a short one, say i have a plane with a normal (0,1,0) and a distance( D ) of -256. is that plane then locatec 256 Above the origin of beneath it?
P
Depends how you’ve defined your Y axis 
Kev
the y axis is the upward/downward ‘vector’ 
OK, but which way have you defined as being up, its all down to base matrix.
Traditionally negative values go up, but then its all down to what you’ve defined in your virtual world.
Kev