How to use Cartesian coordinates to create Grid Surface?

Greetings,

I have been tasked with using Simscape Multibody to investigate contact forces between objects. One step in the Simscape process is to create a Grid Surface, as is described here: https://www.mathworks.com/help/sm/ref/gridsurface.html .

I am provided with CAD files (.stl) and have written a Matlab script that pulls in coordinate points from the STL that describe the shapes I'm interested in. It is simple enough to pull the X and Y values from the STL file and save them as vectors since Grid Surfaces require X and Y to be defined as "Coordinates in the x-direction or y-direction of the grid surface, specified as a real 1-by-m vector".

The Z values, however, are defined as "Elevations of the grid points in the grid surface, specified as a real m-by-n matrix. m and n are the lengths of the vectors for the X Grid Vector and Y Grid Vector parameters."

Does anybody have an idea of how to generate a Z-matrix given cartesian coordinates? I have manually done so with simple shapes, like a cube, but will need to eventually automate the process with a Matlab script.

Thanks

Answer 1

[Torsten]

If the CAD file describes the surface of the body in question, there should be a value for the elevation associated with each (x/y) pair. This is the z-matrix you are asking for.

x = 0:0.05:0.5;
y = 0:0.05:1;
z = x.^2+(y.').^2;
surf(x,y,z)

[Kylen]

Thank you for the quick response. I don't know that this will work, unfortunately. The grid surface function in Simscape needs the z matrix itself. Since I'm given x, y, and z as vectors I'm not sure that I can use the surf() command to generate just the z matrix. And since my shapes aren't necessarily described by an equation I can't apply one to calculate z like your example does.

The CAD filetype I'm stuck using, STL, doesn't describe the surface itself. Rather, it takes represents an object's shape by breaking it up into a series of small triangles. The vertices of each triangle come with cartesian coordinates and can be plotted to show the shape of the object in question.

I think that there must be a way to generate the z-matrix that the Simscape grid surface function requires given cartesian coordinates.

The kicker is that Simscape also has a function called Point Cloud, which does use X,Y,Z cartesian coordinates. However, two point clouds cannot interact using Spatial Contact. Point clouds can only interact with grid surfaces, so I have to create a point cloud and a grid surface that represent each object I'm dealing with...