Technical notes

Explanation of Kinect Fusion reconstruction volume settings

There are two important settings:

• Voxel per meter: the higher the better, we use 640 or 512. The reconstructed mesh vertices have spacing 1000 / 640 = 1.6 mm or 1000 / 512 = 2 mm. That does not mean that the precision is 2 mm. The precision is of the Kinect Fusion is unclear.
• Volume voxel resolution: the name is misleading, this decides how large the scan can be. For example for 640 voxels per meter and 640 x 640 resolution the scan will be 1 m x 1 m. For 512 voxels per meter and 640 x 512 resolution, the scan will be 1.25 m x 1 m. I wouldn't recommend lower resolution.

Based on that, the distance between points depends on Voxel per meter (available choices are 640, 512 and lower), not on the distance of the scanner. The distance of the scanner influences the precision, but that's difficult to quantify.

####Kinect v2 field of view is 70 x 60 degrees which means that to scan 1 m horizontally we get theoretically the minimum Kinect height as (not tested experimentally):

tan(55 degrees * pi / 180) * 0.5 m = 0.71 m

What are the rules for the sandbox?

What is the maximum size of a sandbox?

1.25 x 1.25 m with 512 voxels per meter or better 1 x 1 m with 640 voxels per meter.

What is the sensitivity of Kinect at a given height above sand?

Technically the same as horizontally (see above), practically around 5 mm and better (based on experience, not precise measurements).

What are rules for volume and weight?

This is important if the unit is to be transportable. Depends on materials for models, but both sand and MDF are heavy.

What are the rules for scaling?

Proposed Rule 1.

The minimum x,y interaction at the sand is 1.0 cm X 1.0 cm. This means model scale must be a convenient function of 1 cm2.

Proposed Rule 2.

The minimum vertical dimension in real world is 5.0 mm * scale (e.g. 1000 if scale is 1:1000) / vertical exaggeration.

Example: Sonoma Study Site

Cell size should be at least 1.0 ha.

Sand interaction 1.0 cm. (Note: if cell size was 10 ha to fit more onto the table, a 10 ha intervention would always be square. If cells are 1 ha, a 10 ha intervention could be a chain of 10 cells). Raise projector/kinect until 1 cell = 1 cm2.

Maximum width 140 cm.

Thus, maximum viewable extent would be 100m X 140 = 1,400 m or 1.4 km. Thus, max height is 1.2 km.