AutoCAD

The case of the missing Sketch command

1 Mar, 2000 By: Bill Fane


Captain LearnCurve and his beautiful wife had just driven back to Vancouver from Las Vegas. They welcomed the new millennium with 350,000 of their best friends in front of the Bellagio Hotel & Casino on the Strip, watching the tons of confetti snow down from the top of the Eiffel Tower replica at Paris, Las Vegas. Home again, they now played contentedly with their 6-month-old grand- daughter and contemplated the fact that she could end up living in three different centuries.

Suddenly the wailing voice of a distraught user upset their quiet home.
Woe is me! I want to freehand sketch in my AutoCAD drawing. An old-time user (she started a year ago) told me that it’s possible with the Sketch command, but I can’t find it in the menus or toolbars. Whatever shall I do?

“Hmmm,” the Captain mused to himself. “I wonder what happened to the Sketch command?”

Being the superb detective he is, the Captain immediately reached for the Help menu and searched through the index for the Sketch command.
A quick perusal through the resulting Help text revealed the fate of this command. The bottom line: the Sketch command is still usable, but after Release 13 it disappeared from the menu and toolbars. To invoke it, type Sketch at the Command prompt.

This case solved, the Captain went back to trying to teach Rebecca to say her first word. He was undecided—should it be “carburetor” or “electroluminescence?”

Excuse me, Captain, sir, but now that you have shown us how to start the Sketch command, I wonder if you might be so kind as to tell us how it works?

Whenever brand-new users see AutoCAD for the first time, they are suitably impressed by the speed and ease with which an experienced user can draw lines, circles, arcs, and so on. Use of ortho mode and object snaps for accuracy blow them away, but invariably an early question is, “Very nice, but can I do freehand sketching with it?”
The answer is “Yes, but. . . .”

Start to sketch
The Sketch command lets you sketch in freehand mode—like drawing freely with a pen or pencil. This lets you draw irregular shapes, such as a coastline on a map, or forge the manager’s initials in the Approved By section of the title block.

Sketch starts by asking for a Record increment and offers the default of 0.100 units. Before you reply, let’s review how the Sketch command works so you can better understand what this prompt is asking for and the implications of your response.

Sketch is a variant of the Line command. As such, it doesn’t repeatedly ask you to supply the “to point,” but rather supplies them automatically as you move the cursor. The Sketch command thus actually draws a series of short straight line segments.

The Record increment prompt asks you to supply a length for these segments. A smaller number draws smoother shapes in finer detail, but increases the number of lines and the size of the drawing file, regen, and redraw times. The reverse is true for larger increments.

How big an increment should you pick? An increment of 0.100 (the default) is a good place to start for full-size inch drawings. You also must allow for drawing scale, so 10 is probably a good value for 1:96 drawings, and so on.

In order to see how the command works, start with an increment of 0.500 units. This is coarse enough to let you see the action of the command.

Once you enter a Record increment, it prompts:

Sketch. Pen eXit Quit Record Erase Connect.
The first item serves simply to remind you that you are in the Sketch command. Pen refers to the virtual pen that creates the AutoCAD line entities. Your pointing device (mouse or tablet puck) moves the pen around on the screen. Initially, the pen is up so that movement of the pointing device moves the pen around on the screen, but no line segments are drawn.

When you type P or hit the pick button on your pointing device, the pen goes down and begins to create line segments as you move the pointing device. Do not press Enter after typing P, or the command terminates.

Typing the letter P again or hitting the pick button serves as a toggle to stop the line. Each operation reverses the pen status.

As you sketch, note that if ortho is on, all sketched line segments are perfectly horizontal or vertical. This defeats the intent of sketching.

Make sure snap mode is on so it has priority. Now, the ends of the sketched line segments always land on the snap points. Remember, if snap is on and the snap increment is much larger than the record increment, the intent of sketching is negated.

Object snaps and snap overrides still work while you sketch. Note how the sketched lines appear in green (or red if the current color is green), regardless of the current active color.

Sketched lines don’t actually become part of the drawing until you exit the Sketch command or until you specifically instruct AutoCAD to record them. While they are green (or red), they don’t really exist yet, and you can do limited editing before you accept them.

You must invoke each of the Sketch subcommands with a single keystroke, and they take effect immediately—don’t press Enter or space after them.

P (Pick). Toggles pen up and down.
E (Erase). Erases the end section of a sketched line set. It automatically lifts the pen. Move the cursor around and watch as the line segments between the cursor and the newest end of the sketched series disappear and reappear. When you type P or select the pick button, they disappear for good. Pressing E again cancels the erase.

C (Connect). Lets you connect to the newest end of the last line you created. After you erase part of a line set, you can then pick up and resume sketching from the end of the remaining segments. This subcommand is relevant only when the pen is up and when a current unrecorded (green or red) sketch is active.

When this option prompts you to Move to endpoint of line, move the cursor close to the newest end of the last sketched line. AutoCAD snaps to it and puts the pen down.

R (Record). This turns all the temporary line segments into real lines on the current layer. It leaves the pen up or down as it found it, and returns to sketching.

X, Space, or Enter (Exit). Records all lines and returns to the AutoCAD prompt (now you know why not to press <Space> or <Enter> after any of the Sketch subcommands).

Q, or Esc (Quit). Abandons all temporary lines and returns to the Command prompt.

All the sketching that you’ve done so far is freehand—as though you were drawing directly on the display screen. If you’re one of the very few people who still use digitizer tablets, you can tape down an existing paper image and trace over it.

A mouse is useless for tracing purposes because it provides relative motion information rather than absolute location, so you can’t calibrate it.

Now the but
There are two main problems with using the Sketch command.

  • If the record increment is very small, you can create tens of thousands of line segments in a matter of minutes.
  • Each little segment of a sketched line is a separate, independent line. Editing the general shape of a sketched profile is effectively impossible. Even trying to move, copy, or mirror it can be an interesting exercise.

Simple solutions
Fortunately, two solutions overcome Sketch’s shortcomings.
Before you use the Sketch command, use the SKPOLY system variable and set it to 1. Now the Sketch command creates single polylines (plines) instead of multiple independent lines. These are much easier to move, copy, mirror, and erase. Setting SKPOLY to 0 returns Sketch to the Line mode.

The most practical way to use the Sketch command is as the basis for another command.

Start by sketching your freehand or traced profile into a unique layer, then change to another layer that has a different color.

Now start the Pline command, put it in Arc mode, and draw a new polyline by picking suitable points along the sketched line.

In this manner, you can turn several hundred short line segments into a single smooth, flowing pline with relatively few vertices that closely approximates the sketched line. Finally, erase everything on the sketched layer.

Bingo! You now have a nice small drawing with freehand curves that are smoother and easier to edit than if they were left in their sketched state. You can change the profile by doing a Pedit to move a vertex, then curve Fit to smooth it up again.

And now for something completely different
Are you looking for a bargain when you travel? Here’s a tip: speeding tickets in Utah cost about half of what they do in Washington state.


AutoCAD Tips!

Lynn Allen

Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!
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