What informs the location of the virtual spindle in the GUI

What informs the GUI as to where the virtual spindle is placed in reference to the bounding box? (What else, other than using the center of the min and max joint values for each joint)

 

Most probably from the ini file and the respective values for each axis/joint and in correlation to kinematics used.
That is just off the top of my very tired head, so might want to wait for someone to confirm or deny that.
And i would not call it "virtual", it is an actual representation of the machine, but i am sure it can be argued both ways.

You don't need to worry about the position as its really automatic but if you do want to read the position the pins axis.L.pos-cmd is the commanded position for each axis.