Simplifying GPS Position ReferencingOn Day to Day Surveys

By: Keith Belsham, Technical Sales RepresentativeButler Survey Equipment 1-800-667-5944

- 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 (http://www.geod.nrcan.gc.ca/online_data_e.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