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

• Applying hatching and shading
• Analyzing properties, such as area, using MASSPROP
• Extracting design information, such as the centroid

  

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:

Procedure

To define regions

1. Click Home tabDraw panelRegion. At the Command prompt, enter region.
2. Select objects to create the region.

   These objects must each form an enclosed area, such as a circle or a closed polyline.

3. Press Enter.

   A message at the Command prompt indicates how many loops were detected and how many regions were created.

To define regions by using boundaries

1. Click Home tab Draw panel Boundary. At the Command prompt, enter boundary.
2. In the Boundary Creation dialog box, in the Object Type list, select Region.
3. Click Pick Points.
4. Specify a point in your drawing inside each closed area that you want to define as a region and press Enter.

   This point is known as the internal point.

   NoteYou can make a new boundary set to limit the objects used to determine the boundary.

To combine regions by adding

1. Click Home tab Solid Editing panel Union.
2. Select one region for the union.
3. Select another region.

   You can select regions to unite in any order.

4. Continue selecting regions or press Enter to end the command.

   The command converts the selected regions to a new combined region.

To combine regions by subtracting

1. Click Home tab Solid Editing panel Subtract.
2. Select one or more regions from which to subtract and press Enter.
3. Select the region to subtract and press Enter.

   The areas of the second regions you selected are subtracted from the areas of the first regions.

To combine regions by finding intersections

1. Click Home tab Solid Editing panel Intersect.
2. Select one region of the intersection.
3. Select another intersecting region.

   You can select regions in any order to find their intersection.

4. Continue selecting regions or press Enter to end the command.

   The command converts the selected regions to a new region defined by the intersection of the selected regions.

Quick Reference

Commands

BOUNDARY

Creates a region or a polyline from an enclosed area.

INTERSECT

Creates a 3D solid, surface, or 2D region from overlapping solids, surfaces, or regions.

MASSPROP

Calculates the mass properties of regions or 3D solids.

REGION

Converts an object that encloses an area into a region object.

SUBTRACT

Combines selected 3D solids or 2D regions by subtraction.

UNION

Combines selected 3D solids, surfaces, or 2D regions by addition.

System Variables

DELOBJ

Controls whether geometry used to create 3D objects is retained or deleted.