Ag Leader Technology 5100 User manual
A
Version 1.00
Revision A
Part Number 55510-45-ENG
January 2005
GPS 5100 Receiver
User Guide
ii GPS 5100 Receiver User Guide
Contact Information
Ag Leader Technology
2202 South Riverside Drive
P.O.Box 2348
Ames, Iowa 50010
+1-515-232-5363 Phone
support@agleader.com
www.agleader.com
Copyright and Trademarks
© 2004-2005, Trimble Navigation Limited. All rights
reserved.
Trimble and AgGPS are trademarks of Trimble
Navigation Limited, registered in the United States
Patent and Trademark Office and other countries.
Autopilot, EVEREST, MS750, and SiteNet are
trademarks of Trimble Navigation Limited.
Microsoft and ActiveSync are either registered
trademarks or trademarks of Microsoft Corporation in
the United States and/or other countries. All other
trademarks are the property of their respective owners.
Release Notice
This is the January 2005 release (Revision A) of the GPS
5100 Receiver User Guide, part number 55510-45-ENG.
It applies to version 1.00 of the GPS 5100 receiver.
The following limited warranties give you specific legal
rights. You may have others, which vary from
state/jurisdiction to state/jurisdiction.
Hardware Limited Warranty
Ag Leader warrants that this hardware product (the
“Product”) will perform substantially in accordance with
published specifications and be substantially free of
defects in material and workmanship for a period of two
(2) years starting from the date of delivery. The warranty
set forth in this paragraph shall not apply to software
products.
Software License, Limited Warranty
This Ag Leader software product, whether provided as a
stand-alone computer software product, built into
hardware circuitry as firmware, embedded in flash
memory, or stored on magnetic or other media, (the
“Software”) is licensed and not sold, and its use is
governed by the terms of the relevant End User License
Agreement (“EULA”) included with the Software. In the
absence of a separate EULA included with the Software
providing different limited warranty terms, exclusions
and limitations, the following terms and conditions shall
apply. Ag Leader warrants that this Ag Leader
Technology Software product will substantially conform
to Ag Leader’s applicable published specifications for
the Software for a period of ninety (90) days, starting
from the date of delivery.
Warranty Remedies
Ag Leader's sole liability and your exclusive remedy
under the warranties set forth above shall be, at Ag
Leader’s option, to repair or replace any Product or
Software that fails to conform to such warranty
(“Nonconforming Product”) or refund the purchase price
paid by you for any such Nonconforming Product, upon
your return of any Nonconforming Product to Ag Leader
in accordance with Ag Leader’s standard return material
authorization procedures.
Warranty Exclusions and Disclaimer
These warranties shall be applied only in the event and
to the extent that (i) the Products and Software are
properly and correctly installed, configured, interfaced,
maintained, stored, and operated in accordance with Ag
Leader's relevant operator's manual and specifications,
and; (ii) the Products and Software are not modified or
misused. The preceding warranties shall not apply to,
and Ag Leader shall not be responsible for defects or
performance problems resulting from (i) the
combination or utilization of the Product or Software
with hardware or software products, information, data,
systems, interfaces or devices not made, supplied or
specified by Ag Leader; (ii) the operation of the Product
or Software under any specification other than, or in
addition to, Ag Leader's standard specifications for its
products; (iii) the unauthorized, installation,
modification,or use of the Product or Software; (iv)
damage caused by accident, lightning or other electrical
discharge, fresh or salt water immersion or spray; or (v)
normal wear and tear on consumable parts (e.g.,
batteries). Ag Leader does not warrant or guarantee the
results obtained through the use of the Product.
THE WARRANTIES ABOVE STATE AGLEADER'S
ENTIRE LIABILITY, AND YOUR EXCLUSIVE
REMEDIES, RELATING TO PERFORMANCE OF THE
PRODUCTS AND SOFTWARE. EXCEPT AS OTHERWISE
EXPRESSLY PROVIDED HEREIN, THE PRODUCTS,
SOFTWARE, AND ACCOMPANYING
DOCUMENTATION AND MATERIALS ARE PROVIDED
“AS-IS” AND WITHOUT EXPRESS OR IMPLIED
WARRANTY OF ANY KIND BY EITHER AGLEADER
TECHNOLOGY OR ANYONE WHO HAS BEEN
INVOLVED IN ITS CREATION, PRODUCTION,
INSTALLATION, OR DISTRIBUTION INCLUDING, BUT
NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE, TITLE, AND
NONINFRINGEMENT. THE STATED EXPRESS
WARRANTIES ARE IN LIEU OF ALL OBLIGATIONS OR
LIABILITIES ON THE PART OF AGLEADER ARISING
OUT OF, OR IN CONNECTION WITH, ANY PRODUCTS
OR SOFTWARE. SOME STATES AND JURISDICTIONS
DO NOT ALLOW LIMITATIONS ON DURATION OR
THE EXCLUSION OF AN IMPLIED WARRANTY, SO
THE ABOVE LIMITATION MAY NOT APPLY TO YOU.
AGLEADER TECHNOLOGY IS NOT RESPONSIBLE
GPS 5100 Receiver User Guide iii
FOR THE OPERATION OR FAILURE OF OPERATION OF
GPS SATELLITES OR THE AVAILABILITY OF GPS
SATELLITE SIGNALS.
Limitation of Liability
AGLEADER’SENTIRE LIABILITY UNDER ANY
PROVISION HEREIN SHALL BE LIMITED TO THE
AMOUNT PAID BY YOU FOR THE PRODUCT OR
SOFTWARE LICENSE. TOTHE MAXIMUM EXTENT
PERMITTED BY APPLICABLE LAW, IN NO EVENT
SHALL AG LEADER OR ITS SUPPLIERS BE LIABLE
FOR ANY INDIRECT, SPECIAL, INCIDENTAL OR
CONSEQUENTIAL DAMAGES WHATSOEVER UNDER
ANY CIRCUMSTANCE OR LEGAL THEORY RELATING
IN ANY WAY TO THE PRODUCTS, SOFTWARE AND
ACCOMPANYING DOCUMENTATION AND
MATERIALS, (INCLUDING, WITHOUT LIMITATION,
DAMAGES FOR LOSS OF BUSINESS PROFITS,
BUSINESS INTERRUPTION, LOSS OF BUSINESS
INFORMATION, OR ANY OTHER PECUNIARY LOSS),
REGARDLESS WHETHER AG LEADER HAS BEEN
ADVISED OF THE POSSIBILITY OF ANY SUCH LOSS
AND REGARDLESS OF THE COURSE OF DEALING
WHICH DEVELOPS OR HAS DEVELOPED BETWEEN
YOU AND AG LEADER. BECAUSE SOME STATES AND
JURISDICTIONS DO NOT ALLOW THE EXCLUSION OR
LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR
INCIDENTAL DAMAGES, THE ABOVE LIMITATION
MAY NOT APPLY TO YOU.
NOTE: THE ABOVE LIMITED WARRANTY
PROVISIONS MAY NOT APPLY TO PRODUCTS OR
SOFTWARE PURCHASED IN THE EUROPEAN UNION.
PLEASE CONTACT YOUR AG LEADER DEALER FOR
APPLICABLE WARRANTY INFORMATION.
Notices
USA
NOTE – FCC Part 15 rules; paragraph 15.105
This equipment has been tested and found to comply
with the limits for a Class A digital device, pursuant to
Part 15 of the FCC Rules. These limits are designed to
provide reasonable protection against harmful
interference when the equipment is operated in a
commercial environment. This equipment generates,
uses, and can radiate radio frequency energy and, if not
installed and used in accordance with the instruction
manual, may cause harmful interference to radio
communications. Operation of this equipment in a
residential area is likely to cause harmful interference, in
which case, you, the user, will be required to correct the
interference at your own expense.
If this equipment does cause harmful interference to
radio or television reception, which can be determined
by turning the equipment off and on, the user is
encouraged to try to correct the interference by one or
more of the following measures:
– Reorient or relocate the receiving antenna.
– Increase the separation between the equipment and
the receiver.
– Connect the equipment into an outlet on a circuit
different from that to which the receiver is connected.
– Consult the dealer or an experienced radio/TV
technician for help.
Changes and modifications not expressly approved by
the manufacturer or registrant of this equipment can void
your authority to operate this equipment under Federal
Communications Commission rules.
Europe
This product has been tested and found to comply with
the requirements for the European Directive
75/322/EEC as amended by 2000/2/EC thereby
satisfying the requirements for e-mark compliance for
use in agricultural vehicles in the European Economic
Area (EEA).
This product has been tested and found to comply with
the requirements for a Class A device pursuant to
European Council Directive 89/336/EEC on EMC,
thereby satisfying the requirements for CE Marking and
sale within the European Economic Area (EEA).
CWarning – This is a Class A product. In a domestic
environment this product may cause radio
interference in which case you may be required to
take adequate measures.
iv GPS 5100 Receiver User Guide
Declaration of Conformity
This product conforms to the following standards, and therefore complies with the requirements of the R&TTE
Directive 1999/5/EC, which specifies compliance with the essential requirements of EMC Directive 89/336/EEC and
Low Voltage Directive 73/23/EEC.
The technical file is maintained at Trimble Navigation Limited, 749 North Mary Avenue, PO Box 3642, Sunnyvale, CA
94088-3642, USA.
EMC Emissions BSEN 55022:1998 (W/A1:00) Class A
EMC Immunity EN 55024:1998
Safety EN 60950:2000
Mark First Applied 03
GPS 5100 Receiver User Guide v
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Related Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Technical Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Standard Features of the GPS 5100 Receiver . . . . . . . . . . . . . . . . . 4
Receiver Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Receiver Input/Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
LED Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
GPS Positioning Methods. . . . . . . . . . . . . . . . . . . . . . . . . . 10
RTK GPS positioning . . . . . . . . . . . . . . . . . . . . . . . . 10
Differential GPS positioning (DGPS) . . . . . . . . . . . . . . . . 11
Autonomous GPS positioning . . . . . . . . . . . . . . . . . . . . 12
Sources of Error in GPS Positioning . . . . . . . . . . . . . . . . . . . . 13
Coordinate systems. . . . . . . . . . . . . . . . . . . . . . . . . . 15
3 Installing the Receiver. . . . . . . . . . . . . . . . . . . . 17
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Optional extra . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Mounting the Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Choosing a location . . . . . . . . . . . . . . . . . . . . . . . . . 19
Environmental conditions . . . . . . . . . . . . . . . . . . . . . . 20
Electrical interference . . . . . . . . . . . . . . . . . . . . . . . . 20
Contents
vi GPS 5100 Receiver User Guide
Connecting to an External Device . . . . . . . . . . . . . . . . . . . . . 21
Connectors and Pinouts . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Port A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Port B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4 Configuring the Receiver . . . . . . . . . . . . . . . . . . 27
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
AgRemote Home Screen . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Configuring Differential GPS . . . . . . . . . . . . . . . . . . . . . . . . 30
OmniSTAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
WAAS/EGNOS . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Configuring the GPS 5100 Receiver to Operate in RTK Mode. . . . . . . 33
Configuring the Communication Ports . . . . . . . . . . . . . . . . . . . 33
Configuring input/output communication . . . . . . . . . . . . . . 34
5 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . 39
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Problems and Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Troubleshooting Flowcharts . . . . . . . . . . . . . . . . . . . . . . . . 48
A Specifications . . . . . . . . . . . . . . . . . . . . . . . . 55
GPS 5100 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
GPS Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
L-Band Satellite Differential Correction Receiver . . . . . . . . . . . . . 58
Receiver Default Settings . . . . . . . . . . . . . . . . . . . . . . . . . . 58
B Additional Equipment Interface Requirements . . . . . . 59
Ag Leader Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Third-Party Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Third-Party Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
CHAPTER
1
GPS 5100 Receiver User Guide 1
Introduction 1
Welcome to the GPS 5100 Receiver User Guide. This manual:
• Describes how to install and configure the Ag Leader®5100
GPS receiver.
• Provides guidelines for connecting the receiver to an external
device.
• Provides guidelines for using the AgRemote utility to view and
configure the receiver correction sources and other operating
parameters.
Even if you have used other Global Positioning System (GPS)
products before, Ag Leader recommends that you spend some time
reading this manual to learn about the special features of this product.
If you are not familiar with GPS, go to the Trimble®website at
www.trimble.com for an interactive look at GPS.
1Introduction
2GPS 5100 Receiver User Guide
1.1 Warnings
Always follow the instructions that accompany a warning.
CWarning – Indicates a potential hazard or unsafe practice that could result
in injury or property damage.
1.2 Related Information
Release notes describe new features, provide information that is not
included in the manuals, and identify changes to the manuals.
1.3 Technical Assistance
If you have a problem and cannot find the information you need in the
product documentation, contact your local Ag Leader Reseller.
2Overview
4GPS 5100 Receiver User Guide
2.1 Introduction
This chapter describes the GPS 5100 receiver and gives an overview of
GPS, DGPS, and related information. When used with a Real-Time
Kinematic (RTK) base station, the GPS 5100 receiver provides RTK
positioning for high-accuracy, centimeter-level applications. For
physical specifications, see Appendix A, Specifications.
2.2 Standard Features of the GPS 5100 Receiver
A standard GPS 5100 receiver provides the following features:
• 12 GPS (C/A-code) tracking channels, code carrier channels
• Horizontal RTK positioning accuracy 2.5 cm (0.98 in) + 2 ppm,
2 sigma; vertical RTK positioning accuracy 3.7 cm (1.46 in)
+2ppm,2sigma
• Submeter differential accuracy (RMS), assuming at least five
satellites and a PDOP of less than four
• Combined GPS/DGPS receiver and antenna
• System level cable
•AgRemote utility with four-button keypad to configure and view
system properties (download from the Ag Leader website at
www.agleader.com)
• LED status indicator
• The receiver outputs a 1 PPS (pulse per second) strobe signal on
both ports. This signal enables an external instrument to
synchronize its internal time with a time derived from the very
accurate GPS system time.
• WAAS differential correction compatibility
• Field computer compatibility
• EVEREST™ multipath rejection technology
• OmniSTAR VBS and HP positioning compatibility
GPS 5100 Receiver User Guide 5
Overview 2
• Two ports that support both CAN 2.0B and RS-232:
CAN
– J1939 and NMEA 2000 messages
Note – The GPS 5100 receiver is ISO 11783 compliant. It
supports some ISO 11783 messages.
RS-232
– NMEA-0183 output: GGA, GLL, GRS, GST, GSA, GSV,
MSS, RMC, VTG, ZDA, XTE (the default NMEA
messages are GGA, GSA, VTG, and RMC)
Note – PTNLDG, PTNLEV, PTNLGGK, PTNLID, and
PTNLSM are Trimble proprietary NMEA output messages.
– RTCM SC-104 output
– Trimble Standard Interface Protocol (TSIP) input and
output
2.3 Receiver Connections
Figure 2.1 shows the connector ports and the LED indicator on the
GPS 5100 receiver.
Figure 2.1 GPS 5100 receiver connector ports
LED indicator
Port A Port B
2Overview
6GPS 5100 Receiver User Guide
The two connectors (Port A and Port B) can perform the following
functions:
• accept power
• accept TSIP, RTCM, ASCII, and (if enabled) CMR inputs
• output RTCM, TSIP, and NMEA messages
• output 1 PPS signals
• provide support for the J1939 (CAN) serial bus
For more information about the inputs, outputs, and LED indicators,
see the information in the rest of this section.
2.4 Receiver Input/Output
The GPS 5100 receiver data/power cable connects to a receiver
connector port to supply power. It also enables the following data
exchanges:
• TSIP, RTCM, and ASCII input from an external device
The receiver is able to receive ASCII data from an external
device, convert this data into an NMEA message, and export the
message to another device. TSIP command packets configure
and monitor GPS and DGPS parameters. The receiver is also
able to accept RTCM data from an external device, such as a
radio.
• CMR input from an external device
If the receiver is to be used in RTK mode, set the port that is
connected to the radio to the RtkLnk protocol. This protocol
enables the receiver to receive CMR messages.
• TSIP and NMEA output to an external device
When you are using an external radio, the receiver can also
receive DGPS corrections.
TSIP is input/output when communicating with AgRemote.
GPS 5100 Receiver User Guide 7
Overview 2
NMEA is output when the receiver is exporting GPS position
information to an external device, such as a yield monitor, or to
a mapping software program.
For more information on the National Marine Electronics
Association (NMEA) and Radio Technical Commission for
Maritime Services (RTCM) communication standard for GPS
receivers, go to the following websites:
– www.nmea.org
– www.rtcm.org
On the Trimble website (www.trimble.com), refer to the
document called NMEA-0183 Messages Guide for AgGPS
Receivers.
• 1 PPS output
To synchronize timing between external instruments and the
internal clock in the receiver, the connection port outputs a
strobe signal at 1 PPS (pulse per second). To output this signal,
the receiver must be tracking satellites and computing GPS
positions.
• J1939 (CAN) bus
Both connection ports on the receiver support the J1939
Controller Area Network (CAN) bus protocol. This protocol
standardizes the way multiple microprocessor-based electronic
control units (ECUs) communicate with each other over the
same pair of wires. It is used in off-highway machines, such as
those used in agriculture, construction, and forestry.
For more information, go to the Society of Automotive
Engineers (SAE) International website at
www.sae.org/servlets/index.
• ISO 11783 messages
Both CAN ports support some ISO 11783 messages.
2Overview
8GPS 5100 Receiver User Guide
Position output format
The GPS 5100 receiver outputs positions in Degrees, Minutes, and
Decimal Minutes (DDD°MM.m'). This is the NMEA standard format
and is commonly used worldwide for data transfer between electronic
equipment.
2.5 LED Indicator
The GPS 5100 receiver has an LED light that shows the status of the
receiver. The following tables describe the light sequences for each
positioning method.
Note – WAAS/EGNOS and OmniSTAR VBS use the Satellite
Differential GPS positioning method.
Table 2.1 LED sequences with Satellite Differential GPS or Autonomous positioning
LED color LED flash Status
Off Off No power
Green Solid Normal operation: computing DGPS positions
Green Slow No DGPS corrections: computing DGPS positions using old
corrections
Green Fast No DGPS corrections approaching DGPS age limit: computing
DGPS positions using old corrections
Yellow Solid DGPS corrections being received but DGPS positions not yet being
computed: computing autonomous GPS positions
Yellow Slow No DGPS corrections: computing autonomous GPS positions
Yellow Fast Not enough GPS signals: not tracking enough satellites to compute
position
GPS 5100 Receiver User Guide 9
Overview 2
Table 2.2 LED sequences with RTK positioning
LED color LED flash Status
Off Off No power
Green Solid Normal operation: computing fixed RTK positions
Green Slow Receiving CMR corrections but not initialized: computing float RTK
positions
Green Fast No CMR corrections: computing RTK position using old corrections
Yellow Solid Receiving CMR corrections but unable to calculate RTK position:
computing DGPS (if WAAS/EGNOS is unavailable) or autonomous
position
Yellow Slow No CMR corrections: computing DGPS or autonomous position
Yellow Fast Not receiving CMR corrections: not computing positions
Table 2.3 LED sequences with OmniSTAR HP positioning
LED color LED flash Status
Off Off No power
Green Solid Normal operation: computing converged OmniSTAR HP positions
Green Slow Receiving OmniSTAR HP corrections, but only able to compute
unconverged position
Green Fast Receiving OmniSTAR HP corrections, but an HP error occurred
Yellow Solid Receiving OmniSTAR HP corrections but unable to calculate a
position: computing DGPS or autonomous solution
Yellow Slow No OmniSTAR HP corrections: computing DGPS or autonomous
position
Yellow Fast Not tracking OmniSTAR HP corrections: no positions
2Overview
10 GPS 5100 Receiver User Guide
2.6 GPS Positioning Methods
GPS positioning systems are used in different ways to provide
different levels of accuracy. Accuracy is measured in absolute terms
(you know exactly where you are in a fixed reference frame).
Table 2.4 summarizes the GPS positioning methods. Imperial units in
this table are rounded to two decimal places. The values shown are
2sigma.
Table 2.4 Absolute accuracy of GPS positioning methods
For more information about each positioning method, see below.
26.1 RTK GPS positioning
The GPS 5100 receiver uses the RTK positioning method to achieve
centimeter-level accuracy. To use the RTK method, you must first set
up a base station. The base station uses a radio link to broadcast RTK
corrections to one or more rover receivers. The GPS 5100 receiver is a
rover receiver, so another compatible receiver, such as a Trimble
MS750™ or Trimble AgGPS® 214 GPS receiver, must be used as the
base station.
GPS positioning
method
Corrections used Approximate absolute accuracy
Real-Time Kinematic
(RTK) GPS
Trimble CMR
corrections broadcast
by a local base station
2.5 cm (0.98 in) + 2 ppm horizontal
accuracy,
3.7 cm (1.46 in) + 2 ppm vertical accuracy
Satellite Differential GPS OmniSTAR VBS 78 cm (30.71 in)
Satellite Differential GPS WAAS/EGNOS 95 cm (37.40 in)
OmniSTAR HP
Differential GPS
OmniSTAR HP 10 cm (3.94 in) after the signal has fully
converged1
1Convergence time can vary, depending on the environment. Time to the first fix (submeter accuracy) is typically
<30 seconds; time to the first high accuracy fix (<10 cm accuracy) is typically <30 minutes.
GPS 5100 Receiver User Guide 11
Overview 2
The rover receiver uses RTK corrections from the base station to
calculate its position to centimeter-level accuracy. As part of this
process, the rover receiver must calculate an initialization. This takes a
few seconds. While the receiver is initializing, an RTK Float solution
is generated. Once initialized, an RTK Fixed solution is generated. It is
the RTK Fixed solution that provides centimeter-level accuracy.
The parts per million (ppm) error is dependent on the distance
(baseline length) between the base and rover receiver. For example, if
the distance is 10 km, a 2 ppm error equals 20 mm.
For more information about RTK positioning, go to the Trimble
website at www.trimble.com/
26.2 Differential GPS positioning (DGPS)
For differential positioning, the GPS 5100 receiver uses corrections
from WAAS/EGNOS satellites or from OmniSTAR VBS or HP
satellites.
These differential systems use special algorithms to provide
differential corrections that allow the rover receiver to calculate its
position more accurately.
Free corrections
WAAS/EGNOS corrections are free in North America and Europe.
For more information about WAAS, go to the Federal Aviation
Administration website at
http://gps.faa.gov/Programs/WAAS/waas.htm.
For more information about EGNOS, go to the European Space
Agency website at
www.esa.int/export/esaSA/GGG63950NDC_navigation_0.html.
2Overview
12 GPS 5100 Receiver User Guide
Subscription-based corrections
The GPS 5100 receiver uses OmniSTAR HP or OmniSTAR VBS
differential corrections in the same way that it uses WAAS/EGNOS
corrections.
OmniSTAR corrections are provided on a subscription basis.
The corrections that are produced by OmniSTAR HP algorithms are
more accurate than the corrections that are produced by OmniSTAR
VBS algorithms. The accuracy of the positions reported using
OmniSTAR HP increases with the time that has elapsed since the
instrument was turned on. This process is called convergence.
Convergence to where the error is estimated to be below 30 cm
(approximate 12 inches) typically takes around 20 minutes. Factors
that influence the time to convergence include the environment, the
geographical location, and the distance to the closest OmniSTAR
corrections base station. OmniSTAR is continually improving the
service.
For more information about OmniSTAR, go to the OmniSTAR
website at www.omnistar.com. For information about activating an
OmniSTAR subscription, see OmniSTAR, page 31.
26.3 Autonomous GPS positioning
Autonomous GPS positioning uses no corrections. The rover receiver
calculates its position using only the GPS signals it receives. This
method does not have high absolute accuracy, but the relative accuracy
is comparable to the other methods.
GPS 5100 Receiver User Guide 13
Overview 2
2.7 Sources of Error in GPS Positioning
The GPS positioning method influences the accuracy of the GPS
position that is output by the GPS 5100 receiver. The factors described
in Table 2.5 also affect GPS accuracy.
Table 2.5 Factors that influence the accuracy of GPS positions
Condition Optimum
value
Description
Atmospheric
effects
GPS signals are degraded as they travel through the
ionosphere. The error introduced is in the range of 10 meters.
The error is removed by using a differential or RTK positioning
method.
Number of
satellites used
> 5 To calculate a 3D position (latitude and longitude, altitude, and
time), four or more satellites must be visible. To calculate a 2D
position (latitude and longitude, and time), three or more
satellites must be visible. For RTK positioning, five satellites are
needed for initialization. Once initialized, four or more satellites
provide RTK positions. The number of visible satellites
constantly changes and is typically in the range 5 through 9.
The GPS 5100 receiver can track up to 12 satellites
simultaneously.
Note – To see when the maximum number of GPS satellites are
available, use the planning software and a current ephemeris
(satellite history) file. Both files are available free from the
Trimble website at www.trimble.com.
Maximum PDOP < 4 Position Dilution of Precision (PDOP) is a unitless, computed
measurement of the geometry of satellites above the current
location of the receiver. A low PDOP means that the positioning
of satellites in the sky is good, and therefore good positional
accuracy is obtained.
2Overview
14 GPS 5100 Receiver User Guide
Signal-to-noise
ratio
> 6 Signal-to-noise ratio (SNR) is a measure of the signal strength
against electrical background noise. A high SNR gives better
accuracy.
Normal values are:
•GPS 6
• WAAS 3+
• OmniSTAR HP/VBS 6+
Minimum
elevation
> 10 Satellites that are low on the horizon typically produce weak
and noisy signals and are more difficult for the receiver to track.
Satellites below the minimum elevation angle are not tracked.
Multipath
environment
Low Multipath errors are caused when GPS signals are reflected off
nearby objects and reach the receiver by two or more different
paths. The receiver incorporates the EVEREST multipath
rejection option.
RTCM-
compatible
corrections
These corrections are broadcast from a Trimble AgGPS 214,
MS750, or equivalent reference station.
RTK Base station
coordinate
accuracy
For RTK positioning, it is important to know the base station
coordinates accurately. Any error in the position of the base
station affects the position of the rover; every 10 m of error in a
base station coordinate can introduce up to 1 ppm scale error
on every measured baseline. For example, an error of 10 m in
the base station position produces an error of 10 mm over a
10 km baseline to the rover.
For more information about how to make sure the position of
your base station is accurate, refer to the manual for your base
station receiver.
Multiple RTK
base stations
If you are using several base stations to provide RTK
corrections to a large site area, all base stations must be
coordinated relative to one another. If they are not, the absolute
positions at the rover will be in error.
Table 2.5 Factors that influence the accuracy of GPS positions (continued)
Condition Optimum
value
Description
Table of contents
Other Ag Leader Technology GPS manuals
