Create and Combine Areas (Regions)
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Regions are two-dimensional enclosed areas that have physical properties such as centroids or centers of mass. You can combine existing regions into a single, complex region to calculate area.

You can create regions from objects that form closed loops. Loops can be combinations of lines, polylines, circles, arcs, ellipses, elliptical arcs, and splines that enclose an area.

Regions can be used for

You can create regions out of multiple loops and out of open curves whose endpoints are connected and form loops. You cannot form regions from open objects that intersect to form a closed area: for example, intersecting arcs or self-intersecting curves.

You can create regions using the REGION and BOUNDARY commands. You create composite regions by combining, subtracting, or finding the intersection of regions.

Objects combined using UNION:

Objects combined using SUBTRACT:

Objects combined using INTERSECT:

Invalid Boundaries

When a boundary cannot be determined, it might be because the specified internal point is not within a fully enclosed area. Red circles are displayed around unconnected endpoints of the boundary to identify gaps in the boundary.

The red circles remain displayed even after you exit the REGION or BOUNDARY command. They are removed when you specify a closed boundary, or by using the REDRAW, REGEN, or REGENALL command.

To define regions
To define regions by using boundaries
To combine regions by adding
To combine regions by adding
To combine regions by subtracting
To combine regions by finding intersections
Quick Reference
System Variables