Forum: Questions And Answers About Geocaching
Topic: What's the deal with WAAS
started by: mikechim

Posted by mikechim on Oct. 30 2001,2:26 am
Ok, my garmin extrex venture has the WAAS capability but the instruction booklet warns me against using it since it's a technology still in development.  So what's the deal with it.  I get the general gist is that it uses radio stations or something around to give a better pinpoint of your location.  If that's so what's the disadvantage of using it, should I turn it on.. will it make any difference at all, even a 4 ft diff would be cool just for the purpose of seeing it.  Can it cause messed up readings or something why the warning?  :wstupid:
Posted by Guest on Oct. 30 2001,9:40 am
First let me say I am by no means an "expert" in regards to WAAS.

You are correct in the fact that WASS also employs ground stations to increase accuracy of the GPS. Because it uses these fixed stations (which have a known "fixed" coordinate), WASS is able to calculate errors in the GPS signals and then relay them to your "WAAS enabled" GPS via special satellites.
Your GPS then uses this added info to calculate a more precise location.

Current drawback is that there are only 4 WAAS satellites so, unlike GPS satellites, the signal coverage is not global.  Because of this satellite vies is much closer to the horizon which means physical objects (tress, buildings, mountains, etc) may intefere with, or in some cases totally block WAAS reception. Also because the ground stations are widely scattered, this too may effect overall improvement of accuracy.

Now, while I am not sure why they would recommend you "not" use WAAS, I can see where they may tell you to take the above into consideration when using it.
If you get a good lock on a WASS satellite it is said by the FAA (developers of WAAS) that you can expect your GPS accuracy to be improved to around 5-7 meters. Personally I have tried it with and without and found with it enabled I was averaging down to 3-5' where as with it off was about 15'.

Keep in mind that I live right on the coast (Va. Beach) so I get a very good lock on the WAAS sats. and we also have a ground station (2 I think) here in the area.
Posted by Gimpy on Oct. 30 2001,10:01 am
Another thing to keep in mind when waas is enabled is that it causes more battery drain. I might get a 4-6 ft. better EPE with waas enabled. But I don't concern myself too much with it because I figure out of the roughly 9000 caches placed out there, probably no more than say, 20%, of the posted co-ordinates are taken from a unit with waas capabilities. And, especially in the woods, I'll get much better results with my III Plus, with a really good antenna design & no waas, than I will with my eTrex Vista, with the patch antenna & waas enabled. I generally use my MAP76 with the external antenna & waas enabled. :looking:
Posted by Ascension on Oct. 30 2001,1:15 pm
I wa told by a user of a GPS V that out of dozens of caches only once was WAAS of any use, apparently the satellites are very hard to lock onto in forests and mountains.   I certainly would not upgrade just for WAAS, not yet al least. :looking:
Posted by Quinn on Oct. 30 2001,3:32 pm
Yes...you are correct. Right now in certain area's it is not worth buying a unit just for that function. Even in clear sky there is many times whee you wont even find a WAAS sat. When I go caching I don't even use WAAS for that reason.
Until they make additional changes and add-on's I wouldn't even bother with it. :p
Posted by PC Medic on Mar. 21 2002,4:56 pm
To keep up to date with WAAS scheduled outages (including this weeks) be sure to check the < Raytheon Site > .
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