AutoCAD drawings contain a wealth of data. In them, you can find graphic information such as distances and angles between objects, as well as precise areas and the properties of objects. But as you become more involved with AutoCAD, you will find that you also need data of a different nature. For example, as you begin to work in groups, the various settings-in a drawing become important. Statistics on the amount of time you spend on a drawing are needed when you are billing computer time. As your projects become more complex, file maintenance requires a . greater degree of attention. To take full advantage of AutoCAD, you will want to xchange much of this data with other people and other programs.
You will explore the ways in which all types of data can be extracted
from AutoCAD and made available to you, your coworkers, and other prog-tams. First, you will discover how to get specific data on your drawings. Then you will look at ways to exchange data with other programs such as word processors, desktop publishing software, and even other CAD programs.
Finding the Area of Closed Boundaries
One of the most frequently sought pieces of data you can extract from an AutoCAD drawing is the area of a closed boundary. In architecture, you want to find the area of a room or the footprint of a building. In civil engineering, you want to determine the area covered by the boundary of a property line, or the area of cut for a roadway. In this section, you’ll learn how you can use AutoCAD to obtain exact area information from your drawings.
Finding the Area or Location of an Object
Architects, engineers, and facilities planners often need to know the square footage of a room or a section of a building. A structural engineer might want to find the cross-sectional area of a beam. In this section, you will practice determining the areas of both regular and irregular objects
First you will find out the square-foot area of the living room and entry of your studio unit plan.
1. Start AutoCAD and open the Unit file you created earlier, or use the 14aurrit. dwg file from the companion CD-ROM.
2. – Enter BIipmode.J on.J. This turns on a marking feature that displays a tiny cross called blips whenever you click in the drawing area. The blips do not print and can be cleared from the screen with a redraw. You’ll use it to help keep track of your point selections in this exercise.
3. Zoom into the living room and entry area so you have a view similar.
4. Choose Tools :> Inquiry :> Area, or type Area.J at the command prompt. You can also click and drag List on the Standard toolbar, and then select Area
5. Using the Endpoint Osnap, start with the lower-left comer of the living room and select the points indicated in Figure 14.1. You are indicating the boundary of the entry and living room area. —
6. When you have come full circle to the eighth point,
press .1. You get the message Area· 39570.00 sq in (274.7917 sq ft), Perimeter· 760
7. Now turn off Blipmode by typing Blipmode.J off.J. Then choose View > Redraw to clear the clips from the screen.
There is no limit to the number of points you can pick to define an area, so you can obtain the areas of very complex shapes. Use the Blipmode feature to keep track of the points you select so you don’t lose track of the beginning of the point selections.
Using the Object option of the Area command, you can also select circles and polylines for area calculations. Using this option in conjunction with another AutoCAD utility called Boundary, you can quickly get the area of a bounded spac( Recall from the discussion on hatch patterns in Chapter 6 that a region polyline is drawn when you use the Hatch function; Boundary works similarly. Where Hatch generates a hatch pattern that conforms to the outline of a boundary, Boundary generates a polyline outline without adding the hatch. The following steps show you how to use it.
1. Set the current layer to Floor
2. Turn off the Door and Fixture layers. Also make sure the Ceiling layer is turned on. You want the boundary to follow the interior wall outline, so you need to turn off any objects that will affect the outline, such as the door and kitchen.
3. Choose Draw >Boundary, or type bo.J. The Boundary Creation dialog box appears. Notice that it is actually the Boundary Hatch dialog box with several of the options dimmed.
4.Click the Pick Points button. The Boundary Creation dialog box closes
5. At the Se1ect internal poi nt: prompt, click in the interior of the unit plan. The outline of the interior is highlighted
6. Press .J. Boundary draws an outline of the floor area using a polyline. Since the current layer is Floor, the boundary is drawn on the Floor layer and given the default cyan color of the layer.
7. Choose Tools> Inquiry> Area again, or type Area.J at the command prompt. Then enter O.J for the Object option.
8. Click the boundary; when it is highlighted, press .J. Again you get the following message:
The Boundary command creates a polyline that conforms to the boundary of an area. This feature, combined with the ability of the Area command to find the area of a polyline, makes short work of area calculations. As you saw in step 3, Boundary uses the same dialog box as Boundary Hatch. See Chapter 6 for the options available in the Boundary Hatch dialog box
Finding the Area of Complex Shapes
The Boundary command works fine as long as the area does not contain islands that you do not want included in the area calculation. An island is a closed area within a larger area within which you are attempting to hatch or create a boundary. In the case of the Flange part, the islands are the two circles at the lower end of the part.
For areas that do contain islands, you must enlist the aid of the other Area command options: Object, Add, and Subtract. Using Add and Subtract, you can maintain a running total of several separate areas being calculated. This gives you flexibility in finding areas of complex shapes.
The exercise in this section guides you through the use of these options. First, you’ll look at how you can keep a running tally of areas. For this exercise, you will use a flange shape that contains circles. This shape is composed of simple arcs, lines, and circles.
1. Exit the Unit file and open the file named Fl ange. dwg from the companion CD-ROM (see Figure 14.3). Don’t bother to save’ changes in the Unit file.
3. In the Boundary Dialog box, click Pick Points.
4. Click in the interior of the flange shape. Notice that the entire shape is highlighted, including the circle islands.
You now have a polyline outline of the shape. As you saw in the previous exercise, the polyline aids you in quickly obtaining the area. Now let’s continue by using the Area command’s Add and Subtract options.
1. Choose Tools> Inquiry> Area.
2. Type A.J to enter the Add mode, and then type O.J to select an object.
3. Click the outline of the flange. You see the following message:
Area – 33.8496, Perimeter – 30.8496 Total area – 33.8496
4. Press .J to exit the Add mode.
5. Type S.J to enter the Subtract mode, and then type O.J to select an object.
6. Click one of the circles. You see the following message:
Area – 0.6070, Perimeter – 2.7618
Total area – 33.2426
This shows you the area and perimeter of the selected object and shows a running count of the total area of the flange outline minus the circle.
7. Click the other circle. You see the following message:
Area – 0.6070, Perimeter – 2.7618
Total area – 32.6356
Again, you see a listing of the area and perimeter of the selected object along with a running count of the total area, which now shows a value of 32.6456. This last value is the true area of the flange.
8. .Press .J twice to exit the Area command.
In the exercise, you first selected the main object outline and then subtracted the island objects. You don’t have to follow this order; you can start by subtracting areas to get negative area values, and then add other areas to come up with a total. You can also alternate between Add and Subtract modes, in case you forget to add or subtract areas.
You may have noticed that the Area command prompt offered Speci fly first corner poi nt or [Object/Add/Subtract]: as the default option for both the Add and Subtract modes. Instead of using the Object option to pick the circles, you could have started selecting points to indicate a rectangular area.as you did in the first exercise.
It is important to remember that whenever you press .J while selecting points for an area calculation, AutoCAD automatically connects the first and last points and returns the calculated area. If you are in the Add or Subtract mode, you can then continue to select points, but the additional areas are calculated from the next.point you pick.
As you can see from these exercises, it is simpler to first outline an area with a polyline, wherever possible, and then use the Object option to add and subtract area values of polylines.
In this example, you obtained the area of a mechanical object. However, the same process works for any type of area you want to calculate. It can be the area of a piece of property en a topographical map, or the area of a floor plan. For example, -you can use the Object option to find an irregular area like the one shown in Figure 14.4,as long as it is a polyline.
Recording Area Data in a Drawing File
Once you find the area of an object, you’ll often need to record it somewhere. You can write it down in a project logbook, but this is easy to overlook. A more dependable way to store area information is to use attributes
Consider the following example: In a building project, you can create a block that contains attributes for the room number, room area, and the date when the room area was last taken. You might make the area and date attributes invisible, so only the room number appears. This block can then be inserted into every room. Once you find the area, you can easily add it to your block attribute with the Date command. In fact, such a block could be used with any drawing in which you wished to store area data. See Chapter 10 for more on attributes.