[raxxorrax]

I assume one is active while the other is not. With two cameras you have the option of stereoscopic analysis where you have to match pixels of two cameras looking on the scene from a different angle. That uses significant cpu-time though, difficult for real time applications. Results vary because the matching isn't trivial and the difference in angle in smartphone cameras is very low.

If you have a projector, you can do more. I believe Apple uses a flash, which has a low resolution, but is perhaps less cpu-intensive and less error prone, although it has a lower resolution. That would be a real Lidar, which is an active measurement. Of course combining that with sensible stereoscopy nets better results.

[salicideblock]

All ToF systems are active.

ToF stands for "time of flight". It works exactly by measuring how long the signal takes to go from camera to object and back [1]

Stereoscopic cameras are another type of 3R camera, they are not ToF and they are not active.

Each has pros and cons.

[1] https://en.m.wikipedia.org/wiki/Time-of-flight_camera