How does precision GPS work ( DGNSS , RTK , SBAS , PPP ) ?

This is a synthesized basic explanation of how precision GPS methods work:
-Differential GNSS (DGNSS)
-Real Time Kinematics (RTK)
-Satellite Based Augmentation System (SBAS)
-Precision Point Positionning (PPP)

Sources and more information can be found here:
-European Space Agency (ESA) navipedia (www.navipedia.net)
-Novatel, www.novatel.com

Music by Kevin MacLeod, www.incompetech.com