GPS Heading/Yaw (aka Moving Baseline)

PX4 Guide for RTK

PX4 Firmware GPS Heading with Dual u-blox F9P is supported in the both DroneCAN and UART version. The DroneCAN version requires a different firmware and can be found in the guide below.

RTK GPS Heading with Dual u-blox F9P | PX4 User Guide

RTK GPS | PX4 User Guide

Holybro H-RTK ZED-F9P RTK Rover (DroneCAN variant) | PX4 Guide (main)

Ardupilot Wiki for RTK

GPS for Yaw (aka Moving Baseline) — Copter documentation

GPS/Compass (landing page) — Copter documentation