[jrootabega]

So it's your position in space (3 numbers), your orientation (another 3 number vector), except instead of 6 numbers it can be reduced to 4? Stargate was wrong?

[naavis]

Encoding your whole orientation would require 3 numbers. You are restricted only to the horizon, so one number is enough.

[numerobis]

Orientation is only two numbers, since a unit vector does the job? So, three numbers in total?

[p0nce]

That's why it doesn't encode free orientation.