GPS & Total Station Basics

What is GNSS? Global Navigation Satellite System (GNSS) used by receivers to determine their location anywhere on earth Satellite Systems Include US GPS GLONASS Galileo (Currently not Operational)

GPS Receivers Three general types of GPS Receivers Navigation/Recreational (Autonomous) 10’-50’ (3m-15m)H, V? Location GPS (Differential GPS - dGPS) 0.5’-10’ (0.1m-3m) H, 2-3x more in V Precision GPS (Real-Time Kinematic -RTK) 0.1’ (30mm) or better, 3D! We focus on Precise GPS for Heavy & Highway applications Depending on the application, there are three (3) different types or “grades” of GPS receivers: Navigation or Recreational: These receivers are your typical “fishing/hunting” type receivers

Is it accurate? - YES!! Trimble dGPS: 0.1–3 m RTK:1–2 cm Explain corrections Standalone GPS: 5–10 m

How Does it Work? Rover (s): - Machine Range Pole Site Vehicle Base Station - The Base and Rover (s) receivers track or receive the same satellite signals AT THE SAME TIME. - The Base Station sends it’s position & observations via radio to the Rover. - Base station data and rover data are processed together in rover receiver to produce 3D vector - Base station position + vector = rover position - Result: ALL POSITIONS @ THE ROVER (S) ARE RELATIVE TO BASE POSITION

How Does it Work (explained) The Base and Rover (s) receivers track or receive the same satellite signals AT THE SAME TIME. The Base Station sends it’s position & observations via radio to the Rover. Base station data and rover data are processed together in rover receiver to produce 3D vector Base station position + vector = rover position Result: ALL POSITIONS @ THE ROVER (S) ARE RELATIVE TO BASE POSITION How dGPS works: Base Station located on a known point Receiver computes difference between the SV measurement and the expected measurement and broadcasts the correction to a rover receiver via radio How do we have an expected measurement? Base Station Location Known SV Location Known Distance to SV therefore known

What do we Need? Precision GPS uses 2 receivers In addition you need Base Receiver Rover Receiver In addition you need GPS Antennas Radios Radio Antennas Explain GNSS

What is a Modular GPS Receiver? Separation of components Allows mix and match of GPS & Radio antennas Optimized use Permanent, semi permanent, vehicle or marine vessel setups Security Accessible, secure, and environmentally protected Describe need for GPS ant, receiver, and radio at both base and rover before modular / smart

What is a Smart GPS Antenna? Fully integrated GPS receiver unit Optimized for pole mounted rover solution A rapid setup, high mobility base station Receiver incorporates: GPS receiver GPS antenna Radio and radio antenna Removable battery Bluetooth for cable free operation Quick, easy setup and tear down for small sites and rapid mobilization

NEE Tying it all together… GPS Site Calibration GPS Coordinates What is a site calibration? Defines the relationship between GPS Coordinates and local northing, easting, and elevation Why is a site calibration required? Allows multiple GPS-based rover systems to work in your local site coordinate system What is needed for site calibration Onsite control based on local coordinates GPS Coordinates NEE

What can go wrong? Bad Base Location - Multipath Base-Rover Radio Link Bad base observations, bad rover corrections Setup GPS base station antenna with 360° view of the sky. If limited try to set up with clear visibility to the equator. Multipath Avoid sources of multipath (deflection of the GPS signal) Base-Rover Radio Link Radio “Line-of-sight” Other Radio Interference PDOP Position Dilution Of Precision (SV Geometry) Human Error Bad base position or calibration Change south to accommodate both north / south hemisphere GNSS applies to multipath, pdop

SPS Total Stations Total Stations are used for the highest accuracy work Heavily used on highways, railways, bridge, and tunnel projects Many contractors need both total stations and GPS When a contractor buys a total station they should strongly consider Trimble SPS universal instruments SPSx20 SPSx30 Talk about difference between x20 and x30 What kind of accuracy vs GPS? TS requires better control TS get less accurate over distance

How does a TS work? A total station measures angles and distances relative to its position By measuring known control points, a TS can calculate its position relative to the known points and coordinate system. Known points should be high order control In robotic mode, the TS measures the position of the rover target and reports the position information via radio link to the rover SCS900/GCS900 compares the position to design information calculating Cut/Fill

Total Station Setup Minimum of 2 control points Should be very accurate control Optimally you want adequate number of control points for multiple TS Setups Avoid setting additional control if possible Remember TS get less accurate over distance Optical limitations Earth curvature TS Setup errors compounded Should be high order control. What’s the purpose of using TS otherwise, unless environmental.

Total Station Setup 2 primary setup types Known Control Point – TS on one known point and backsight to other Arbitrary Location – TS setup up unknown and backsight to two know control points Should be high order control. What’s the purpose of using TS otherwise, unless environmental.

TS Setup – Known Control Point Pros Only need a backsight to one known point to establish the position Quicker setup as you only have to visit one other point Cons Restricted as to where to place the instrument Location may be harder to set up the legs Must measure instrument height Should always have another point not used in the setup for checking the setup. Must measure instrument height

TS Setup – Arbitrary Location Pros Freedom of where to place the instrument Easy to set up the legs No instrument height measurement Cons Must visit two known points to establish the position – Takes extra time Should always have another point not used in the setup for checking the setup. This method is used most often in construction This is easiest way (use this most often)

TS Arbitrary Setup CP1 CP2 BAD SETUP! Resection angle <30 degrees

GOOD SETUP! TS Arbitrary Setup Resection angle 30 – 150 degrees CP1

What can go wrong? TS out of calibration Bad setup Bad TS Location Perform all user capable calibrations on regular basis Bad setup HA out of tolerance We are chasing high accuracy. Do not accept a setup if out of tolerance, even if the point deviations are acceptable Bad TS Location Setup TS with clear visibility to the rover and limited potential obstructions Do not place TS close to vibratory compacter operation Weak tripod You need a heavy duty tripod with sturdy top plate Do not use aluminum

Total Station vs GPS Total Station GPS Ruggedness Less Rugged (moving parts & user maintenance) Water and dust resistant Rugged (no moving parts) Water & Dust proof Range 700m Robotic 350m Grade Control Typical 1-3miles / 2-5km Accuracy .01ft / 3mm .1ft / 30mm Setup Quick daily setup and use Initial infrastructure requirement Line of Sight Line of sight to instrument Line of sight to sky Ruggedness of solution (TS not fully water proof, can’t drop it, and has maintenance – moving parts) Put numbers in the accuracy boxes Initial setup vs daily setup

Questions / Comments? Thank You!