Wetland biologist uses a Trimble GEO XT with WAAS corrections to record wetland flags. The GEO display shows him that real time positional quality is typically 2-5 feet. I was thinking positional quality using WAAS corrections is more likely 10-12 feet?
Anyone more familiar with this? I intend to post-process his .ssf files with CORS to compare.
Thanks and regards,
Mike Moran
> Wetland biologist uses a Trimble GEO XT with WAAS corrections to record wetland flags. The GEO display shows him that real time positional quality is typically 2-5 feet. I was thinking positional quality using WAAS corrections is more likely 10-12 feet?
>
> Anyone more familiar with this? I intend to post-process his .ssf files with CORS to compare.
>
> Thanks and regards,
> Mike Moran
I have not used the Geo XT but I have used the Geo XH with a zephyr antenna. It often reports real time accuracy of 2-3 feet and reports post processed accuracies of 4-10"
The problem with these mapping grade units is their accuracies are just estimates. Most of the time they are good estimates but they are not guaranteed. WAAS is usually a lot better than 10-12 feet. I know a lot of farmers use WAAS only units for spraying and they report pass to pass accuracies of around a foot with larger drifts over long periods of time.
I believe WAAS is meter level accuracy, from tests I have done, although I don't know about that particular unit. It has been quite a few years since I did the tests, so I don't know if the accuracy has improved, although I doubt it. However, one must be careful and realize that the reference system for WAAS corrections is WGS84. If I were to use WAAS corrections for anything, and wanted NAD83, I would apply a transformation. The difference in datums is around 1.5 meters.
I use waas correction all the time for stationing road jobs being rehab'd. These are jobs that TxDot does not put any effort into for surveying. They just use the old plans and ride thru with a distance meter to inventory driveways/mailboxes.
3 feet accuracies or less are reasonable to expect. I don't know about the GEO XT. Mission planning is more important than RTK. I
James
Spec sheet says sub-meter RMS - 68% confidence.
Multiply by 2 for 95% confidence.
It assumes clear view of the sky.
If they are under trees, accuracy is worse.
I use an XT and recently I have been checking its accuracy against known points. I find that in the open, it returns real-time coordinates that are about 2-3 feet from the known point. In any trees it is very unreliable and the accuracy goes to 5-10 feet every time. WAAS real-time coordinates are WGS-84. If you post process against a community base station, the coordinates are usually NAD-83. There is a 3-4 feet difference between the two systems now.
Tom
The XT is certainly more than able to get down to that range, with typical running between 2 feet to 4 feet if conditions are good. The XH can do down to a foot, or even less. ( XH is claimed down to 4" if conditions are optimal and data collection is performed as per Trimble guidelines ).
However to get that, you need to ensure the correct antenna is used ( if an external antenna is connected ), not all of them remove multi path, you need to collect enough data, and if you capture carrier data for carrier phase processing, it can get even more accurate. The XT is capable, it depends on the user to a large degree. Personally I would recommend they use an external hurricane antenna with XT and capture at minimum two or three minutes of solid data per point.
> Wetland biologist uses a Trimble GEO XT with WAAS corrections to record wetland flags. The GEO display shows him that real time positional quality is typically 2-5 feet. I was thinking positional quality using WAAS corrections is more likely 10-12 feet?
>
> Anyone more familiar with this? I intend to post-process his .ssf files with CORS to compare.
>
> Thanks and regards,
> Mike Moran
