union

Boolean union of 3-D geometries

Since R2025a

Syntax

g3 = union(g1,g2)

g3 = union(g1,g2,KeepBoundaries=boundaries)

Description

g3 = union(g1,g2) merges 3-D geometries g1 and g2 into one geometry g3.

g3 = union(g1,g2,KeepBoundaries=boundaries) specifies whether the function preserves the boundaries of the geometries when merging them.

Examples

Merge Cylinder and Cuboid

Merge geometries representing a cylinder and a cuboid into one geometry.

Create and plot a hollow cylinder geometry.

gcyl = multicylinder([4 5],10,Void=[true false]);
pdegplot(gcyl,CellLabels="on")

Create and plot a single cuboid geometry.

gcube = multicuboid(sqrt(50),sqrt(50),10);
pdegplot(gcube)

Convert both geometries to fegeometry objects.

gcyl = fegeometry(gcyl);
gcube = fegeometry(gcube);

Merge the geometries into one by using the Boolean union operation.

g = union(gcyl,gcube);

Plot the resulting geometry.

pdegplot(g,CellLabels="on",FaceAlpha=0.3)

Create Heat Sink Geometry

Create a geometry representing a heat sink with the base plate and 12 cylindrical fins.

First, create and plot a geometry of the base.

gBase = multicuboid(0.01,0.008,0.0005);
gBase = translate(gBase,[0.005,0.004,0]);
gBase = fegeometry(gBase);
pdegplot(gBase,CellLabels="on")

Create a geometry representing one fin.

gFin = multicylinder(0.0005,0.005);
gFin = fegeometry(gFin);

Now, create a geometry representing 12 fins by shifting the original fin to locations on top of the base and adding the fin to the geometry each time.

g = fegeometry;
for i = 0.002:0.002:0.008
   for j = 0.002:0.002:0.006
    gFinT = translate(gFin,[i,j,0.0005]);
    g = union(g,gFinT);
   end
end

Plot the fins.

pdegplot(g,CellLabels="on")

Merge the geometry of the base with the geometry of the fins by using the Boolean union operation.

g = union(g,gBase);

Plot the resulting heat sink geometry.

pdegplot(g,CellLabels="on")

Preserve Boundaries

Merge two cubes into one geometry while preserving the original boundaries.

Create a geometry of a unit cube.

g1 = fegeometry(multicuboid(1,1,1));

Create the second cube by moving the original cube along the z-axis.

g2 = translate(g1,[0 0 0.7]);

Merge two geometries into one by using the Boolean union operation. By default, the union function does not preserve any boundaries that become internal in the merged geometry. Plot the resulting geometry.

g = union(g1,g2);
pdegplot(g,FaceAlpha=0.3,CellLabels="on")

Merge the same two geometries, but this time use the KeepBoundaries argument to preserve all boundaries of both geometries. Plot the resulting geometries.

g = union(g1,g2,KeepBoundaries=[true true]);
pdegplot(g,FaceAlpha=0.3,CellLabels="on")

Merge the geometries again. This time, specify that the merged geometry must preserve all boundaries of the second geometry (g2) but not the boundaries of the first geometry (g1) that become internal in the merged geometry. Plot the resulting geometry.

g = union(g1,g2,KeepBoundaries=[false true]);
pdegplot(g,FaceAlpha=0.3,CellLabels="on")

Input Arguments

g1 — 3-D geometry

fegeometry object

3-D geometry, specified as an fegeometry object.

g2 — 3-D geometry

fegeometry object

3-D geometry, specified as an fegeometry object.

boundaries — Geometry boundaries to preserve

[false false] (default) | vector of two logical values

Geometry boundaries to preserve, specified as a vector of two logical values. The values indicate whether the boundaries of the geometries g1 and g2 must appear in the merged geometry g3. For example, KeepBoundaries=[false true] specifies that the merged geometry must preserve all boundaries of the second geometry (g2) but not the boundaries of the first geometry (g1) that become internal in the merged geometry.

Output Arguments

g3 — Merged geometry

fegeometry object

Merged geometry, returned as an fegeometry object.

Limitations

• union works only on 3-D geometries. Use decsg to merge 2-D geometries.

Version History

Introduced in R2025a