RTK-GPS with APM3.1 or Omnibus F7

I’m new here and I have a question.
I have a Hexacopter with a APM 3.1 and a GPS Module on Top.
I have the problem that I need a precision GPS that have a accuracy about ~1m.
At the moment I have a accuracy about ca 3-5m.
In the Missionplaner are the option RTL/GPS Inject , so if have a Telemetry connection to the drone and a GPS attached so the apm will count the real position or I need a RTK Kit?
I have also an Omnibus F7 flightcontroler with more power.
I hope you can help me.