boundaryshape

R2026b

Create polyshape from 2-D triangulation

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Syntax

polyout = boundaryshape(TR)
[polyout,vertexID] = boundaryshape(TR)

Description

polyout = boundaryshape(TR) creates a polyshape object from the boundary of a 2-D triangulation. TR can be either a triangulation object or a delaunayTriangulation object.

Once you create the polyshape object polyout, you can analyze its properties or perform additional computations using polyshape functions. For example, you can access the vertices that define the boundary with the property polyout.Vertices, and you can plot the shape using the command plot(polyout).

example

[polyout,vertexID] = boundaryshape(TR) also returns a vector vertexID that maps the vertices of the polyshape to the vertices of the triangulation.

Examples

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Open Live Script

Create and plot a simple triangulation object.

P = [2.5 8.0;
     6.5 8.0;
     2.5 5.0;
     6.5 5.0;
     1.0 6.5;
     8.0 6.5];
T = [5 3 1;
     3 2 1;
     3 4 2;
     4 6 2];
TR = triangulation(T,P);
triplot(TR)
xlim([0 9])
ylim([4.5 8.5])

2-D triangulation with four triangles connecting six vertices

Create and plot a polyshape object whose boundary is equal to the boundary of the triangulation.

polyout = boundaryshape(TR);
plot(polyout)

Filled hexagonal polygon representing the outer boundary of the triangulation

Open Live Script

Create and plot a triangulation object.

T = [5 1 3;
     6 1 4;
     5 4 1;
     2 6 3;
     3 6 5;
     2 1 6];
P = [3 0.5;
     3.5 1.5;
     4 0.5;
     3.25 0.6;
     3.75 0.6;
     3.5 1];
TR = triangulation(T,P);
triplot(TR)
xlim([2.8 4.2])
ylim([0.4 1.8])

2-D triangulation with six triangles arranged around a central void

Create and plot a polyshape object whose boundaries are equal to the boundaries of the triangulation. Due to the inner and outer closed boundaries of the triangulation, polyout contains both a hole boundary and a solid boundary.

polyout = boundaryshape(TR)
polyout = 
  polyshape with properties:

      Vertices: [7×2 double]
    NumRegions: 1
      NumHoles: 1


plot(polyout)

Filled triangular polygon with a smaller triangular hole in the center

Input Arguments

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Triangulation, specified as a 2-D triangulation object or a 2-D delaunayTriangulation object.

Output Arguments

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Output polyshape, returned as a polyshape object.

Vertex identification, returned as a vector of integers. Each element in vertexID corresponds to the row number of the triangulation vertex in the Points property. The length of vertexID is equal to the number of rows in the Vertices property of the polyshape object.

Data Types: double

Version History

Introduced in R2018b

See Also

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