Glossary
Definitions of concepts and terms used for Navigation Software
Glossary
Definitions of concepts and terms used for
Navigation Software
Snap to Road
NMEA and SiRF
Where does MAP data come from ?
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Snap to Road
(a.k.a. as Lock to
Road) This is a feature used by all high-end navigation systems to ensure that your position is shown on a road and not a few millimeters next to it, something that most people would consider distracting. The downside to this is that when reception is bad, your GPS position can be too erroneous to enable the program to interpret it correctly and as a result it might get confused and "snap" you to the wrong road and re-route you. I've seen this happen with Destinator (in NMEA mode) but also with Garmin's GPS V standalone unit. Still this is a feature that's desirable. AFAIK only two programs currently do not implement it, Teletype and Mapopolis | ||||||
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NMEA and SiRF These two terms describe two different languages/protocols output by GPS receivers. While all GPS receivers output the NMEA, only receivers built on the SiRF chipset can output to SiRF. Besides almost all GPS receivers based on this chipset can be switched between the NMEA or SiRF output, the Navman sleeve being the exception. The utilities to switch your GPS can be found here Should this technicality matter to you ? Not really, because most mapping programs use the NMEA protocol, some can use both (TomTom GPS, although SiRF seems to be broken in v1.36 of their driver). One program however, Destinator, one of the better solutions out there, currently performs poorly when fed NMEA information, read more about this issue here Here's a write-up by Sven from PPCPassion's board: "NMEA is the National Marine Electronics Association. They wrote some standards. One is NMEA 0183 which "defines electrical signal requirements, data transmission protocol and time, and specific sentence formats for a 4800-baud serial data bus." Of course RS232 only goes up to 20K too, according to the standard. One of the groups of folks that have adopted the NMEA standard is the GPS community. People can choose to ignore specifics of any standard or selectively support portions of the standard, and so, sure, you can run NMEA 183 at a higher data rate. Bit if either the transmitter or receiver does not support the aberration, you are normally limited to the 'standard'. My Garmin eTrex can output data in a number of 'standards'. My TOPO! program can accept several of them, including the Garmin proprietary one, and the NMEA standard. PocketStreets only accepts NMEA 0183. My Delorme Tripmate only outputs NMEA. You can read some about SiRF at http://www.SiRF.com/index2.html. They are a company touting another standard (theirs). May be better, but just as WMA may be better than MP3, the latter is more widely implemented, and you would just be well advised to ensure the additional purchases you may make will support the one you adopt, or better still, both (...)Nothing wrong with SiRF, but look to see how many commercial mapping programs support it. (Today anyway). " | ||||||
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Where does MAP data come from ? Currently map data used in navigation programs or in standalone GPS receivers has three main sources
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