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Heavy & Highway GNSS & Total Stations Basics

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Presentation on theme: "Heavy & Highway GNSS & Total Stations Basics"— Presentation transcript:

1 Heavy & Highway GNSS & Total Stations Basics

2 Global Navigation Satellite System
What is GNSS? Global Navigation Satellite System used by receivers to determine location anywhere on earth Satellite Systems include GPS (USA) GLONASS (Russia) Galileo (Europe, currently not operational)

3 Three 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! Precision GNSS for Heavy Highway 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

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

5 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 THE ROVER (S) ARE RELATIVE TO BASE POSITION

6 How Does GNSS Work The base and rovers track or receive the same satellite signals AT THE SAME TIME. The base station sends its 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 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

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

8 What is a Modular GNSS 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

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

10 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

11 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

12 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 Total Stations require more accurate control Total Stations get less accurate over distance Talk about difference between x20 and x30 What kind of accuracy vs GPS? TS requires better control TS get less accurate over distance

13 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 0.01ft / 3mm 0.1ft / 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

14 How Does a Total Station Work?
Measures angles and distances By measuring known points, a TS calculates it´s position relative to 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

15 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)

16 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

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

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

19 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 Use a heavy duty tripod with sturdy top plate Do not use aluminum

20 Questions?


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