3D Scanning as Dense Microphone Array

Sound is the displacement of matter over time.

A microphone detects sound at a single point, either via direct physical coupling, or using optical methods (as with Laser microphones).

3D scanning can also detect displacement of reflective matter over time. Using a 3D scanning setup with a very large angle between the camera and projector, very minor displacement variations can be detected. Using a high framerate camera, this displacement can be measured at audio frequencies. Every pixel then corresponds to a virtual laser microphone: instead of the usual microphone at a point, a fringe analysis microphone is comprised of N points as determined by the camera resolution.

3D Video Scanner for Cheap

Here's a way you might try making a 3D video scanner for the cost of a webcam:

• Weccam with VSYNC broken out
• Bright LED or LED array
• Ambient illumination

Mount the LED at approximately the same location as the camera lens. Turn the LED on for alternating VSYNC pulses. The 3D decoding process is as follows: the light intensity at every point can be modeled using the equation i = r * (a + s), where:

• i is the captured intensity at that pixel
• r is the reflectivity at that point
• a is the ambient illumination at that point
• s is the illumination due to the LED source at that point

Sampling with the LED on and off yields two equations:

1. i_on = r * (a + s)
2. i_off = r * (a + 0)

And s corresponds to distance proportionally to an inverse square law:

• s(d) = f / d^2

Where f is a scaling factor that relates s to a. Solving for d yields:

• i_off = r * a
• i_off / a = r
• i_on = (i_off / a) * (a + (f / d^2))
• ((a * i_on) / i_off) - a = f / d^2
• a * ((i_on / i_off) - 1) = f / d^2
• d = sqrt(f / (a * ((i_on / i_off) - 1)))

The values for a and f can be approximated by hand, or calibrated based on a reference plane. a must be truly uniform, but if the LED is approximately at the same location as the lens then f can be calibrated for automatically to account for its non-point-source qualities.

The disadvantages here are primarily the assumption about ambient illumination, and the simplified material model. The advantages would be the cost and utter simplicity. The fact that it relies on a non-coded point source for illumination means you can work with infrared just as easily as visible light. Furthermore, it actually relies on ambient illumination while many other systems try to minimize it.

Projection Mapping with a 3D Projector

Projection mapping is the art of working with non planar projection surfaces.

APPARATI EFFIMERI Tetragram for Enlargment from Apparati Effimeri on Vimeo.

I'd like to explore this idea with a 3D projector. Normally, 3D projection happens on a plane, which allows for a rectilinear 3D space. If you project onto anything but a plane, the 3D space will be distorted. But if you account for these distortions in advance (for example, with a 3D scan of the scene to be projected on) then you can augment the scene with an overlaid 3D form.

While installations like the video above rely on the observer's large focal distance and visual tricks (like drop shadows) for implying a depth offset, with a 3D projector and shutter glasses you can create genuine depth offsets.

Flash Mob 3D Scanning

1. Pick a local monument.
2. Organize a flash mob via Craigslist.
3. Instruct everyone to take photos of the monument.
4. Everyone then uploads and tags their photos.
5. These photos are then uploaded to Photosynth for 3D reconstruction.

As a variant, people can just record video and walk around. This relies on the videos being high resolution.