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ALTAs & RTK
So, in this new era of multi-constellation RTK, I’m assuming there are surveyors preparing ALTA surveys wherein most, if not all, monumentation is tied with base-rover RTK. How does one prove compliance with the positional accuracy requirement?
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20 Replies
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I took my Leica RTK to the calibrated baseline – the results were impressive.
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I would suspect they will ship out their QC report generated with their RTK DC.
That would probably wow most attorneys asking for it.
But, if you locate all the monuments twice and adjust them Trimble will create an impressive report that should satisfy most anyone.
Are there some kind of ALTA police out there? I’ve never encountered anyone asking for mathematical proof of monument accuracy.
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play the game any way you like.
I opt for Personal Integrity…
if the ALTA standards are being complied with, fine
have Proof* of verification in your pocket and move on.*if you Can’t please be honest with yourself
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Whether our data are RTK, NRTK, static, PPK, total station, taping, etc., relative positional precision is evaluated by the prescribed method per ALTA/NSPS standards – a properly weighted, minimally constrained least squares adjustment yielding error ellipses at the 2-sigma level.
Vectors are vectors, whether from RTK, NRTK, static, or PPK. (Or reduced mark-to-mark vectors from conventional data, for that matter.)
WA is poised to modify our statutes, to require surveyors to explicitly state the relative accuracy achieved and the method used. Our statutes also require that we utilize relative accuracy when data are not amenable to evaluation using traverse standards, so basically anyone incorporating GNSS in a survey is required to evaluate using RPP.
Personally, I would love to see this go through, because I do not like seeing the boilerplate “this survey meets traverse closure standards” next to a statement that says “this survey was performed using RTK and total station”, and then finding out that there’s something seriously screwy about their bearings & distances.
Forcing surveyors to explain what they did helps me see right off the bat whether someone knows what they’re doing with respect to RPP and adjustments, and whether I can expect to come close to their values or not.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman -
Don’t even need redundancy to run that report in TBC.
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How does one prove compliance with the positional accuracy requirement?
A properly weighted least squares adjustment report. Also- note that the loop closure of a classical traverse does not fulfill the requirement. You need a properly weighted least squares adjustment report for that, too.
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@rover83 What Least squares software do you use?
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Trimble Business Center for 98% of my work, StarNET for the rest.
(That’s mainly because we’re a full Trimble shop, so there’s not much point to exporting and transforming to a different format. Unless something goes horribly wrong and I have to manually mess with the data, at which point I’m more likely to get a crew back out there and reobserve.)
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman -
I am with @rover83 and @Norman_Oklahoma A properly weighted LSA minimally constrained and I also use TBC and run the ALTA RPP report. Even when not doing an ALTA static rtk robot i use all the tools a lot on jobs and I just run that RPP report and it gets saved with all projects regardless. It’s an extra piece of mind and a indication if i might had missed some in the Network Adjustment Report as well. I will often crank down the RPP from ALTA standards of .07 + 50ppm just to get something to fail between control and property corners so it makes me take a look at that data and such. Make sure i did miss something. Doesn’t take but a second is all.
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OK, I think I get the whole minimally-constrained-least-squares-adjustment thing. I’ve been adjusting conventional traverses, with OPUS static as control on traverse points, in Carlson SurvNet since 2009. Lately I’ve been dipping my toes into base-rover RTK, but I cannot for the life of me get SurvNet to like my rw5 files. Any SurvNet users out there who adjust RTK “traverses”?
Thanks!-SS
Edit: My remembery is failing; I just went thru my files and the earliest SurvNet project I could find was from 2013, so 10 years, anyway
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Javad software had a PLS from Kentucky on the development team and Kentucky has Relative Positional Accuracy requirements for boundary work. They managed to incorporate a nice bit of massageable software that will do the heavy math lifting and provide a report.
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I cannot for the life of me get SurvNet to like my rw5 files
I can’t give you a specific answer, but I can point out that rw5 files are generated by at least 3 dc softwares that I know of (TDS/Survey Pro, Fieldgenius, and SurvCE). They are very similar, but not identical. Different enough that StarNet has different converters for each.
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So after reading these responses, I’m curious…how many of you provided reports justifying what you did pre-GPS? And how many of you reviewed/evaluated/etc reports from other surveyors pre-GPS?
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I have never provided the LS adjustment reports for an ALTA, but I do have them if I was ever asked to.
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There is a youtube video I watched on carlson survey rtk least squares and conventional. It was supposed to be more on least squares but was using that software. I have never used it but from watching it i would think it is right up there with tbc and starnet. Now another option is opus project’s management. It will take the gvx rtk data and you can do it through that. I have not tested it for rtk yet. It’s truly all about the field procedures. I am a spoke hub type of guy for gnss I usually almost always move my base and re tie everything again sometimes 3 times with a move of base depending on project requirements and time on job allowed. Here i don’t get many jobs i can rtk only so I usually have conventional ties as well and always try to get those tied to some rtk points as well to build a good network figure. We have a lot of trees. Now i will have the crews as they search for corners go ahead and ti the corners in th worst conditions. I will decide if they fit or not. To other conventional ties. What i have found is that with 24 sats and able to collect 180 epochs without loosing a fixed solution and at-least two observations with 4 hrs separation most of that rtk data proves to be good. When it drops fixed solution during the 180 epochs it’s suspicious and not as reliable. This all so far has been meeting alta specs 95% of the time . I have built some great confidence over time and have ran some very good traverses independently over time to prove this. Now this is with full Gnss equipment r10 and r12s. I have followed a Javad system and carlson brx7 and we all had a great agreement. The brx6 it was hit or miss. I developed my field procedures using a roughly 1 acre lot in middle of wide open. Close distances between points i could easily tie and cross tie traverse and even tape between many points for independent cks . I also did larger aeras that i ran static on so 100 acres using minimal two 4 hr sessions. Then did a rtk base rover design independent to ck. Now I run the numbers on a job and most of the time rtk base and rover meets the requirements and saves a lot of time. Always multiple observations at different times and base in different locations. Its not necessary as you can do a least squares from the same base point radially with multiple observations. But i like triangles lol. And so does most surveyors.
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a little off point, but an Opinion of ALTAs by an old pundit I found interesting
https://www.xyht.com/surveying/title-insurance-and-boundary-surveys/
xyht.com
Title Insurance and Boundary Surveys - xyHt
Legal Boundaries What many surveyors might not know about title insurance and boundary surveys is they are intricately intertwined, due primarily to the unilateral efforts of the title companies issuing title insurance policies. Unilateral in the sense that the title … Continue reading
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Nothing about least squares in that article. As it should be.
Adjustment reports would be about #50 on the list of important items for an ALTA.
It’s like my tax forms at year’s end, gets thrown in a file and is there in case it’s ever asked for; cross my fingers I haven’t had to produce my Taxes,,,,,,,,,, or an adjustment report ever.
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I wouldn’t expect there to be anything about LSA in that article either…
I don’t need to cross my fingers when it comes to the ALTA accuracy specs, because while they might be pretty far down on the list, it’s still an item on the list that will absolutely get verified before we deliver. I’m certifying to it, so you better believe I’m going to confirm it.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman -
Yeah, the LS report doesn’t concern me,,,,,,,,,Taxes, whole nuther ballgame.
Calls from a Title officer are often very welcome, calls from the IRS, that could ruin your day.
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There may be a little confusion here…
When you certify an ALTA, you are certifying, in part, that your positional accuracy meets the ALTA specification. The question has been asked, “how do I know that I’m meeting the positional accuracy?”. The answer is by subjecting your data to an LS adjustment. Nobody is asking you to regurgitate that adjustment report in your ALTA submissions. Nevertheless, if you are going to certify to something mathematically provable shouldn’t you have some objective basis to base your statements on?
With practice it takes mere minutes to run that adjustment. Certainly no more time than compass rule. You get a lot more out of it – blunder detection wise- than just this report. If you are combining GPS vectors and TS data, forget about it- there is no slicker, faster way.
I really don’t get the stubborn, hard headed resistance to doing LS. Then again, I guess maybe I do.
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