Lesson learned,?ÿdouble or triple shoot all your boundary points if they are under canopy.
Tie/dump/tie has been our mantra for any boundary or control points for as long as I can remember, regardless of conditions.
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Sounds like the mysterious 8-foot problem I encountered a few weeks back.?ÿ In my case the data did not match my own previous data from a few years earlier.?ÿ Without that doublecheck it is extremely easy to assume perfection.
With an EDM it was possible to have what appeared to be a 10 meter error in the distance reading.?ÿ Hard to know at a half mile but very easy to tell at 50 feet.
If I am running full GNSS multi-constellation RTK/VRS...
Observe 1 minute, turn rod 180 degrees, observe another minute, then average.
Wait 15-20 minutes (30 is better), dump init, and repeat. If those observations agree, I'm likely in the clear.
J a v a d?ÿ
Don't ever be too proud to just set up the gun and shoot it in.
Never.?ÿ GPS came from the gun tapes tensioners and edms.?ÿ I prefer "Real surveying" because the GPS is always a source of b.s. and assumptions anyway.
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Rock on!!!!
We do 4 shot averages with our r10 r12 rigs and even just a single shot for testing the waters.
Using planning online with goldilocks or hexalex's version helps too.
Also, beware the random scrambling events the DOD and FAA do more often than they used to for any GPS setup and can potentially ruin a whole day.?ÿ The usually have a posted warning but its always so far in advance no one keepa that in their memory.
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The young fella on the crew yesterday said, ??GPS, great product sometimes.?
where can you find out about stuff like that? I'm next to a large military base with 3 airfields & near 2 commercial airports. I've found out the hard way some days I guess but never knew they'd do such things
Sure thing:?ÿ
https://www.gps.gov/support/user/
Poke around, its new and improved.
They've been busy as squirrels hiding nuts at the FED level redesigning their web services and data products and availability.?ÿ This site is the newest iteration of the process I used to use.
Normally FAA used to be the director of all of these events with DOD etc, and now its being headed up here, and few other places.
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I'll post up some of my other resources in this string when I finish up some of the dry wall im working on this weekend.
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great site too:
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https://www.notams.faa.gov/dinsQueryWeb/
contained in this above site:
https://www.notams.faa.gov/dinsQueryWeb/displayGPSWAASNotamAction.do
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Regarding the advice above about "observe-dump initialization-reobserve" and similar variations of the technique, I believe adding one more variable change is a good idea.?ÿ If your GNSS antenna is mounted on a variable height rod, changing the antenna height by a foot or so, or maybe 0.3 meter, would give you an additional check.?ÿ Several years ago while "playing" with an RTK receiver on a point where the solution would have been suspect at best (note, I did say playing) I stored a series of float solutions on a point wherever the residuals the DC was reporting were under 0.15 on the horizontal value.?ÿ Over a period of 20-25 minutes, I accumulated about 30 or so observations.?ÿ When I looked at them in my CAD software, I found?ÿ the collected positions were drifting about N10?øW over a spread of about 1.5 feet.?ÿ The point I am making is that on points re-observed after clearing the initialization, if the time span between observations is only a few minutes, all you may prove is that you got approximately the same multipath.
So, instead of only re-observing the point with the same setup parameters, vary the antenna height too.?ÿ If you can duplicate the position with that changed parameter of your setup variables, then your confidence in the stored position would be justifiably higher.?ÿ Because when you change the antenna height, you're solving a different 3D position.?ÿ You may still get a multipath solution, but it would have to be a different position when expressed and north, east, and elevation.
THe could be a moot point with so many satellites available these days, but it was an interesting observation to me, at least.
The whole tie / dump / retie thing doesn't have as much value as it once did. All of these receivers are solving and resolving the fix from scratch constantly these days. What that procedure does that is useful is cause a little time to pass between ties. But the time could be spent as well in other ways.
