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Author Topic: Delorme GPS  (Read 3699 times)
gumpy
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« Reply #15 on: October 31, 2006, 05:58:09 PM »

Yep, read it.

It has nothing to do with positional accuracy. As the website states, the WAAS (or SBAS augmentation as they refer to it) is based on relative position and is only good over a 15 minute time period. It states a +/- 3 ft repeatability on a year to year (hour to hour) basis. That's not accuracy. That's relativity. Most modernl receivers will perform with similar results given a clear sky, which presumably most farmland offers.

The rest of their system uses DGPS based on beacon and subscription services. You might get similar accuracy (to WAAS) with beacon, but again, it's not repeatable and is basically relative on a short term basis. The subscription services are basically the same as the beacons. The omnistar system is not going to offer much more then beacon systems. RTK offers the best performance of all. It uses a second receiver as a ground station in conjunction with the base stations, and also uses the L2 frequency.

You cannot get that kind of accuracy from WAAS on a repeatable basis, or over extended periods. You can get it for short periods, but when the satellites change, so does the accuracy.

Still, there's some impressive computations going on in those sytems to be able to maintain that kind of driving accuracy even if for a short period.

No weeping here. I know a little more about GPS then the casual user.   Wink
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Craig Shepard
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bobofthenorth
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« Reply #16 on: October 31, 2006, 06:29:09 PM »

Craig - in the post I responded to, you stated:
"WAAS cannot provide that kind of precision. It can bring the accuracy down to about 3-7 meters."

Now you say 3 feet. 

All I know is there are 1000s of pieces of farm equipment happily travelling up and down the field using WAAS and they aren't overlapping by 3 feet.  Trimble's site which I already referenced says 7" for pass to pass accuracy.  I'd say that is pretty close to what users are experiencing at 15 MPH on 1/2 mile fields. That's around 5 minutes between complete passes.  At slower speeds it's probably closer to 1 foot accuracy between passes.  Either way it's sub-meter accuracy from the user's perspective.  And yes, they won't get back to the same a-b line a day later but they won't be out by 7 meters either.

This technology still amazes me.  When I was a kid we would have said it was impossible.  Now I have a customer with a Cat Challenger who gets out of the tractor, leaves it to drive unattended and runs out to the outside of a 60' drill to watch his overlap which he claims is under 4" with a satellite correction.  Leaving aside the questionable wisdom of his actions, that is pretty amazing.  Most human operators would be delighted if they could drive that rig to under a 1 foot overlap using conventional mechanical drill markers. 


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R.J.(Bob) Evans
Used to be 1981 Prevost 8-92, 10 spd
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gumpy
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« Reply #17 on: October 31, 2006, 07:28:14 PM »

Craig - in the post I responded to, you stated:
"WAAS cannot provide that kind of precision. It can bring the accuracy down to about 3-7 meters."

Now you say 3 feet. 


Yeah, that 3 ft thing was from their website.

I don't doubt they are getting that accuracy on a yearly basis, but to get within 1 foot pass to pass is pretty interesting.

And by the way, you did say "pass to pass" on your initial post. I should not have contradicted you, because that is possible with WAAS, as long as you don't care about positional accuracy or repeatability. In my line of work, that's kind of critical. In farming, it's more about the short term accuracy. Interesting how one system can be used to both applications with great results.

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Craig Shepard
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bobofthenorth
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« Reply #18 on: October 31, 2006, 07:43:31 PM »

Its an amazing feat of technology.  You folks truly are the greatest nation on the face of the earth - ever.  To put that system in the air and then just let every schmuck in the world derive the benefit of it is mind boggling in its generosity. 

I have watched the precision thing evolve for agriculture and never bought into the hype - in fact I was downright skeptical.  When people first started talking about GPS we were going to apply prescription fertilizer to sub samples of fields and that was going to revolutionize farming and yields and lower costs at the same time.  For the most part that was pure bunk.  What it has done is revolutionize guidance.  Particularly for seeding equipment.  In dryland farming we routinely use seeding equipment wider than 50' - some of the prairie mfrs are building 80' equipment now.  Mechanical markers for that width of equipment are incredibly complex and expensive.  We bought a GPS marker for one of our custom app trucks last spring for $2000.  Now I'll grant you it wouldn't be adequate for seeding but its getting close.  But at $2000 its less total capital cost than we used to spend in a season for marker soap.

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R.J.(Bob) Evans
Used to be 1981 Prevost 8-92, 10 spd
Currently busless (and not looking)
My website
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Simply growing older is not the same as living.
NewbeeMC9
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« Reply #19 on: October 31, 2006, 08:25:27 PM »

JR,

Yes 102b is Wifi you can use at hot spots like starbucks and hotels and campgrounds.  Some are included or free, some need a password and charge you.
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It's all fun and games til someone gets hurt. Wink
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