Which is easiest?
>>>>
>>>> I am really new to this, please give me some guide line, I will further
>>>> operation on my work.
>>>>
>>>> Thank you very much for your kind help.
>>>>
>>>> Tao
>>>>
>>>>
>>>> --
>>>> ******************************************************
>>>> Tao Lu (M. Eng)
>>>> Laboratory of River Engineering and Hydrology,
>>>> Dept. of Civil and Environmental Engineering,
>>>> Graduate School of Science and Engineering,
>>>> Chuo University
>>>>
>>>> 1-13-27,Kasuga,Bunkyo-ku,Tokyo
>>>> 112-8551, Japan
>>>> TEL: 03-3817-1805; Phone: 070-2188-7509
>>>> Email1: hakufu.asano at gmail.com <mail%3Amet.yamos at gmail.com>
>>>> Email2: lutao at civil.chuo-u.ac.jp <mail%3Ayamoto at civil.chuo-u.ac.jp>
>>>> *****************************************************
>>>>
>>>> _______________________________________________
>>>> ncl-talk mailing list
>>>> ncl-talk at ucar.edu
>>>> List instructions, subscriber options, unsubscribe:
>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>
>>>>
>>>
>>>
>>> --
>>> Barry H. Lynn, Ph.D
>>> Senior Lecturer,
>>> The Institute of the Earth Science,
>>> The Hebrew University of Jerusalem,
>>> Givat Ram, Jerusalem 91904, Israel
>>> Tel: 972 547 231 170
>>> Fax: (972)-25662581
>>>
>>> C.E.O, Weather It Is, LTD
>>> Weather and Climate Focus
>>> http://weather-it-is.com
>>> Jerusalem, Israel
>>> Local: 02 930 9525
>>> Cell: 054 7 231 170
>>> Int-IS: x972 2 930 9525
>>> US 914 432 3108 <(914)%20432-3108>
>>>
>>
>>
>>
>> --
>> ******************************************************
>> 盧 涛 (ル タオ) 修士課程2年
>>
>> 〒112-8551 東京都文京区春日1-13-27
>>
>> 中央大学理工学研究科都市環境学専攻
>>
>> 河川・水文研究室（山田正教授）
>>
>>
>> TEL: 03-3817-3406; Phone: 070-2188-7509
>> Email1: hakufu.asano at gmail.com <mail%3Amet.yamos at gmail.com>
>> Email2: lutao at civil.chuo-u.ac.jp <mail%3Ayamoto at civil.chuo-u.ac.jp>
>> *******************************************************
>> ******************************************************
>> Tao Lu (M. Eng)
>> Laboratory of River Engineering and Hydrology,
>> Dept. of Civil and Environmental Engineering,
>> Graduate School of Science and Engineering,
>> Chuo University
>>
>> 1-13-27,Kasuga,Bunkyo-ku,Tokyo
>> 112-8551, Japan
>> TEL: 03-3817-1805; Phone: 070-2188-7509
>> Email1: hakufu.asano at gmail.com <mail%3Amet.yamos at gmail.com>
>> Email2: lutao at civil.chuo-u.ac.jp <mail%3Ayamoto at civil.chuo-u.ac.jp>
>> *****************************************************
>>
>
>
>
> --
> Barry H. Lynn, Ph.D
> Senior Lecturer,
> The Institute of the Earth Science,
> The Hebrew University of Jerusalem,
> Givat Ram, Jerusalem 91904, Israel
> Tel: 972 547 231 170
> Fax: (972)-25662581
>
> C.E.O, Weather It Is, LTD
> Weather and Climate Focus
> http://weather-it-is.com
> Jerusalem, Israel
> Local: 02 930 9525
> Cell: 054 7 231 170
> Int-IS: x972 2 930 9525
> US 914 432 3108 <(914)%20432-3108>
>
> _______________________________________________
> ncl-talk mailing list
> ncl-talk at ucar.edu
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>
>
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