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Class: TriRep

(Not recommended) Unit normals to specified triangles


FN = faceNormals(TR, TI)


FN = faceNormals(TR, TI) returns the unit normal vector to each of the specified triangles TI.

    Note:   This query is only applicable to triangular surface meshes.

Input Arguments

TRTriangulation representation.
TIColumn vector of indices that index into the triangulation matrix TR.Triangulation.

Output Arguments


m-by-3 matrix. m = length(TI), the number of triangles to be queried. Each row FN(i,:) represents the unit normal vector to triangle TI(i).

If TI is not specified the unit normal information for the entire triangulation is returned, where the normal associated with triangle i is the i'th row of FN.


Triangulate a sample of random points on the surface of a sphere and use the TriRep to compute the normal to each triangle:

numpts = 100;
thetha = rand(numpts,1)*2*pi;
phi = rand(numpts,1)*pi;
x = cos(thetha).*sin(phi);
y = sin(thetha).*sin(phi);
z = cos(phi);
dt = DelaunayTri(x,y,z);
[tri Xb] = freeBoundary(dt);
tr = TriRep(tri, Xb);
P = incenters(tr);
fn = faceNormals(tr);
trisurf(tri,Xb(:,1),Xb(:,2),Xb(:,3), ...
     'FaceColor', 'cyan', 'faceAlpha', 0.8);
axis equal;
hold on;

Display the result using a quiver plot:

quiver3(P(:,1),P(:,2),P(:,3), ...
     fn(:,1),fn(:,2),fn(:,3),0.5, 'color','r');
hold off;

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