TrueDepth Sensor Depth Measurement: Direct or Perpendicular?

I'm working on an app that use the TrueDepth sensor, and I have a question about how exactly the depth values are measured. I've been looking at the AVDepthData class documentation, but I couldn't find a clear answer to my specific question.

My question is: Does the TrueDepth sensor measure the direct distance from the object to the sensor, or the perpendicular distance from the object to the plane of the sensor?

TrueDepth Sensor Depth Measurement: Direct or Perpendicular?
 
 
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