January 9, 2007 Justin Chin

SketchUp Rigging Hack

So this weekend I came up with an idea on how to make a “posing rig” in SketchUp. Crazy, I know. If you listen closely you can almost hear the collective of 3D artist everywhere are cringing.

What can I say, if SketchUp wasn’t already married to Google I’d marry her.

I’m only going to do this for the vehicles in my book, characters won’t be rigged this way so don’t go and freak out on me…yet.

This is the idea –

  • The posing rig is comprised of simple geometric shapes that frame the vehicle’s important features, i.e. wheels and movable parts.
  • With careful arrangement in the outliner I can affect the high poly geo nested underneath the posing rig in the outline hierarchy.
  • In addition by assigning the posing rig geometry to a specific layer I can turn it off and on at will. Or even make it semi transparent .

The reasoning behind doing this:

  • I can manipulate the scene without having to render the heavy load of the full poly models.
  • I can quickly target the item I want to manipulate and rotate them with within a prescribed axis.

Here is an example of the simple rig, and the high poly geo side by side:

JUMPrig.jpg  JUMP3x.jpg
(Click on the image and click on the “next” and “prev” buttons)

You can see that the geometry in the scene on the left would be much faster to work in then the scene on the right – and both exists in the same scene and file! I now I have a choice as to what to see on screen as well as how to manipulate it. 

The posing rig geo is made up of registration points, that allow for quick snapping of your tools. Here is an example of rotating the front wheel at it’s plane of rotation using the registration point:

ScreenTowRot.jpg  TowRig.jpg  TowModel.jpg

In the example screens above you can see that I selected the right wheel in the outliner, and focused the rotation tool on the registration mark at the top of the wheel. The shape of the simple geo is a little funky because the turning angle on the axle is slanted. So I modeled the simple geo to reflect that angle. The orange and beige registration marks allow me to quickly see my intended rotation points. 

It is important to note that the individual pieces of the posing rig’s geometry are not linked together like an animation rig in Maya or Max would be. The pieces are just arranged geometry in space. Their only association to each other is how they are “grouped” within the outliner’s hierarchy.

Here’s what the outliner looks like for the scene:


All of the individual pieces of the posing rig are given the “CN_” designation at the head of the name. These nodes represent the simple geometry rig. This allows me to use the filter to expose them in the outliner. Selecting them in the outliner automatically selects them in the scene.

I arranged the posing rig geo in a hierarchical way that allows me to move the chassis of the vehicle and thus move everything under it, i.e. wheels, doors, suspension etc. with it. For example the door on the Tow Rig is under; Tow_RIG>CN_ALL>CN_Body. Each door is at the same level under the CN_Body.

For those of you who are animators, you’d know that this rig is only good for forward animation (as opposed to Inverse Kinematics). Nothing new, and not the easiest way to animate, but it’ll do for my needs. I’m posing not animating. 

In SketchUp I associate the posing rig geo (not its group) with its own layer. This layer is designated with a, “//” and the name of the vehicle, like in this image:


I use the, “//” designation so the layer will sort to the top of the list window for quick access. Obviously, by checking the layer on or off I can can hide/show the rig in the scene. In SketchUp you can also create pages (a powerful camera/viewing tool) that will configure the scene to show the rig, or the full model. I toggle between the two to check the results of the rig poses.

Was that clear as mud?