Originally Posted by
Photosmith
There's three main contributions to GPS accuracy:
1) WAAS capability - without it, no better than 10 meter accuracy. With it, 3-5 meter accuracy on average.
2) Antenna - A patch antenna is pretty omnidirectional, but only something like 50% as efficient as a Quadrifilar Helix when the Quad Helix is oriented correctly. This of course means sometimes the patch antenna actually tunes a better signal, but the potential is higher with the Quad Helix.
3) Chip design - There's a variety of GPS chips out there and they are not all equal. The latest, greatest are those with the SiRF chipset. Those have the quickest, most accurate signal acquisition and tracking, especially under cover and in obstructed areas.
The reason I bother pointing all this out is that generally the Palm-Pilot and cel phone style GPS will be acceptable for automobile driving directions, but it will never be as accurate as dedicated units like the high end stuff from Garmin. It's up to the user to decide what fits their budget and demands of course, but remember that not all GPS receivers are equal.
The Palm pilot is an antique. New Palms are many generations ahead of those things. Garmin does not produce there own components. They have there products produced by manufactures like every one else. Currently Tyco electronics holds the patent on SiRF GPS technology and is the sole source for SiRF GPS receiver chip sets.
http://www.tycoelectronics.com/gps/modules.asp
The latest Tyco Electronics’ SiRF chip set is the III generation A1080-A. This is the chip set used in all GPS receivers with SiRF III labeling. This is true for all suppliers including Garmin. Hand held computers, and PDA's do not have GPS receivers built into these devices. These devices use a wireless connection to a bluetooth capable GPS unit. If you purchase a bluetooth GPS unit with SiRF III chip set you get GPS accuracy as good as any other SiRF III equiped GPS receiver. Smart Phones have a GPS receiver but may not allow you to access the internal GPS receiver without purchasing that function from your cell phone network provider as is the case with cell phone only devices. Purchasing a SiRF III wireless GPS unit avoids extra charges from your cell phone network provider and you get a much better GPS receiver as well. Currently DX has a SiRF III bluetooth receiver for $61.68.
http://www.dealextreme.com/details.dx/sku.10614
This receiver is just as accurate as any other GPS unit with SiRF III chip sets including the Garmin units. It also is paired with there smart GPS antenna.
http://www.tycoelectronics.com/gps/smart.asp