Getting the Value from
Guidance Systems, Light Bars, and GPS
Marvin Stone
Biosystems and Agricultural Engineering
GPS – How it works

Constellation of more than 24 satellites
– Known positions (at any time)
– Each continuously transmits time and position data
• Two frequencies (L1-1575.42MHz and L2-1227.6MHz)
– Each orbits twice per day

Ground receiver (Your GPS receiver)
– Calculates Position and Time
• Times signal and calculates distance to each satellite
received
• Triangulates Latitude and Longitude
• Calculates time
Components of a “GPS” system
GPS Assisted
Guidance System
GPS
Receiver /
Antenna
Electronic
Control
Unit
User
Interface
Light Bar
Components of a “GPS” system
GPS Assisted
Guidance System
with Mapping
GPS
Receiver /
Antenna
Electronic
Control
Unit
Data
Logger
User
Interface
Light Bar
Components of a “GPS” system
GPS Based Yield
Monitor
with Mapping
GPS
Receiver /
Antenna
Electronic
Control
Unit
User
Interface
Data
Logger
Mass flow
Meter
Chip Card
Components of a “GPS” system
GPS Based Yield
Variable Rate
Planter
GPS
Receiver /
Antenna
Electronic
Control
Unit
User
Interface
Data
Logger
Planter
Drive
Chip Card
Components of a “GPS” system
GPS Based
Automatic
Steering System
GPS
Receiver /
Antenna
Electronic
Control
Unit
User
Interface
Steering
Servo
Device
Components of an auto-steering system
Steering Servo Device
Wiring harness
User Interface
GPS Receiver and
Antenna
Electronic
Control
Unit
http://www.newholland.com/h4/products/products_series_detail.asp?Reg=NA&RL=ENNA&NavID=000001277003&series=000005423311
MidTech system configuration
Midwest Technologies IL
Differential GPS

Differential GPS is required for guidance
– Without differential corrections, precision is ± 100 ft.
– With corrections ±3 ft, ±4”, ±0.3”

Method:
– Nearby ground station at known position uses GPS to
determine errors in distance to satellites
– Errors are sent to roving GPS units

Issues
– Where do you get the correction signals?
•
•
•
•
Coast Guard
Omnistar
Deere
other
Differential GPS communications
pathways
PRN 2
PRN 12
PRN 8
PRN 18
Reference
Station
Differential Correction
Pathway
Roaming
GPS
Differential correction sources
Source
Cost
Terrestrial differential correction
USCG Beacon
Free
User provided
?
URL
users.erols.com/dlwilson/gpswaas.htm
Self
SBAS (Satellite based Augmentation System)
Omnistar
$800/yr www.omnistar.com/faq.html
OmnistarHP
$1500/yr www.omnistar.com/faq.html
Deere Starfire1
$500/yr StarFireGlobalHighAccuracySystem.pdf
Deere Starfire2
$800/yr StarFireGlobalHighAccuracySystem.pdf
WAAS
Free
users.erols.com/dlwilson/gpswaas.htm
Coast Guard Beacon Coverage
http://www.navcen.uscg.gov/dgps/coverage/CurrentCoverage.htm
Deere Starfire™ SBAS
John Deere’s StarFire System: WADGPS for Precision Agriculture
Tenny Sharpe, Ron Hatch, NavCom Technology Inc.; Dr. Fred Nelson, John Deere & Co.
Agriculture GPS Type Comparison
Performance
Low
Middle
High
Very High
Technology
Low cost
DGPS
DGPS
Two Frequency
DGPS
Real Time
Kinematic
RTK GPS
Price
$100 to 600
$600 to $3,000
$1,500 to 10000 $25,000 to $42,000
Differential
Source
WAAS
WAAS +
C.G. Beacon +
SBAS
WAAS +
C. G. Beacon +
HP SBAS
User Base Station
HP SBAS
Static
Accuracy
5’-12’
1’-3’
4”-10”
1”
Application
Scouting
Mapping /
Guidance
Mapping /
Guidance
Elevation mapping,
Precision row
operations
GPS Technology vs. Precision
(New Holland IntelliSteer ™ )

1. DGPS
–
–

2. DGPS VBS (Virtual Base Station)
–
–

Differential correction signal provided by OmniSTAR™ subscription.
Typical accuracy: +/- 4 inches
4. RTK (Real Time Kinematics)
–
–

Differential correction signal provided by OmniSTAR subscription.
Typical accuracy: +/- 10 inches
3. DGPS HP (High Performance)
–
–

Differential correction signal provided by free WAAS service.
Typical accuracy: +/- 10 inches
Differential correction signal provided by base station.
Typical accuracy: +/- 1 inch
http://www.newholland.com/h4/products/products_series_detail.asp?Reg=NA&RL=ENNA&NavID=000001277003&series=000005423311
Equipment on the market
M. Sullivan, Ohio State Univ.
GPS Receiver Types

Low cost GPS
– Example: Handheld GPS
–
–
–
–
–

Receiver Channels – 12
Position update rate 1 per 5 sec.
Likely to provide WAAS differential
Precision probably not better than ~ 5’
Data output may or may not have NMEA 0183 output
Mapping quality GPS (Simple DGPS)
– Example: Trimble AgGPS 132
–
–
–
–
–
–
Receiver channels – 12
US GPS/EGNOS capability
Position update 10 per second
WAAS, C. G. Beacon, Omnistar/Racal SBAS
Precision better than 3 ft
Data Output, NMEA 0183 + CAN
GPS Receiver types

High Precision differential GPS
– Example Deere Starfire-2
–
–
–
–
–
–
–
Receiver channels 20 GPS, 2 SBAS both L1, L2 freq.
US GPS/EGNOS capability
Position update 5 to 50 per second
WAAS, Deere SBAS
Precision better pass to pass 4”
Data Output, NMEA 0183 + CAN
Slope compensation
GPS Receiver types

RTK GPS
– Example: Trimble Ag GPS 252
–
–
–
–
–
–
Receiver channels – 24
US GPS/EGNOS capability
Position update to 10 per second
WAAS, OmnistarHP, RTK
Pass to pass accuracy 0.3” to 2”
Data Output, NMEA 2000 ISO 11783 CAN
• Requires user provided base station
– 2 x $8000 + $3000 lightbar + radio link
– Within 6 mi. radius line-of-site
Using Automatic Steering

Easy to use – 15 min to learn
–
–
–
–
–
–
Enter field and move to start position.
Press “Start” or “A”
Drive the first pass
Press “Continue” or “B”
Turn to the next pass, System will lock on
Release the steering wheel or press “Resume”
Operating modes
Parallel Linear Swathing
Curve following
A
A
B
B
Additional features

Headland Indicator
 Return to Point
 Snap to Path
 Tilt Sensors
Return on investment

Optimize Machine Efficiency (more acres with fewer hours)
– Operate at faster field speeds
– Reduce overlap
• Reduce per acre fuel consumption
• Reduce overlap on implements and sprayers

Extend Machine Operating Time
– Efficient night operation
– Run in dust and fog

Reduce Operator Fatigue
– More comfortable working hours
– More time to supervize machine functions

Increase Yield
– Manage compaction with planned traffic patterns
– Place fertilizer and herbicides and pesticides more accurately
Automatic Steering may result in
different farming practices




Controlled compaction
Tramlines
Night operations
Higher speeds
Midwest Technologies IL
Calculated returns

Manual guidance allows a 13 percent increase in field speed while DGPS
and RTK auto guidance allow a 20 percent increase. (Deboer and Watson,
Purdue 1984)

Net revenues above variable and technology costs by $28 to $30 per acre
(Watson, Purdue, 1983).

Impact of automatic guidance on an 1,800-acre corn/soybean farm
(Lowenberg-DeBoer, Purdue 1984).
–
–
Reduced field time by 17%, enabling the farm to expand while using the same
machinery and increase returns by $7.36 per acre.
If soils suffered moderate yield loss from compaction, the controlled-traffic
capabilities of a high-accuracy guidance system could increase returns by
$18.84 per acre.
Issues in selecting a GPS based
guidance system

Do’s
–
–
–
–
–
Assure system fits your vehicle(s)
Meets current and near term accuracy requirement
Is adequately portable for the need
Satisfies you on a test drive
Understand the differential correction requirements
• Subscription (SBAS)
• Hardware (RTK)
– Compatible with other PF equipment you plan on
using
Resources

Review of auto-steering systems
–

Beelines link
–

http://www.beelinenavigator.com/
Trimble link
–

http://farmindustrynews.com/mag/farming_straightline_showdown/
http://www.trimble.com/agriculture.shtml
Successful Farming (Richenburger)
–
http://www.findarticles.com/p/articles/mi_m1204/is_8_102/ai_n6178077