When you're creating a rectangular array, it's easier than you think to confuse columns and rows when you're asked to specify their distance. Columns are vertical, and the icon illustrates that in the dialog box. Keep in mind that the distance between rows and columns is the distance from a point on one item to the same point on the next item.

A rectangular array can be created at any angle by selecting the Angle Of Array option in the Array dialog box, even if you don't know the angle. Suppose you want to array the shape on the left in Figure 1.5 to form the shape on the right.

In the example, both the angle and the size of the object are randomly assigned. In other words, you don't know the exact size or angle, and you can't estimate because you want the result to have no gaps or overlaps of the objects as they're arrayed. You can approach this situation using two methods, one of which works with either the command-line version or the dialog-box version of ARRAY.

Figure 1.5. Precision array at an angle

Geometry with a repeated angular pattern is often found in mechanical applications and sometimes in architectural and civil applications. To create polar arrays efficiently, avoid repeating the same set of editing operations for each feature arrayed. Start by identifying a repeatable pattern on the object. Draw the whole pattern once, and then array the result, rather than arraying each of the components of the pattern separately. Be careful. It's easy to select an extra entity when you use the Polar option of ARRAY. The result looks fine, but you have entities on top of each other. The image in Figure 1.7 illustrates an efficient technique for using polar arrays by identifying and creating the repeatable pattern before arraying anything. The repeatable pattern is shown on the left, and the result of doing a single array of that pattern is on the right. The alternative involves multiple construction lines and six times more editing for each feature.

PEDIT

After using ARRAY to create geometry from lines and arcs, you can determine whether the result is perfect using the PEDIT command. If you use PEDIT to join lines into a closed object, they can only be joined if they connect perfectly at all intersections. Your geometry is perfect if the first option of PEDIT, Close, changes to Open after you've joined all your lines. If the geometry isn't perfect (and sometimes that can't be helped), you can still join the segments into a single object using the MPEDIT command.

Figure 1.7. Arraying the repeatable pattern

REDUCE CONSTRUCTION LINES

Try to use as few construction lines as possible when creating geometry. The more lines you use to locate points or edges, the more chances that you may confuse one or more for actual lines, or leave lines behind that are on top of each other. I've seen this lead to subtle, but often important, errors.

The often-related problem of lines on top of lines may seem like no big deal, because everything plots fine; but if you have a short line segment on top of a longer one, it's possible to snap to the wrong endpoint or midpoint without noticing it and create inaccurate geometry. The OVERKILL Express Tool can help fix this problem.

MPEDIT was once an Express Tool. It allows you to set a fuzz factor for combining lines, arcs, or plines into a single object. To use it, run MPEDIT, and then select all the objects you want to join. You're prompted for a fuzz factor. Enter a number that is greater than your likely error, and MPEDIT cleans up the mess. (I hope you're working on someone else's mess, because you should be able to avoid sloppy drawing if you use the accuracy tools available in AutoCAD.)

There are also some alternatives to PEDIT for finding areas, even if your closed geometry has overlapping lines. Using the BOUNDARY command, you can select a point and have a closed pline or a region created automatically. This works great for interior spaces, but you can use this command even in situations that are less obvious. For example, when you have overlapping construction lines and want to create a clean set of double lines (a floor plan, for example), use the technique shown in Figure 1.8: Enclose the entire group of lines with a circle, and select a point inside the circle but outside the lines.

Figure 1.8. Using BOUNDARY for quick shapes

For many drawings, you know the length of each line and the angles between lines. However, you probably don't know the absolute angle of each line in the X-Y plane (angle from 0°–East). There is a strategy for doing drawings of this kind; it involves recognizing that supplemental angles form a straight line (180°). It also involves using the often-overlooked Relative option of AutoCAD's polar tracking feature.

Figure 1.9. New shapes from regions

Figure 1.10. Polar tracking settings

Figure 1.11. Supplemental angles with relative tracking

If you know that you need to start drawing an object a specific distance from an existing object, use the From osnap and the @ symbol. For example, if you want to start a rectangle 10 units over and 45 units up from an existing endpoint, do the following:

Figure 1.12. Hover over an osnap to acquire a point

If you have POLAR, OSNAP, and OTRACK on, and the Extension osnap is set as a running osnap, you can pause over any running osnap, acquire a temporary tracking vector, and use it with direct-distance entry to quickly draw an object relative to another object. See Figure 1.12.

Even better, play with the Temporary Track Point osnap until you understand how to use it, because it allows you to chase points all over the screen by typing TT prior to acquiring a tracking point. The new tracking point is temporary until you actually select it. I use TT a lot, and if you haven't figured it out, it's worth trying.

Another common shape involves tangent arcs. The quickest way to create an inside (concave) arc between two circles is to use the FILLET command with the proper radius set. However, an outside (convex) arc can't be drawn between two circles or arcs using FILLET. You must use the CIRCLE command with the TTR option and trim out the unwanted portion of the circle. The location of your cursor on the circles when you select tangent points determines whether a concave or a convex arc result. (See the Deferred Tangent tooltip in Figure 1.13.)

Figure 1.13. Circle TTR for tangent arcs

One overlooked feature of the FILLET command is its ability to quickly close two parallel lines with a tangent arc. Select both lines, and AutoCAD will calculate the size of an arc that it will use to join them on the end nearer your selection.

Most justification options are logical. Every line of text has four vertical locations for justification: Top, Middle, Baseline, Bottom, in that order. The Bottom is a line running through the lowest point on a lowercase letter with a descender (j, g, p, y). These locations are shown in Figure 1.14. The Justify options of DTEXT are [Align/Fit/Center/Middle/Right/TL/TC/TR/ML/MC/MR/BL/BC/BR]. The two-letter combinations match the locations: TL is Top Left, ML is Middle Left, and so on.

It's easier to work with circle, pline, or region entities when determining areas, particularly if you're trying to add or subtract areas to get a final total. This section will give you some advice about using other entities to create plines or regions so you can easily find their areas.

Figure 1.14. Understanding DTEXT justification options

ENTITY SELECTION

When you use the AREA command, it's easier to select objects than it is to pick points. To find the area of a large object minus the areas of several smaller objects, you can use the Add and Subtract options of the AREA command. Pay attention to the command prompts. Type AREA

Note

The alias for the AREA command is AA, which doesn't follow the normal pattern used for other commands. Why not? A (ARC) and AR (ARRAY) are already taken. RENDER (RR) is the only other alias with this format.

The DIST command gives you an accurate distance if you use object snaps to pick the points. It's also the quickest way to get an angle in the X-Y plane. Pick the points in the proper order, or the angle will be off by 180°. To get the angle between two lines, use DIMANGULAR (DAN). The lines don't have to exist; you can select three points with DIMANGULAR and get the angle between the segments defined by the points.

Both these commands give you information that varies by entity selected, including the arc length of an arc. PROPERTIES can be used to change the properties of multiple objects as well as individual objects. For example, you can change the height of all text in the drawing without changing the locations.

Figure 1.15. Using regions to calculate a complex area

TIME gives you the total time during which a drawing has been open for editing. You can also use it as a running timer by selecting the Reset option before beginning something new. Use this timer as you try to develop more drawing speed. Pick one object, and draw it several times using different strategies. The TIME command can tell you if you're getting any faster. I've also used the TIME function to see if one computer in an office really is slower than another, or if it's just the perception of a frustrated user. See Chapter 7, "AutoCAD Scripts" for a benchmark system to test computers with no user input.

This command displays the Properties palette of selected entities. If more than one object is selected, the properties common to all are displayed. Properties of similar objects can be changed simultaneously.

Let's walk through an example. Let's say you have a drawing that has a lot of text. Every text entity must stay in its current location, but the height must change for all. At one time, that was a difficult problem, but not any more. Open the Properties palette, and click the Quick Select icon (the button with the funnel icon in the upper-right corner). Select text in the window, and all the text entities are highlighted (but not the MText entities). Now, change the text height in the Properties palette; the height of all the text changes. You can change any of the properties of the entire group. You could do the same for all the circles in a drawing or within a selection set, and change their diameters.

You can use either of these commands to clean up sharp corners or extend two unconnected lines into sharp corners by setting their values to 0. As of AutoCAD 2006, you have the following option: Hold down the Shift key while selecting the second line to create a sharp corner.

If you're having trouble snapping to what you think is an intersection between two lines, use FILLLET with a radius of 0, select the two lines, and then try again. If that works, you don't have to take the time to zoom into the intersection to see if there's a gap.

These commands behave similarly. The difference is that DIVIDE results in an entity divided into a specified number of segments, all the same length. MEASURE divides the entity into segments of a given length, with one shorter segment (usually) at the end. Entities aren't actually segmented; instead, a point is placed at each division.

It's also possible with either DIVIDE or MEASURE to have a block inserted at each division instead of a point, which is a useful and often overlooked feature. You can quickly approximate a complex linetype, for example, by placing any block along a line, pline, or spline object. This works well for placing arrows on an egress map (see Figure 1.17).

Figure 1.17. Using MEASURE to place blocks

You can use EXPLODE with the following entities: blocks, hatches, mlines, plines, solid objects, and blocks of text created with the MTEXT command. Any blocks can be exploded except those placed using the MINSERT command. For that reason, MINSERT should not be used unless you want a block that can't be exploded. When you use EXPLODE, be careful not to select more objects than you want.

This command has always had two options: Distance and Through. The Through option allows you to offset an object through a selected point, even if the object isn't long enough to actually pass through the point.

AutoCAD 2006 added some nice features to OFFSET. You can offset an object onto the current layer. You can also elect to erase the source object after using offset. That sounds like it would just become the MOVE command, which it would, except that a multiple option was also added that lets you continue picking through points or offsetting the same distance multiple times.

People use UNDO sometimes when they really should use the OOPS command. OOPS can be used at any time to restore all the entities erased as a single selection set the last time the ERASE command was used. It doesn't have to be issued immediately after the entities are erased. More often than I should, I erase objects that are in the way of a delicate editing operation, and then I use OOPS to get them back after I'm done editing. I don't recommend this approach, but I do it.

The remarkably useful and often overlooked option of ROTATE is Reference. You can use the Reference option by entering any angle at the keyboard or by picking two points on the screen. You then type the angle to which you want the selected points to align.

Instead of typing the new angle, you can also make one more selection. It becomes the second point on a new angle, using the first point selected as a reference for a base point.

SCALE also has a Reference option that's similar to ROTATE's but that may be even more useful. I use it frequently to resize an image using a feature on the image that I know the size of—this can be a photograph of landscape, nautical charts, a mechanical part, or anything else that's not to scale when inserted. In the example in Figure 1.18, a National Oceanic and Atmospheric Administration (NOAA) nautical chart has been referenced as an image. Scaling it using the Reference options involves the following steps:

Figure 1.18. Using the Reference option of the SCALE command

The UNDO command displays the following options at the command prompt: Auto/Control/BEgin/End/Mark/Back<Number>:

Auto Auto requires an additional specification of On or Off. When Auto is on, any operation taken from the menu, no matter how complicated, is treated as a single command, reversible by a single U command.

Back Back takes the drawing back to the state it was in when the most recent mark was entered. If you don't enter a mark, the drawing goes back to the beginning of the editing session. AutoCAD automatically places marks when some commands are used, but normally you must place them yourself. You can place multiple marks and UNDO each.

Control Control limits the UNDO operation or disables it completely. It offers the following options:

BEgin and End BEgin and End cause a group of commands to be treated as a single command for the purposes of U and UNDO. A group, once ended, is always treated as a single, indivisible operation.

Mark Mark makes a special mark in the undo information, to which you can later back up with the Back option. If you're about to go off on a design tangent, you may want to set a mark with UNDO so you can return to that point quickly if the tangent doesn't work out.

Number Number (default is 1) specifies the number of preceding operations to be undone. UNDO 1 is the equivalent of the U command. When you use a different value, 20 for example, 20 operations are undone at once. Typing REDO restores all 20. Using this option allows you to search back through the drawing history (only during the current editing session) for a specific point in the design process by typing in large values. Don't forget to save the drawing before doing this.

This interesting command can be used to change the length of a line, polyline, or an arc. It's the only way to quickly create an arc with a specific arc length. To do that, create the arc, and use the Total option of LENGTHEN to change the total length to whatever you want.

LENGTHEN's options include the following:

DElta DElta allows you to add a specific amount to the length of an existing line or arc, or to add a specific angle to the existing included angle of an arc.

Percent Percent allows a specific percentage increase in the length of a line or pline or the included angle of an arc.

Total Total lets you set a new overall length for a line, a pline, or an arc.

DYnamic DYnamic allows you to change the length of a line (but not a pline) or the included angle of an arc by picking a new point and watching it change.

<Select object> <Select object> gives the existing length or angle of a line or arc.

In my experience, most users don't understand rotated dimensions. All linear dimensions are either aligned or rotated, but most are rotated. Vertical dimensions are rotated to 90, horizontal dimensions to 0. Because those angles are built in, users often overlook the possibility of rotating dimensions to other angles and frequently attempt to use an aligned dimension where a rotated one is needed. Figure 1.19 shows the problem with trying to use DIMALIGN.

Figure 1.19. Rotated dimensions versus aligned

To place a rotated linear dimension between two points at any angle, use DIMLINEAR and select the Rotated option. You can specify a rotation angle directly or by picking any two points that are at the desired angle of rotation.

Ordinate dimensions are used to set dimensions as coordinates in the X and Y axes. Ordinate dimensioning is used most often in mechanical drawing, but it's increasingly being used in architectural and other fields as well. When I draw a structure that I'll be building myself, I always dimension it with ordinate dimensions rather than with continuous dimensions, which is the traditional method. That way, I can hook a tape to one end of a sole or top plate and mark all locations of openings from a fixed point.

Although there's a DIMORD command, the quickest way to place ordinate dimensions is with QDIM. Select the points you wish to dimension, and then select a new datumPoint for 0,0. Now you can choose the Ordinate option, select your objects, and place all ordinate dimensions with one pick. If you have objects with different base points, use the datumPoint option again.

If you don't use QDIM, you must first establish a new base point by setting a UCS with its origin at the 0,0 location on the part you're dimensioning. Use the UCS command, select the Origin option, and then select the 0,0 point on the part. If UCSICON is ON and set to ORigin, the icon representing the UCS moves to the new origin point. AutoCAD automatically places the correct distance in the X or Y direction, depending on which direction you move from the dimension origin point you pick.

These dimension values are associated with defpoints, not the objects themselves, if DIMASSOC is 1 or 2. This association is maintained for the UCS that was current when the dimension was placed. Stretching the defpoints of the dimensions results in the values being updated correctly, even if a new UCS has been set since the dimension was created.

AutoCAD 2007 includes 79 dimension variables. The easiest way to change them is using the Dimension Style Manager dialog box. You don't have to know all of them, but there are two you should understand.

The APERTURE variable allows you to control how close you must be to an object, measured in pixels, when using an osnap. It can also be set using the Drafting tab of the OPTIONS dialog box. If you're having trouble isolating an object in a cluttered area, try setting this value to a smaller size—I prefer a setting of 3. If you're having trouble picking an object because you have to get too close to it, try a larger size.

PICKBOX is similar, but it controls the size of the box that shows up when you're asked to select an object for editing. You can also control it visually using the Drafting tab of the OPTIONS dialog box. I like a setting of 3 for this one, as well.

In the past, it was common to set this variable to the reciprocal of the intended plot scale. If you use layouts properly, however, you shouldn't use LTSCALE to control the appearance of linetypes, because it's global and affects all lines in a drawing. Instead, set LTSCALE, CELTSCALE, and PSLTSCALE all to 1 and ignore the appearance of your linetypes until you set up a layout. With PSLTSCALE set to 1, your linetypes scale automatically in Paper Space, so they plot the same regardless of the ZOOM factor used for the viewport in which they appear.

If some of your entities have linetypes that aren't scaled to your liking, instead of changing that with LTSCALE, use PROPERTIES to make changes to each individual object in a viewport in the layout.

A number of things about layers can give you problems. Here are a few of them:

It surprises me how few people use this feature. It allows you to save a specific view on the screen, or as defined by a window, so that you can immediately call it up later. This approach reduces the number of regenerations necessary. It's particularly useful in 3D drawings, and some people use this feature for plotting a specific view. If you haven't ever tried saving named views, try it. You'll be surprised at how useful it can be, particularly when using AutoCAD sheet sets.

This function is essential in 3D drawing and often useful in 2D drawing as well. It allows you to divide your screen in Model Space into multiple views. In 3D, this permits you to create geometry while seeing it in a front, top, right side, and iso view. You can then have a different UCS in each viewport and get a different view of the same geometry.

To create a set of standard views for 3D, select the 3D option in the Viewports dialog box. Don't forget to use the SAVE option to save a configuration you've set up. Don't confuse saving viewports with saving views. You can restore saved views within any Model Space viewport and then save the viewport configuration. Now, whenever the viewport configuration is restored, it will contain the views exactly as they appeared when the viewport was saved.

Roll the middle wheel away from you to zoom in or toward you to zoom out. The increment is controlled by the variable ZOOMFACTOR—the larger the value, the bigger the jump when using the wheel. If you hold down the scroll wheel, you can pan. If you hold down the wheel while holding the Ctrl key, you get a joystick pan—not that useful, but kind of fun.

AutoCAD 2006 added a view transition feature that smoothly changes magnification or location when zooming or panning. This replaced the abrupt transitions of prior releases. Some people love it, and some people don't. VTENABLE allows you to turn it off for everything, for panning only, for zooming only, for scripts only, or for some combination. The VTFTS and VTDURATION variables control the threshold and speed of the transition. Personally, I turn it off to speed things up a little.

The PURGE command is used to selectively remove unused layers, blocks, styles, linetypes, and dimstyles. You can do this by name or using the Purge All option (ALL at the command line). If your drawing has nested block definitions (blocks used to create other blocks), you can select Purge Nested Items starting with AutoCAD 2002. In earlier releases, use the PURGE command as many times as there are levels of nesting in your block definitions in order to ensure that you're purging everything. The Purge dialog box also allows you to select individual entities individually or in groups. To select a consecutive list of entities, select the beginning item, hold down the Shift key, and select the last item in the group. The Ctrl key lets you add or remove items from the selection set. See Figure 1.20.

Many people still use the WBLOCK command as a quick and complete PURGE command. That requires you to use the Entire Drawing option in the dialog box for WBLOCK, or the * option at the command line.

This is a great way to rename blocks, dimension styles, layers, linetypes, materials, table styles, text styles, UCSs, views, and viewports. You can use wildcards, allowing you to quickly change all names created when binding external references (if you used the Bind option for binding, which I recommend you do, and not the Insert option). For example, if you bind an externally referenced drawing named STP123.dwg to a host drawing, the block definitions have names like STP123$0$BLOCK1, STP123$0$BLOCK2, STP123$0$BLOCK3, STP123$0$BLOCK4, and STP123$0$BLOCK5. If you want them to have the names BLOCK1 and so on, type STP123$0$* in the Old Name field and * in the Rename To field, as shown in Figure 1.21.

Figure 1.20. Purge All

You can elect to open part of a drawing to reduce regeneration time on large drawings. Highlight a file and then select the Open button in the lower-right corner of the Select File dialog box that's used to open an existing drawing. The Partial Open dialog box that's displayed can be used to select only those layers or views with which you want to work. Once you've used PARTIALOPEN to open part of a drawing, you can use the PARTIALLOAD command (found on the File pull-down menu) to select different layers. There is a design flaw in PARTIALLOAD: You must reselect all layers each time you do a partial load. The layers you first selected aren't remembered. This issue wasn't addressed in AutoCAD 2007, but I'm hoping it will be fixed someday.

This command is indispensable, and it has finally evolved from an Express Tool into a native command in AutoCAD 2007. It lets you change objects between Paper Space and Model Space while retaining their relative scales. This makes it possible to place text or dimensions wherever it's convenient while working and then move them to their permanent home later. If you ever decide you placed something in the wrong space, you need this command.

LAYWALK This tool allows you to walk though the objects on various layers to give you a visual clue as to what you've placed where. It's valuable when you're dealing with someone else's disaster drawing. The objects on each layer are isolated temporarily while you cycle through the layers. Like CHSPACE, LAYWALK is now a native command in AutoCAD 2007.

TXT2MTXT TXT2MTXT is used to combine individual lines of text into a single MTEXT object. It doesn't format the final result as individual lines, so you almost always need to do some editing; but if you want to group text from older drawings into a single object, it's nice.

FLATTEN I've recommended this command to a lot of people in companies that do civil design. They call me because they're having trouble with a drawing from someone else. Object snapping to endpoints produces odd results because, it turns out, the elements aren't all at the same elevation. FLATTEN quickly and thoroughly places every object at an elevation of zero.

MKSHP and MKLTYPE These commands give you the ability to create complex linetypes: those containing text or shapes. This process requires that a shape be created first (MKSHP) and then the linetype (MKLTYPE).

LAYMERGE I often advise new users and companies to use as many layers as they may need so they'll have control over the related elements of a drawing. Sometimes this results in too many layers, which is always easier to fix than too few. When you do have too many layers, this command lets you put them together into one. This is another of the Express Tools that have become actual commands.

DIMEX and DIMIN These are related commands that allow you to export dimension styles and then import them into a different drawing. You can do this through AutoCAD DesignCenter or by inserting a drawing that contains the dimension style, but these Express Tools make it a little easier.

DIMREASSOC This is a nice tool. It permits you to individually or globally update dimensions that have been overridden by the operator. In other words, the value in the dimension and the actual size of the object don't match. My favorite application of this command is to find any dimensions that were overridden. I have overridden a dimension purposely on rare occasions when I had an imminent deadline and had to plot something out immediately. With DIMREASSOC, I can find those places and go back and fix the geometry.

You can also change the overwritten dimensions automatically, which may cause even more problems if you don't notice what got updated. The problem is that the value is probably overridden because the geometry is wrong.

SYSVDLG The System Variables editor is a wonderful tool. It gives you a concise list of each system variable, tells you where its value is stored, and describes what it does. The best thing is that you can save the settings to an SVF file and restore them if you ever have to. If you do any training using computers that aren't your own, take this file with you; it will reduce the number of surprises you may encounter.

Figure 1.22. Overkill dialog box

OVERKILL This command gets rid of overlapping lines, line segments that connect in what appears to be a single object, and duplicate objects on top of other objects. It can clean up a mess of a drawing in a hurry; see Figure 1.22.