Increased accuracy for GPS, etc

• https://en.wikipedia.org/wiki/Real-time_kinematic_positioning — ~2 centimeters [amazon]   [aliexpress]   [ebay]
• https://en.wikipedia.org/wiki/Differential_GNSS — 1–3 centimeters
• https://en.wikipedia.org/wiki/Precise_Point_Positioning — a few centimeters
• https://en.wikipedia.org/wiki/GNSS_augmentation#Satellite-based_augmentation_system [prices]
• International GNSS Service [1] [2]
  • [app] GnssLogger App
  • [app] Geo++ RINEX Logger
  • [Windows app] GNSS Analysis app
• Multiple-GNSS