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Hardware for GPS and GIS

Jeff Grussing

Leader of GIS Development

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Topics for Discussion

• Understanding of how GPS works• Become familiar with the GPS equipment, accuracy's

and cost• Other peripherals for GPS systems• Discuss hardware for GIS systems • Discuss the pros and cons of Rugged Hardware vs.

Standard for GIS in field• How to choose hardware for field use• Understanding the standards for rugged computers• Total cost of ownership for rugged vs. standard

hardware• Recap

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What is GPS?

Global Positioning System (GPS) is a Satellite-Based Navigation System made up of a network of 24 satellites placed into orbit by the United States Department of Defense. This System works in any weather condition, anywhere in the world 24 hours a day. It is free of charge.

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How GPS Works

The 24 GPS satellites circle the earth twice a day in a very precise orbit and transmits signal information to earth. The GPS receivers take this information and use the triangulation of three or more satellites to calculate the user’s exact location.

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Triangulation

Your Location

Triangulation occurs when the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. When the GPS receives a time signal from at least three satellites simultaneously, an exact location is obtained.

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• Ionosphere and troposphere delays – The satellite signal

slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error.

Sources of Error

Ionosphere

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• Signal multipath — This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.

Sources of Error

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• Receiver Clock Errors – A receiver's built-in clock is not as accurate as the atomic clocks

onboard the GPS satellites. Therefore, it may have very slight timing errors.

• Orbital Errors – Also known as ephemeris errors, these are inaccuracies of the satellite's

reported location. • Number of Satellites Visible

– The more satellites a GPS receiver can "see“, the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.

Sources of Error

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Sources of Error

• Satellite Geometry/Shading – This refers to the relative

position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.

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• Intentional Degradation of the Satellite Signal– Selective Availability (SA) is an intentional degradation

of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.

Sources of Error

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Sources of Error• Human Error

– Equipment Configuration/Setup, Equipment Use

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• What is DGPS?– DGPS stands for differentially corrected GPS

• What are the Advantages of DGPS?– The GPS signal is corrected real time in the field– No port processing required

• What are some Disadvantages to DGPS?– You may be required to carry additional equipment into the field– Costs more– Difficult to get a corrected signal in some areas

• Types of Correction – WAAS– Radio Beacon– Television Frequencies– External RTCM– EGNOS

Differentially Corrected GPS

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• WAAS – Wide Area Augmentation System is a system of two Geosyncronis satellites

and 25 ground stations that provide GPS signal corrections

• The Origins of WAAS– The Federal Aviation Administration (FAA) and the Department of

Transportation (DOT) are developing the WAAS program for use in precision flight approaches.

• How it Works– WAAS consists of approximately 25 ground reference stations positioned

across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message.

• Who benefits from WAAS?– Currently, WAAS satellite coverage is only available in North

America.

Types of Correction

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• Beacon– The U.S. Coast Guard operates the most common

DGPS correction service. This system consists of a network of towers that receive GPS signals and transmit a corrected signal by beacon transmitters

Types of Correction

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Types of Correction

• Television

– There are roughly 2,800 television antennas around the U.S. These won’t have to be modified in any way for TV-GPS to work.

– A GPS device, cell phone, laptop, PDA or other portable gadget equipped with a Rosum TV Measurement Module chip picks up television signals being broadcast in a given area, much like a typical GPS device picks up satellite signals. From these signals it triangulates its latitude and longitude.

– Unlike the GPS system, TV stations don't have a common synchronized clock, which is necessary to give an accurate position. So the system uses a computerized monitor unit to track and measure TV signals

– The location server crunches data from the monitor unit and synchronizes the broadcast-channel clocks to determine the position of Rosum’s TV-GPS chips. It then transmits that location data to the chips.

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Types of Correction• Television

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• External RTCM– Radio Technical Commission For Maritime Services – RTCM Recommended Standards for Differential GNSS

(Global Navigation Satellite Systems) Service, Version 2.3 (RTCM Paper 136-2001/SC104-STD) – This standard is used around the world for differential satellite navigation systems, both maritime and terrestrial.

– RTCM Recommended Standards for Differential Navstar GPS Reference Stations and Integrity Monitors (RSIM), Version 1.1 (RTCM Paper 137-2001/SC104-STD) – A companion to the preceding standard, this standard addresses the performance requirements for the equipment which broadcasts DGNSS corrections.

Types of Correction

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• EGNOS– European Geostationary Navigation Overlay

Service – Is Europe’s first venture into satellite navigation. It

will augment the two military satellite navigation systems now operating, the US GPS and Russian GLONASS systems, and make them suitable for safety critical applications such as flying aircraft or navigating ships through narrow channels.  

Types of Correction

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• Data Collectors– With integrated GPS Receivers– With External GPS Receivers

• GPS Receivers and Accuracy – Mapping Grade– Survey Grade

• GPS Peripherals– Beacon Receivers– Different types of antennas– Laser Range Finders

• GPS Hardware Cost– Is directly related to accuracy– Is also dependant on the Peripherals

GPS Equipment

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• Communication with GPS Receivers– RS232 connector Cable between the collector and receiver– Blue Tooth Wireless Connection– Data collectors with GPS receivers built in

• Other Blue Tooth Enabled Hardware that can be used as a data collector– Table PC – PDA using Windows Pocket PC– Laptops

• Communication with Peripherals– RS232 connector Cable between the collector and external device– Blue Tooth Wireless Connection

Data Collectors

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Data CollectorsTrimble Data Collectors

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Data CollectorsLeica Data Collectors

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• Mapping Grade Receivers– From sub meter to 2 to 5 Meter accuracy– Fairly low cost – Good for GIS Mapping – Verticals are not very accurate

• Survey Grade Receivers– From centimeter to decameter accuracy – Very expensive– Good where precision three dimensional

accuracy is required

GPS Receivers

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Mapping Grade Receivers

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Mapping Grade ReceiversData Collectors with integrated onboard GPS

receivers

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Survey Grade GPSGPS Total Station

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• Antennas– Used to increase accuracy

– Vehicle mounted

– Reference location for survey grade receivers

• Beacon Receivers– Needed for real time DGPS

– Some are integrated into the GPS receiver

– Some are external and communicate through cable or Blue Tooth Wireless Connection

Additional Antennas andBeacon Receivers

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Additional Antenna's and Beacon Receivers

GPS Equipment

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Other GPS Possibilities• GPS PCMCIA cards for Laptops and Notebooks• GPS compact flash cards for PDA’s • Low cost external USB or nine pin GPS devices• Most of these devices are mapping grade 2 to 5

meter accurate.• There is some talk about a sub meter accurate

PCMCIA card that is in the works and is to be released sometime this fall

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Office Support Module which includes cradles for Data Collectors and batteries and also communication ports for connection to the Desktop PC

GPS Equipment

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GPS Equipment

Laser Range Finders can be connected to GPS collectors for use in field data collection which can greatly improve the rate at which data is collected. The laser is aimed at the object in which you wish to obtain a GPS location for and the lasers internal compass and distance information are the feed into the GPS receiver and a location is derived from the combination of this data and the GPS signal received by the GPS receiver.

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Mounting Options

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• Mapping Grade– 2 to 5 Meter Accurate GPS units range from $2,500 to $5,000– Sub Meter Accurate GPS units range from $5,000 to $10,000

• Survey Grade– Centimeter Accurate GPS Total Stations are approximately

$25,000 to $50,000

• GPS Peripherals– Beacon Receivers range from $1,500 to $2,500– Different types of antennas cost vary depending on accuracy– Laser Range Finders range from $2,500 to $5,000

GPS Hardware Cost

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• Office Use• Field Use• How to choose a hardware for the field• Rugged vs. Standard• Specifications for rugged• Total cost of ownership for Rugged vs.

Standard• Other things to consider

Hardware for GIS Systems

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• In the Office

– Desktop• Buy the fastest CPU you can afford• Don’t skimp on RAM Memory -- Minimum 51 2mb• Video card should be at least 64 mb• Fast Hard drive SCSI Preferred• 21” Monitor• CDRW or DVD/CDRW

– Laptop• The same specs apply to Laptops • Fastest CPU, good video card and fast hard drive• CDRW or DVD/CDRW

Simple Hardware Specs for GIS

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• In the Field

– Laptop• Rugged vs. standard• Same specs as office laptops • Blue Tooth Wireless enabled

– Tablet PC• Rugged vs. standard• Transflective Screen• Blue Tooth Wireless enabled

– PDA• Rugged vs. standard• Transflective Screen• Fastest Processor possible• Memory and flash card memory• Blue Tooth Wireless enabled

Simple Hardware Specs for GIS

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How to Choose Hardwarefor Field Use

• Laptop – Laptops are good in trucks– Cumbersome to carry into the field– Has the most CPU Power– Can get by with standard instead of rugged if kept in the truck

• Tablet PC– Easier to take in the field but still bulky– Has good screen size– Pen based for easier data entry in the field

• PDA– Lightweight– Screen size is small– Least amount of processing power

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Rugged Hardware vs. Standard

• Disadvantages of Rugged Hardware– Heavier due to protective materials

– Not as sleek and streamlined as typical office sizes

– Processors are typically slower

– Initial cost is more

• Advantages of Rugged Hardware– More durable for field use

– The average total cost of ownership is less

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Rugged Hardware for GIS

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Popular Classifications for Ruggedized Devices

• MIL Spec (MIL-STD-810F)– Originates from a US Air Force document of

test methods for aerospace and ground equipment

– Vendors who do test to full MIL will trumpet it loudly, so they’ll be easy to identify

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Popular Classifications for Ruggedized Devices

• Ingress Protection (IP44)– Developed by the European Committee for

Electro technical Standardization.

– First digit - protection from solid object• Scale 0 – 6

– Second digit – protection from liquids• Scale 0 - 8

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Popular Classifications for Rugged Devices

Ingress Protection

Protection From Solid Objects

1-

2-

3-

4-

5-

6-

Protection From Liquid

1-

2-

3-

4-

5-

6-

7-

8-

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Popular Classifications for Ruggedized Devices

• National Electrical Manufacturers Association (NEMA 250)– NEMA 250 specification describes a variety

of different enclosures and how they hold up against environmental impact.

– Further defined at www.nema.org

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Popular Classifications for Ruggedized Devices

• Market terms used to identify “classes of ruggedness”– Semi-rugged

– Fully-rugged

– Ultra-rugged

– Combat-rugged

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Total Cost of Ownership for Rugged vs. Standard Hardware

• Initial cost for Rugged hardware is $500 to $1,500 more• You need to look beyond the initial cost to the total cost

of ownership• According to a recent study, the five year total cost of

ownership for rugged hardware was approximately 20% less than standard.

• How can this be?

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Total Cost of Ownership for Rugged vs. Standard

Hardware • As part of the study 197 IT Managers were polled

and 230 laptop and notebook end users.• Findings were that the average mobile computer

damage incident cost their company $3,400.• This is based on the cost to repair the unit and the

employees inability to perform the job without the hardware.

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Other Things to Consider • The average effective life to today's PC is approximately

three years.• GIS takes a lot of bandwidth across your network. Be sure

that your network infrastructure is adequate.• If you are dealing with editing GIS data from multiple

outposts, be sure the communication infrastructure will support this.

• Be sure you have an adequate back up and recovery system in place to restore data incase of hardware failure.

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Recap

• Talked about how GPS works• Went through GPS equipment, accuracy's and costs• Discussed other peripherals for GPS systems• Discussed hardware for GIS systems• Discuss the pros and cons of Rugged Hardware vs.

Standard for GIS in field• Talked about choosing a field device • Understanding the standards for rugged computers• Discussed the total cost of ownership for Rugged

Hardware vs. Standard

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Questions

Thank you!