Editorial Reviews. Review. " Although developed as a classroom text, the book is also useful as a reference source for professional surveyors and other GPS. Introduction to GPS: the Global Positioning System/Ahmed El-Rabbany. p. cm. Positioning System: Theory and Practice, 3rd ed., New York. Gps Theory and Practice Hofmann PDF - Free download as PDF File .pdf), Text File .txt) or read online for free. gps-theory-and-practice-hofmann-pdf.
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Request PDF on ResearchGate | Global Positioning System, Theory and Practice , 5th Edition | The Global Positioning System (GPS) is rapidly becoming as. The project of writing a Global Positioning System (GPS) book was con ceived DRM-free; Included format: PDF; ebooks can be used on all reading devices Dr . Lichtenegger is a geodesist with broad experience in both theory and practice. The Global Positioning System (GPS) is rap idly becoming as much a part of our daily lives as the Internet, and it is now being used to navigate and locate cars.
Daniel Rainham: ac. This article has been cited by other articles in PMC. Abstract Background An increasing number of studies suggest that characteristics of context, or the attributes of the places within which we live, work and socialize, are associated with variations in health-related behaviours and outcomes. The challenge for health research is to ensure that these places are accurately represented spatially, and to identify those aspects of context that are related to variations in health and amenable to modification. This study focuses on the design of a wearable global positioning system GPS data logger for the purpose of objectively measuring the temporal and spatial features of human activities. Person-specific GPS data provides a useful source of information to operationalize the concept of place.
Alternatively, basic spatial units can be grouped into larger ones automatically using automated zoning software. Existing methods of spatial bounding are subject to several limitations. First, the majority of studies assume that the relationships between context and health operate within the confines of a single spatial unit, usually represented by an individual's residential census tract.
This assumption may lead to the misclassification of context to variations in health status since it is unlikely that a person would spend all of their time in their residential census tract. Places that influence health are more likely to be spatially interdependent, linked by functional, cognitive and, possibly, sentimental relationships between what happens at one point in space and what happens elsewhere [ 13 ].
People live and function in various places that interconnect in complex ways, and to represent place as a single spatial area risks losing important exposure information. Second, researchers must ascertain the spatial scale appropriate for analysis, the level of aggregation characteristic to the data available, as well as the appropriate temporal frame within which to study causal relationships. Publicly-available datasets are usually static in space and time, and data is routinely collected without consideration of spatial or dynamic process [ 14 ].
Moreover data for health research are limited by lack of attention to spatiality, specifically how the spatial-temporal structuring of daily life defines how social action and relationships are represented [ 15 ].
Third, the scale of observation can influence inference [ 16 , 17 ]. This effect is called the "modifiable aerial unit problem" and, because changing the shape or size of the units on which data are mapped will change average values of the variables recorded, this can change the resulting correlations or statistical models generated from the data [ 18 ].
Spatial units such as postal codes or census tracts may also be changed over time, so altering statistical estimates [ 6 , 13 , 19 - 22 ]. Several solutions to the problem have been proposed, including statistical bounding [ 23 ], multi-scale and zone sensitivity analyses [ 24 ], and spatially-weighted regression techniques [ 25 , 26 ].
An alternative approach to delineating spatial boundaries makes use of time-location data. Recording changes in spatial location through time ultimately provides the most complete source of evidence on how place may influence health.
All human activities have spatial and temporal dimensions: activities occur at particular places for limited durations [ 27 , 28 ]. By capturing simultaneously the locations and activities individuals through time it is possible to construct a series of space-time paths that represent objectively both spatial extent and the intensity of activity as represented by time in one or more places.
Information about time, location and activity is usually acquired from interviews, personal observation shadowing or through time-diaries [ 29 ]. Other approaches using electronic sensors and loggers have been employed quite successfully in the context of transportation research and time-activity studies [ 30 - 33 ]. Recent efforts have improved on GPS tracking technologies for the purpose of measuring harmful exposures in human health research [ 34 , 35 ].
These limitations also make it difficult to capture individual time-location information in a variety of contexts. The present article describes the development of a new time-location measurement tool suitable for studies where information about location and time is used in predicting variation in human health outcomes. Global Positioning Systems In the US Department of Defence DOD developed a satellite-based radio navigation system capable of determining within centimetres a position on the earth's surface.
The system consists of 24 active and several "back-up" satellites, that orbit the earth providing all-weather navigation and surveying worldwide [ 36 ]. Global positioning systems GPS consist of three components: satellites in space, a ground control system, and the user's instrument.
The space component consists of orbiting GPS satellites equipped with atomic clocks, and transmitting two radio frequencies modulated with two types of code: precise and standard. The precise code is reserved for U.
The civilian code comprises a 50 bs-1 radio signal transmitted at 1, Together these provide information on the satellites available for fixing a position, the current time and date, and the approximate constellation of the satellites at any time throughout the day.
The ground control segment consists of five monitoring stations, three ground antennas, and a master control station. Unfortunately, the timing was less than ideal for Dr. Therefore, I decided to start the project with other coauthors. Remondi agreed and indicated his willingness to be a reviewer. I selected Dr. James Collins from Rockville, Maryland, U.
In my opinion, the knowledge ofthe three authors should cover the wide spectrum of GPS. Lichtenegger is a geodesist with broad experience in both theory and practice. Since , Dr. Lichtenegger's main interest is dedicated to GPS. Up to 10 GPS satellites are normally seen assuming a 10 degree elevation. The satellites are equipped with several cesium clocks, which provide high timing accuracies.
The satellites are in synch with each other. Positional accuracy of meters, timing accuracy of nanoseconds and frequency accuracies of a few parts in can be obtained. These accuracies are achievable with the selective availability arti cial degradation in e ect. Each satellite transmits on two L band frequencies, L1 L2 carries the P code. Incidentally, when P code is encrypted it is known as Y code. A navigation data message is superimposed on these codes.
The same navigation data message is carried on both frequencies. The groups are des- ignated as blocks.
The block I satellites were intended for system testing. The block II satellites were the rst fully functional satellites, including cesium atomic clocks for timing as well as the ability to implement selective availability.
The latest satellites, the block IIR versions, include autonomous navigation. If such internal failures are detected, users are noti ed within six seconds. Other failures may take from 15 minutes to several hours to rectify. Some receivers compute an estimated gure of merit, which indicates the con dence level of the position information. The development of integrity capabilities to meet safety requirements of various applications is underway.
Each satellite has two identifying numbers. Second is the space vehicle SV number. This number is assigned in order of launch. The third is the pseudo-random noise code number PRN. This is a unique integer number which is used to code the signal from that satellite. Most receivers are 8 capable of receiving and using the SPS signal.
This service provides meters horizontal accuracy, meter vertical accuracy and nanoseconds time accuracy. The signals providing standard positioning service are inherently capable of greater accuracy than this. PPS signals can only be accessed by authorized users with cryptographic equipment and keys and specially equipped receivers.
The accuracies achievable using PPS are The SA bias on each satellite signal is di erent, and so the resulting position solution is a function of the combined SA bias from each SV used in the navigation solution.
Di erential corrections must be updated at a rate less than the correlation time of SA and other bias errors. This process is based on the principle that most of the errors seen by GPS receivers in a local area will be common errors. These common errors are caused by factors such as clock deviation, selective availability explained in Section 3.
If a GPS receiver is placed at location for which the coordinates are known and accepted, the di erence between the known coordinates and the GPS-calculated coordinates is the error. Since the sources of the error are continuously changing, it is necessary to match the error correction data from the base station very closely in time to the rover data. One way of doing this is to record the data at the base station and at the rover. The data sets can be processed together at a later time.
This is called post processing and is very common for surveying applications. The other way is to transmit the data from the base 9 station to the rover. The error calculation is made in the rover in real time. This process is called real-time DGPS.
Di erential GPS o ers accuracies of a few meters better than the military's precise position- ing service. It also facilitates detection of erroneous signals from the satellites.
Currently commercial services exist for getting real time di erential data. The satellites operate in circular 19, km orbits at an inclination angle of Each satellite transmits on two L frequency groups. Each satellite transmits on a unique pair of frequencies.
Two versions are currently in operation: Loran C, which serves civilian users and Loran D, which serves the military. These are medium to long range, low frequency time-di erence measurement systems. A master and usually up to four secondary transmitting stations put out a set of radio pulses centered on kHz, in a precisely timed sequence.
The receiver measures the di erence in arrival time between these transmissions from di erent stations and estimates the position. Loran C transmissions can be worked out to ranges over kilometers from master stations, providing accuracies of to meters.
Shorter range accuracies of better than 30 meters are also available. Developed by Johns Hopkins Applied Physics Laboratory, the system was intended as an aid to submarine navigation.
The Transit system allowed users to determine position by measuring the Doppler shift of a radio signal transmitted by the satellite. Users were able to calculate position to within a few hundred meters as long as they knew their altitudes and the satellite ephemeris.
First, the system is inherently two dimensional. Second, the velocity of the user must be taken into account. Third, mutual interference between the satellites restricted the total number of satellites to ve. Thus, satellites would only be visible for limited periods of time.
These drawbacks pretty much eliminate aviation applications and severely limit land-based applications. The original satellite ew with stable quartz crystal oscillators. Later models ew with the rst space-borne atomic clocks. The third satellite acted as a GPS technology demonstrator. This could greatly reduce the cost of determining position.
GPS time is a composite time composed of the times of all available satellite and monitor station clocks. The exact di erence is provided as constants in the GPS navigation message.
GPS can be used to determine accurate time globally. GPS belongs to the dynamic system achieved by the atomic time scales. Inexpensive GPS receivers operating at known positions provide a timing accuracy of about 0. With more sophisticated techniques, one can globally synchronize clocks precisely.
Presently achievable accuracy of time via GPS is some tens of nanoseconds, however one nanosecond is considered possible. Ultra precise time transfer is possible few nanoseconds but requires advanced preparation, coordination of the two sites and tracking of speci c satellites during speci c time periods.
Loran-C transmissions are also used for time dissemination and frequency reference purposes. Typically frequency accuracies of 1 part in and time accuracies of better than one microsecond can be achieved.
Both USNO and NIST provide telephone voice messages accuracy 30 milliseconds , com- puter modem time transfer several milliseconds and remote synchronization of time bases 1 part in For real-time processing, special formats are employed. There are two predominant formats currently being employed. NMEA is a data format standard commonly employed for communications between ship-borne navigation electronics. GPS receivers output this format but do not accept it.
Version 2. With absolute time synchronization a special time synchronization receiver picks up the sig- nals from a single GPS satellite as it travels overhead. When clock y-overs are used, the satellite swings up over the two sites, one after the other. As it passes over each site, careful clock synchronization operations are performed to determine for each ground based clock relative to the satellite.
Under typical conditions this 12 mode yields a clock synchronization error of around 50 nanoseconds. The common view mode can be implemented when two distant sites have direct line-of-site access to the same GPS satellite at the same time.
This mode yields synchronization errors of 10 nanoseconds or less. The multi-satellite common view mode involves four or more satellites that are being observed simultaneously from the two di erent clock sites. Experts believe that they can achieve synchronization errors as small as 1 nanoseconds.
With increasing sales volume, the costs are coming down and new applications are being reported in the news everyday. However, very few applications of GPS in distributed systems and networking have been reported. Before discussing them, it is useful to take a brief look at other applications. These can provide us new ideas about computer applications.
Accurate frequency counters, time interval counters, frequency calibrators and phase comparators can be built using the GPS technology. Accurate frequency and timing o set measurements can be made. In the GPS clock, one pulse per second signal exhibits an RMS pulse-to-pulse jitter of 1 nanosecond rather than 20 to 60 nanoseconds observed on 1 pps outputs from time based GPS receivers.
It may provides services like the shortest route, etc. This is the most publicized application of GPS. These systems com- bine cellular data networks for communication, GPS for vehicle location, and geographic information system tools for mapping display.
With the aid of a wireless communication link, the emergency system communicates the GPS derived position information and the speci cs of the situation to the base station. Several other emergency products exist currently. GPS technology can be used to plot aircraft altitude to a pitch of one-tenth of one degree.