Amazon.com: SparkFun GPS-RTK Dead Reckoning pHAT Compatible with Raspberry Pi-Concurrent Reception of GPS GLONASS Galileo BeiDou High Precision GPS - Receives L1C/A & L2C Bands Voltage:5V or 3.3V Logic:3.3V : Electronics
simpleRTK2B: the first multiband RTK shield based on ZED-F9P by Ardusimple — Kickstarter
Ardumower Sunray – www.wiki.ardumower.de
GPS-RTK Hookup Guide - learn.sparkfun.com
GSM GPRS GPS Module 3-In-1 Module Shield
GPS-RTK Hookup Guide - learn.sparkfun.com
GPS-RTK Hookup Guide - learn.sparkfun.com
GitHub - sparkfun/SparkFun_u-blox_GNSS_Arduino_Library: An Arduino library which allows you to communicate seamlessly with the full range of u-blox GNSS modules