Simplifying GPS Position Referencing On Day to Day Surveys By: Keith Belsham, Technical Sales Representative Butler Survey Equipment

- Types of Professional GPS Used - Working in a Local Coordinate System with Real-Time GPS Receivers - Geo-referencing a Survey - Common Errors with GPS

 GNSS Rovers with reference station connection over the internet via cellular modem

 Base & Rover with Radio Connection

 Dual or Single Frequency Static GPS Receiver

 Want to work in a local ground based coordinate system (5000,5000,100)  Same principle as a resection or Helmert’s or Least Square adjustment with a total station, with line of sight being to satellites  By measuring local points with the GPS you can shift, rotate & scale to match your coordinates

RESECTION GPS LOCALIZATION

 Most systems will store a GPS position in the background that you can later reference to  Keep in mind what you are referencing your GPS to (ie what corrections is your Rover receiving)  May need to use a service like the Federal Governments Precise Point Positioning to verify base positions in remote areas ( php) php

 No correction data being received & accuracy warnings are ignored  GPS base position isn’t corrected  When localizing, the residuals aren’t checked

 Modern GPS systems are designed to make the transition from total station surveying to GPS seamless  We now have more satellites making GPS work better than ever ◦ Glonass constellation from Russia ◦ Compass constellation coming from China ◦ Galileo constellation coming from Europe ◦ Extra frequency coming on US GPS satellites