someting wrong using interp2

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)

[KSSV]

Can you tell us the dimensions of point_seabed_e,point_seabed_n,I ? I suspect the problem is in here.

Share your data.

[Valeria Leto]

Hi! they are 318x2000

[Valeria Leto]

I

Answer 1

[Image Analyst]

You can use scatteredInterpolant instead of griddedInterpolant. I'm attaching a demo.

[Valeria Leto]

nice demo! I'll try to adapt it to my code. I'll let you know

[Image Analyst]

So how did it work out? If it worked, please "Accept this answer".

[Valeria Leto]

Hi, no it didn't :( The problem is that my image is georeferenced. What I mean is that I have east and north coordinates in two different matrices and I with is my image in which there are gray values. I use surf to visualize it and it is not saved as .png. Maybe I shoud convert it into a .png format but I must respect the pixel location expressed in east and north and I don't know how to do that....If you have any ideas...

[Image Analyst]

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]

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);