how to grid data

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ahmad Saad 2023-10-17

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https://ww2.mathworks.cn/matlabcentral/answers/2034664-how-to-grid-data

评论： ahmad Saad 2023-10-17

data.mat

在 MATLAB Online 中打开

Hi;

I have the attached data:

Col1: time,

Col2: lat,

Col3: long,

Col4: obs

I need to grid these data (2.5 lat x 5 long).

My trial:

clear all;

load('data.mat')

x=data(:,3);

LON=-50:5:50;

y= data (:,2);

LAT=-50:2.5:50;

z= data(:,4);

[X,Y] = meshgrid(LAT, LON);

Z = griddata(x,y,z,X,Y,'cubic');

Warning: Duplicate x-y data points detected: using average values for duplicate points.

figure

contourf(X,Y,Z);

grid on

ylim([-20 40])

xlim([-20 50])

shading('interp')

view(0,90)

colormap('jet')

colorbar

xlabel('LONG')

ylabel('LAT')

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Walter Roberson 2023-10-17

在 MATLAB Online 中打开

data.mat

load('data.mat')
x = data(:,3);
y = data(:,2);
z = data(:,4);
xy = [x, y];
[C, ~, IC] = unique(xy, 'rows');
counts = accumarray(IC(:), 1);
groups_with_dups = find(counts ~= 1);
for gidx = groups_with_dups(:).'
    fprintf('\npoint [%g, %g] occurs at multiple data rows:\n', C(gidx, :));
    for drow = reshape(find(IC == gidx), 1, []);
        fprintf('row %d, z = %g\n', drow, z(drow));
    end
end
point [-144.51, -6.73] occurs at multiple data rows:
row 47280, z = 4.1113
row 47283, z = 4.1107
point [-75.78, -1.99] occurs at multiple data rows:
row 17301, z = 8.6068
row 34415, z = 5.1247
point [-61.66, -9.88] occurs at multiple data rows:
row 10323, z = 7.0779
row 15532, z = 10.0557
point [-55.54, -6.1] occurs at multiple data rows:
row 31862, z = 8.8563
row 31863, z = 8.8596
point [-33.82, -4.96] occurs at multiple data rows:
row 21227, z = 18.4858
row 21228, z = 18.4862
point [-11.76, 0.47] occurs at multiple data rows:
row 27779, z = 1.8626
row 27782, z = 1.863
point [133.26, -9.25] occurs at multiple data rows:
row 39336, z = 5.4963
row 46912, z = 11.4154
point [138.27, -1.99] occurs at multiple data rows:
row 14161, z = 6.6767
row 32244, z = 3.7447
point [148.27, 27.37] occurs at multiple data rows:
row 23840, z = 11.7684
row 53067, z = 3.1711
point [150.92, -6.33] occurs at multiple data rows:
row 1010, z = 4.9438
row 24012, z = 2.754

Walter Roberson 2023-10-17

@ahmad Saad

And you already did that.

However, you have duplicate points with different Z values. How do you want to handle those points? griddata() handles the situation by taking mean() of the z at the locations with duplicates.

ahmad Saad 2023-10-17