Can WAAS be a hindrance for geocaching?

[Guest Anton]

Greetings,

 

Since most geocachers are probably using older GPS receivers that DON'T have WAAS, is it better to turn off the WAAS in a new model, so you will more likely approximate a cache owner's readings on an older model GPS when you go hunting?

 

I ask this because several times I have stood on cache coordinates as given on the clue page using my Garmin Map76 with the WAAS turned on, and been unable to find the cache. Afterwards, I was informed by the cache owners that their cache was maybe 75 feet away, but was assured that the coordinates are accurate. I've now taken to using both the Map76 and the basic eTrek GPS units, to check against each other. The only difference operating here is the WAAS function. So what do you think? To WAAS or not to WAAS? That is the question!

 

Anton, 11H/16F

[Guest rebobbitt]

I have a Map76 also, and I would think it would be best to leave WAAS on. Always use the most accuracy you have. It's true that a non-WAAS unit might be 50ft off, but if you use a non-WAAS unit to find it, that one could be 50ft off, and your total error could be 100ft. If you use your Map76 with WAAS on, that error would be around 10ft, so the maximum error would be 60ft instead of 100ft.

 

You will not get the same reading from the Map76 with WAAS off, as a non-WAAS unit. The errors involved are constantly changing, and positions taken at different times will have different errors, and you will be back to the 100ft error.

 

The best thing for people to do is to average their position as long as they can, the longer the better.

 

Rick.

[Guest Prime Suspect]

Generally, you want the most accuracy possible. However, there are times when you can achieve better accuracy by turning WAAS off. You need to understand what's going on behind the scenes. On Garmin units, once you get WAAS data on at least 4 satellites, it will use only the satellites it has WAAS data on to calculate your position. However, it's possible that these satellites form a poor constellation. They may all be grouped together overhead, for example. In this case, turning off WAAS will allow your GPS to use all the available satellites for calculations. If you're in an area with poor coverage, the WAAS corrected constellation may be constantly changing. That because WAAS data is very perishable. After about 2 minutes, Garmin units consider it to be out of date, and discard it. So if you're in a clearing, and have good WAAS signals, once you walk into a heavily tree-covered area, you have about 2 minutes to use the WAAS corrected calculations before they expire. So walk fast!

[Guest morganw]

Maybe people should post what the accuracy reading was when they took their final position.

 

The cache I found this weekend was in an excellent clearing and my MAP76 was able to lock on to a full 12 satellites... However, I had turned WAAS off because the unit kept unsuccessfully trying to lock bird 35 while I was under cover that would prevent this. I don't know whether or not this helped, but it seemed like a waste of power for the unit to keep looking for WAAS when it wouldn't get it.

[Guest k2dave]

Just because your unit has locked on to 12 sat's doesn't mean it's using all 12 in it's calculations.

 

Also IIRC there are times that waas can give you poorer accuracy then non waas - most likely due to the reasons stated above. In tree cover It seems like waas isn't reliable.