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BO is for Boundary

I know what you’re thinking but in AutoCAD, BO is anything but stinky! BO is the command alias to launch the BOUNDARY command, which was introduced in AutoCAD Release 13… or was it R12? Anyway, it’s a valuable (and little known) byproduct of the BHATCH (boundary hatch) command and I think you’ll recognize the similarities!

The BOUNDARY command displays the Boundary Creation dialog box. You can also use the dash “-“ to access the command line version (-BOUNDARY). Choose Pick Points to pick a point in the drawing. AutoCAD automatically determines the boundary using the same underlying technology that is uses when you pick a point to create a hatch. Notice that you can even specify island detection, similar to creating a hatch. 

Instead of creating a hatch, however, the BOUNDARY command creates a polyline. Why would you want to create a polyline? Many reasons! In my previous post, for example, I wanted to determine the area of a floor plan. Unfortunately, picking all the boundary points with the AREA command was cumbersome and inaccurate. Using the BOUNDARY command, I can quickly create a polyline boundary and then use the AREA command to select the polyline! Finding the enclosed area of the floorplan using the AREA command went from 40 point picks to a single object selection! And, not only does it save time, but it’s more accurate because it accounts for the curve and small jogs in the wall.

Various controls in the Boundary Creation dialog box offer additional flexibility for creating boundaries. For example, instead of creating a polyline boundary, you can set the Object type to Region. A region looks similar to a polyline but has mass properties and other “solid” properties. Maybe I’ll discuss regions in a future post.

In order for AutoCAD to determine the boundary surrounding the selected point, it analyzes all the objects in the current display. If you try to create a boundary or hatch with an excessive amount of objects displayed, AutoCAD warns you and asks if you want to proceed.

In many cases, you can simply zoom in to display only the area in which you are interested. For example, to create the boundary of the apartment in this floor plan, I could zoom into the highlighted area and AutoCAD would have no problem analyzing those objects, quickly. 

As an alternate, you can manually limit the objects that AutoCAD analyzes during the boundary detection by specifying a boundary set in the Boundary Creation dialog box.

AA is for AREA

In this post, I’ll continue my review of the AutoCAD alphabet with the AREA command. You can launch the AREA command using the AA command alias or from various locations in the AutoCAD user interface, including the Inquiry panel of the Tools ribbon panel. 

The AREA command enables you to find the enclosed area by picking boundary points or selecting closed objects. For example, to find the area of the stairwell in the following image, launch the AREA command and then pick the 4 corners defined by the magenta segments. If the magenta segments are defined by a single polyline, you can save picks by using the Object option and selecting the polyline.

The default behavior of the AREA command enables you to continue picking points to define a single area. In the following image, for example, you could start with point 1 and continue picking points all the way around the floor plan to point 40 to determine the area. I said you *could*, I didn’t say you should! I’ll use this example to explain the Add and Subtract options as well as to point out a few tips and inaccuracies. 

When you begin picking points, pay attention to your first pick because in AutoCAD 2009 and earlier (unless you have the AutoCAD 2009 Subscription Bonus Pack 1), there are no visual indicators to remind you of where you started. Also, it’s up to you to determine how accurate you need to be. In this example, notice the jog in the wall between points 2 and 3 as well as 6 and 7. You could account for these jogs with additional picks or decide the difference is insignificant (as I did in this example) and save a few picks. Also notice the curve between points 7 and 8. When picking points with the AREA command, AutoCAD assumes linear segments. So, in this example, it will calculate the area as if there were a straight line between points 7 and 8.

The AREA command includes two other options (in addition to the Object) option. The Add option enables you to determine the cumulative value of multiple areas by picking multiple closed objects, multiple sets of points, or a combination of both. The Subtract option behaves the same way but it sums the area as a negative value. You can switch between the Add and Subtract options as you continue to select objects or pick sets of boundary points.

The AREA command works great for selecting objects or picking a few boundary points. But, as you can see from this example, picking many boundary points can be time-consuming and prone to error. Curved areas provide an additional challenge.

In my next post, I’ll show you how you can simplify the process of determining the area by first using the BOUNDARY command.

ALIGN vs 3DALIGN

In my last post, I described the ALIGN command and how you can use it to move and rotate objects in 3D space. In this post I’ll compare it with the 3DALIGN command (3AL command alias).
The purpose of ALIGN and 3DALIGN is the same but the procedure differs. When you use the ALIGN command, you pick 3 sets of 2 points (source 1, destination 1; source 2, destination 2; source 3, destination 3). When you use the 3DALIGN command, you pick all the source points first and then pick the destination points. The following image illustrates the difference in pick points resulting in the same transformation.

The 3DALIGN command provides the added benefit of enabling you to copy the objects as you align them.  Simply choose the Copy option before picking the source points. The selected object remains in its original location while a copy is automatically aligned according to your pick points.

ALIGN in 3D

In a previous post, I described how you can use the ALIGN command (AL alias) to move, rotate, and even scale geometry in a 2D drawing. With a few additional picks, ALIGN is a powerful tool for performing similar move and rotate operations in 3D space.

To align an object in 3D space, you’ll need to provide three sets of points between the source and destination. The following image illustrates the process of aligning the 3D wedge with the 3D box by picking the specified points. After picking all six points in the order indicated by the first image, AutoCAD automatically moves the wedge to ensure point 1 is coincident with point 2. Then it rotates the wedge so that edge 1-3 is aligned with edge 2-4. Finally, it rotates the cube again to ensure edge 1-5 aligns with edge 2-6.

 

Scenes from Shanghai

Last week I had the pleasure of presenting AutoCAD at our office in Shanghai, China. It was a long flight (and I only stayed 3 nights) but well worth it. The room was packed with enthusiastic partners and the translation/interpretation obstacles didn’t prevent them from remaining engaged and asking great questions!

AL is for… ALIGN!

In my previous post I mentioned that the “A” command alias launches the ever popular ARC command, but there are many less popular yet equally useful commands in the AutoCAD alphabet! One of my favorite “A” commands is ALIGN. The ALIGN command has been in AutoCAD for as long as I can remember and it would get my vote as “the most underappreciated command”. ALIGN is often considered a 3D command but it can be just as useful for 2D drawing.

Use the ALIGN command to align a selected object with another object in the drawing. You can launch the ALIGN command by typing the “AL” command alias. You’re prompted to provide 2 or 3 sets of points depending if you’re aligning in 2D or 3D space. The first pair of points (source and destination) determines the move point. The second pair of points (source and destination) determines the rotation. If you’re using this tool to align objects in a 2D drawing, press Enter to continue through the prompt for a third set of points without picking. The following image illustrates the results when aligning various sets of points on the selected triangle (source) with points on the rectangle (destination). In each case notice that point 1 (on the triangle) moves to point 2 (on the rectangle). The triangle then rotates so that point 3 aligns with point 4.

In addition to moving and rotating, the ALIGN command provides an option to scale the selected object during the same operation. After picking two pairs of source/destination points and continuing through the third set of points, you can enter Yes to the last prompt “Scale objects based on alignment points?” AutoCAD automatically moves, rotates, and scales the selected objects making the source points coincident with the destination points.

 

The ABC’s of AutoCAD Command Aliases

If you’re relatively new to AutoCAD or if you tend to access commands from the user interface, you may not be aware of AutoCAD’s powerful command alias functionality. A command alias is an abbreviation that you enter at the command line to launch a command or action macro. AutoCAD includes many default command aliases. For example, you can type “A” to launch the ARC command, B to launch the BLOCK command, and C to launch the CIRCLE command. You can easily modify the default command aliases or create new ones to meet your needs.

Command aliases are defined in the AutoCAD Program Parameters (ACAD.PGP) file, which is installed under Documents and Settings for the local user. In the following image, you can see where it’s located on my system for each version of AutoCAD.

  
 
In AutoCAD 2009 you can easily access the PGP file from the Menu Browser under Tools>Customize>Edit Program Parameters (acad.pgp).

Selecting this option automatically opens the acad.pgp file in the text editor. Scroll down to view the default command aliases, which are listed in alphabetical order. Before making changes, it’s a good idea to save a copy of the acad.pgp file in case you want to restore it. To modify or add command aliases, follow the same syntax. For example, if I created an action macro (only available in AutoCAD 2009) called MYNEWCOMMAND, I could create the following command alias in the acad.pgp file:

After making changes, save the file. If AutoCAD was running when you made the changes, you can use the REINIT command to reload the updated version of the PGP file. The updated version is automatically loaded the next time you launch AutoCAD.