Testing Accuracy

[Guest Tom Sawyer]

How do I know that my GPS really is accurate to within the 8 metres that it keeps telling me? Is there anyway of testing it?

 

The reason I ask is that whenever I set a waypoint (I'm a beginner) and then drive back to it my, GPS always says I'm between 20-30 metres away.

[Guest Jeff Renner]

Check out the "Has anyone tried looking for NGS Benchmarks?" forum topic at http://forums.Groundspeak.com/ubb/Forum2/HTML/000869.html. The NGS site http://www.ngs.noaa.gov/cgi-bin/ds_radius.prl allows you to find government placed benchmarks, so you can find one of those and check out your GPS receiver's accuracy. Who knows, you might even enjoy the hunt for the marker!

 

Jeff

[Guest arffer]

Check out THIS page for an explaination of the accuracy of GPSRs, both the one making the waypoint, and the one trying to find it.

 

I originally created this info to answer another forum thread about accuracy. In a nutshell, a consumer GPSR without WAAS is accurate to 49 feet at best. That's it, period.

 

With WAAS, its accurate to 6 feet.

 

So, considering that your GPSR you used to mark the waypoint could be off by 49 feet OR MORE, and when hunting for that waypoint could again be off by 49 feet OR MORE, you will see that your 20-30 meters is pretty good. Go look at the graph and info on the above link, it should help.

 

Then use the benchmark suggested by Jeff. At least then you will know that the waypoint is precise, and the only remaining error is in your GPSR.

 

[This message has been edited by arffer (edited 08 September 2001).]

[Guest Tom Sawyer]

Thanks for the fast replies. Alas Jeff I live in the UK so the NGS info can't help me :-(

 

Thanks anyway

[Guest arffer]

Tom,

 

Check with a local airport. They will have a benchmark with known co-ordiantes somewhere on their property. Just make sure you find out what datum was used to record the benchmark's co-ordinates, and set your GPSR to the same before entering it as a waypoint.

[Guest Tom Sawyer]

Cheers Arffer! Will do

[Guest arffer]

What part of the UK? My folks used to have a flat in Sudbury, Suffolk.

 

You can take this off-line if you would like and e-mail me.

 

You can use the email link in the header of this post.

 

[This message has been edited by arffer (edited 08 September 2001).]