Interpolation of 2D matrix using Interp2 to eliminate NaN

I have a 310*400 matrix, that contain NAN values. I will like to interpolate the data to eliminate the NAN. After applying this code, I observed that the NAN is still retained. A sample of my code is here.

 load('km100.dat');          % load the z column data
[x,y] = ndgrid(310,400);    % arrange the data into grid
data_nan=reshape(km100,[],400);        %
row_vect = 1:310;                       %
col_vect = 1:400;                       %
[X,Y] = meshgrid(col_vect, row_vect);
[Xq,Yq] = meshgrid((1:1:310),(1:1:400));
V = data_nan;
data_interp = interp2(X, Y, V, Xq', Yq', 'cubic');

How do I correct it? Thanks.

[Stephen23]

@Ope: please upload your data by clicking the paperclip button.

[Ope]

Please find the file as attach.

Answer 1

[Stephen23]

"How do I correct it? Thanks."

NaN data is missing data, so although you think that you have gridded data in reality you don't, because some of it is missing. Therefore you need to use some method that can interpolate non-gridded data:

https://www.mathworks.com/help/matlab/math/interpolating-scattered-data.html

To use: remove NaN values (giving vectors) and then interpolate at the requires grid points.

The easiest solution would be to download John D'Errico's excellent FEX submission, it might do what you want:

https://www.mathworks.com/matlabcentral/fileexchange/4551-inpaint-nans

[Stephen23]

I just tried inpaint_nans on your data and it worked as expected:

>> old = load('km100.txt');
>> new = inpaint_nans(old);
>> nnz(isnan(old))
ans =                47270
>> nnz(isnan(new))
ans =                    0
>> [old,new]
ans =
           452.8535767           452.8535767
           453.9577942           453.9577942
           453.0496521           453.0496521
           455.6515198           455.6515198
           452.5939636           452.5939636
           452.6958923           452.6958923
           454.7310181           454.7310181
           448.0514832           448.0514832
           443.7440186           443.7440186
           442.4247437           442.4247437
           447.3446655           447.3446655
           464.2363586           464.2363586
           458.6205444           458.6205444
           451.6611328           451.6611328
           448.5695496           448.5695496
           450.1520996           450.1520996
           448.7554016           448.7554016
           450.8416443           450.8416443
           438.6665344           438.6665344
           433.2290649           433.2290649
           447.3460693           447.3460693
           455.7644653           455.7644653
            455.448822            455.448822
            453.618042            453.618042
           455.2015076           455.2015076
           453.8422852           453.8422852
           457.0555725           457.0555725
           468.3102112           468.3102112
           470.1549683           470.1549683
           473.3843079           473.3843079
            477.168457            477.168457
           466.2926941           466.2926941
           477.1495056           477.1495056
           467.2353821           467.2353821
           474.5125122           474.5125122
           477.6864624           477.6864624
           480.7120972           480.7120972
           474.8183899           474.8183899
           471.5950928           471.5950928
           468.0055542           468.0055542
            475.824585            475.824585
           468.5657349           468.5657349
           467.0472107           467.0472107
           472.8373108           472.8373108
           467.2086487           467.2086487
           454.8962097           454.8962097
           455.7807922           455.7807922
           461.6356506           461.6356506
           448.2521362           448.2521362
           462.8482666           462.8482666
           466.4006958           466.4006958
   ...
           141.0991211           141.0991211
           72.76783752           72.76783752
           37.56958008           37.56958008
           95.11649323           95.11649323
                       NaN        140.0638330942
                       NaN      173.459108598242
                       NaN      196.349828667769
                       NaN      209.783502228422
                       NaN      214.807638205843
                       NaN      212.469745525675
                       NaN      203.817333113559
                       NaN      189.897909895138
                       NaN      171.758984796054
                       NaN      150.448066741949
                       NaN      127.012664658465
                       NaN      102.500287471243
                       NaN      77.9584441059274
                       NaN      54.4346434881588
                       NaN      32.9763945435796
                       NaN       14.631206197832
                       NaN     0.446587376558134
                       NaN     -8.52995299459991
          -11.25090599          -11.25090599
          -6.668762684          -6.668762684
          -18.93135834          -18.93135834
          -44.52261734          -44.52261734
 ... etc

It worked for me. What did you try?

[Ope]

Many thanks, the function 'inpaint_nans' solved the problem.