Surface 'interpolation' along a specific contour

Hi, I am really new to MatLab so apologies if this is an exceedingly stupid question or the answer is glaringly obvious...

I have a large amount of data in the following structure:

    A        rho     RMSE
   500       0.10    NaN
   500       0.11    NaN
   500       0.12    12.34
   ...
   500       0.50    56.78
   600       0.10     9.01
   ...
   3000      0.50    NaN

I need to plot the surface to see how the RMSE value changes with the value of A and rho. I then need to interpolate the surface order to obtain all the A,rho pairs that give an RMSE value of zero (i.e.interpolate along the zero contour).

I understand that surface plotting requires the data to form a grid: I therefore follow this to restructure my data (as it is in the same format) and can thus use surf() to plot the surface.

My question is thus: How do I display the Z(RMSE) = 0 contour on top of the plotted surface?

How do I 'interpolate' the surface such that I produce a list of x,y combinations that give z=0?

Any pointers in the right direction would be gratefully received.

Many thanks

Answer 1

[Kelly Kearney]

I would let contour do most of the work:

[x,y,z] = peaks(20); % some example data, replace with yours
surf(x,y,z);
shading flat;
hold on;
[c, hc] = contour(x,y,z,[0 0],'k'); % Plot the 0 contour
S = contourcs(x(1,:),y(:,1),z,[0 0]); % same points as c, but clearer

The contourcs function is from the File Exchange; it's a nice wrapper around contourc that reformats the data to be more usable.