LT Unlimited

Convert Spline to Polyline

Splines can be useful objects in a drawing, but sometimes you need to edit them with tools that apply to polylines instead. AutoCAD LT 2010 includes a function to enable you to convert a spline into a polyline so you can edit away.

You can find this function in two places: the Edit Spline command and the Edit Polyline command. It doesn't matter which one you choose; Edit Polyline just adds an extra prompt at the beginning to confirm that you want to make the conversion.

So here's the original spline:

When I start the Convert function, I'm prompted for a precision. This number can be anywhere from 0 to 99, with a higher number generating more fit points. As you'll see, low numbers tend to work pretty well.

Here's the spline after being converted with a precision of 10:

Pretty close, right? But this polyline only consists of straight-line segments. You can get an even better fit with an even lower precision value if you choose to create a poyline consisting of arc segments instead. This is controlled by the PLINECONVERTMODE variable -- 0 means straight lines and 1 means arcs.

Here's the spline again, after being converted with PLINECONVERTMODE set to 1 and a precision of 2:

You'll probably want to play around with different combinations of precisions and conversion modes to see what will work best for your own splines.

P.S. I promise there are differences between the last two images and the first! I know it's hard to spot here, but I wanted to show how well the conversion works. Try converting a spline with PLINECONVERTMODE = 0 and a precision of 0 and you'll see the "least accurate" version.

Reverse Line Direction

Another of the tiny-yet-amazingly-helpful new commands in AutoCAD LT 2010 is Reverse. Available either as a stand-alone command (on the Modify panel of the Home tab) or as an option inside the Polyline Edit and Spline Edit commands, Reverse was added to help you control the display of linetypes that contain text or symbols.

For most linetypes (Hidden, Dashdot, etc.), it doesn't matter whether they go up or down, backwards or forwards -- they'll still look the same. For linetypes that contain text or symbols, though, the direction makes a big difference in readability. If objects with these linetypes are drawn left-to-right, the text comes in right-side up. But if they're drawn right-to-left, the text shows upside down.

In this screenshot, the "Gas" line is clearly upside down -- it would be much more readable if the text were right-side up.

No problem. Just start the Reverse command, select the line, and it gets flipped so that the text is readable.

Objects that can be reversed include lines, polylines, and splines. There's no "global" option -- you have to specify which objects to reverse -- but it sure beats swapping endpoints one object at a time!

Stretch Multiple

A recent improvement (introduced sometime after version 2004) to the STRETCH command means that you no longer need to get exactly what you meant to stretch with the first crossing window. It now accepts multiple window selections, so if you either miss the first time, or have objects in different areas that can’t be selected with a single window, you don’t have to start the command over again.

Quick Fillet

When prompted to select the first object, type “c” (for crossing) instead. Use the crossing window to select the two objects to fillet.

Move or Copy with Click-and-Drag

You can move or copy an item without an active command! Simply click on the object (so that the grips are displayed), then left-click-and-hold somewhere on the object (not on a grip). You can now move the object to a new location, or copy it by holding CTRL. Warning: This technique cannot use OSNAPS, so be careful when you use it.

The MULTIPLE Command

If you want to repeat a command over and over again, without having to hit Enter or right-click – there’s MULTIPLE. Simply type it at the command line and it will ask you for a command to repeat. It’ll keep going until you hit ESC – right-clicking and Enter won’t exit the “multiple” part of the command. MULTIPLE’s only limitation is that it doesn’t work with commands that use a dialog box.

Select Cutting Edges

When using the Trim or Extend commands, the first prompt is to “select cutting edges” (or “boundary edges” for Extend). Hitting ENTER turns everything in the drawing into a cutting/boundary edge, so you don’t have to do it manually.

Multiple Fillet/Chamfer

The fillet and chamfer commands now have a “multiple” option. After you start the command, but before you select the first object, hit “M”. You can then fillet/chamfer as many lines as you like before exiting the command.

For previous versions (at least up to 2004, maybe 2005), the "multiple" option is triggered by "U". Don't ask me why...

Move/Copy by Displacement

When moving or copying objects, you don’t always have to pick the second point. Instead, use the option. Here’s how it works:

1. Select your objects, then hit Enter.<\li>
2. Now – instead of picking a point on the screen, type in the displacement amounts (X,Y) and hit Enter. (In other words, if you want to move something 6 inches over and 3 up, type “6,3”.)
3. At the next prompt, Specify second point of displacement or : hit Enter.

Be careful though – if you pick a point on the screen at the first prompt and hit Enter at the second, (or if you just hit Enter twice) your objects could end up flying into space (they will be moved by the value of the first point’s coordinates, which could be large).

Fillet Parallel Lines

When using the FILLET command on two parallel lines, AutoCAD creates a half circle connecting the two ends. If the lines are different lengths, AutoCAD uses the first endpoint picked to determine the placement of the arc.