A DIY Cruise Missile

[brightnorm]

[ QUOTE ]
e=mc² said:
...Since they removed SA, my GPS fixes have been extremely satisfactory. Prior to its removal, the accuracy was +/- 50 ft at best....


[/ QUOTE ]

Ed,

What is the accuracy with SA removed?

Brightnorm

 

[ewick]

Brightnorm,

I might be able to help a litle on this one. I use a program called Waypoint to download waypoints, routes, etc. from my Garmin to my PC, and from there I import those waypoints into ArcExplorer and overlay them onto ortho-rectified (adjusted to accurately "flatten" images taken of spherical objects) aerial images.

These aerial images aren't the greatest resolution, but they're good enough to give me an idea within a couple of feet. Now if I shoot a landmark with my Garmin that's pretty obvious in the aerials, and average that waypoint two or three times, I usually wind up with a waypoint that's right on top of the landmark in the aerial. So I think it's safe to say that 2 or 3 feet plus/minus is possible. I've not checked the Garmin accuracy against a total station, so I can't tell you exactly how far out the reading will be.

Maybe somebody here can give you a more precise answer than I have, but that's all I can say given what I've seen. Hope this helps.

 

[e=mc²]

Brightnorm, although I don't have the sophistication of ewick's arrangement, I do have USGS 7.5 minute maps to compare against in my neighborhood, and I can say with confidence that the unit is at most, off by 11 feet. The only time this is not so, is on those rare occasions when the satellite "constellation" lacks sufficient geometry for an accurate fix. In that case, without further augmentation (WAAS), ALL GPS units under the same constellation will be affected. Again, this phenomenon is rare and IS transient.

In a nutshell, to answer your question, +/- 11 ft. SA removed.


Ed