Question

I am plotting a 3D object, say a cube, in MATLAB.

Node = [0 0 0; 1 0 0; 1 1 0; 0 1 0; 0 0 1; 1 0 1; 1 1 1; 0 1 1];
Elem = cell(1); Elem{1} = 1:8;
figure
for elm = 1:size(Elem,1)    
    X = Node(Elem{elm},:); K = convhulln(X); hold on;    
    patch('Faces',K,'Vertices',X,'FaceColor',rand(1,3),'FaceAlpha',1.0);
end
view(3); grid off; axis equal; cameramenu; axis off;

In the plot, how do I remove the internal diagonal lines? The plot should just show edges of cube. I am looking for a general solution which is applicable to any polyhedron.

Answer 1

the output of K=convhulln(X); is causing this, because convex hull will have triangular facets… (that’s the default).
if instead you’d define K to be:

K= [1 2 3 4; ...
    2 6 7 3; ...
    4 3 7 8; ...
    1 5 8 4; ...
    1 2 6 5; ...
    5 6 7 8];

You’ll get it right.

Another option is to use geom3D from the FEX.