2. Definition The Global Positioning System (GPS) is a
space-based satellite navigation system that provides location and
time information in all weather conditions, anywhere on or near the
earth where there is an unobstructed line of sight to four or more
GPS satellites. 1
3. The Generic Term The generic term for these systems is
Global Navigation Satellite System, GNSS. There is such systems as
Russian`s GLONASS, USA`s GPS, European project Galileo, etc. 2
4. How GNSS Works 3 The satellites orbit around earth and
broadcast information. That information is basically a time
stamp.
5. GNSS Receivers Receive GNSS receivers do not have two-way
communication with the navigation satellites; the satellites are
broadcast-only. 4
6. GNSS is not Great at Elevation Horizontal accuracy for
recreational/consumer devices and many cell phones is about +/- 10
meters (within a tennis court) while vertical accuracy can be two
or three times that, about +/- 20 or 30 meters. The cause of this
relies to geometry. 5
7. Assisted GPS With multiple GNSSs online, or coming online,
and a variety of non-GPS locating technologies in use (wi-fi, cell
tower, etc.), theres an effort to bring them together for enhanced
solutions. 6
8. GPS Interference Because GPS signals from satellites are
very weak radio signals, they are susceptible to interference by
natural and man-made signals. 7
9. Government Control of GPS While the U.S. Department of
Defense developed and operates GPS, it serves a wide range of
civilian users. To date, the Department of Defense has never shut
off GPS in any part of the world, for any reason. 8
10. Navigating by GNSS The GNSS only provides information to a
receiver to determine its current location, velocity and time. Any
other information, such as the direction of motion, a suggested
route to a destination, a map, is provided by software algorithms
and stored map data. 9
11. The GPS is Wrong! Most of the time a GPS receiver is
correct in determining its position, within its tolerance. If a
navigation system fails to provide an accurate route, other things
are more likely to be the culprit, for example: poor algorithm
out-of-date street network wrong destination address The U.S.
government received so many complaints on this matter it compiled
an article to explain to users how to fix such errors. 10