How to do matrix regridding in matlab

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Anne 2018-4-4

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评论： xinyu dong 2019-7-19

Hello, I am trying to use matlab to regrid a dataset. The original dataset is 128x193x12 (longitude x latitude x time) and I want to regrid it to a 180x193x12 matrix. I have the latitude of the original dataset as a 64x1 single (Dust_Data_lat), the longitude as a 128x1 single (Dust_Data_lon). For the 'final' grid (180x193x12), I have a latitude matrix 180x193 (constant columns, DUST_IN_lat) and a longitude matrix 180x193 (constant rows, DUST_IN_lon). I think the function griddata is best for this as the grid is irregular. If I try however, it complains about 'Z', which I don't know, see here for the first time dimension of the data:

a=Dust_LGM(:,:,1);
data_regridded = griddata(Dust_Data_lon,Dust_Data_lat,a,DUST_IN_lon,DUST_IN_lat);

The error I get is:

Error using griddata (line 109)
The lengths of X and Y must match the size of Z.

Would you know where the mistake is?

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Matt J 2018-4-4

You should close your previous question by accept-clicking Jos' answer, since it appears you were happy with that answer. This will increase the likelihood of responses to future questions.

Anne 2018-4-5

Ok, thanks for letting me know!

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Answer 1

Matt J 2018-4-6

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编辑：Matt J 2018-4-6

In griddata(x,y,z,xq,yq) the input arrays x,y,z must have the same number of elements. You have 128*193=24704 elements in a. You must therefore have 24704 corresponding elements in both Dust_Data_lon and Dust_Data_lat.

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Anne 2018-4-9

在 MATLAB Online 中打开

Thank you, I used meshgrid to make a grid of the lon lat data:

[Xlon Ylat] = meshgrid(Dust_Data_lat, Dust_Data_lon);

The result looks very strange however, so I think something is still wrong - mixing up lon and lat maybe.. Here is the full script I use now:

clear all
% Input path
Tpath = '/home/mypath';
% Get the dust input data
ncid      = netcdf.open([Tpath 'INPDUST_mhw.nc'],'NC_NOWRITE');
varid1    = netcdf.inqVarID(ncid,'DUST');
fillval   = netcdf.getAtt(ncid,varid1,'_FillValue');
Dust_IN   = netcdf.getVar(ncid,varid1,'double');
varid2    = netcdf.inqVarID(ncid,'lon');
DUST_IN_lon = netcdf.getVar(ncid,varid2,'double');
varid3      = netcdf.inqVarID(ncid,'lat');
DUST_IN_lat = netcdf.getVar(ncid,varid3,'double');
% Get the dust input data
ncid        = netcdf.open([Tpath 'DustFlux_Lambert2015_cp.nc'],'NC_NOWRITE');
varid4      = netcdf.inqVarID(ncid,'Flux');
Dust_Data   = netcdf.getVar(ncid,varid4,'double');
varid5     = netcdf.inqVarID(ncid,'lon');
Dust_Data_lon   = netcdf.getVar(ncid,varid5,'double');
varid6          = netcdf.inqVarID(ncid,'lat');
Dust_Data_lat   = netcdf.getVar(ncid,varid6,'double');
varid7          = netcdf.inqVarID(ncid,'time');
Dust_Data_time  = netcdf.getVar(ncid,varid7,'double');
% get the LGM period
Dust_LGM  = Dust_Data(:,:,:,2);
% Prepare the Lambert Data lon and lat as a grid
[Xlat Ylon] = meshgrid(Dust_Data_lat, Dust_Data_lon);
% Regrid
for i=1:size(Dust_LGM,3)
    %linear interpolation is applied. some boundary values can not be interpolated. these are filled with nearest values
  Dust_LGM_regridded(:,:,i) = griddata(Ylon,Xlat,Dust_LGM(:,:,i),DUST_IN_lon,DUST_IN_lat,'linear');
    if Dust_LGM_regridded==NaN
       Dust_LGM_regridded=griddata(Ylon,Xlat,Dust_LGM(:,:,i),DUST_IN_lon,DUST_IN_lat,'nearest');
    end
end  
% create a netcdf
delete('DustFlux_Lambert2015_regridded.nc');
outfile_nc       = 'DustFlux_Lambert2015_regridded.nc'; % New output file
nccreate(outfile_nc,'lon','Dimensions',{'x',size(Dust_LGM_regridded,1),'y',size(Dust_LGM_regridded,2)},'Datatype','double','Format','classic');
nccreate(outfile_nc,'lat' ,'Dimensions',{'x',size(Dust_LGM_regridded,1),'y',size(Dust_LGM_regridded,2)},'Datatype','double','Format','classic');
nccreate(outfile_nc,'time','Dimensions',{'time',size(Dust_LGM_regridded,3)},'Datatype','double');
nccreate(outfile_nc,'DUST','Dimensions',{'x','y','time'},'Datatype','double');
% Write data to the created variables
ncwrite(outfile_nc, 'lon',DUST_IN_lon);
ncwrite(outfile_nc, 'lat',DUST_IN_lat);
ncwrite(outfile_nc, 'time',Dust_Data_time);
ncwrite(outfile_nc, 'DUST',Dust_LGM_regridded);

The netcdf files used are here: https://www.dropbox.com/sh/i9m5p15ni8ybpzc/AABzJA_a8TTy3sWOCT4jkga1a?dl=0

Where does it go wrong?

Anne 2018-9-22

Hey Yoichi, thank you for your suggestion. This post is already very old, and I learned CDO and NCO to handle netcdf data in a more efficient way. I can recommend them to anyone that has to analyze/regrid/handle a lot of netcdf files:)

xinyu dong 2019-7-19

Hey Anne. I am struggling how to regrid with lon and lat right now. Do you have any recommandation? Thank you very much!

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How to do matrix regridding in matlab

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