MATLAB: Finding surface height at x,y coordinates

evaluatingMapping Toolboxsurfm

Dear all,
using the mapping toolbox, I've created an interpolated surface from a scattered dataset. x,y,z are read from a file.
[yi,xi] = meshgrid(min(y):0.5:max(y), min(x):0.5:max(x)); % sets up mesh grid for x/y coords, step-size=0.5
zi = griddata(y,x,z,yi,xi,'linear'); % interpolates z values
surfm(yi,xi,zi);
Now, I need to read out the interpolated zi value at a given location (say… -10, -50). I feel like there's a very simple solution, but half an hour of googling and reading up in the documentation hasn't led me to success. Could someone point me in the right direction? Thank you!

Best Answer

Instead of GRIDDATA, I think "scatteredInterpolant" is what you want. This creates an object that you can use to query points freely.
% Make some data
x = -30+60*rand(1000,1);
y = -30+60*rand(1000,1);
z = sin(x/10).*sin(y/15);
% set up the scatteredInterpolant object
method = 'linear';
extrap = 'none';
S = scatteredInterpolant(x,y,z,method,extrap)
% Evaluate on the grid
[yi,xi] = meshgrid(min(y):0.5:max(y), min(x):0.5:max(x)); % sets up mesh grid for x/y coords, step-size=0.5
zi = S(xi,yi);  % <-- This is equivalent to zi = GRIDDATA(...)
% You can call S(x,y) to evaluate at specific points
S(-10,20)
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