WAAS / EGNOS

WAAS stands for Wide Area Augmentation System. It is a system that increases the accuracy of a GPSr using ground-based receivers at known locations in the US to receive GPS signals and send correction data via additional satelites.

EGNOS stands for European Geostationary Navigation Overlay Service and is a similar system used in Europe.

Enabling this feature allows the GPSr to receive and use these additional signals to calculate a more accurate position than from GPS alone. I'm not aware of any reason to not leave it enabled.

If you are out of the coverage area for these signals (pretty much the 48 contigious states for WAAS) then having it enabled can actually increase your error. So users in places like South America, Africa and Australia would want to disable this. Otherwise, leaving it enabled should produce much more accurate results.

1. Uses extra processor cycles to compute WAAS corrections. This may or may not be noticeable but realize that it does require more of the CPU when WAAS is enabled. Also, if WAAS satellites are NOT seen or locked (because they tend to be low on the horizon and blocked by buildings, etc), the unit will continue to search for them, which again takes additional processor cycles.

2. Automotive GPS units won't see any benefit to having WAAS enabled since these units are automatically set to lock-on-road. Any additional increase in positional accuracy gained by using WAAS will be negated by lock-to-road.

The units that will gain from WAAS are aviation units, marine units and hand-held units used for geocaching where lock-to-road is not used nor needed.

IMO, just turn it off as you wont see any benefit to using it.

Here are just a few links concerning WAAS:
http://www.poi-factory.com/node/5698
http://www.poi-factory.com/node/847
http://www.poi-factory.com/node/11390
http://www.poi-factory.com/node/16891
http://www.poi-factory.com/node/6864
http://www.poi-factory.com/node/10647
http://www.poi-factory.com/node/7957
http://www.poi-factory.com/node/2199

RT

See:

http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System

"Also, if WAAS satellites are NOT seen or locked (because they tend to be low on the horizon and blocked by buildings, etc), the unit will continue to search for them, which again takes additional processor cycles."

which also increases the battery usage!

Which nüvis have WAAS? I tried Garmin's product selector and WAAS is no longer listed as a feature.

I like the WAAS, but it takes a bit to lock but more accurate.

Only the older 3xx/6xx series had WAAS advertised and configurable on them. After those units, WAAS was neither advertised nor configurable on any other nuvi that I know of. The fact is that it's not needed on autonav units for the reasons I mentioned above.

While Garmin seems mute on the topic, Amazon claims that some 2xx units have WASS in their on-line descriptions. And the accuracy of my nuvi 250 has me believing that it must have WASS even though the satellite and diagnostic screens give me no indication that it does. Road lock or not, a WASS capable receiver is more accurate when used in a WASS covered area. I have seen prior claims in these forums that WASS is not needed because the new receivers use a "high sensitivity" chip. This is wrong and completely fails to understand the differences between sensitivity and accuracy and error correction. It would be like saying someone should understand you even if you mumbled as long as the audio was amplified.

You can actually notice a difference?

Does Canada have and WAAS ground stations?

Yup my 350 has it,i got it turned off.