Triangular surface

Question

Dougie 2012-5-3

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https://ww2.mathworks.cn/matlabcentral/answers/37372-triangular-surface

I have a surface defined in x, y, z and i am able to get a surface produced using surf(x,y,z). However i want to produce a surface composing of triangles rather than quadrilaterals. The surface is essentially a sphere. And i would like it to be displayed as a triangular surface.

I think i need to use trisurf(tri, x,y,z) but i dont understand the "tri" input. Examples use the delauney(x,y) function but i dont understand what this does and what the alternative for a sphere would be.

Thanks

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Answer 1

Richard Brown 2012-5-4

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Simple example using DelaunayTri. First create a set of points

N = 1000;
theta = 2*pi*rand(N, 1);
phi = acos(2*rand(N, 1) - 1);
x = cos(theta).*sin(phi);
y = sin(theta).*sin(phi);
z = cos(phi);

Mesh the volume using DelaunayTri

Tfull = DelaunayTri(x, y, z);

Find the triangulation on the boundary using freeBoundary

[T, X] = Tfull.freeBoundary();
trisurf(T, X(:, 1), X(:, 2), X(:, 3))
axis equal

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Dougie 2012-5-5

Thanks that's great, only i'm using matlab2008 and i dont think trirep and freeBoundary are included in it. Is there a way i can download them?

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Answer 2

Teja Muppirala 2012-5-7

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https://ww2.mathworks.cn/matlabcentral/answers/37372-triangular-surface#answer_46934

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There is also the SURF2PATCH function, which can turn quadrilaterals into triangles. For example:

figure;
[x,y,z] = sphere;
s = surf(x,y,z);
patch(surf2patch(s,'triangles'));
delete(s);
shading faceted;
view(3);
axis equal

Or, without the intermediate call to SURF

figure;  
[x,y,z] = sphere;
p = surf2patch(x,y,z,'triangles');
p.facevertexcdata = p.vertices(:,3); %Need this to add color
patch(p);
shading faceted;
view(3);
axis equal