gps & total station basics. what is gnss? global navigation satellite system (gnss) –used by...
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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!