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Can your GPS give you a solid, fixed solution,

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 trah
(@trah)
Posts: 39
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It is pretty tough to find any comparisons...Here are a few below, mainly for network RTK. Might not be too much but at least there are some numbers to compare!

http://www.fig.net/pub/fig2012/papers/ts05b/TS05B_martin_mcgovern_5582.pdf

http://www.gnss.com.au/JoGPS/v9n1/JoGPS_v9n1p78-89.pdf

http://www.cadcom.hr/slike/GNSS%20Test.pdf

 
Posted : July 1, 2013 5:10 pm
(@plparsons)
Posts: 752
 

Nate, the sad but true fact is that RTK is a crapshoot in the woods. Wish it weren't so, have too much of my day that would be easier if I just took the chance. The fact is, when I set 3 point control in thick woods with RTK and then break out the total station, I'm not always pleased with the results. Oh, it's OK for topo, but I'm never happy starting out with .22' in distance and 3 minutes of angle flapping in the breeze, as well as the normal .2' in vertical error. Once again, no biggie for topo and surprisingly good for vertical when I have a convenient 3rd order TBM to sideshoot, am usually within half a foot of a recent published elevation.

The only way to know you are there accurately is redundant observations with both conventional and GPS equipment. I've had some I gladly hang my hat on, others not so much. I'm not the guy signing or bidding the jobs so our similarities part company there.

I do know I'm never 100 per cent certain of overall accuracy in the type of terrain you and I work daily, solely with ANY GPS system.

 
Posted : July 1, 2013 5:44 pm
(@nate-the-surveyor)
Posts: 10522
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I have pushed the system a long ways. There are certain danger zones. IF you are within 3-5 feet, of any kind of large tree, it is a serious potential multipath. Multipath, such as a flat spot on a tree. Or a large trunk. Those guys are prone to throw you that curve. I have done many double shots, and total station checks, and tape checks. The fact is, if you can live within 0.10' you can do alot. If you cannot live within a tenth, then you have to abandon RTK. I have wasted alot of time, to learn how to break it. Funny thing is, that a situation that yields GOOD data at 11:55 am, yields a bust shot, at 1:55 pm, and back to good at 1:30 pm. So, when you are under canopy, you have to be sure that it is busted, some of the time. IMHO. I am interested in seeing what company is in the lead, with the best gps system. Who busts least, and who goes the fastest in the trees. Fast in the trees, allows you to CHECK it faster. I do alot of checks.

Nate

 
Posted : July 1, 2013 6:16 pm
(@tatsurveyman)
Posts: 53
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I have heard and read that L5 is where it's at. When a receiver is able to get a solid L2 signal as well as a solid L5 signal, it should be able to better decifer the carrier phase ambiguities. This is due to the difference in the frequencies between L1, L2 and L5. There isn't much of a change between L1 and L2. When L5 comes along it will be much easier for the recever engine to obtain a "correct" result in difficult areas. Galileo also runs close to the high frequency of L5. So, in my opinion, be ready in the next few years with a Galileo & L5 capable receiver (try to find one that is upgrade able to save some cash now) and we should see a little more realistic results.

 
Posted : July 1, 2013 8:28 pm
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