featureEdges

Sharp edges of surface triangulation

Syntax

F = featureEdges(TR,theta)

Description

F = featureEdges(TR,theta) returns the feature edges in a 2-D triangulation according to an angle theta. This function is typically used to extract sharp edges in a surface mesh plot.

Examples

Surface Feature Edges

Find and plot the feature edges of a surface.

Create a 2-D Delaunay triangulation.

x = [0 0 0 0 0 3 3 3 3 3 3 6 6 6 6 6 9 9 9 9 9 9]';
y = [0 2 4 6 8 0 1 3 5 7 8 0 2 4 6 8 0 1 3 5 7 8]';
DT = delaunayTriangulation(x,y);
T = DT.ConnectivityList;

Add elevations to the triangulation to create a surface and plot the surface.

z = [0 0 0 0 0 2 2 2 2 2 2 0 0 0 0 0 0 0 0 0 0 0]';
trisurf(T,x,y,z,FaceColor="cyan")
axis equal

Create a new triangulation on the elevated surface, and compute and plot its feature edges using a filter angle of $$\frac{\pi }{6}$$.

TR = triangulation(T,x,y,z);
F = featureEdges(TR,pi/6)';
plot3(x(F),y(F),z(F),"k",LineWidth=1.5);
axis equal

Input Arguments

TR — Triangulation representation

scalar triangulation object

Triangulation representation for 2-D triangulations only, specified as a scalar triangulation or delaunayTriangulation object.

Data Types: triangulation | delaunayTriangulation

theta — Filter angle

scalar

Filter angle in radians, specified as a scalar in the range [0,π]. featureEdges returns adjacent triangles that have a dihedral angle that deviates from π by an angle greater than theta.

Data Types: double

More About

Feature Edge

A feature edge is a triangulation edge that has any of the following attributes:

• The edge belongs to only one triangle.

• The edge is shared by more than two triangles.

• The edge is shared by a pair of triangles with angular deviation greater than the angle theta.

F is a two-column matrix whose rows correspond to a feature edge. The first element of each row is the identification number of the starting edge vertex, and the second element is the identification number of the ending edge vertex. A vertex identification is the row number of the corresponding vertex in the Points property.

Extended Capabilities

Thread-Based Environment
Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

Version History

Introduced in R2013a

R2013a: TriRep and DelaunayTri are not recommended

This syntax using TriRep and DelaunayTri objects as triangulation representations TR is not recommended:

• F = featureEdges(TR,theta) returns an edge matrix F. This method is typically used to extract the sharp edges in the surface mesh for the purpose of display. Edges that are shared by only one triangle and edges that are shared by more than two triangles are considered to be feature edges by default. For 2-D triangulations in MATLAB^®, the triangles are arranged in counter-clockwise order around the attached vertex.

  Note

  This query is only applicable to triangular surface meshes.

Use triangulation and delaunayTriangulation instead.