In GPS receivers can store the geographical coordinates ( latitude and longitude ) of a specific point, either the destination or intermediate route, for reference. With this type of application is possible to follow a series of waypoints using a GPS unit on the ground and through a set of maps to pinpoint the availability of many points of interest that would be even categorized by a specific application filters to perform the map based on these categories.

Viewed another way, Waypoints are points that mark a GPS user at any time for future reference, and can create their own sites, sites visited or just to remember who was there. One of the practical uses of these points, which can later be reviewed, downloaded to a computer for use in maps or simply to get back to the place marked, it becomes very handy when visiting places with little or no point reference points such as fishing in a lake , the location of caves in the mountains , and so on.

The term “geomatics” is composed of two branches “GEO” (Earth) and “nuances” (Computer). That is, the study of Earth’s surface through information technology (automatic data processing). This term, born in Canada, is part of the ISO standardization standards International Organization for Standardization and is being recognized in Europe , Asia , Africa, Central America and South as a new discipline. Other agencies especially in the U.S. , have opted for the term geospatial technology or recently “geomatics science.”

The term was coined in 1969 by Bernard Dubuisson ¹ and integrate all the basic sciences and technologies used for knowledge about the area as remote sensing or remote sensing, Geographic Information Systems (GIS), Global Navigation Satellite System (GNSS ) and related knowledge.

• Land navigation (and pedestrian), sea and air. Quite a few cars now incorporate it being particularly useful for finding addresses or indicate the status of the crane .
• Mobile Phones
• Surveying and geodesy .
• Location agriculture ( precision farming ), livestock and wildlife.
• Salvage and rescue.
• Sports, camping and leisure.
• For location of sick, disabled and children.
• Scientific applications in field studies (see Geomatics ).
• Geocaching is a sport that in seeking “treasures” hidden by other users.
• Tracking and vehicle recovery.
• Yachting.
• Aerial sports: paragliding , hang gliding , gliders , etc.
• There are those who draw using tracks or play using the cursor movement as (common in Garmin GPS).
• Safety management systems and fleets.

Military

• Navigation by land, air and sea.
• Guided missiles and projectiles of various kinds.
• Search and Rescue .
• Recognition and mapping.
• Detection of nuclear detonations.

The rationale lies in the fact that the errors produced by the GPS system apply equally (or very similar) to the receptors located close together. The errors are strongly correlated in the next recipients.

A ground-based GPS receiver (reference) who knows exactly its position based on other techniques, get the position given by GPS, and can calculate the errors caused by GPS, comparing with it, known in advance. The receiver transmits error correction receivers next to him, and so these can, in turn, also correct the errors produced by the system within the coverage area of ​​transmission of signals from GPS reference computer.

In short, the structure would DGPS as follows:

• Monitored station (reference) , which knows its position with high accuracy. This station consists of:
  • A GPS receiver.
  • A microprocessor to calculate the GPS system errors and to generate the structure of the message sent to recipients.
  • Transmitter to establish a data link to the receivers one-way end-users.
• User equipment , comprising a DGPS receiver (GPS + receiver link monitored data from the station).

There are several ways to get DGPS corrections. The most commonly used are:

• Received by radio , through a channel prepared for it, as the RDS on a radio FM .
• Downloaded from the Internet or a wireless connection .
• Provided by a satellite system designed for this purpose. In the U.S. there is WAAS in Europe, the EGNOS and Japan theMSAS , all compatible.

The messages that are sent to the recipients next can include two types of corrections:

• A correction applied directly to the position . This has the disadvantage that both the user and the monitoring station will use the same satellites since the correction is based on the same satellites.
• A pseudo-correction applied to each of the visible satellites . In this case the user can make the correction using the 4 satellites better signal to noise ratio (S / N). This correction is more flexible.

The error produced by selective availability (SA) varies even faster than the speed of data transmission. Therefore, with the message that is sent corrections, also sent the validity period of the corrections and trends. Therefore, the receiver must do some interpolation to correct the mistakes made.

If you wish to increase the coverage area DGPS corrections and at the same time minimizing the number of fixed reference receivers will need to model the spatial and temporal errors. In this case we are talking about wide area differential GPS.

With the DGPS can correct errors in part due to:

• Selective Availability (removed from the year 2000 ).
• Spread the ionosphere – troposphere .
• Errors in satellite position ( ephemeris ).
• Errors caused by problems in the satellite clock.

For DGPS corrections are valid, the receiver must be relatively close to a DGPS station, generally, less than 1000 km. The details which are handled centimeter differential receivers, so it can be used in engineering.

The GPS receiver uses the information sent by the satellites (time at which broadcast signals, locating them) and tries to synchronize its internal clock with the atomic clock that have satellites. Synchronization is a process of trial and error a portable receiver that occurs once every second. Once synchronized the clock, you can determine its distance to the satellites, and uses that information to calculate your position on earth.

Each satellite indicates that the receiver is at a point on the surface of the sphere, centered on the satellite radio and the total distance to the receiver.

Getting information from two satellites indicates that the receiver is on the circle that results when the two spheres intersect.

If we acquire the same information from a third satellite we noticed that the new sphere intersects the circumference just above two points. One of them can be ruled out because it offers an absurd position. In this way we would have 3D position. However, since the clock incorporating GPS receivers are not synchronized with atomic clocks in GPS satellites, the two fixed points are not accurate.

Taking information from a fourth satellite, we eliminate the inconvenience of the lack of synchronization between the clocks of the GPS receiver and satellite clocks.And at this point that the GPS receiver can determine a precise 3D position ( latitude , longitude and altitude ). Not being synchronized clocks between the receiver and the satellites, the intersection of four spheres centered on these satellites is a small amount rather than a point. The correction is to adjust the receiver time so that this volume becomes a point.

• Adding a new signal on L2 for civilian use.
• Adding a third civil signal (L5): 1176.45 MHz
• Protection and availability of the two new signs for services Safety For Life (SOL).
• Improved signal structure.
• Increased signal strength (L5 will have a power level of -154 dB).
• Improvement in accuracy (1 – 5 m).
• Increased number of monitoring stations: 12 (twice)
• Allow better interoperability with the L1 frequency of Galileo

The GPS III program aims to ensure that the GPS will meet military and civilian requirements planned for the next 30 years.This program is being developed to use an approach in 3 stages (stage of transition is the GPS II), very flexible, allowing future changes and reduce risks. The development of GPS II began in 2005 and the first of which will be available for launch in 2012, with the goal of complete transition GPS III in 2017. The challenges are:

• Representing the requirements of users, both civil and military, in terms of GPS.
• Limit GPS III requirements within the operational objectives.
• Provide flexibility to allow future changes to meet user requirements until 2030.
• Provide strength to the growing reliance on the positioning and precise time as international service.

The system has evolved and new systems have led him positioning IPS-2 refers to Inertial Positioning System, inertial positioning system, a data capture system, which allows the user to perform measurements in real time and in motion, called Mobile Mapping. This 3D mobile mapping system gets based on a device that includes a laser scanner, an inertial sensor, and an odometer GNSS system aboard a vehicle. They get great precision, thanks to three positioning technologies: GNSS + IMU + odometer, that working at the same time give the option of measuring even in areas where satellite signal is not good.

In 1957 , the Soviet Union launched the space satellite Sputnik I , which was monitored by observing the Doppler shift of the signal transmitted. Because of this, we began to think that, similarly, the position of an observer could be established by studying the Doppler frequency of a signal transmitted by a satellite whose orbit was determined precisely.

The U.S. Navy quickly applied this technology to provide navigation systems for their fleets of observations to date and accurate positions. Thus arose the systemTRANSIT , which became operational in 1964 , and by 1967 was available also for commercial use.

The position updates, then, were available every 40 minutes and should remain almost static observer to obtain adequate information.

Later in that decade and through the development of atomic clocks, we designed a constellation of satellites, each carrying one of these watches and being all synchronized based on a reference of time.

In 1973 we combined the programs of the Navy and the Air Force United States (the latter consisting of a transmission technique that provided accurate data encoded using a signal modulated with a PRN code (Pseudo-Random Noise: pseudo noise -random), in what became known as Navigation Technology Program (navigation technology), later renamed as NAVSTAR GPS.

Between 1978 and 1985 were developed and released eleven satellites NAVSTAR experimental prototype, the following generations of satellites to complete the current constellation, which is said to “initial operational capability” in December 1993 and with “full operational capability “in April 1995 .

In 2009 , this country offered the service standard for determining the position to support the needs of the ICAO , and she accepted the offer.

[ edit ]Technical features and benefits

 

Satellite operator controlling the NAVSTAR-GPS, Schriever Air Force Base.

 

Launch of satellites for the NAVSTAR-GPS by a Delta rocket.

The Global Navigation Satellite component:

• Satellite System : It consists of 24 units with synchronized paths to cover the entire surface of the globe. More specifically, distributed in 6 orbital planes of four satellites each. The electrical energy required to operate the acquired from two composite panels of solar cells attached to its sides.
• Ground stations : send control information to control the satellite orbits and perform maintenance on the entire constellation.
• Receiving terminals : Indicate the position you are, also known as GPS units, are that we purchased at specialty stores.

[ edit ]Space segment

• Satellites in the constellation: 24 (4 × 6 orbits)
  • Altitude: 26,580 m
  • Period: 11 h 58 min (12 hours sidereal )
  • Tilt: 55 degrees (relative to the Earth Ecuador).
  • Shelf Life: 7.5 years
• Control segment (ground station)
  • Main Station: 1
  • Ground antenna: 4
  • Monitoring station (tracking): 5
• RF Signal
  • Carrier frequency:
    • Civil – 1575.42 MHz (L1). Use the coarse acquisition code (C / A).
    • Military – 1227.60 MHz (L2). Use the Precision Code (P) encryption.
      • Level of signal strength: -160 dBW (surface soil).
      • Polarization: circular clockwise.
• Correctness
  • Location: officially stated approximately 15 m (95% of time). In reality a portable GPS 12 parallel channel single frequency provides an accuracy of 2.5 to 3 meters in more than 95% of the time. With WAAS / EGNOS / MSAS enabled, the accuracy rises from 1 to 2 meters.
  • Time: 1 ns
• Coverage: global
• User Capacity: Unlimited
• Coordinate system:
  • World Geodetic System 1984 ( WGS84 ).
  • Earth-centered, fixed.
• Integrity: notification time of 15 minutes or more. Not enough for civil aviation.
• Availability: 24 satellites (70%) and 21 satellites (98%). It is not enough as the primary means of navigation.