csgdel

Delete boundaries between subdomains

Syntax

[dl1,bt1] = csgdel(dl,bt,bl)

[dl1,bt1] = csgdel(dl,bt)

Description

[dl1,bt1] = csgdel(dl,bt,bl) deletes the boundaries bl between subdomains. If deleting the boundaries in bl makes the decomposed geometry matrix inconsistent, then csgdel deletes additional border segments (edge segments between subdomains) to preserve consistency.

Deleting boundaries typically changes the edge IDs of the remaining boundaries.

csgdel does not delete boundary segments (outer boundaries).

[dl1,bt1] = csgdel(dl,bt) deletes all boundaries between subdomains.

Examples

Delete Edges to Merge Faces of 2-D Geometry

Delete edges in a 2-D geometry created in the PDE Modeler app and exported to the MATLAB^® workspace.

Create a geometry in the PDE Modeler app by entering the following commands in the MATLAB Command Window:

pdecirc(0,0,1,"C1")
pdecirc(0,0,0.5,"C2")
pderect([-0.2 0.2 0.2 0.9],"R1")
pderect([0 1 0 1],"SQ1")

Reduce the geometry to the first quadrant by intersecting it with a square. To do this, enter (C1+C2+R1)*SQ1 in the Set formula field.

From the PDE Modeler app, export the geometry description matrix, set formula, and name-space matrix to the MATLAB workspace by selecting Export Geometry Description, Set Formula, Labels from the Draw menu.

In the MATLAB Command Window, use the decsg function to decompose the exported geometry into minimal regions. This creates an AnalyticGeometry object dl. Plot dl.

[dl,bt] = decsg(gd,sf,ns);
pdegplot(dl,"EdgeLabels","on","FaceLabels","on")
xlim([-0.1 1.1])
ylim([-0.1 1.1])

Remove edges 1, 2, and 13 using the csgdel function. Specify the edges to delete as a vector of edge IDs. Plot the resulting geometry.

[dl1,bt1] = csgdel(dl,bt,[1 2 13]);
pdegplot(dl1,"EdgeLabels","on","FaceLabels","on")
xlim([-0.1 1.1])
ylim([-0.1 1.1])

Now remove all boundaries between subdomains and plot the resulting geometry.

[dl1,bt1] = csgdel(dl,bt);
pdegplot(dl1,"EdgeLabels","on","FaceLabels","on")
xlim([-0.1 1.1])
ylim([-0.1 1.1])

Input Arguments

dl — Decomposed geometry matrix

matrix of double-precision numbers

Decomposed geometry matrix, returned as a matrix of double-precision numbers. It contains a representation of the decomposed geometry in terms of disjointed minimal regions constructed by the decsg algorithm. Each edge segment of the minimal regions corresponds to a column in dl. Edge segments between minimal regions (subdomains) are border segments. Outer boundaries are boundary segments. In each column, the second and third rows contain the starting and ending x-coordinates. The fourth and fifth rows contain the corresponding y-coordinates. The sixth and seventh rows contain left and right minimal region labels with respect to the direction induced by the start and end points (counterclockwise direction on circle and ellipse segments). There are three types of possible edge segments in a minimal region:

• For circle edge segments, the first row is 1. The eighth and ninth rows contain the coordinates of the center of the circle. The 10th row contains the radius.

• For line edge segments, the first row is 2.

• For ellipse edge segments, the first row is 4. The eighth and ninth rows contain the coordinates of the center of the ellipse. The 10th and 11th rows contain the semiaxes of the ellipse. The 12th row contains the rotational angle of the ellipse.

All columns in a decomposed geometry matrix have the same number of rows. Rows that are not required for a particular shape are filled with zeros.

Row number	Circle edge segment	Line edge segment	Ellipse edge segment
1	1	2	4
2	starting x-coordinate	starting x-coordinate	starting x-coordinate
3	ending x-coordinate	ending x-coordinate	ending x-coordinate
4	starting y-coordinate	starting y-coordinate	starting y-coordinate
5	ending y-coordinate	ending y-coordinate	ending y-coordinate
6	left minimal region label	left minimal region label	left minimal region label
7	right minimal region label	right minimal region label	right minimal region label
8	x-coordinate of the center		x-coordinate of the center
9	y-coordinate of the center		y-coordinate of the center
10	radius of the circle		x-semiaxis before rotation
11			y-semiaxis before rotation
12			Angle in radians between x-axis and first semiaxis

Data Types: double

bt — Boolean table relating original shapes to minimal regions

matrix of 1s and 0s

Boolean table relating the original shapes to the minimal regions, returned as a matrix of 1s and 0s.

Data Types: double

bl — Boundaries to delete

positive integer | vector of positive integers

Boundaries to delete, specified as a positive integer or a vector of positive integers. Each integer represents a boundary ID.

Data Types: double

Output Arguments

dl1 — Modified decomposed geometry matrix

matrix of double-precision numbers

Modified decomposed geometry matrix, returned as a matrix of double-precision numbers.

Data Types: double

bt1 — Boolean table relating remaining original shapes to minimal regions

matrix of 1s and 0s

Boolean table relating the remaining original shapes to the minimal regions, returned as a matrix of 1s and 0s.

Data Types: double

Version History

Introduced before R2006a