2d Fixes

[TygerD]

I'm currently entering cache coordinates manually. I usually do this in the house and my unit (exp. 210) tells me this is a 2d fix do I want to continue?

 

My question is, will this affect accuracy in the field.

 

Of the last 2 caches I tried locating, one I found was 64 feet off the mark, and the other that I dnf. was 400 feet off the mark which would of put me in somebody's house or backyard.

 

Or could it have been the weather? the first was in heavy tree cover with no leaves on the trees and the second there were very few trees, both were looked for on the same day, which was heavly overcast threatning to snow.

[Photobuff]

Entering coordinates manually has nothing to do with the GPS units present fix. Since you enter the coordinates by marking the present location, then editing the numbers, it's warning you that the present location fix is 2d and probably pretty inaccurate. If you were marking your present location, then yes, the result could be hundreds of feet off. Whenever you need good accuracy, try for 7 or more satellites and a WAAS indication (may take 10 minutes or so). If the error indicator (take with large grain of salt, though I find it conservative) is telling you 20' or less, results will be pretty good. If all is right with the satellite world, you might see as low as 7', and the position will often be better than that.

[+zedd10]

You need to consider where you are caching too. I've been in places where there are buildings close by to the south and block the WAAS satellites and accuracy suffers. Trees and buildings can also degrade the signal. If you're not sure check the sat reception page and move the GPSr around or walk to a place where there is better reception. Once your reception is good (or as good as it'll get) then start walking back toward the cache. Watch the arrow and distance to get an idea of where the cache should be.

[+JDandDD]

Photobuff is right. The manual entering of waypoints is irrelevant to accuracy. All the GPS is telling you is that at the time you are entering it is only receiving signals from 3 satellites so that the coords that first show up when you hit Goto might be affected. But since you are then entering your own it doesn't matter.

 

In the field there are a couple of things that can affect accuracy. One is the geometry of the satellites. The most accurate geometry is to have one almost dierctly overhead and at least 3 others close to the horizon. However, you almost never get that and in fact can have very bad geometry. About 2 weeks or so ago the satelite configuration I had was four in a direct line from the horizon to the zenith (overhead). Terrible geometry and the GPSr reported a postion at 3200m altitude (I was at 235m) and about 1.5km south-southeast of where I actually was. All based on poor geometry of the satellites.

 

Another thing that can affect the calculations is reflection of the signal off a rock wall, or cement or something else like a hillside. That will lengthen the time that signal takes to get from the satellite to your receiver enough to throw the calculation of your position off.

 

JDandDD

[TygerD]

Thanks for the replies.

Kinda thought that would be the case but wasn't sure.

 

Still findin my way around the sport, the unit, the web site, the forums

 

TygerD