Project PDA

The Global Positioning System, usually called GPS, and originally named NAVSTAR, is an intermediate circular orbit (ICO) satellite navigation system used for determining one's precise location and providing a highly accurate time reference almost anywhere on Earth.

Global Positioning System (GPS) receivers can supply very cheap and accurate time information to a master host running ntp. Sites concerned with security should have a source of accurate time.

A GPS unit receives time signal transmissions from multiple satellites, and calculates its position by triangulating this data. Te GPS was designed by and is controlled by the United States Department of Defense and can be used by anybody for free.

IPosDet Interface provides direct access to the handset's assisted Global Positioning System (GPS) facility gpsOne, in which the handset monitors both the cellular network and GPS satellite signals and offloads expensive processing to location servers on the network, permitting location fixes with as little as one cell site and one GPS satellite's worth of data.

When utilizing your PDA for GPS functions, remember that the appliance might not be intended for harsh outdoor actions. Your PDA screens will most probable be complete of glass and the component itself might not be water-resistant.

Application included in the software package standard Pocket PC operating system from Microsoft. This is a guide map of various cities, which can be expanded and updated from the Internet.

The availability of Microsoft(R) Streets & Trips 2005 with GPS Locator, a landmark product that combines the company's first Global Positioning System (GPS) hardware device with the latest version of the best-selling mapping and travel planning software for the United States and Canada. Streets & Trips 2005 with GPS Locator provides real-time GPS tracking and a comprehensive array of maps, driving directions and points of interest to help travelers know exactly where they are and where they are headed at all times.

Mapping and GIS

Mapping of resources and other less precise applications typically used with Geographic Information Systems often require greater precision than is possible with autonomous GPS receivers, but do not justify the expense of a survey grade receiver. Mapping grade GPS receivers use the carrier wave data from only the L1 frequency, but have a precise crystal oscillator which reduces errors related to receiver clock jitter. This allows positioning errors on the order of one meter or less in real-time, with a differential GPS signal received using a separate radio receiver. By storing the carrier phase measurements and differentially post-processing the data, positioning errors on the order of 10 centimeters are possible with these receivers.

How It Works

The Global Positioning System is a "constellation" of at least 24 well-spaced satellites that orbit the Earth and make it possible for people with ground receivers to pinpoint their geographic location. The location accuracy is anywhere from 1 to 100 meters depending on the type of equipment used. The GPS is owned and operated by the U.S. Department of Defense, but is available for general use around the world.

• A minimum of 24 GPS satellites are in orbit at 20,200 kilometers (12,600 miles) above the Earth. The satellites are on six orbits with a declination of 60°. They are spaced so that from any point on Earth, at least four satellites could be above the horizon.
• Each satellite contains a simple computer, atomic clocks, and various radios. With an understanding of its own orbit and the clock, the satellite continually broadcasts its changing position and time. The satellites use their on-board atomic clocks to keep precise time, but are otherwise very simple and unsophisticated when compared to other modern spacecraft.
  
• A number of times per day, depending upon various requirements, 2 SOPS of the USAF contacts each of the GPS space vehicles (or SV or satellite) and provides it with a new navigational upload. The NAV upload is built using a continuously running Kalman Filter that determines the true time and position of each using an array of Remote Sites around the globe, space weather information, and other various inputs.
  
• On the ground, any GPS receiver contains a computer that calculates its own position by getting time signals from three of the four satellites, using a process called trilateration (similar to triangulation). The result is provided in the form of a geographic position — longitude and latitude — to, for most receivers, within 100 meters.
  
• If the receiver is also equipped with a display screen that shows a map, the position can be shown on the map.
• If a fourth satellite can be received, the receiver/computer can figure out the altitude as well as the geographic position.
• If you are moving, your receiver may also be able to calculate your speed and direction of travel and give you estimated times of arrival to specified destinations.
• Some specialized GPS receivers can also store data for use in Geographic Information Systems (GIS) and map making.
• The coordinates are calculated internally according to the WGS84 system.