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GPS Solution - GPS can measure the moving direction of a rigid object

Январь 12th, 2016 by homesecuirtycameras and tagged , , ,

Currently, GPS ( tracking platform ) is the best known and most used satellite positioning system. Over the past 30 to 40 years, several other positioning solutions have been deployed for use in various scenarios, based on various approaches, using infrared, ultrasound, image processing or electromagnetic waves. Positioning or location can be understood as the unambiguous placement of a certain individual or object with respect to a known reference point. This reference point is often assumed to be the center of the Earth coordinate system. In practice, Mobile Positioning and Tracking João Figueiras and Simone Frattasi the reference point can be any point on the Earth that is known to the system and which all the coordinates can relate to. Although the position itself is obviously a very important source of information, this position must be related to a specific time to be even more useful.

In particular, when we consider tracking systems, time information is a key necessity, not only for knowing the position of a certain device at a specific time, but also for inferring higher-order derivatives of the position, i.e., speed and acceleration. Thus, “tracking” is a method for estimating, as a function of time, the current position of a specific target. “Navigation” is a tracking solution that aims primarily at using position information in order to help users to move towards a desired destination. The sever has associated a relational database to store all information about users, devices, and sessions, and a spatial database to support the storage of spatial information, such as the GPS magnetic tracker fixes from all the mobile devices. The location-based application here also responds to queries sent from the “control station,” or main monitoring station, to obtain the GPS fixes of a particular user or group of users and display their positions in a graphical user interface in real time.

GPS also employs TOA ranging and threedimensional positioning model to calculate user position. The measurement of vehicle GPS tracking device positioning model is similar to two dimensional positioning model. Assume that each satellite transmits a unique ranging signal in space. A satellite has a clocks synchronized with others clocks built on other satellites. The clock synchronization and orbit plane of these satellites are monitored and controlled by the control segment (MCS).

GPS also can measure the moving orientation (direction) of a rigid object, e.g., a vessel, an aircraft, etc. A GPS receiver also has a clock synchronized to GPS system time. Ranging signals transmitted from GPS satellites contain time information. It enables the receiver to measure the propagation time of the ranging signal left the satellite based on satellite clock time. We can find that the user position would be at two possible points, and only one of the points is the correct user position. For the user position, it is generally locates on the surface of the earth. Therefore, the lower one of two points will be the true position. In order to measure the more accurate user position, the fourth satellite will be applied to calculate and fix the user’s altitude. In addition GPS can determine the user velocity. The most popular used method is based on estimating the Doppler frequency of the received GPS signals.

More GPS Tracking Solution at http://www.jimilab.com/ .

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The accuracy of a electronic tracker

Декабрь 30th, 2015 by homesecuirtycameras and tagged , ,

GPS Sources of accuracy

With satellites, the electronic signals travel about 300,000,000 meters per second (the speed of light). So the errors in the satellite clock and the receiver clock contribute profoundly to errors in distance measurements. One billionth of a second (one nanosecond) of inaccuracy in a satellite clock results in about 30 centimeters (one foot) of error in measuring the distance to that satellite. For this reason, the satellites are equipped with very accurate (Cesium) atomic clocks. Even these very accurate clocks accumulate an error of 1 billionth of a second every three hours. To resolve the satellite clock drifts, they are continuously monitored by ground stations and compared with the master control clock systems that are combinations of more than 10 very accurate atomic clocks. The errors and drifts of the satellites’ clock are calculated and included in the messages that are transmitted by the satellites. In computing the distance to the satellites, GPS 3G receivers subtract the satellite clock errors from the reported transmit time to come up with the true signal travel time. Even with the best efforts of the control centers in monitoring the behavior of each satellite clock, their errors cannot be precisely determined. Any remaining satellite clock errors accumulate typically to about a few nanoseconds, which cause a distance error of about one meter.

the accuracy of our computed position also depends on how accurately we know the location of the satellites (the points of references). The orbits of satellites are monitored continuously from several monitoring stations around the earth and their predicted orbital information is transmitted to the satellites, which they in turn transmit to the receivers. The history of GPS has shown, thus far, that the accuracy of the orbital prediction is in the order of a few meters. This will create about a few meters of error in computing our position.

GPS receiver

A fair number of geocachers use only their GPS tracking device for cars to get them to a cache, but a good local map of the area can be very helpful. Although a receiver can lead you directly in a straight line to cache, it’s probably not going to tell you about the river, deep canyon, or cliffs between you and the cache. Even GPS receivers that display topographic maps often won’t show enough detail that can help or hinder you on your way to a cache. Additionally, a map and compass serve as a backup just in case something goes wrong with your GPS.

You can certainly find caches by using only a map and compass (my adventure racing team does this to practice our navigation skills), but it’s sure a lot easier when using a GPS receiver. You don’t need an expensive GPS unit with lots of whistles and bells to geocache; a basic model around or under $100 will work just fine; receivers that support WAAS (Wide Area Augmentation Service) usually are more accurate than those that don’t. Don’t forget to bring the GPS receiver user manual, especially if you just purchased your receiver and are still trying to figure out how to use it.

More GPS tracking solutions at http://www.jimilab.com/ .

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