State of Connecticut guidelines
> Connecticut GNSS guidelines
Thanks! There is also this from California which suggests as little as 5 seconds of occupation, repeated 20 minutes later, will be satisfactory.
> ...we monitor GDOP and increase occupy time to suit when necessary
By how much?
> ..I'd recommend talking to Mark R(iggins) down in Marion County. ..
Mark is a friend. I will give him a call.
> I would suggest that you also speak with Mark Armstrong...
I am also acquainted with Mr. Armstrong. I will make that call.
Something about people named Mark getting together to discuss surveying in Oregon....what's up with that?
British Columbia guidelines
British Columbia
Bottom of page 6 suggests occupation time of 15 seconds or less while stressing the need for redundant observations. On page 3 and again on page 16 the practice of rotating the rod 180° is discussed.
New CORS antennas have to be oriented to true north or NGS won't accept the data. They feel orientation of the antenna does play a somewhat important part in accuracy of the data. Why? No idea.
Ton of good information here. Just a suggestion but maybe spend time educating crew on the type of multipath situations to avoid. I've found some RTK operators will attempt RTK in dicey locations when much less obstructed locations are perfectly viable but require someone to break out the total station. Those total station conventional checks have really helped me in spotting bad fixes.
BTW, any chance you'll change your handle to Norman Oregon any time soon? Kind of rolls off the tongue, don't it? 😉
Just because I'm paranoid, doesn't mean they aren't out to get me.
Must be a pre-requisite ! 🙂
Good for you!! We've spent years on this subject and getting it down in writing is important. One thing I will say, and you probably are already aware of it, is that changes in equipment causes changes in practice.
Dumping a fix by turning over the unit was considered good practice years ago, but some newer units don't work that way. We always use two rod bubbles and now have an e-bubble which so far has been in sync. Also, we are testing the tilt function, which if you think it through is pretty simple to check and it does work.
There are other options on the newer units that are really nice.
Redundancy is so important, I can't imagine just doing one 1 second location on a point and then walking away. But I've seen that done by other users. Section corners no less.:-(
> Ton of good information here. Just a suggestion but maybe spend time educating crew on the type of multipath situations to avoid. I've found some RTK operators will attempt RTK in dicey locations when much less obstructed locations are perfectly viable but require someone to break out the total station. Those total station conventional checks have really helped me in spotting bad fixes.
This was the issue in OK, with guys pressing on with the RTK way beyond the point where they should have broken out the TS. If it recorded, it was all good. That attitude was condoned, if not shared, by many PLSs.
> BTW, any chance you'll change your handle to Norman Oregon any time soon? Kind of rolls off the tongue, don't it? 😉
Maybe Eugene Oregon would be appropriate.
> > ...we monitor GDOP and increase occupy time to suit when necessary
> By how much?
Norman, generally by a factor enough that CORS can either substantiate the RTN vector or stand alone with defensibility. in other words, rather than four, two minute sessions/measurements we would use two, ten minute sessions. this works for us, but your mileage may vary.
the way i see it, this provides a measure of accuracy, redundancy, and precision (not to mention an indication of whether the RTN values are good enough to be usable).
:good:
> There is a guide in the UK from the TSA and Ordnance Survey which I have attached.
>
Dropbox File (Private or Invalid)
Here is the money line in that report:
"Testing performed in this report has determined that rms errors can be reduced by around 5 mm, particularly in the Up coordinate component, through the adoption of the mean of two 3-minute averaged windows separated by 20 minutes. The separation of the two windows was also investigated and found not to yield significant improvement beyond 45 minutes."
Norman -British Columbia guidelines
> I think you are finding in your research that various outfits around the world who have developed guidelines based on their actual experiences are challenging a lot of the conventional wisdom of those who have not used such tools extensively. This is not a 1990 static-GPS-only world anymore.
The British Columbian document discusses many matters, including DOP and CQ numbers, at some length but mentions occupation time (15 seconds) only in passing. The Caltrans document specifies 5 epochs, with epochs at 1-15 second intervals. So as little as 5 seconds for 3rd order control! The UK document goes for 3 minutes, mainly for vertical. NGS has 3 minutes for the RT1 accuracy class, their most precise.
All 4 stress the need to average with time separated re-observations.
In short, it seems that - according to these sources - if your DOP is good then your CQ number is going to settle down within seconds, and when your CQ number is where you want it you've been on the point long enough. Nothing to be gained by sitting longer unless you want to collect enough to post process.
> Some simple field tests can lead you to the best practices as well.
Standby for that.
Norman -British Columbia guidelines
Will do. Of course, I'll want to try it with higher DOPs as well.
Initially these tests will be done with 2002 model Topcon Hipers. Would you expect receivers of that age to behave significantly different than more modern units?
No Worries!
Glad it was useful - and it seems to have sparked a good debate!
Tim