someting wrong using interp2

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Valeria Leto
Valeria Leto 2021-7-5
评论： Valeria Leto 2021-7-8
I would like to interpolate the values of an image I. The pixels of I have a specified position in point_seabed_e and point_seabed_n wich are not regularly spaced. I get: Error using griddedInterpolant Grid arrays must have NDGRID structure. How coul I fix it? Thanks
figure(20)
x=[-20:0.01:20];
y=[0:-0.05:-20];
[Xq,Yq] = meshgrid(x,y);
I=[SSS_ground_left SSS_ground_right];
Tq = interp2(point_seabed_e,point_seabed_n,I,Xq,Yq,'nearest');
surf(Xq,Yq,Tq)
view(2)
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回答（1 个）

Image Analyst
Image Analyst 2021-7-6
You can use scatteredInterpolant instead of griddedInterpolant. I'm attaching a demo.
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Image Analyst
Image Analyst 2021-7-8
No. Sounds like it might need the Mapping Toolbox, which I don't have. Do you have that, and is it using that?
An image is an array in memory. It makes no difference where it came from - a PNG file on disk, or created by your program or whatever. Once it's in an array, all that is forgotten and all you need is the array.
Meshgrid can take floating point numbers - they don't have to be pixel coordinates.
Valeria Leto
Valeria Leto 2021-7-8
I have the Mapping Toolbox, but I don't have the knowledge to use it. Anyway this is what I have done reading your demo. The problem is that I get negavite values in vq which shoud vary from 0 to 255.
%east coordinate
x=zeros(1,318*2000);
for i=1:1:318
x(1,1+(i-1)*2000:1+(i-1)*2000+1999)=point_seabed_e(i,:);
end
%north
y=zeros(1,318*2000);
for i=1:1:318
y(1,1+(i-1)*2000:1+(i-1)*2000+1999)=point_seabed_n(i,:);
end
%image gray level
C=zeros(1,318*2000);
for i=1:1:318
C(1,1+(i-1)*2000:1+(i-1)*2000+1999)=I(i,:);
end
x=x';
y=y';
C=C';
F = scatteredInterpolant(x,y,C);
%query points
u=[-20:0.01 :20];%1 cm
v=[0:-0.01:-20];
[Xq,Yq] = meshgrid(u,v);
Zq=zeros(2001,4001);
figure(20)
mesh(Xq,Yq,Zq)
xq = Xq(:);
yq =Yq (:);
% Evaluate the interpolant at query locations (xq,yq).
vq = F(xq, yq);

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