An excellent portrait of Grace Kelly

I’m really excited about StippleGen.  And, if you like drawing, robots, or drawing robots I think you’re going to be really excited about it too.  StippleGen is a new free open source program released by our friends Evil-Mad-Scientist-Laboratories.  If you’ve ever purchased or coveted an EggBot, you definitely know who they are.¹

For most CNC machines (such as a MakerBot Unicorn, EggBot, or DrawBot) a traveling salesman / single line art drawing is easiest produce.  Single line drawings are faster than drawings comprised of more than one line, since the drawing robots don’t need to spend time lifting up the pen.  However, if you’re going to require a pen-lift for a drawing, you might as well do it with style – such as with stipples.

Definitely check out EMSL’s blog post announcing StippleGen for more information about this cool program.  It can be used to create an SVG file showing a TSP-style path, a stippled image, and apparently a combination of the two.

1. I cannot believe I didn’t go for the egg puns here… [↩]

R. Maker TSP Single Line Drawing

A recent commentor to this blog, Mr T, aske, “How come TSP routes are not used as infill pattern in the slicer?”

I thought this was an interesting question and that you, dear reader, might be interested in my response.  An infill pattern for a 3D model slicer is dependent upon the external structural features of an object.  All the slicers I’m aware of provide a uniform interior, so the infill pattern ends up being a similarly uniform pattern.  Setting aside the mathematical differentiations between a 3D model slicer and a TSP solver, a they are very very different animals.  Let’s look at a PNG of the PBM (“Portable Bit Map”) file:

R. Maker - Portable Bit Map file

Let’s suppose, for a moment, we think of a TSP drawing as a single thin slice of a 3D model. ¹  When printing a 3D object, we don’t generally care about the pattern used to fill the inside of the object. ²  Once completed, we should never see the interior.  But, with a TSP drawing we’re getting a LOT of information about the density of points in one spot versus another spot.  Unlike a 3D object, where we don’t really care about the interior fill of a given slice, the interior of a TSP is where all the cool stuff happens.  As the TSP solver figures out a reasonably efficient route to hit all of the points, it will naturally create a tighter path where points are closer together and looser paths where the points are farther apart.

And, as for the title of the post…  that’s really a reference to the distinction between a 3D point cloud which can be used to create a 3D object and a 2D point “puddle” used to create a TSP drawing.

1. I know they’re not analogous, but bear with me [↩]
2. I suppose there might be some structural advantages to one type of fill versus another, but usually this just won’t matter. [↩]

TSP crossing

The question behind the “Traveling Salesman Problem” is basically, what’s the most efficient path through a large number of points? ¹  There are probably many important applications of this difficult mathematical problem, but the most interesting for me is line art.  If you’ve been following the progress of the MakerBot Unicorn or Egg-Bot projects, you’ve already seen some incredible examples of “TSP” line art.

Untitled by mifga

This thing brought to you by

Untitled by mifga

This thing brought to you by

Untitled by mifga

This thing brought to you by

The current process for converting a picture to TSP line art is pretty involved.  From the excellent TSP line art tutorial over at Evil Mad Scientist labs, the process involves converting the image to greyscale, converting it into a stippled image, putting the points through a TSP solver such as the Concorde TSP solver package to create the TSP line art from the stippled image and end up with an SVG file.  At that point you could probably use Schmarty’s Inkscape GCode extension. ²³

I would love to see this process become simplified.  I suspect the best method for doing so might lie in the creation of a GIMP⁴ plugin.  GIMP already has the mechanisms for many of the above steps.  A GIMP plugin could probably automate the “grayscale -> stippled image -> point puddle” process.⁵⁶  Once that was done, the resulting “point puddle” would still need to be fed through the TSP solver.  However, I suspect this might be able to be done by having GIMP call the Concorde TSP solver.  This would take it from “point puddle -> TSP solver -> SVG file” which could then be turned into GCode using the above Inkscape extension.

Besides my belief that there just isn’t enough TSP line art in the world, there are a bunch of reasons I’d love to see this plugin pop into existence.   The top three reasons being the Unicorn, the Egg-Bot, the CNC Etch-a-Sketch.    After that, I’d have to say – TSP line art renderings of photographs and old master works of art.  I would love to see a web cam hooked up to a Unicorn for instant TSP line art photobooth style sticky note generation!

1. Photo courtesy of robotson [↩]
2. Basically, image -> gray image -> point puddle -> TSP solver -> printable SVG path [↩]
3. I say point puddle since it’s not a 3D point cloud.  Just a 2D … puddle of points. [↩]
4. My favorite open source image manipulation/editing software [↩]
5. See note above last for explanation of “point puddle.” [↩]
6. “Point puddle” you heard it here first! [↩]