Creating Regions in AutoCAD


Regions are 2D enclosed areas you create from closed shapes called loops. A loop is a curve or a sequence of connected curves that defines an area on a plane with a boundary that does not intersect itself. Loops can be combinations of lines, polylines, circles, arcs, ellipses, elliptical arcs, splines, 3D faces, traces, and solids. The objects that make up the loops must either be closed or form closed areas by sharing endpoints with other objects. The objects must also be coplanar (on the same plane).

You can create regions out of multiple loops and out of open curves whose endpoints are connected and form loops. If the open curves intersect in their interior, they cannot form a region. Objects such as 3D polylines and face meshes can be converted to regions by being exploded. You cannot form regions from open objects that intersect to form a closed area: for example, intersecting arcs or self-intersecting curves.
You can apply hatching and shading to regions, and you can analyze properties such as their area and moments of inertia.

To create regions by selecting objects

  1. From the Draw menu, choose Region.
  2. Select objects to create the region (must be closed loops).
  3. Press ENTER.

A message on the command line indicates how many loops were detected and how many regions were created.
Command line: REGION
Related: BOUNDARY creates regions by first creating polyline boundaries from intersecting objects, whether they share endpoints or not. BHATCH creates an associative hatch boundary. BLOCK creates a compound object (a block definition) from a group of objects.

To create regions by using boundaries

  1. From the Draw menu, choose Boundary.
  2. In the Boundary Creation dialog box under Object Type, select Region.
  3. If you want to limit the number of objects that AutoCAD analyzes when you use Pick Points to create boundaries (by default, AutoCAD analyzes all objects visible in the current viewport), under Boundary Set, choose the New button.
  4. Select the objects that you want AutoCAD to analyze when you define boundaries and press ENTER.
  5. Choose Pick Points.
  6. Specify a point in your drawing inside each area that you want to be defined as a region and press ENTER.

Command line  BOUNDARY
Related  REGION creates a region object from a selection set of existing objects. BHATCH fills an enclosed area or selected objects with a hatch pattern.
You can create composite regions by subtracting, combining, or finding the intersection of regions. You can then extrude or revolve composite regions to create complex solids (see chapter 17, “Working in Three-Dimensional Space”).

When you subtract one region from another, you first select the region from which you want to subtract. For example, to calculate how much carpeting is needed for a floor plan, select the outer boundary of the floor space and subtract all the uncarpeted areas, such as pillars and counters. Find the area of the resulting region with the AREA command.

To create a composite region by subtraction

  1. From the Modify menu, choose Solids Editing  Subtract.
  2. Select the region from which to subtract (1) and press ENTER.
  3. Select the region to subtract (2).

Command line  SUBTRACT
Related  UNION and INTERSECT also create composite regions.
You can select regions in any order to unite them with the UNION command or to find their intersection with the INTERSECT command. AutoCAD ignores objects within the selection set that are not regions.
The following illustration shows the uniting of two regions.

The following illustration shows the intersection of three regions, which you find using the INTERSECT command.

You can select in any order the regions whose intersection you want to find. The resulting object is also a region.



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4 comments ↓

#1 Nicolas on 11.21.10 at 9:35 pm

Hi,

Regarding self-intersecting curve, you stated:

“You cannot form regions from open objects that intersect to form a closed area: for example, intersecting arcs or self-intersecting curves.”

What are the steps to deal effectively with self-intersecting curves? What about the FLATTEN command?

Regards,

Nicolas.

#2 cadMONKEY on 05.05.11 at 12:42 am

I know this an old post, but I would like to know the underlying theory. Why would you want to create a region? What benefits does it give you over a closed pline?

#3 admin on 05.11.11 at 11:58 am

@cadMONKEY
Regions are easier to create then joining polylines or curves using the PEDIT command.

#4 Selim on 06.02.13 at 1:11 am

@admin how can i find open points in a complex 60 pieces drawing to create a region or polyline?

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