Here's your primer on GPS. The scope of this document is mostly limited to carputing but may apply in other applications as well.
How Does GPS Work?
Here are a few sites which have excelent write-ups on how GPS functions:
http://electronics.howstuffworks.com/gps.htm
http://www.nasm.si.edu/exhibitions/gps/work.html
http://www.pocketgps.co.uk/howgpsworks.php
http://http://www.gpspassion.com/fr/...rentVersion=EN
Reviews
GlobalSat BR-355 :: highly rated w/ it's users.
GlobalSat BT-338
...& more reviews at the various GPS sites.
Some Terms you may see:
Accuracy :: is largely dependent on signal and timing but w/in 1 to 3 meters is sufficent for auto-navigation
Acquisition time :: aka
Time
To
First
Fix This is the time the receiver requires before outputing it's first fix/position. It is based on a few conditions of the dataset held with in the GPS Receiver. They are: Factory, Cold, Warm and Hot --see
More Reading ~TTFF for full details/discussion.
Antenna :: A physical device which picks up the GPS signals being broadcast by the GPS Satelites. (NOTE: in many instances, GPS Antenna and Receiver are located in the same physical unit so their names are often interchangeable)
DeadReconing :: Dead Reckoning (DR) is the process of estimating your position by advancing a known position using course, speed, and time when loosing satellite signals (in cities, tunnels, etc.).
GEOCACHE(ing) :: An activity something like a treasure hunt. But instead of clues leading to a location or object, GPS coordinates or clues to them are given. Often with trinkets to be found there. (read more:
http://www.geocaching.com &
http://www.navicache.com)
GPS :: Global Positioning System (a man made constelation of satelites which broadcast an array of signals. Computations are performed on these signals to triangulate the exact location XYZ axis of the GPS Antenna.
GPS Receiver :: GPS signal processing hardware. (NOTE: in many instances, GPS Antenna and Receiver are located in the same physical unit so their names are often interchangeable)
GPS Software :: This software interfaces (usualy via drivers of some sort) to your GPS Receiver(/antenna) and plots your current location on the GPS Maps which are typicaly supplied with the GPS Software.
GPS Unit :: combined GPS antenna and GPS signal processing hardware. (NOTE: in many instances, GPS Antenna and Receiver are located in the same physical unit so their names are often interchangeable)
MAPS :: GPS software comes with data maps. These maps must be applicable to the area you're trying to navigate in or GPS will be mostly useless. Typical maps are: (NorthAmerica, UK, Austrailia, etc)
NMEA :: (National Marine Electronics Association) designed for trasnmission speed of 48000bps, used to decribe the encoding method of GPS information as read by various GPS software. Many GPS applications will read GPS info from 'any' GPS antena/receiver as long as the out put of that unit is 'NMEA' compliant.
Points of Interest :: database of various locations by type (parks, campting, business, fuel, etc)
Re-Routing :: When navigating via GPS navigation software you may miss a turn. Re-Routing is a feature of (some) GPS Software applications that senses when you have missed a turn or gone off track. Re-Routing will then plot a new rout from your new current position an display any new routing commands to the driver.
Route Calculation :: The ability to choose from different route methods (Shortest Time, Shortest Distance, Least Use of Freeways, Most use of Freeways, toll avoidance, etc)
SiRF :: A new(er) chipset used in some GPS units which transmits data at current serial port speeds (115200bps). --See:
Brief Introduction of SiRF and NMEA
TTFF :: Time To First Fix (see acquisition time)
Turn By Turn Directions :: Most GPS Navigation software can provide live turn by turn directions including pre-announcing upcoming directions. These announcements can take any of the following forms. Voice prompts spoken to the driver, Display changes indicating distance and direction/type of turn or simple text.
Update Rate :: Typicaly once per second.
WAAS :: Wide Area Agumentation System is a form of differential GPS (DGPS) giving enhanced position accuracy developed primarily for aeronautical navigation but usable by other users. The goal of WAAS is to obtain at least a 7-meter horizontal and vertical accuracy.
More Terms from Bugbyte...
here
What Do I Need? --in order to get GPS navigation working..
Make sure you have the following:
GPS Antenna, GPS Receiver, GPS Software, GPS Maps
Most GPS gizmos today combine the antenna and reiver
Most GPS software comes with maps (just make sure your area is covered by the maps provided)
Make sure the GPS Unit can connect to your computer (serial, USB, Bluetooth, etc) and that there are drivers (if required).
Some Pitfalls to avoid:
Buying wrong hardware for your computer :: Buying Serial GPS for a PocketPC that doesn't have a serial port
Buying (aquiring) software that only works w/ a specific GPS Antenna/receiver set
WindowTinting :: Some (metalic) window tinting may interfere with the GPS signal receiption. Plan your antenna placement carefuly to avoid this.
Features to consider when buying GPS Navigation software:
Maps :: Originaly, they come from one of two sources. This means that copilot, delorme, tomtom, etc do not make their maps. THEY DO control the level of detail interpreted by their maps, they DO control how the data is displayed. So, you may find some more to your liking than others.
Display :: Most directly impacts the usability of your NavSystem. If the features and tags are clear and simple to read. If the directions are clear to see and hear (if voice enabled).
Touch Screen Friendly :: Not all GPS Software was written with the TouchScreen user in mind. Take care to find one that suits your needs.
Update Speed :: While driving it's generaly usefull to have your navigation system keep up with you. If your GPS software can't update at least once per second then you risk missing turns while your NavSystem is catching up.
POIs :: Points Of Intrest help you find resturants, gas, banks/ATMs, etc.. a 'healthy' POI database can really brighten your NavSystem.
Features to consider when buying GPS Hardware:
USB/Bluetooth/Serial :: Most GPS devices connect to the computer via USB. (Some are Bluetooth, others are serial, CF, PCCard, etc) Make sure you get the one that suits you best.
DeadReckoning :: Few of the GPS devices out now have this capabilit but if you're in an area that is prone to loss of GPS signal, this might be a critical option for you.
Weatherproof :: Where you mount your GPS antenna will impact your need for a weatherproofed unit or not.
Brief Introduction of SiRF and NMEA
Connecting to the GPS Receiver is the first hurdle to overcome, but first a brief introduction. Firstly there are two GPS Standards, NMEA and SiRF. Although SiRF is the up and coming new boy on the block, NMEA is the acquired standard and one used by 95% of GPS applications. Why two standards ? NMEA is getting old, it was designed to talk at 4800 baud (4kbps). Modem speeds today are 56kbps so you can see NMEA is slow. SiRF has brought about that change by increasing speeds and utilising full serial speeds up to 115200kbps. The thing is although NMEA is slow, some GPS Receivers will work at higher than 4800, but this is what NMEA prefers. The amount of GPS data sent down the serial port is very small and can easily be transmitted in 4800 baud so although you could reach higher speeds, there isn't really any necessary to do so. SiRF uses higher speeds because it can transmit the data quickly and put the processor into a wait state which in theory means it utilises less power, newer SiRF chipsets like SiRF IIe also have low power consumption which help even further with sustaining power to the GPS Receiver.
More Reading:
http://www.gpspassion.com
http://www.gpsinformation.org/dale/nmea.htm
http://www.routeplanners.co.uk
http://www.pocketgps.co.uk/ttffcomparisons.php :: TTFF
Additional Content provided by NiN^_^NiN -- Thanks!
Getting Started with GPS
Linear Mode
