GPS (Global Positioning System) is a radio-navigational satellite system, a part of the NAVSTAR complex, which is designed and operated by the US Department of Defense. GPS permits land, sea, and airborne users to determine their three-dimensional position, speed, and time 24 hours a day, in all weather, anywhere in the world with a precision and accuracy far better than other radio-navigation systems available today or in the foreseeable future. GPS consists of three segments: the Space Segment, the Management Segment and the User Segment.
The Space Segment consists of 24 operational and 8 reserve satellites in 6 circular orbits 20 180 km above the Earth at an inclination angle of 55 degrees with a 12 hour period. The satellites are spaced in orbit so that at any time a minimum of 6 satellites will be in view to users anywhere in the world. The satellites continuously broadcast position and time data to users throughout the world. Each satellite contains an atomic clock providing a very accurate time keeping. Time synchronization of all atomic clocks on all the satellites is controlled by the control segment.
The Control Segment consists of a master control station in Colorado Springs, with about ten monitor stations and three ground antennas located throughout the world. The monitor stations track all GPS satellites in view and collect ranging information from the satellite broadcasts. The monitor stations send the information they collect from each of the satellites back to the master control station, which computes extremely precise satellite orbits. The information is then formatted into updated navigation messages for each satellite. The updated information is transmitted to each satellite via the ground antennas, which also transmit and receive satellite control and monitoring signals.
The User Segment consists of personal navigation devices, which allow the users to receive satellite signals and to calculate exact coordinates, speed and time. The concept of GPS is based on measuring distance to the satellites. The user determines his position on the surface of the Earth by measuring their distance to each satellite in the group. In this case the satellites act as precise reference points. Each satellite transfers data about its precise position (ephemerides) and time. The user’s receiver measures the delay of the signal from the satellite to the receiver, which is equal to measuring distance to the satellite. Simultaneous measurements from four satellites allow to calculate the precise three-dimensional coordinates, speed and time.
GPS (Global Positioning System) is a radio-navigational satellite system aimed at precise position, speed and time determination.
GPRS (General Packet Radio Service) is a secondary structure over the GSM cellular communication technology, which provides packet data transmission. GPRS allows a user of the cellular communication network to exchange data with other devices connected to the GSM network and having access to an external network, including the Internet.
Therefore, these are two completely different systems, which are not directly interconnected, even though the abbreviations sound similar.
The satellite signal, which is transferred on a frequency of L1=1575,42 MHz, is aimed for civil use and is transmitted without any limitation, free of charge, with no usage fee.
The concept of the GPS is based on measuring distance to a group of satellites, which act as precise reference points. Each GPS satellite transfers precise data about its position and time. The user’s navigation device measures the delay of the signal from each satellite, which allows to determine the distance to each of them. The measurements received from 4 or more satellites simultaneously are treated by a processor for calculating three-dimensional space coordinates, speed and time.
The GPS provides two levels of service: the SPS (Standard Positioning Service) for general use and the encoded PPS (Precise Positioning Service) primarily intended for use by the US Department of Defense. The accuracy of positioning for the Standard (SPS) level was significantly degraded to protect U.S. national security interests (the so-called Selective availability (SA) mode). Since the 1st of May, 2000, the USA have stopped the Selective Availability (SA) mode, which was aimed at reducing the accuracy of positioning by civil users, whereupon the accuracy was increased by about five times and now starts from 5 meters (or more) depending on the number of satellites whose signals may be received by the GPS navigation device, and on their relative position in space (their configuration).
Today only the GPS is in full operational capability that is it has the full set of satellites providing navigation around the globe 24 hours a day for all civil users.
The Russian Federation is developing its own GLONASS navigation system. According to IAC website, on 8.12.2011 the number of satellites in GLONASS constellation has reached 24, providing 100% coverage of the Earth surface around the clock. The satellites are located above the Earth in three orbital planes, with orbit inclination of 64.8° and orbit height of 19 100 km.
The European Space Agency and the European Union are planning to launch their own satellite navigation system called Galileo. It is expected to transmit a signal available to users in two frequency ranges, which would reduce the inaccuracy in determining the coordinates to less then a meter.
On the 16th of July, 2009 an Agreement about the launch of four Galileo satellites to an orbit on the height of 23 600 km by the end of 2010 was signed. This will help to move on to another stage of testing the system segments. It is clear that the system will not be ready for real use in navigation soon.
The Wide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay Service (EGNOS) are the parts of the Satellite Based Augmentation System (SBAS), which is aimed at augmenting the accuracy of coordinate determination by the GPS receivers. The WAAS system works in the North America and the EGNOS system works in Europe. There are also some similar regional systems included in the SBAS, in particular GAGAN in India and MSAS in Japan.
The operation principle for all these systems is based on measuring the insignificant deviations of the signal received from the GPS satellites by the ground basic stations. These deviations are calculated and a correcting signal is transmitted to the users through the geostationary satellites of the SBAS system. A lot of navigation devices allow the user to choose whether to consider this correction or not. If the user is not far from the SBAS grould station, considering the correction may improve the accuracy up to 3-5 meters and even better. However, if the user is far from such station, it may, on the contrary, decrease the accuracy, because the air condition, which influences the changes in the satellite signal, can be quite different in this case. The map of the location of the basic EGNOS stations.
To enable the GPS navigation device to determine its coordinates it is necessary to ensure the receipt of the signals from no less then 3 (for 2D coordinates) or 4 (for 3D coordinates) GPS satellites.
The accuracy of the position finding will be the better, the more satellites are within the field of vision. In addition, it depends on the relative position of the satellites. So, it will be the highest, for example, when three satellites are a little higher than the horizon, the azimuth being 120 degrees one from another with regard to the user and one more is at the zenith. On the other hand, it will be the lowest when all the 4 satellites are visible to the user at one space angle and are close to each other.
It is important to take into account that the signal from the satellites can not be received far from the window inside a building, can not be received or is substantially weakened under canopy trees or in the forest, where the horizon is practically closed for reception; it can not penetrate some kinds of car glass and window glass with additives ensuring athermal properties, or with some glass-covering films. Sometimes this problem can be solved by using an additional remote antenna.
The GPS measures the speed on the basis of the precise data about the position and the Doppler’s effect. The discrepancy does not exceed 5sm per second (0.18 km/hour). The speed measured by the speedometer depends on its calibration (which usually overrates the actual speed), the tire pressure, the condition of the road coverage, the coefficient of adhesion etc.
If a switched off GPS navigation device is transported more than 300 km away, or if a navigation device which has not been in use for a long time is switched on, the device will first try to use the almanac and the ephemerides saved in its memory. As this data will be invalid for its new position or after a substantial period of time, the device will start searching through the satellites in turn until it receives the new data about the almanac and the ephemerides from them. This process, which is called the “cold start”, may take 5-20 minutes or sometimes longer. During the cold start it is necessary to stay in one place. In some devices the process of the cold start can be accelerated by indicating an approximate position of the device through the menu or with the help of some other options.
The “warm start” is the start with a relevant almanac, but with the out-of-date ephemerides data. The warm start takes about 1 minute.
The “hot start” is switching on the device after it was out of work for only a short period of time, so that the data about the almanac and the ephemerides does not become out-of-date and the device can determine its position within a short period of time.
An almanac is the information about the due position of each of the satellites at any time. This data is transmitted by every GPS satellite and concerns all the satellites of the system. The almanac data is not very precise and remains relevant for several months before the satellites orbits are adjusted.
The ephemerides are the information set including the precise data about the parameters of the orbits and the adjustment of the atomic clock, which concern only the satellite transmitting this data. The satellites transmit the ephemerides every 30 seconds, this data is only relevant for 30 minutes.
In the end of the past decade and in the beginning of the current one all the GPS chipsets were capable of receiving only the direct signals from the satellites, as a rule they were 12-channel and required a thorough choice of place with favorable receiving conditions.
In the middle of this decade SiRF Technology Holdings, Inc. created a new generation chipset SIRFstar III, which soon became a bestseller due to its increased sensitivity, lower energy consumption and an ability to receive both direct and reflected signals from the satellites. This chipset has 12 channels and provides the SBAS support.
MediaTec Inc. created their own chipsets МТ3328 and МТ3329, which can decently compete with SIRFstar III and are generally similar to it in their specification, but have 30 channels and a bit higher sensitivity.
Both SIRFstar III and MTK chipsets from MediaTec are the most popular nowadays and provide the GPS navigation devices with the best capabilities. At the same time it should be understood that the possibility to receive reflected signals in general decreases to some extent the accuracy of the position determination. However, as to their use for navigation this does not make a problem for the majority of users.
To enable the GPS navigation device to determine its coordinates it is necessary to ensure the receipt of the signals from no less 3 (for 2D coordinates) or 4 (for 3D coordinates) GPS satellites.
In fact, the Earth has the form of a geometric body which is not a sphere nor even a spheroid. Its form is more complicated, however, in geodesy the form of the Earth is represented with a spheroid. This allows to determine the coordinates of each point of the Earth without using overcomplicated mathematical methods. The parameters of the spheroid are chosen so that the mean-square deviations of the model from the reality are minimal for the Earth as a whole or for any particular country or region. That is why there are more than a hundred reference spheroids. The chosen spheroid model and the coordinate system based on this spheroid compose the datum.
The GPS system uses the WGS84 coordinate system based on the GRS80 spheroid model.
The established coordinate system, the latitude, the longitude and the height unambiguously determine the coordinates of any point on the Earth.
The most widely used are the polar coordinate system and the Cartesian (rectangular) coordinate system.
In the polar system a coordinate (latitude and longitude) is measured in degrees, minutes and seconds.
1 degree=60 minutes, 1 minute=60 seconds. The minutes and seconds are often substituted with the decimals of a degree, a minute or a second. So, the basic formats are as follows:
This should be taken into account when using the coordinates for marking or searching a certain point in your navigation device.
The Cartesian coordinate system is connected with using the Universal Transverse Mercator projection and implies the evolution of 6-degree segments of the Earth surface (zones) on a flat surface. The coordinates are defined by the zone number, the distance (in km) from the central meridian of the zone (the X coordinate) and from the equator (the Y coordinate). To avoid negative numbers, Eastern displacement and Northern displacement are introduced for the Southern Hemisphere.
Nowadays, the GPS is widely used for various navigational purposes. They may be conventionally divided into the following groups:
Specialized navigation devices for tourists, hunters, fishers and so on. These devices have a user interface demanding certain knowledge in navigation and a moisture-resistant body; some of them even float on water.
Specialized devices for use in aviation.
Specialized devices for navigation on sea or river vessels.
Portative automotive and motorcycle navigation devices. The body of an automotive navigator is not protected from moisture, the body of motorcycle one has such protection. The user interface is simplified so that to reduce the time needed to find the necessary functions when driving a car or riding a motorcycle. Navigation devices constituting a part of in-built automotive multimedia systems.
Navigation units designed for linking to in-built automotive multimedia systems which do not include a GPS navigation device. They are linked through video and audio inputs. A lot of them support control through the touch screen of the multimedia system. As a rule they also have a remote control.
Personal digital assistants and smart phones with touch screen having an in-built GPS-module or capable of being connected to an external GPS module through Bluetooth, COM-port or USB-port with the relevant software.
Laptop personal computers or netbooks having an in-built GPS-module or capable of being connected to an external GPS-module through Bluetooth, COM-port or USB-port with the relevant software.
Laptop computers or netbooks with an additional GPS-module and the relevant software.
The А-GPS uses the space segment of the GPS, cellular networks and mobile phones or smartphones which do not necessarily have their own real GPS module for position finding. The A-GPS is a paid service. In the online mode, which is the basic one, the coordinates are determined outside the terminal device, thus it is not necessary to have a real GPS module. However, thick cellular network coverage is needed. In the offline mode the A-GPS system is used to transmit an almanac and ephemerides through the cellular network, which decreases the time of the cold and warm start for a real GPS-receiver.
POI (Points of Interest) are objects on the map connected with the infrastructure of the society, such as shops, pharmacies, fuel stations, hospitals, theatres, sightseeing attractions etc. As a rule they are divided into groups. POI may be used to find a relevant place when travelling. The information about such object may include address, telephone number, opening hours etc.
Maps on DVDs have their own format, which is different than Garmin® one or iGO one used for our maps. At the moment the manufacturers of the regular navigation system (the ones installed on the car manufacturer’s plant) do not offer any detailed maps of Ukraine. That is why it may be considered as a solution to install an additional navigation unit that would be connected to the main device through touchscreen cable, audio and video inputs and would start the iGO 8-based CarteBlanche Navigator software from an SD memory card.
If you find any inaccuracies on the map, please fill in the form on the page. We will be grateful if you provide an up-to-date track and/or otherwise illustrate the map fragment. All notices will be considered by our cartographers and taken into account in one of the next map updates.
TomTom navigation devices use their own map format, which is different from Garmin® or iGO formats. That is why our map is not compatible with TomTom devices and software.
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