SparkFun GPS-RTK-SMA Kit - Includes GPS breakout- Magnetic Mount Antenna- Ground Plate & USB-C Cable - u-Blox ZED-F9P & RTK- High precision accuracy in milimeters- Both Rover & Base station operations: Amazon.com:
accuracy - Low-cost centimeter-level accurate satellite positioning (GNSS/ GPS) - Geographic Information Systems Stack Exchange
High-Accuracy GPS System Tracking Module - China GPS Module, GPS Positioing Module | Made-in-China.com