The SKETCH Command - Drawing Freehand in AutoCAD®

William Forty
William Forty

The SKETCH command is one of those little known commands, but it really is a great command when you have the opportunity for some artistic license in your AutoCAD® drawings. You know when you have an irregular line to draw that represents existing ground level, or some other arbitrary uneven surface? For this kind of thing, it's a great command to use. SKETCH allows you to draw geometry, freehand, in AutoCAD®. You simple click a start point, move the mouse in any direction, and the path your mouse follows will be drawn into AutoCAD®. You'll probably end up thinking you're in MS Paint, and I defy anyone to not scribble all over the screen when testing it out... !

Normal Usage

To begin the command, input SKETCH into the command line. You will be prompted for a start point, or [Type/Increment/toLerance]. If you want to just get stuck in, pick a point, do your scribble (heh), and then pick your final point. This will terminate that line, but the command will continue. You can then pick another point and repeat the process. If you prefer, you can actually click and drag to draw one sketch, which does make it somewhat easier to draw one sketch after another. To complete the command, press spacebar or enter or whatever method you usually use to complete a command. It should be noted that if you exit the command at this point (i.e. press escape), your lines will be deleted. This one trips me up quite often, because this is different to how the PLINE command works for example.

Command Options

After invoking the SKETCH command you are prompted for a point or [Type/Increment/toLerance]. These settings are very useful for ensuring the SKETCH command behaves in the way that we want.

Pressing T for the type option allows you to change what is created with your sketch. By default, this is set to draw lines, which frankly speaking I think is just stupid. If you want to fill up your drawing with tiny little individual lines then this is the perfect option for you... I tend to use polylines personally, as I like to keep my geometry logically grouped depending on what they are. So if it represents existing ground level for example, that's one logical entity, therefore it should be one actual entity in AutoCAD®. The other option for the type is to draw splines. I have personally not used this one much (as I'm not a fan of splines in general), but it's there if you want to use it.

Pressing I for the increment option allows you to specify a minimum length of a segment in your sketch. This is really useful where you want a certain level of coarseness in your sketch, which I often like to see. It is also great for reducing the total number of segments you actually produce with this command.

Finally, pressing L for the tolerance option refers only to splined sketches - it controls how closely a spline follows the path drawn.

System Variables

The SKPOLY system variable is where your setting for the type is actually saved. This system variable is saved in the drawing, which can be somewhat annoying if you'd prefer it was always set to polyline by default. But there is of course a work around as always.

As with all drawing-saved system variables such as this, you can edit acaddoc.lsp so that each time you open a drawing, your system variables are set automatically. Input the following into your acaddoc.lsp file, found in your support directory:

(setvar "SKPOLY" 1)

This will ensure that the SKETCH command will be set up to drawing polylines in all drawings.

The SKETCHINC and SKTOLERANCE system variables do the same for the increment and tolerance options respectively. You can of course edit the lisp code above for those two system variables too, should you need to.

Final Notes

As you can imagine, the SKETCH command can potentially add a lot of geometry to your drawing. Be mindful of how much information you're putting in, and how much is actually required. If you're just drawing an indicative line for example, it hardly needs to be drawn with the increment set to 0.0000001... and doing so will add significant bloat to your drawing. I tend to ensure that there is a slight pause between each point when drawing the line - that way I am actually thinking about the points I'm adding to the line, which means there can't be (much) more than required.

Hope this helps you all, and happy doodling!


P.s. for all you newcomers, please subscribe below!


neil jones
2011-10-06 09:44:50

SKETCH is a great tool for digitising contours but requires a very steady hand when using a mouse - pen tablet is arguably a better input device??

2011-10-08 07:23:01

Yes perhaps!

Panos Tzortzis
2012-07-02 06:53:59

I use the sketch command but instead of a PLINE I end up with a sum of lines... any suggestions so that the final result is a PLINE?

2012-08-08 18:41:18

You'll want the T option for Type - it was covered in the tutorial :-)