why interp2 report "input grid is not a valid meshgrid" since input grid is generated by meshgrid?

조회 수: 149 (최근 30일)
Dear Community,
I need to do a 2D interpolation for a matrix data, but when I use the interp2, the function report error "input grid is not a valid meshgrid". I am really confused since the input grid is generated by meshgrid function. If anyone knows this issue, could you please give me some suggestions?
% original coordinate
je=167;
ke=117;
dy=4e-8;
dz=dy;
ya=[0:dy:je*dy];
za=[0:dz:ke*dz];
ya=ya-mean(ya);
za=za-mean(za);
% interpolation
load data.mat
[Z,Y]=meshgrid(za,ya);
aymap = interp2(Y,Z,ay,squeeze(newcord_Y),squeeze(newcord_Z));

채택된 답변

KSSV
KSSV 2020년 6월 5일
load("data.mat") ;
% original coordinate
je=167;
ke=117;
dy=4e-8;
dz=dy;
ya=[0:dy:je*dy];
za=[0:dz:ke*dz];
ya=ya-mean(ya);
za=za-mean(za);
% interpolation
load data.mat
[Zi,Yi]=meshgrid(za,ya);
Y = squeeze(newcord_Y) ;
Z = squeeze(newcord_Z) ;
aymap = interp2(Y,Z,ay,Yi,Zi);
  댓글 수: 6
Jiali
Jiali 2020년 6월 5일
by the way, do you have any idea why "interp2" doesn't work for me? does it come from version bugs?

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추가 답변 (1개)

Stephen23
Stephen23 2020년 6월 5일
편집: Stephen23 2020년 6월 5일
"If anyone knows this issue..."
Explanation: you swapped around the order of the variables:
[Z,Y] = meshgrid(za,ya); % order: Z,Y
interp2(Y,Z,...) % order: Y,Z
By design meshgrid swaps the first dimensions anyway to make them compatible with X-Y coordinates that people often prefer to use for plotting. The documentation explains how the data is arranged in the output arrays, I will not reproduce it here, but suffice to say by swapping the array order the data is arranged incorrectly for interp2.
Note that the correct array order is clearly shown in all of the interp2 examples, e.g.:
[Xq,Yq] = meshgrid(-3:0.25:3); % order: Xq,Yq
Vq = interp2(X,Y,V,Xq,Yq); % order: Xq,Yq
Solution: use the variables in the same order.
It is worth nothing that the first line of the interpolation functions state:
  • for interp2 use meshgrid
  • for interpn use ndgrid
and then you simply need to provide the arguments in the same order (unlike your code).
See also a more detailed explanation here:

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