Alpha Shape

Associated Constructors

Alpha Shape

Syntax: ashape = Alpha Shape(Triangulation)

Description: Returns the alpha shape for the given triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );

Item Messages

Get Alpha

Syntax: alpha = obj << Get Alpha

Description: Returns the current alpha value.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
ashape << Get Alpha();

Get Edges

Syntax: edges = obj << Get Edges

Description: Returns the indices of the edges in the form an Nx2 matrix.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get Edges;

Get Hull Edges

Syntax: ind = obj << Get Hull Edges

Description: Returns the indices of the edges on the boundary of the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get Hull Edges;

Get Hull Path

Syntax: ind = obj << Get Hull Path

Description: Returns the boundary of the triangulation as a path.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get Hull Path;

Get Hull Points

Syntax: ind = obj << Get Hull Points

Description: Returns the indices of the points on the boundary of the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get Hull Points;

Get N Edges

Syntax: nedge = obj << Get N Edges

Description: Returns the number of edges in the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get NEdges;

Get N Hull Edges

Syntax: nhull = obj << Get N Hull Edges

Description: Returns the number of edges on the boundary of the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get N Hull Edges;

Get N Hull Points

Syntax: nhull = obj << Get N Hull Points

Description: Returns the number of points on the boundary of the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get N Hull Points;

Get N Points

Syntax: npt = obj << Get N Points

Description: Returns the number of unique points in the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get N Points;

Get N Triangles

Syntax: ntri = obj << Get N Triangles

Description: Returns the number of triangles.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get N Triangles;

Get Points

Syntax: {x1,x2} = obj << Get Points

Description: Returns the coordinates of the unique points in the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get Points;

Get Tri Alpha

Syntax: [alpha1, ...] = obj << Get Tri Alpha

Description: Returns the alpha values for each triangle.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
ashape << Get Tri Alpha();

Get Triangles

Syntax: m = obj << Get Triangles

Description: Returns the indices of the triangles in the form of an Nx3 matrix.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get Triangles;

Get Y

Syntax: y = obj << Get Y

Description: Returns the Y values of the unique points in the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
tri << Get Y;

Peel

Syntax: tri = obj << Peel

Description: Peel the boundary layer of a triangulation, returning a new triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
Show( tri << Get N Triangles );
tri2 = tri << Peel;
Show( tri2 << Get N Triangles );

Set Alpha

Syntax: obj << Set Alpha( alpha )

Description: Sets the current alpha value and recomputes the triangulation.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
ashape << Set Alpha( 0.5 );

Subset

Syntax: tri = obj << Subset( {indices} )

Description: Returns a triangulation resulting from the given subset of points.

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
triang = Triangulation( X( :X, :Y ), Y( :POP ) );
ashape = tri = Alpha Shape( triang );
Show( tri << Get N Triangles );
tri2 = tri << Subset( tri << Get Hull Points );
Show( tri2 << Get N Triangles );