Interpolate both dataset on a same grid

Question

Sophia 2018-3-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/389269-interpolate-both-dataset-on-a-same-grid

编辑： Sophia 2018-3-20

sid_ncep_quants.xls

Hi, i have the two different datasets (PFA the excel file) as following

Dataset A size (119*177) with each lat and long file of same size

Dataset B size (145*73) with long size of (145*1) and lat size of (73*1)

The steps according to my understanding are-

Make a lat, long file for dataset B of size (145*73) - question how to do that?
Interpolate the dataset A to the size of Dataset B, which i am guessing using interp2

5 个评论
显示 3更早的评论隐藏 3更早的评论

Sophia 2018-3-19

在 MATLAB Online 中打开

Hi, The reason why i attached the file was to give a detailed idea about the matrix sizes.

The simplest way to define my problem is i have the results from two different datasets which are on two different lat/long grids. I want to interpolate them on to a common grid and find the normalized two-dimensional cross correlation.

I tried this for my first question ( Make a lat, long file for dataset B of size (145*73) - question how to do that?), and it seem to work but not sure until i have the final result

%%change the long and lat from 1D to 2D
  [mm,nn] = size(skw_16); %skw_16 is of the size 119*117
    %long is 1*145, lat is 1*73 %change them to 145*73
    nlong = zeros(mm,nn); nlat = zeros(mm,nn);
    for i = 1:mm  
        nlong(i,:) = lat(:)'; %nlong(i,:) = long(longstart:longend)';
    end
    for j = 1:nn
        nlat(:,j) = long(:)'; %nlat(i,:) = lat(latstart:latend)';
    end
  %The result %nlong 145*73, nlat 145*73

Now i am onto my second question- *Interpolate the dataset A to the size of Dataset B, which i am guessing using interp2*

skw_mtn_ncep = interp2(long,lat,skw_ids_2016,nlong,nlat);
%long 119*177, lat 119*177, skw_ids_2016 119*177

or should i interpolate the 145*73 onto 119*73?

Jan 2018-3-20

在 MATLAB Online 中打开

An abbreviation for the first part:

nlong = repmat(lat, mm, 1);
nlat  = repmat(long(:), 1, nn);

But you do not need to create matrices with the grid coordinates, because interp2 accepts vectors directly.

See my answer...

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Jan 2018-3-20

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/389269-interpolate-both-dataset-on-a-same-grid#answer_310856

编辑：Jan 2018-3-20

在 MATLAB Online 中打开

I assume that this helps:

B  = rand(145, 73);
A  = rand(119, 177);
y  = linspace(1, 145, 199);
x  = linspace(1, 73, 177);
BB = interp2(1:73, (1:145).', B, x, y.');

Now BB is the linear interpolation of B with the same size as A.

Note: I still find the order of the coordinates for interp2 counter-intuitive:

Vq = interp2(V,Xq,Yq) assumes X=1:N and Y=1:M where [M,N]=SIZE(V)

I'd expect the 1st input to be correlated to size(V, 1) and the 2nd to size(V,2), but MathWorks decided to swap the order. This is at least consistent with e.g. gradient.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Sophia 2018-3-20

编辑：Sophia 2018-3-20

在 MATLAB Online 中打开

Okie, here comes the part why i attached the excel file. From my understanding of your code A and B are two datasets. But x and y, i am not sure what they are representing here. In my case i have lat and long for each A and B. And the max and min lat/long values in both case are different.

I am not sure if i am explaining my question well enough or not. let's assume for example you have the data for United States at a grid of 25km*25km. And another dataset in which the data might be extended upto Canada but still has the data for United States, at a grid of 2.5 degree.

The idea is to plot them on a common grid, and find the 2D cross-correlation between them for just the common areas.

so in that case-

y  = linspace(1, 145, 199);
x  = linspace(1, 73, 177);

I am wondering, if its the right way?

请先登录，再进行评论。

Answer 2

Sophia 2018-3-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/389269-interpolate-both-dataset-on-a-same-grid#answer_310804

编辑：John D'Errico 2018-3-20

I just received this e-mail. I am worried how come MATHWORKS can share my personal email with any random person. The e-mail is as following-

This message was sent to you by this author via your author page on MATLAB Central.

Hello, I read your question in Matlab Central and would like to offer you my instant 1-to-1 programming service. An affordable, quick and tailored matlab-programming service to your needs. Check it out at: www.bit.ly/******** Thank you*