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

Is it accurate? - YES!!

Standalone GPS: 5–10 m

Trimble dGPS: 0.1–3 m

RTK:1–2 cm

How Does it Work?

Base Station

Rover (s):- Machine- Range Pole- Site Vehicle

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

What do we Need? Precision GPS uses 2 receivers

– Base Receiver– Rover Receiver

In addition you need– GPS Antennas– Radios– Radio Antennas

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

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

Tying it all together…

GPS Site Calibration– 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

GPSCoordinates NEE

What can go wrong?

Bad Base Location - – 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

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

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

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

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.

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

TS Arbitrary Setup

CP1 CP2

BAD SETUP!Resection angle <30 degrees

TS Arbitrary Setup

CP1

CP2

GOOD SETUP!Resection angle 30 – 150 degrees

What can go wrong?

TS out of calibration– 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 Robotic350m 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

Questions / Comments?Thank You!