[MightyMoe]

>1000mm vs <8mm

[john-hamilton]

I would say that RTK is a subset of DGNSS. As MightyMoe said, typically standard differential GNSS (WAAS, etc) is about 1 m accuracy. RTK is just a more rigorous and accurate form of DGNSS. 

[lee-d]

RTK is a form of differential GNSS, but typically when the term DGNSS is used that implies a differential code solution, whereas RTK is typically a fixed integer carrier phase solution. It’s possible, with a good receiver and antenna, to get DGNSS down to about 30cm horizontal and meter level vertical.