Ag Leader GPS 5200 User Guide

GPS 5200 Receiver

User Guide

www.agleader.com

User Guide

GPS 5200 Receiver

Version 1.00 Revision B Part Number 56110-40-ENG December 2008

Contact Information

Trimble Navigation Limited Agriculture Business Area 9290 Bond Street, Suite 102 Overland Park, KS 66214 USA

+1-913-495-2700 Phone

trimble_support@trimble.com www.trimble.com

Legal Notices

trademarks of Trimble Navigation Limited, registered in the United States and other countries. 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 December 2008 release (Revision B) of the GPS 5200 Receiver User Guide, part number 56110-40-ENG. It

applies to version 1.00 of the GPS 5200 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

Trimble Navigation Limited 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 one (1) year starting from the date of delivery. The warranty set forth in this paragraph shall not apply to software products.

Software License, Limited Warranty

This Trimble software product, whether provided as a standalone 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. Trimble warrants that this Trimble Software product will substantially conform to Trimble’s applicable published specifications for the Software for a period of ninety (90) days, starting from the date of delivery.

Warranty Remedies

Trimble's sole liability and your exclusive remedy under the warranties set forth above shall be, at Trimble’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 Trimble in accordance with Trimble’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 Trimble'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 Trimble 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 Trimble; (ii) the operation of the Product or Software under any specification other than, or in addition to, Trimble'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). Trimble does not warrant or guarantee the results obtained through the use of the Product.

THE WARRANTIES ABOVE STATE TRIMBLE'S ENTIRE LIABILITY, AND YOUR EXCLUSIVE REMEDIES, RELATI NG 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 TRIMBLE NAVIGATION LIMITED 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 TRIMBLE 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. TRIMBLE NAVIGATION LIMITED IS NOT RESPONSIBLE FOR THE OPERATION OR FAILURE OF OPERATION OF GPS SATELLITES OR THE AVAILABI LITY OF GPS SATELLITE SIGNAL S.

Limitation of Liability

TRIMBLE’S ENTIRE LIABILITY UNDER ANY PROVISION HEREIN SHALL BE LIMITED TO THE AMOUNT PAID BY YOU FOR THE PRODUCT OR SOFTWARE LICENSE. TO THE MAXIMUM EXTENT PERMITTED BY APPLICABLE LAW, IN NO EVENT SHALL TRIMBLE OR ITS SUPPLI ERS BE LIABLE FOR ANY INDIRECT, SPECIAL , INCIDENTAL OR CONSEQUENTIAL DAMAGES WHATSOEVER UNDER ANY CIRCUMSTANCE OR LEGAL THEORY RELATI NG IN ANY WAY TO THE PRODUCTS, SOFTWARE AND ACCOMPANYING DOCUMENTATION AND MATERIALS, (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS OF BUSINESS PROFITS, BUSINE SS INTERRUPTION, LOSS OF BUSINESS INFORMATION, OR ANY OTHER PECUNIARY LOSS), REGARDLES S WHETHER TRIMBLE HAS BEEN ADVISED OF THE POSSIBILITY OF ANY SUCH LOSS AND REGARDL ESS OF THE COURSE OF DEALING WHICH DEVELOPS OR HAS DEVELOPED BETWEEN YOU AND TRIMBLE. 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 TRIMBLE DEALER FOR APPLICABLE WARRANTY INFORMATION.

2 GPS 5200 Receiver User Guide

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Related information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Technical assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Your comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Standard features of the GPS 5200 receiver . . . . . . . . . . . . . . . . . . . . . . . .8

Receiver connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Receiver input/output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

LED indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

GPS positioning methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

RTK GPS positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Differential GPS positioning (DGPS). . . . . . . . . . . . . . . . . . . . . . . 15

Autonomous GPS positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Sources of error in GPS positioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Coordinate systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3 Installing the Receiver . . . . . . . . . . . . . . . . . . . . . . .21

System components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Optional extra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Mounting the receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Choosing a location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Environmental conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Electrical interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Connecting to an external device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

GPS 5200 Receiver User Guide 3

Contents

Connectors and pinouts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Port A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Port B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Radar output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4 Configuring the Receiver . . . . . . . . . . . . . . . . . . . . .31

AgRemote Home screen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Configuring Differential GPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

OmniSTAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

WAAS/EGNOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Configuring the GPS 5200 receiver to operate in RTK mode . . . . . . . . . . . . 35

Configuring the communication ports. . . . . . . . . . . . . . . . . . . . . . . . . . 36

Configuring input/output communication. . . . . . . . . . . . . . . . . . . 36

5 Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . .41

Global Positioning System (GPS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Interference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

GPS receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

AgRemote utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

FlashLoader 200 upgrade utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

A Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

GPS 5200 receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

GPS channels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

L-band satellite differential correction receiver . . . . . . . . . . . . . . . . . . . . 52

Receiver default settings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

B Third-Party Interface Requirements . . . . . . . . . . . . . . .53

Third-party software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54

Third-party hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

4 GPS 5200 Receiver User Guide

CHAPTER

Introduction 1

In this chapter:

 Warnings

 Related information

 Technical assistance

 Your comments

Welcome to the GPS 5200 Receiver User Guide. This manual:

• Describes how to install and

configure the GPS 5200 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, we recommend 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.

GPS 5200 Receiver User Guide 5

1 Introduction

Warnings

Always follow the instructions that accompany a warning.

WARNING – Indicates a potential hazard or unsafe practice that could

result in injury or property damage.

WARNING – For continued protection against the risk of fire, the power

source (lead) to the model GPS 5200 receiver should be provided with a 10 A (maximum) fuse.

Related information

Release notes describe new features, provide information that is not included in the manuals, and identify changes to the manuals. You can download release notes from the AgLeader website.

Technical assistance

If you have a problem and cannot find the information you need in the product documentation, contact your local Reseller.

Your comments

Your feedback about the supporting documentation helps us to improve it with each revision. Email your comments to

ReaderFeedback@trimble.com.

6 GPS 5200 Receiver User Guide

CHAPTER

Overview 2

In this chapter:

 Standard features of the

GPS 5200 receiver

 Receiver connections

 Receiver input/output

 LED indicator

 GPS positioning methods

 Sources of error in GPS

positioning

This chapter describes the GPS 5200 receiver and gives an overview of GPS, DGPS, and related information. When used with a Real-Time Kinematic (RTK) base station, the GPS 5200 receiver provides RTK positioning for highaccuracy, centimeter-level applications. For physical specifications, see

Appendix A, Specifications.

GPS 5200 Receiver User Guide 7

2 Overview

Standard features of the GPS 5200 receiver

A standard GPS 5200 receiver provides the following features:

• 12 GPS (C/A-code) tracking channels, code carrier channels

• Horizontal RTK positioning accuracy 2.5cm (0.98in) + 2ppm,

2 sigma; vertical RTK positioning accuracy 3.7 cm (1.46 in) + 2 ppm, 2 sigma

• 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. You can download this utility 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.

• Radar output

• WAAS differential correction compatibility

• AgGPS

• EVEREST

• OmniSTAR VBS, XP, and HP positioning compatibility

• Two ports that support both CAN 2.0B and RS-232:

CAN

– J1939 and NMEA 2000 messages

Note – The GPS 5200 receiver is ISO 11783 compliant. It supports some ISO 11783 messages.

8 GPS 5200 Receiver User Guide

170 Field Computer compatibility

™

multipath rejection technology

RS-232

LED indicator

Port A Port B

– 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

Receiver connections

The following figure shows the connector ports and the LED indicator on the GPS 5200 receiver:

Overview 2

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

GPS 5200 Receiver User Guide 9

2 Overview

• 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.

Receiver input/output

The GPS 5200 receiver data/power cable (P/N 50166) 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.

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.

10 GPS 5200 Receiver User Guide

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.

Overview 2

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.

Position output format

The GPS 5200 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.

GPS 5200 Receiver User Guide 11

2 Overview

LED indicator

The GPS 5200 receiver has an LED light that shows the status of the receiver. The following tables describe the light sequences for each 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

Note – WAAS/EGNOS and OmniSTAR VBS use the Satellite Differential GPS positioning method.

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

12 GPS 5200 Receiver User Guide

Overview 2

Table 2.2 LED sequences with RTK positioning (continued)

LED color LED flash Status

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

GPS 5200 Receiver User Guide 13

2 Overview

GPS positioning methods

GPS positioning systems are used in different ways to provide different levels of accuracy. Accuracy is measured in absolute terms, that is, 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

GPS positioning method

Real-Time Kinematic (RTK) GPS

Satellite Differential GPS OmniSTAR VBS 78 cm (30.71 inch)

Satellite Differential GPS WAAS/EGNOS 95 cm (37.40 inch)

OmniSTAR HP Differential GPS

Convergence 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.

Corrections used Approximate absolute accuracy

Trimble CMR corrections broadcast by a local base station

OmniSTAR HP 10 cm (3.94 inch) after the signal has fully

2.5 cm (0.98 inch) + 2 ppm horizontal accuracy,

3.7 cm (1.46 inch) + 2 ppm vertical accuracy

converged

For more information about each positioning method, see below.

RTK GPS positioning

The GPS 5200 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 5200 receiver is a rover receiver, so another compatible receiver, such as a Trimble

™

MS750 receiver, must be used as the base station.

, AgGPS 214, AgGPS RTK Base 450, or AgGPS RTK Base 900

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

14 GPS 5200 Receiver User Guide

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/gps/

Differential GPS positioning (DGPS)

For differential positioning, the GPS 5200 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

Overview 2

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.

Subscription-based corrections

The GPS 5200 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.

GPS 5200 Receiver User Guide 15

2 Overview

Autonomous GPS positioning

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 33.

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.

16 GPS 5200 Receiver User Guide

Sources of error in GPS positioning

The GPS positioning method influences the accuracy of the GPS position that is output by the GPS 5200 receiver. The factors described in Table 2.5 also affect GPS accuracy.

Table 2.5 Factors that influence the accuracy of GPS positions

Overview 2

Condition Optimum

value

Atmospheric effects

Number of satellites used

Maximum PDOP < 4 Position Dilution of Precision (PDOP) is a unitless, computed

Signal-to-noise ratio

Minimum elevation

> 5 To calculate a 3D position (latitude and longitude, altitude,

> 10 Satellites that are low on the horizon typically produce weak

Description

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.

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 5200 receiver can track up to 12 satellites simultaneously.

Note – To see when the maximum number of GPS satellites are available, use the Trimble Planning software and a current ephemeris (satellite history) file. Both files are available free from the Trimble website at www.trimble.com.

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.

Signal-to-noise ratio (SNR) is a measure of the signal strength against electrical background noise. A high SNR gives better accuracy.

and noisy signals and are more difficult for the receiver to track. Satellites below the minimum elevation angle are not tracked.

GPS 5200 Receiver User Guide 17

2 Overview

Table 2.5 Factors that influence the accuracy of GPS positions (continued)

Condition Optimum

value

Multipath environment

RTCM-compatible corrections

RTK Base station coordinate accuracy

Multiple RTK base stations

Low Multipath errors are caused when GPS signals are reflected off

Description

nearby objects and reach the receiver by two or more different paths. The receiver incorporates the EVEREST multipath rejection option.

These corrections are broadcast from an AgGPS 214, MS750, or equivalent reference station.

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.

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. For more information about how to use several base stations to cover your site, contact your local Trimble Reseller.

Coordinate systems

Geographic data obtained from different sources must be referenced to the same datum, ellipsoid, and coordinate format. Different formats provide different coordinate values for any geographic location. In North America, the datums NAD-27 and NAD-83 are commonly used in Agricultural mapping applications.

18 GPS 5200 Receiver User Guide

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