help me in using "interp2"

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Mahmood
Mahmood 2015-9-19
评论： Mahmood 2015-9-20
I want to expand my matrix using interpolation. I followed the instructions but it shows some errors:
clc
clear
rw=0.10795;
n = linspace(-pi,pi,30);
m = linspace(rw,2.5,30);
[theta,r] = meshgrid(n,m);
[X,Y] = pol2cart(theta,r);
V = peaks(X,Y);
figure
surf(X,Y,V)
title('Original Sampling');
nn = linspace(-pi,pi,360);
mm = linspace(rw,2.5,200);
[thetaaa,rrr] = meshgrid(nn,mm);
[Xq,Yq] = pol2cart(thetaaa,rrr);
Vq = interp2(X,Y,V,Xq,Yq,'cubic');
figure
surf(Xq,Yq,Vq);
title('Cubic Interpolation Over Finer Grid');

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Walter Roberson
Walter Roberson 2015-9-19
your input grid, X, Y, must be cuboid.
Leave your inputs the same, but change the command from interp2 to griddata (with the same arguments).
Also you will want to add 'edgecolor','none' to the surf() call.
griddata() is going to tell you that duplicate values have been averaged. I suspect -pi and +pi map to the same point with pol2cart. If you were to linspace() with 31 points and then delete the last then the overlap should disappear.
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Walter Roberson
Walter Roberson 2015-9-19
编辑：Walter Roberson 2015-9-19
rw=0.10795;
n = linspace(-pi,pi,31);
n(1) = [];
m = linspace(rw,2.5,30);
[theta,r] = meshgrid(n,m);
[X,Y] = pol2cart(theta,r);
V = peaks(X,Y);
figure
surf(X,Y,V, 'edgecolor','none')
title('Original Sampling');
nn = linspace(-pi,pi,360);
mm = linspace(rw,2.5,200);
[thetaaa,rrr] = meshgrid(nn,mm);
[Xq,Yq] = pol2cart(thetaaa,rrr);
Vq = griddata(X,Y,V,Xq,Yq,'cubic');
figure
surf(Xq,Yq,Vq, 'edgecolor', 'none');
title('Cubic Interpolation Over Finer Grid');
Mahmood
Mahmood 2015-9-20
Thanks a lot for your help. I really appreciate that.

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