someting wrong using interp2

7 views (last 30 days)
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)
  3 Comments
Valeria Leto
Valeria Leto on 6 Jul 2021
Hi! they are 318x2000

Sign in to comment.

Answers (1)

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

Sign in to comment.

Categories

Find more on Interpolation in Help Center and File Exchange

Products

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!