Camera calibration and coordinates for skeleton joints

Dear community,

I am completely new to Nuitrack and attempt a C++ SDK integration with my app. What I want to do is to trace the coordinates of skeleton joints with Intel RealSense D435i. I looked through the examples and as far as I understood, there are 2 types of coordinates: real and proj. However, some things resulted incomprehensible - here they are:

  1. How is the rotation matrix formed?
  2. Is there any possibility to get the axis-aligned skeleton joints coordinates, say, I’m in a room and I want its (0; 0; 0) to be the middle of the room and my head coordinate (if I’m in the middle of the room) output as (0; 0; 1.7) or all I can get is the distance between my head and the sensor? Does Nuitrack automatically “adjust to the scene” somehow or should I go for Intel RealSense SDK to make own calibration functions?

Would you be so kind as to clarify the above-mentioned? Thanks in advance!
Best regards,