paulnorthrop / r2stl

Visualizing Data using a 3D Printer

r2stl

R package for visualizing data using a 3D printer

The r2stl function generates STL files. The command is:

r2stl(x, y, z, filename = '3d-R-object.stl', object.name = 'r2stl-object', 
      z.expand = FALSE, min.height = 0.008, show.persp = FALSE, 
      strict.stl = FALSE)

• x, y and z should be vectors of numbers, exactly as with R’s normal persp() plot. x and y represent a flat grid and z represents heights above this grid.

• filename is pretty obvious, I hope.

• object.name The STL file format requires the object that is being described to have a name specified inside the file. It’s unlikely anybody will ever see this, so there’s probably no point changing it from the default.

• z.expand By default, r2stl() normalizes each axis so it runs from 0 to 1 (this is an attempt to give you an object that is agnostic with regard to how large it will eventually be printed). Normally, the code then rescales the z axis back down so its proportions relative to x and y are what they were originally. If, for some reason, you want your 3D plot to touch all six faces of the imaginary cube that surrounds it, set this parameter to TRUE.

• min.height Your printed model would fall apart if some parts of it had z values of zero, as this would mean zero material is laid down in those parts of the plot. This parameter therefore provides a minimum height for the printed material. The default of 0.008 ensures that, when printed, no part of your object is thinner than around 0.5 mm, assuming that it is printed inside a 60 mm x 60 mm x 60 mm cube. Recall that the z axis gets scaled from 0 to 1. If you are printing a 60mm-tall object then a z-value of 1 represents 60mm. The formula is min.height = min.mm / overall.mm, so if we want a minimum printed thickness of 0.5mm and the overall height of your object will be 60mm, 0.5/60 = 0.008, which is the default. If you want the same minimum printed thickness of 0.5mm but want to print your object to 100mm, this parameter would be set to 0.5/100 = 0.005.

• show.persp Do you want to see a persp() plot of this object on your screen as the STL is being generated? Default is FALSE.

• strict.stl To make files smaller, this code cheats and simply describes the entire rectangular base of your object as two huge triangles. This seems to work fine for printing, but isn’t strictly proper STL format. Set this to TRUE if you want the base of your object described as a large number of triangles and don’t mind larger files.

To view and test your STL files before you print them, you can use various programs. I have had good experiences with the free, open-source Meshlab, which even has iPhone and Android versions so you can let people interact with your data even when you’re in the pub. Even if all you ever do is show people your 3D plots using Meshlab, I believe r2stl() still offers a useful service, as it makes viewing data far more interactive than static persp() plots. To actually get your hands on a printer, you might try your local school - apparently lots of schools have got rapid prototypers these days.