someting wrong using interp2

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Valeria Leto
Valeria Leto on 5 Jul 2021
Commented: Valeria Leto on 8 Jul 2021
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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Answers (1)

Image Analyst
Image Analyst on 6 Jul 2021
You can use scatteredInterpolant instead of griddedInterpolant. I'm attaching a demo.
  5 Comments
Valeria Leto
Valeria Leto on 8 Jul 2021
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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