Quote:
Originally Posted by tgreenstein
You're right. Actually, some routing software and GPSr allow you to input a "known" latitude and longitude (or sometimes a city name) from which it starts the process of searching for satellites based on what's called an ephemeris (a fancy name for a table that lists the projected locations of all of the GPS). My Garmin Nuvi 660 does this and some of the standalone PPC software does as well.
Back in the "early" days of consumer GPSr use this was fairly common as the "time to acquisition" of these devices was pretty slow -- 10-20 minutes wasn't uncommon. Current devices can usually obtain a fix in far less time and, probably as a result, don't offer the option to input a "known" location to serve as a starting point.
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Thanks for your response.
Would you happen to know which older and/or current PPC softwares utilize ephemeris? I would be interested in trying something like this out in my area where it can take up to 5-6 minutes to aquire a fix from a cold start. The aquisition time is significantly increased while moving. (Likely due to downloading partial almanacs)
I would be interested in seeing if there is a significant difference in aquisition time by using ephemeris in my neighborhood.