How do I plot interpolated grid data and original datapoint set in the same plot?

Hi,

After creating a grid data series (Data Terrain Model) from interpolating contour lines, I would like to plot everything on the same layer, but I am not sure if it is possible in matlab. Here is the gist of what I've done:

    [xi,yi] = meshgrid(Xmin:res:Xmax, Ymin:res:Ymax);
    f = scatteredInterpolant(contour_grid.X,contour_grid.Y,contour_grid.Z);
    zi= f(xi,yi)
    Xi=[xi(:); contour_grid.X];
    Yi=[yi(:); contour_grid.Y];
    Zi=[zi(:); contour_grid.Z];

Is there a way to plot Xi, Yi, and Zi? I'd have to turn these arrays back into grids to be able to use mesh(X,Y,Z) but I am struggling to write how to do that.

Has anyone ever had to do that?

Thanks,

Answer 1

[Bjorn Gustavsson]

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

[NP]

Thanks for this elaborate answer. I had a go at the different functions and they give interesting results. Ploting all the points is a bit taxing for the computer though. Ideally, I'd like to plot Xi, Yi and Zi that include the interpolated points and the original contour line points in a mesh, but can a mesh function even do that? Not sure.

[Bjorn Gustavsson]

This whish of yours confuse me. First you say that "plotting all the points" are too taxing, then you say that you want to plot Xi, Yi and Zi - that are explicitly all points you have.

The terse answer is: matlab's mesh function cannot do what you want. It requires, just as its plot-function siblings pcolor, surf et al., points in 2-D arrays (you have such for xi, yi and zi, but your contour_grid.X, contour_grid.Y, and contour_grid.Z are in 1-D arrays. It is not straightfor (impossible) ward to merge these into 1 set of regular 2-D arrays).

You might get what you request with the trimesh function. That would give you a mesh-plot of all points if you call it with something like:

tri=delaunay(Xi,Yi);
trimesh(tri,Xi,Yi,Zi);

Then adjust and add contour-plots and other stuff as you whish.

HTH

[NP]

Hi Bjorn,

Thank you very much for taking the time to try to understand my twisted mind! It makes sense for the mesh functions not to plot my interpolated grid + the original points. Pretty cool that the trimesh one does though. Thank you for the suggestion!