Meant to be Seen

I'm not going to have time to attempt this, so I thought I'd share:

You could do positional tracking using the speckle pattern from diffuse laser light.

Sketch of prototype:

A couple of lasers (of the handheld low power type ~1-5mw), with diffusers pointing inwards into a space.
A couple of webcams mounted to the Rift, with their lenses removed.
The lasers will produce a speckle effect on the CCDs as the coherent light interferes with itself.
You can then use SIFT or other to grab the features from the CCDs and insert into an SFM (Structure from motion) pipeline.

This would be an adaptation of this:
http://specklesense.media.mit.edu/

Naively using SFM on the input is likely to transform in place rotations of the CCD to orbits within the pose estimation space, but I'm sure you can adjust for this.

I couldn't say how well this would work in practise.

Don't know too much about this, but it sounds interesting.

This sounds similar to the way an optical mouse works with a farther focus. I wonder how well this works on irregular surfaces like a populated room. The demos used clean flat surfaces so its hard to tell.

After reading the papers on the site, it doesn't look like it's much good for absolute position sensing. I think a higher resolution and higher response version of kinect is the way to go.

I've given this a quick go. It's not going to work for distances more than a meter or so, shame.

Incidently, this could be the way the leap motion works...

The leap uses two custom lens assemblies (on two cameras of course) that are quoted to give it a 140 degree FOV, so I'm fairly certain this is not how the leap works.