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Lassen-SK8 Embedded GPS Module xix
Preface
The Global Positioning System (GPS) is a satellite based navigation system operated and
maintained by the U.S. Department of Defense. The GPS consists of a constellation of 24
satellites providing world-wide, 24 hour, three dimensional (3-D) coverage. Although
originally conceived for military needs, GPS has a broad array of civilian applications
including surveying, marine, land, aviation, and vehicle navigation. GPS is the most
accurate technology available for vehicle navigation.
As a satellite based system, GPS is immune to the limitations of land based systems such
as Loran. Loran navigation is limited in coverage and is encumbered by adverse weather.
In addition, the accuracy of Loran navigation varies with geographic location and, even
under ideal conditions, cannot compare with GPS. By computing the distance to GPS
satellites orbiting the earth, a GPS receiver can calculate an accurate position. This process
is called satellite ranging. A 2-D position calculation requires three satellite ranges. A 3-D
position calculation, which includes altitude, requires four satellite ranges. GPS receivers
can also provide precise time, speed, and course measurements which are beneficial for
vehicle navigation.
Differential GPS (DGPS) is a sophisticated form of GPS navigation which provides even
greater positioning accuracy. Differential GPS relies on error corrections transmitted from
a GPS receiver placed at a known location. This receiver, called a reference station,
calculates the error in the satellite range data and outputs corrections for use by other GPS
receivers. These GPS receivers are designated as mobile units and can be dispersed as far
as 100 Km from the base station. Differential GPS eliminates virtually all the
measurement error in the satellite ranges and enables a highly accurate position
calculation. The Lassen-SK8 is differential-ready for applications requiring DGPS
accuracy.
Scope and Audience
Even if you have used other Global Positioning System (GPS) receivers, we recommend
that you spend some time reading this manual. The following section provides you with a
guide to this manual, as well as to other documentation included with this product.