the new iQue 3600 arrived late yesterday. by the time i was done with the inital setup it was dark and raining so i had to wait until late to day to play with the gps features. i know there were discussions about this topic some time ago but since my little etrex summit did not have this feature then and still doesn't i could have cared less about this subject. so now the question is do i enable WAAS or leave it turned off? i'm giddy with excitement about being paperless and having maps.

Ripped from the Garmin website after a short google...

quote:

You've heard the term WAAS, seen it on packaging and ads for Garmin® products, and maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.

WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.

You got it, it's paid for, turn it up!
I use mine and look where it's gotten me!!
Congratulations on your ascent into GPS mapping and PDAdom, my friend!

I have mine turned on, but can't really see much difference in accuracy - except that the battery life is diminished.
Sat accuracy hasn't been great for the last couple of months, for me. Maybe it's my GPS?

WAAS can increase position accuracy, especially in open areas where the GPSR can lock on several satellites. In a place where the GPS is having a really hard time computing a position due to obstructions or signal reflections, I sometimes turn WAAS off, to give the unit less to deal with. And in some cases that seems to help. The WAAS satellite for eastern US is #35 and it is low on the horizon to the SE, so if there are obstructions to the SE, WAAS will not work anyway.

I am going to take off my geocacher cap and replace it with my surveyor's hat. It certainly is encouraging to notice that some people like jbzhow have been doing their homework and know what differential positioning is all about. I see the logs and cache pages whereas folks are correcting their coordinates a few feet or the other when someone disagrees or has "better" coordinates. The fact is, a gps position in the open without a differential correction can be as much as 90 feet off. Imagine two circles 45 feet in radius. One circle is the hider circle and the other is the finder circle. The circles represent error. They can move over each other or they can be tangent to each other. If they are tangent to each other, that represents the worst case. Draw a circle around the two error circles, tangent to each and that represents the total area a cache may be in and not exceed the stated accuracy of the handheld, non-survey grade gps unit. Now reduce the size of the two circles(error ellispe) to about ten feet and that represents the area of error with WAAS. You can play around with that in your mind if you wish so you have a 9 foot circle representing the hider and a 50 foot circle representing the finder and so on. BEAR in mind however, that in canopy or in a ravine all this goes to heck in a handbasket because of multipath reflections! That is why I am so fond of micros in a ravine, under canopy where there are an infinate number of possibilities. I will leave those caches to memaw, pawpaw and the kids. I wish hiders would add a small note to their description stating the WAAS status such as: "nine satellites observed with WAAS correction on six, accuracy should be acceptable" See "Ol Gene".

quote:

Originally posted by phat.bak:
I have mine turned on, but can't really see much difference in accuracy - except that the battery life is diminished.
Sat accuracy hasn't been great for the last couple of months, for me. Maybe it's my GPS?

I also have noticed a reduction in accuracy the last couple of months.

I first noticed it while in FL (orlando). No differential signals whatsoever. On the return trip, I had several occasions while driving under clear skies that satelite reception was lost. In a few seconds up to about a minute, satelite reception would return--10-11 strong signals all at once.

I haven't seen differential positioning since then.

Any ideas? WAAS is still turned on in my GPS72, maybe something else is turned off?

I checked yesterday in Fayetteville and I could not get a correction. I tried it again around three pm today and 35 was slow coming up, but when it did I got corrections for seven birds. 35 is in the low southern sky so if you were headed North in a vehicle with the gps on the dash, you might have a problem with 35. I have had it blocked by a building or a tree, but you can move around a little and it will come on.

Thanks George.

I understand a little better now, thanks. Thanks also for your 3D geometry explanation above.

I also now understand that in Battery Save mode, differential correction is turned off!

The light bulb finally came on after thinking about it some time later.