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Permalink Reply by Joel on September 29, 2010 at 3:10pm

like one that is WAAS ready?

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Permalink Reply by Patrick Mccabe on September 29, 2010 at 3:22pm

I did this with a EM406 http://www.youtube.com/watch?v=Tci2MOLHdL8, i still use the same GPS for my new off road UGV.

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Permalink Reply by Joel on September 29, 2010 at 3:26pm

very cool Patrick! but the EM406 has a 10M accuracy. Is there something compatible with arduino or ardu-mega which would do <3m? because that was a wide road!

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Permalink Reply by Ken on September 29, 2010 at 4:33pm

"Is there something ... which would do <3m?"

Not reliably / repeatedly, though you might make it work on any given day.

You'll need a vision system to detect the side of the road, or augment the roadway with your own beacons / markers if you want to stay on a road.

The GPS system was never intended to do what you are asking of it. If you can deliver a nuke +/- 50m we call it a hit.

Oh, and don't let the posted accuracy numbers fool you. GPS accuracy is a probability (usually 95%), not a guarantee, that you are where it says you are. But in another 5 years when the new birds are up and dual frequency receivers are available, accuracy will get a bit better.

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Permalink Reply by Patrick Mccabe on September 29, 2010 at 4:41pm

I dont get this 10m accuracy stuff, i am always way way more accurate than that. Like ken says, other sensors would be good for keeping you on track. Im hoping to get some sonar sensors so i can hit the target without hitting other things. I did get lucky that day because sometimes it works, other times its a meter off and now your in the grass or stuck on the curb.

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Permalink Reply by Ken on September 29, 2010 at 4:48pm

Long time no hear, Patrick. Chillin' on the beach for summer?

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Permalink Reply by Patrick Mccabe on September 29, 2010 at 6:22pm

Has been a while since you gave me all that nice help. Not quite the beach person, spent all summer working on projects. Back in school just looking to find time to work on projects and school work.

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Permalink Reply by Joel on September 29, 2010 at 3:40pm

This looks good: http://www.sparkfun.com/commerce/product_info.php?products_id=8266

I wonder how hard it will be to get it to work with ardu-mega

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Permalink Reply by Ken on September 29, 2010 at 4:54pm

Advertised 3.3m CEP (50% probability) is about 8m to 10m to 95% probability.

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Permalink Reply by Joel on September 29, 2010 at 6:26pm

according to this page it can be pretty accurate using WAAS: http://www8.garmin.com/aboutGPS/waas.html

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Permalink Reply by Joel on September 29, 2010 at 8:17pm

seriously, out of this whole site no one has used an accurate(<3m) gps??!??!??!

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Permalink Reply by Ground Loop on September 29, 2010 at 11:47pm

I have. It doesn't work by itself.

You have to set up a reference base station somewhere stationary, preferably close to the rover. This second receiving station observes the signals receives from the satellites, while knowing its own static position.

It sends this correction data to the mobile GPS via local data link (or DGPS, etc).

The mobile GPS uses this additional error-correcting information while it is computing position solutions, and effectively factors out the locally-perceived errors.

Note that you can NOT do this with regular uncoordinated GPS units. You need these error corrections before computing a position solution.

WAAS and DGPS do this on a large scale, but the smaller error factors are very local. So you need your own reference station if you want corrected results in real-time.

Trimble, Novatel, and other professional GPS gear does this stuff to the n'th degree. 10 centimeter accuracy is repeatable. (Four inches.)

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