Accuracy Issues

Nate The Surveyor

Well-Known Member
If you do ALL shots, pointing the same direction, this also "removes" pole centering errors. Same is true at the base... If you always point the tribrach north, then error stays the same. Then, you've zeroed out the tribrach error, and the pole plumbing error. All sideshots from base will be off the same. And, your relative positioning will be good.
Just think about it....
:)
 

Shawn Billings

Shawn Billings
5PLS
Also, for the record, 1:50,000 is a ridiculous tolerance because it allows for now constant error. A ratio of 1:50,000 is no problem on a one mile line because is allows for almost 0.11' of error. But on a 100' line, it only allows for 0.002' of error. I would certify to that with a total station.
 
Instead of setting just two nails, set three nails intervisible and at 175-200' apart with the LS. Before you stake out your points (monuments) check into to the 3rd nail with your TS. This will give some idea of good your set monuments will be. It's redundant but I did this every time until I got comfortable with the LS (it's hard to break the TS/traverse habits...)
First off, thanks to everyone for their replies.

Matthew, is there a specific reason you asked about the monopod?

Sdrake, the tilt correction is off, I already went through that bit of a rough patch thinking I could keep it on all the time. I understand 1:45,000 is spectacular but that's not necessarily what i'm getting. I'm looking to set 2 control points to work off of in order to set monuments on the very far side of the job without having to traverse it. They are approximately 200' apart. My first control point difference between the two shots 2 hours apart was .03 which is acceptable but the one i'm having an issue with is the second which is .06. They were both open areas and I'm just confused on how one could be double the other error-wise.

Clifton, It's not something that we typically do but we were looking to help mitigate any potential problems.

Aaron, what does your boundary profile set up look like?

James, where did you read or hear about the 600 epochs? I generally have about 1100 epochs over my 240 seconds on the shots.

Matt, what length of time do you suggest? I look forward to testing that out.

Everyone, do most of you use the monopole and J-pod? Also is there a functional purpose to the flashlight blink feature?

Thanks again, very much appreciated responses, like Nate says, the Javad community is incredible.
 

Darren Clemons

Well-Known Member
I wouldn't be able to sleep at night certifying to 0.002' with any equipment I have.
I agree Adam. The somewhat “obsession” with accuracy in today’s surveying world sometimes just astonishes me really. We’re all doing a million times better work with the most unbelievable equipment ever produced and for some crazy reason many surveyors and lots of clients are passionate about getting distances within ridiculous tolerances.
1:50,000, as Sean stated, is basically impossible. Sure, you can get closure loops and equipment to”say” it’s that tight, but in all reality, it’s not. You can’t plumb (and keep) any base pole, rover pole or EDM rod to that amount. No one can drive a spike, nail or rebar to that specific of a distance.
I realize different people work in much different areas and deal with different “standards” of sorts that are outside each individuals State board regulations and I certainly respect that. I have worked most of my career in very rural areas. I follow a lot of deeds that have NEVER had a distance on them, period. I’ll establish lines across multiple ridges and valleys of 2000’ or more. I ran hundreds of thousands of EDM loops and prayed to get em within 1:5000. Now, with the Javad LS, I am getting those lines within 0.1’, or better, for each point. That is truly amazing and all of us in our company are proud to sign it.
Now, that’s not to say when I’m working in the city closest to me, and it’s a 2 million dollar lot a Meier store is going on, I’ll accept the same tolerance. Those will, and should be, much much tighter and the LS will attain that, with the proper profiles and settings and multiple shots.

This is obviously nothing against Tyler for asking the question. He’s simply trying to find out how to get what his client is asking for, no matter how unreasonable it is. Again, just think about the “math” a moment - very possibly driving in a 1/2” or 5/8” rebar for the corner, but the client wants accuracy to 0.002’ per 100’? I’ve had this post “ in my craw” for a while and this just seemed like a good time and spot to post it. In my humble opinion, far, far too much time in today’s surveying world is spent obsessing over a few hundredths of a foot.

Good luck to you Tyler!
 

Tyler

Member
I agree Adam. The somewhat “obsession” with accuracy in today’s surveying world sometimes just astonishes me really. We’re all doing a million times better work with the most unbelievable equipment ever produced and for some crazy reason many surveyors and lots of clients are passionate about getting distances within ridiculous tolerances.
1:50,000, as Sean stated, is basically impossible. Sure, you can get closure loops and equipment to”say” it’s that tight, but in all reality, it’s not. You can’t plumb (and keep) any base pole, rover pole or EDM rod to that amount. No one can drive a spike, nail or rebar to that specific of a distance.
I realize different people work in much different areas and deal with different “standards” of sorts that are outside each individuals State board regulations and I certainly respect that. I have worked most of my career in very rural areas. I follow a lot of deeds that have NEVER had a distance on them, period. I’ll establish lines across multiple ridges and valleys of 2000’ or more. I ran hundreds of thousands of EDM loops and prayed to get em within 1:5000. Now, with the Javad LS, I am getting those lines within 0.1’, or better, for each point. That is truly amazing and all of us in our company are proud to sign it.
Now, that’s not to say when I’m working in the city closest to me, and it’s a 2 million dollar lot a Meier store is going on, I’ll accept the same tolerance. Those will, and should be, much much tighter and the LS will attain that, with the proper profiles and settings and multiple shots.

This is obviously nothing against Tyler for asking the question. He’s simply trying to find out how to get what his client is asking for, no matter how unreasonable it is. Again, just think about the “math” a moment - very possibly driving in a 1/2” or 5/8” rebar for the corner, but the client wants accuracy to 0.002’ per 100’? I’ve had this post “ in my craw” for a while and this just seemed like a good time and spot to post it. In my humble opinion, far, far too much time in today’s surveying world is spent obsessing over a few hundredths of a foot.

Good luck to you Tyler!
Thank you for the response! Prior to this we had come to the same conclusion that this was not a possible request and probably a misunderstanding by the client considering the boundary he was speaking of was only a few hundred feet long. I was hoping to find out what kind of accuracy IS possible with the LS in the hands of more experienced users and I was wondering what the steps I would take to achieve those accuracies might be.
 

Jim Frame

Well-Known Member
I work in a very different set of circumstances than Darren does, but I come to pretty much the same conclusion he does: if you're trying to get within 0.02' (let alone 0.002') in 100', RTK is the wrong tool for the job. That's what a total station is for.
 

Tyler

Member
I work in a very different set of circumstances than Darren does, but I come to pretty much the same conclusion he does: if you're trying to get within 0.02' (let alone 0.002') in 100', RTK is the wrong tool for the job. That's what a total station is for.
What horizontal accuracy would you be comfortable certifying to with an RTK unit? Yeah I am in Marin County and there is a lot of money flying around and a lot of unreasonable expectations when it comes to boundary location.
 

Jim Frame

Well-Known Member
What horizontal accuracy would you be comfortable certifying to with an RTK unit?

There's no hard-and-fast rule. Sky view, occupation time, number of redundant observations, constellation at each observation, and ionospheric conditions are all going to affect results. With rare exceptions, I roll all observations into Star*Net and let it tell me what kind of accuracy I can expect. But also with (very) rare exceptions, if I'm dealing with points only a few hundred feet apart, I'm shooting them with a total station.
 

Donald E Robinson

Active Member
Both DPOS and OPUS are now processing using absolute phase center variations now so the receivers need to be aligned to north to get good vertical results (T-2 and T-1M record button and green triangles to the north, LS display to the north with the compass reading 180 degrees). Processing with phase center variations mostly improves the vertical results. A good paper about this topic is Influence of GPS antenna phase center variation on precise positioning.

I have not done any testing to see if fixing time decreases when both receivers are aligned to north. If both GNSS antennas have similar phase center variations then I expect this may help some.
I've have always orient the LS with the compass reading 0° azimuth (north). Why should it read 180°?
 

Joe Paulin

Well-Known Member
Screen to the north for proper orientation using absolute antenna calibrations (DPOS & OPUS). The Triumph LS's offsets from phase center to ARP are very small horizontally, under 1mm in Northing and Easting according to the NGS published calibrations. If one is concerned about squeezing the most out of the unit, make sure it is oriented to north properly for static observations and for RTK, the unit should be oriented the same way for all points to be consistent. The height offset is substantial (as all gnss antennas are) at over 100mm for the LS, but that is accounted for.

Matt, I don't see how the azimuthal orientation of the LS will affect the height here. If the vertical offset wasn't accounted for (which it is), sure you would see a 100mm+ elevation bust, but how would rotating the antenna change that?
 
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