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 SatelliteBased 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
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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Your Location
Sources of Error
• 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.
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Ionosphere
Sources of Error
• 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.
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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.
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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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Sources of Error
• 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.
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Sources of Error
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Human Error
– Equipment Configuration/Setup, Equipment Use
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Differentially Corrected GPS
• 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
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WAAS
Radio Beacon
Television Frequencies
External RTCM
EGNOS
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Types of Correction
• 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.
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Types of Correction
• 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
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Types of Correction
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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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Types of Correction
• 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.
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Types of Correction
• 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.
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GPS Equipment
• 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
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Data Collectors
• 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
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Data Collectors
Trimble Data Collectors
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Data Collectors
Leica Data Collectors
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GPS Receivers
• 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
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Mapping Grade Receivers
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Mapping Grade Receivers
Data Collectors with integrated onboard GPS receivers
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Survey Grade GPS
GPS Total Station
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Additional Antennas and
Beacon Receivers
• 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
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GPS Equipment
Additional Antenna's and Beacon Receivers
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Other GPS Possibilities
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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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GPS Equipment
Office Support
Module which
includes cradles for
Data Collectors and
batteries and also
communication
ports for
connection to the
Desktop PC
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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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GPS Hardware Cost
• 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
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Hardware for GIS Systems
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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
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Simple Hardware Specs for GIS
• In the Office
– Desktop
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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
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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
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Rugged vs. standard
Transflective Screen
Fastest Processor possible
Memory and flash card memory
Blue Tooth Wireless enabled
How to Choose Hardware
for Field Use
• Laptop
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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
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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
Protection From Liquid
1-
4-
1-
4-
7-
2-
5-
2-
5-
8-
3-
6-
3-
6-
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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
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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!
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