how to plot 3D surface from a data file in Matlab

Question

I have a data file with 3 columns, x, y, z and I would like to do a 3D plot to visualize the surface.

I could have used meshgrid, but the problem is that I only have data for those y that y<=x. Is there a way to do it?

An example:

x    y    z
============
1    1    0.5
2    1    0.3
2    2    1.2
3    1    1.1
3    2    8.0
3    3    1.4
============

Answer 1

In many cases, a simple solution is to use trisurf. For example...

x = [1, 2, 2, 3, 3, 3];
y = [1, 1, 2, 1, 2, 3];
z = [0.5, 0.3, 1.2, 1.1, 1.8, 1.4];

tri = delaunay(x,y);
trisurf(tri,x,y,z)

Answer 2

You can fill the missing values deterministically, just a small script with two nested loops for both x and y .

Otherwise look again at the function meshgrid in the MATLAB documentation. There you see See Also section. Not accidentally there is a function griddata listed there. That's what you need! I can also recommend gridfit which is even better.

Answer 3

You could fit a surface through the points you have and then graph the surface. I like to use the x2fx function to generate a full quadratic model, then use the \\ operator to fit the data to the model. Do you have any idea about the underlying nature of the surface you're trying to graph? Does your data have a lot of noise? That 8.0 looks a bit out of place, is that an outlier or is that proper data?