MATLAB: How to create a surface or contour plot with x, y, and z vectors

datagridgriddedMATLABnote;techtechnicalvector

I have three vectors that represent X-Y-Z triplets. How do I produce a contour or surface plot of this data using "meshgrid" and "griddata"?

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In creating three-dimensional representations of data, it is often necessary to have data defined over evenly spaced, two-dimensional grids. The "surf", "mesh", "contour" and "quiver" functions are examples of graphics functions that use data in this form.

Please refer following documentation for detail example.

- MATLAB: Interpolating Scattered Data

https://mathworks.com/help/matlab/math/interpolating-scattered-data.html

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MATLAB: How to interpolate and plot 3-D surfaces in MATLAB

MATLAB has surface fitting capabilities in the Curve Fitting Toolbox™ that provide an easy way to interpolate and plot surfaces in MATLAB. To learn about interactive surface fitting, please see the following link:

http://www.mathworks.com/help/curvefit/interactive-curve-and-surface-fitting-.html

To learn about programmatic surface fit objects, please see the following link:

<http://www.mathworks.com/help/curvefit/surface-fitting.html>

If you have a MATLAB version prior to R2009a, please read the following for workarounds.

The function GRIDDATA can be used to interpolate and plot data in 3-D as follows:

ZI = griddata(x,y,z,XI,YI) fits a surface of the form z = f(x,y) to the data in the (usually) nonuniformly spaced vectors (x,y,z). GRIDDATA interpolates this surface at the points specified by (XI,YI) to produce ZI. The surface always passes through the data points. XI and YI usually form a uniform grid (as produced by meshgrid).

You can also fit a spline to a surface defined by the data in the same sized matrices "x", "y", and "z", where "x" and "y" are plaid (evenly-spaced) meshes. An example of using the Curve Fitting Toolbox to perform this operation is included in our online documentation starting at the following URL: "Example: Approximation by Tensor Product Splines"

http://www.mathworks.com/help/releases/R2008b/toolbox/splines/examples5.html

MATLAB: Make a 3D surface plot instead of plot3

The following code should accomplish plotting the data as a 3D surface:

[xi, yi] = meshgrid(x,y);
F = scatteredInterpolant(x,y,z);
zi = F(xi,yi);
surf(xi,yi,zi, 'EdgeAlpha', 0)
hold on
plot3(x, y, z)

The "surf" function needs a grid in the X-Y plane and values in Z for each point on the grid in order to plot a surface. This will result in a square surface patch. Original data is not sufficient to plot a surface as it is just scattered X, Y and Z data. This is why we need to use interpolation (e.g. "scatteredInterpolant" function), and both interpolate the points in-between the original data, and extrapolate for points the corners of the grid (outside the outer "contour"). You can control how fine of a mesh you want to use. In the above example we have

[xi, yi] = meshgrid(x,y);

which created a grid line for every single point in the original data, so a very fine mesh. For comparison, consider using only 100 grid lines evenly spaced between maximum and minimum values of x and y:

xgrid = linspace(min(x), max(x), 100);
ygrid = linspace(min(y), max(y), 100);
[xi, yi] = meshgrid(xgrid, ygrid);

You can also change the interpolation method (by default it is 'linear'). Even with the "square" surface, you should be able to see that the interpolated surface coincides well with the original data (by plotting "plot3" over the surface):

View from above:

To emphasize, the resultant shape is a square because we needed to use a grid to create the surface. For cosmetic reasons, you could exclude points outside the outer contour from the mesh. But you would still need to use interpolation to create the surface.

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MATLAB: How to interpolate and plot 3-D surfaces in MATLAB

MATLAB: Make a 3D surface plot instead of plot3

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