By default, Vic-3D uses the "Best Plane Fit" to assign a coordinate system. This option calculates a transform into the best fit plane of the surface.

Sometimes it is preferred to leave the data in camera coordinates. By deselecting the Auto Plane Fit option, the data will be in camera coordinates.

This is how Vic-3D assigns the camera coordinates system:

1. The x-axis is the baseline between the center of the two camera sensors.

2. The origin is the center point between the two camera sensors, along that baseline/X-axis.

3. The Z-axis is defined as perpendicular to that X-axis, starting at the origin.

4. One more constraint is required to define the Z-axis, or it could just spin around the X-axis at the origin point. The average plane between the two sensor planes is used to determine that one degree of freedom that is missing to determine the Z-axis (without this constraint, the z-axis would just spin around the x-axis).

5. The Y-axis is normal to X-axis and Z-axis, so that the three axes form a coordinate system with all axes normal to each other.

## Nick Lovaas

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