Interpolating from one grid to another

Question

Luís Henrique Bordin 2024-4-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2103476-interpolating-from-one-grid-to-another

评论： Star Strider 2024-4-23

采纳的回答： Star Strider

data.mat

Hello experts

Please, could someone help me with an interpolation?

I have two different 2D scattered grids (X = longitude, Y = depth), and a variable temperature, from two different datasets. On the first one x and y are 41x37, and on the second 24x10. Also Temp1 (41x37) and Temp2 (24x10).

I need to compute the difference (Temp1 - Temp2), but for that, I need Temp2 to be on the same format (and coordenates) as Temp1, that is, 41x37. Then, I guess I have to interpolate X2, Y2, Temp2, to the coordinates of X1, Y1.

I tried scatteredInterpolant function, but I it doesn't work, moreover, it does not allow me to inform the reference coordinates, that is, X1,Y1.

Both scatteredInterpolant and TriScatteredInterp has the structure F = function(x,y,v), but I need something like NewTemp2 = function(X1,Y1,X2,Y2,Temp2).

Please, could someone help me with this?

The data is attached, thank you very much in advance!

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Answer 1

Star Strider 2024-4-5

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2103476-interpolating-from-one-grid-to-another#answer_1437171

编辑：Star Strider 2024-4-5

在 MATLAB Online 中打开

data.mat

It appears that ‘Temp1’ seems to not have made it to the save function argument llist.

This interpolates ‘Temp2’ to the (X1,Y1) grids using scatteredInterpolant —

load('data.mat')

whos

Name Size Bytes Class Attributes Temp2 24x10 1920 double X1 41x37 12136 double X2 24x10 1920 double Y1 41x37 12136 double Y2 24x10 1920 double ans 1x32 64 char cmdout 1x33 66 char gdsCacheDir 1x14 28 char gdsCacheFlag 1x1 8 double i 0x0 0 double managers 1x0 0 cell managersMap 0x1 8 containers.Map

figure

surfc(X2, Y2, Temp2)

grid on

xlabel('X2')

ylabel('Y2')

zlabel('Temp2')

X2Y2 = [X2(:), Y2(:)];

X2Y2(isinf(X2Y2)) = NaN;

X2Y2 = fillmissing(X2Y2, 'linear');

X2v = X2Y2(:,1);

Y2v = X2Y2(:,2);

FTemp2 = scatteredInterpolant(X2v(:), Y2v(:), Temp2(:));

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

Temp2i = FTemp2(X1, Y1);

figure

surfc(X1, Y1, Temp2i)

grid on

xlabel('X1')

ylabel('Y1')

zlabel('Temp2 — Interpolated To (‘X1,Y1’)')

Do the same sort of approach to interpolate ‘Temp1’ to the ‘Temp2’ grids, if necessary.

EDIT — Corrected typographical errors.

.

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Star Strider 2024-4-22

在 MATLAB Online 中打开

data.mat

You can certainly use griddata, however I am not getting good results with it using the available data using either the 'linear', 'cubic' or 'natural' interpolation methods —

load('data.mat')

whos -file data.mat

Name Size Bytes Class Attributes Temp2 24x10 1920 double X1 41x37 12136 double X2 24x10 1920 double Y1 41x37 12136 double Y2 24x10 1920 double

figure

surfc(X2, Y2, Temp2)

grid on

xlabel('X2')

ylabel('Y2')

zlabel('Temp2')

X2Y2 = [X2(:), Y2(:)];

X2Y2(isinf(X2Y2)) = NaN;

X2Y2 = fillmissing(X2Y2, 'makima');

X2v = X2Y2(:,1);

Y2v = X2Y2(:,2);

FTemp2 = scatteredInterpolant(X2v(:), Y2v(:), Temp2(:), 'linear');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

Temp2i = FTemp2(X1, Y1);

figure

surfc(X1, Y1, Temp2i)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Temp2 — Interpolated To (‘X1,Y1’)')

title('scatteredInterpolant (linear)')

FTemp2 = scatteredInterpolant(X2v(:), Y2v(:), Temp2(:), 'natural');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

Temp2i = FTemp2(X1, Y1);

figure

surfc(X1, Y1, Temp2i)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Temp2 — Interpolated To (‘X1,Y1’)')

title('scatteredInterpolant (natural)')

Temp2i = griddata(X2v(:), Y2v(:), Temp2(:), X1, Y1, 'linear');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

figure

surf(X1, Y1, Temp2i)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Temp2 — Interpolated To (‘X1,Y1’)')

title('griddata (linear)')

Temp2i = griddata(X2v(:), Y2v(:), Temp2(:), X1, Y1, 'cubic');

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

figure

surf(X1, Y1, Temp2i)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Temp2 — Interpolated To (‘X1,Y1’)')

title('griddata (cubic)')

Temp2i = griddata(X2v(:), Y2v(:), Temp2(:), X1, Y1, 'natural');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

figure

surf(X1, Y1, Temp2i)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Temp2 — Interpolated To (‘X1,Y1’)')

title('griddata (natural)')

Are you using the same data as provided here, or a different data set?

Star Strider 2024-4-23

在 MATLAB Online 中打开

data2.mat

I tried something new here, specifically using fillmissing on all three matrices (converted to vectors) and then using reshape to their original dimensions. That works reasonably well for the scatteredInterpolant results although not for the griddata results, with the last two having completely NaN elements even though none of the arguments (as far as I can tell) have any NaN values at all.

I am not certain what you want to do, however this approach may be an option —

load('data2.mat')

whos -file data2.mat

Name Size Bytes Class Attributes Nit 24x10 1920 double X1 41x37 12136 double X2 24x10 1920 double Y1 41x37 12136 double Y2 24x10 1920 double

% NrNaNX1 = nnz(isnan(X1))

% NrNaNY1 = nnz(isnan(Y1))

figure

surfc(X2, Y2, Nit)

grid on

xlabel('X2')

ylabel('Y2')

zlabel('Nit')

title('Original N_2 Data')

X2Y2Z2 = [X2(:), Y2(:) Nit(:)];

X2Y2Z2(isinf(X2Y2Z2)) = NaN;

X2Y2Z2 = fillmissing(X2Y2Z2, 'linear');

X2v = X2Y2Z2(:,1);

Y2v = X2Y2Z2(:,2);

X2r = reshape(X2Y2Z2(:,1), 24, []);

Y2r = reshape(X2Y2Z2(:,2), 24, []);

Nitr = reshape(X2Y2Z2(:,3), 24, []);

figure

surfc(X2r, Y2r, Nitr)

grid on

xlabel('X2')

ylabel('Y2')

zlabel('Nit')

title('‘fillmissing’ N_2 Data')

FNit = scatteredInterpolant(X2v(:), Y2v(:), Nitr(:), 'linear');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

Niti = FNit(X1, Y1);

figure

surf(X1, Y1, Niti)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Nit — Interpolated To (‘X1,Y1’)')

title('scatteredInterpolant (linear)')

FNit = scatteredInterpolant(X2v(:), Y2v(:), Nitr(:), 'natural');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

Niti = FNit(X1, Y1);

figure

surfc(X1, Y1, Niti)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Nit — Interpolated To (‘X1,Y1’)')

title('scatteredInterpolant (natural)')

Niti = griddata(X2v(:), Y2v(:), Nitr(:), X1, Y1, 'nearest');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

figure

surf(X1, Y1, Niti)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Nit — Interpolated To (‘X1,Y1’)')

title('griddata (linear)')

Niti = griddata(X2v(:), Y2v(:), Nitr(:), X1, Y1, 'cubic');

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

figure

surf(X1, Y1, Niti)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Nit — Interpolated To (‘X1,Y1’)')

title('griddata (cubic)')

Niti = griddata(X2v(:), Y2v(:), Nitr(:), X1, Y1, 'natural');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

figure

surf(X1, Y1, Niti)

grid on

view(0,90)

xlabel('X1')

ylabel('Y1')

zlabel('Nit — Interpolated To (‘X1,Y1’)')

title('griddata (natural)')

.

Luís Henrique Bordin 2024-4-23

Okay. Thank you very much, have a good day!

Star Strider 2024-4-23

As always, my pleasure!

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