42 AutoCAD and Its Applications—Advanced Copyright Goodheart-Willcox Co., Inc. Working with Regions Working with Regions A region is a closed, two-dimensional solid. It is a solid model without thick- ness (Z value). A region can be analyzed for its mass properties. Therefore, regions are useful for 2D applications where area and boundary calculations must be quickly obtained from a drawing. Boolean operations can be performed on regions. When regions are unioned, subtracted, or intersected, a composite region is created. A composite region is also called a region model. A region can be quickly given a thickness, or extruded, to create a 3D solid object. This means that you can convert a 2D shape into a 3D solid model in just a few steps. An application is drawing a 2D section view, converting it into a region, and extruding the region into a 3D solid model. Extruding is covered in Chapter 6. Constructing a 2D Region Model The following example creates, as a region, the plan view of a base for a support bracket. In Chapter 6, you will learn how to extrude the region into a solid. First, start a new drawing. Next, create the profi le geometry in Figure 2-27 using the RECTANGLE and CIRCLE commands. These commands create 2D objects that can be converted into regions. The PLINE and LINE commands can also be used to create closed 2D objects. The REGION command allows you to convert closed, two-dimensional objects into regions. When the command is initiated, you are prompted to select objects. Select the rectangle and four circles and then press [Enter]. The rectangle and each circle are now separate regions and the original objects are deleted. You may need to switch to a wireframe visual style in order to see the circles. You can individually pick the regions. If you pick a circle, notice that a grip is displayed in the center, but not at the four quadrants. This is because the object is not a circle anymore. However, you can still snap to the quadrants. In order to create the proper solid, the circular regions must be subtracted from the rectangular region. Using the SUBTRACT command, select the rectangle as the object to be subtracted from, and then select all of the circles as the objects to subtract. Now, if you select the rectangle or any of the circles, you can see that a single region has been created from the fi ve separate regions. If you set the Conceptual or Realistic visual style current, you can see that the circles are now holes in the region. See Figure 2-28. Solids created in this manner can be given a thickness using either the EXTRUDE or PRESSPULL command. Calculating the Area of a Region A region is not a polyline. It is an enclosed area called a loop. Certain properties of the region, such as area, are stored as a value of the region. The MEASUREGEOM command can be used to determine the length of all sides and the area of the loop. This can be a useful advantage of a region. REGION Ribbon Home Draw Region Type REGION REG Figure 2-27. These 2D objects can be converted to regions in order to create a region model. The region model can then be made into a 3D solid.