MATLAB: Plotting griddata

plot griddata

Hey All, I was wondering if there was a way to modify the griddata program to include plotting. Given that I am using data points I know I will have to use meshgrid and was trying to figure out how it would be possible to include into the program. Any ideas? Mel

Best Answer

From the doc:

x = rand(100,1)*4-2;  
y = rand(100,1)*4-2;
z = x.*exp(-x.^2-y.^2);
ti = -2:.25:2; 
[XI,YI] = meshgrid(ti,ti);
ZI = griddata(x,y,z,XI,YI);
mesh(XI,YI,ZI), hold
plot3(x,y,z,'o'), hold off

EDIT

So do this:

>> edit griddata % Once the file is up, do this:
ctrl+a,ctrl+c,ctrl+n,ctrl+v,ctrl+s  % I recommend using mygriddata

Then look in the new file, and find the last switch statement of the main function. Immediately after that switch statement, put this:

mesh(xi,yi,zi)
hold on 
plot3(x,y,z,'o')
hold off

Or whatever you want.

Related Solutions

MATLAB: How to plot interpolated grid data and original datapoint set in the same plot

You can always simply plot all your points:

plot3(Xi,Yi,Zi,'r.')

Or with scatter:

scatter(Xi,Yi,32,Zi,'filled')

But to me this seems to be more interesting:

pcolor(xi,yi,zi),
% shading flat % or interp adjust shading to fit taste
hold on
plot(xi,yi,'k.','markersize',6)
scatter(contour_grid.X,contour_grid.Y,23,contour_grid.Z,'filled')

Or you could compare contour-plots:

Levels = linspace(min(Zi(:)),max(Zi),10);
contour(Xi,Yi,Zi,Levels,'k')
hold on
tri=delaunay(contour_grid.X,contour_grid.Y);
[c,h]=tricontour(tri,contour_grid.X,contour_grid.Y,contour_grid.Z,Levels);
plot(contour_grid.X,contour_grid.Y,'k.')

You can find the tricontour function on the file exchange: TRICONTOUR

HTH

MATLAB: Plotting a surface or mesh

This sort of works (it runs and produces an interpolated surface):

x1 = [2,4,6];
x2 = [2,4,4];
x3 = [0.1,0.3,0.5];
x = x1; y = x2; z = x3;                         % Assumption
xi = [2:0.1:6];
yi = [2:0.1:4];
[XI,YI] = meshgrid(xi,yi);                      % Interpolation Grid Must Match Data Range
ZI = griddata(x,y,z,XI,YI);
mesh(XI,YI,ZI), hold;
plot3(x,y,z,'o'), hold off

The griddata function does not allow extrapolation (extrapolation is not mentioned in the documentation), so asking it to do so produces a matrix of NaN values, and NaN values do not plot. This was the reason you were not getting any surface plotted. The scatteredInterpolant class allows extrapolation, so consider using it if you want to extrapolate.

Best Answer

Related Solutions

MATLAB: How to plot interpolated grid data and original datapoint set in the same plot

MATLAB: Plotting a surface or mesh

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