Interp2 Function error using meshgrids

Hi! i got a question concerning the interpolation 2 function. I am trying to interpolate some data matrix wich is in respect to a cartesian grid. i have to interpolate the data to a polar grid (not with cart2pol). Yet when i create my new grid and use the function interp2 or griddata i only get 1 column of interpolated matrix and a whole lot of NaN's.

Here is a simplified version of my code:

zpoints=1024;
xpoints=512;
zmax=10e-6
w0=0.6e-6;
rmax=10*w0;
z=linspace(-zmax,zmax,zpoints);
r=linspace(0,rmax,xpoints);
[R,Z]=meshgrid(r,z);
I=peaks(R,Z);
pp=surf(R,Z,I)
rmax=1;
rpoints=512;
thetapoints=1024;

asmall=linspace(0,rmax,rpoints);
Theta=linspace(0,2*pi,thetapoints);
[a,TH]=meshgrid(asmall,Theta);
X=a.*cos(TH);
Y=a.*sin(TH);
I2=interp2(R,Z,I,X,Y);
% % figure
% % pp=surf(X,Y,I);
  set(pp,'edgecolor','none');

Can anyone help to see my problem here?

thanks!

[Rohan Kotecha]

How did you end up fixing it? I'm in a similar situation

Answer 1

[Matt J]

The problematic line is,

rmax=1;

This means that X,Y will mostly be located well outside the R,Z grid where they cannot be interpolated. Removing it gives reasonable results:

zpoints=1024;
xpoints=512;
zmax=10e-6;
w0=0.6e-6;
rmax=10*w0;
z=linspace(-zmax,zmax,zpoints);
r=linspace(0,rmax,xpoints);
[R,Z]=meshgrid(r,z);
I=peaks(R,Z);
pp=surf(R,Z,I,'EdgeColor','none'); view (-70,70)

rpoints=512;
thetapoints=1024;
asmall=linspace(0,rmax,rpoints);
Theta=linspace(0,2*pi,thetapoints);
[a,TH]=meshgrid(asmall,Theta(1:end-1));
X=a.*cos(TH);
Y=a.*sin(TH);
I2=interp2(R,Z,I,X,Y);
  
  trisurf(delaunay(X(:),Y(:)),X(:),Y(:),I2(:),'EdgeColor','none'); view (-70,70)

Warning: Duplicate data points have been detected and removed.
Some point indices will not be referenced by the triangulation.