Coordinate-Only surveying

I often use delta xyz data from previous surveys, but never publish without verifying them. That includes checking the current Corner Record if one exists. I know folks who use old data without checking. It does not IMO meet standard...

Okay, then when is the line drawn? The survey you personally did ten years ago with the greatest care, or the one last year, or the one last month. What is the cut off?

If, through rugged forested mountains, you spent a month breaking down a section with a total station, would you repeat the feat every time you surveyed an aliquot part of that section? I think not.

I don't think the standard of care has really changed since total station days. But the wrong "survey clerk" could probably give you hell over it. Another reason that Minimum Technical Standards have got to go...

In Virginia the law says a coordinate survey is sufficient. This is boilerplate language that I think may appears in many state law.

§ 55-296. Use of system not compulsory.

For purposes of describing the location of any survey station or land boundary corner in the Commonwealth of Virginia, it shall be considered a complete, legal, and satisfactory description of such location to give the position of said survey station or land boundary corner on the system of plane coordinates defined in this chapter. Nothing contained in this chapter shall require any purchaser or mortgagee to rely on a description any part of which depends exclusively upon either Virginia Coordinate System.

(1946, p. 168; Michie Suppl. 1946, § 2849(8); 1984, c. 726.)

A bit more detail

A tract in the Southwest Quarter of Section 4-5-6 commencing at the southwest corner of said section, thence north (something )west along the west section line 400.00 feet; thence south (something) east, parallel with the south section line, 214.50 feet to the point of beginning; thence x east, y north, w west, z south to p.o.b., containing X.XX acres.

In the above description, are you obliged to actually find and report the location of the monuments that control, which includes the southwest section corner, the west quarter corner and the south quarter corner? Or, can you simply prepare the description and then go find it on the ground using coordinates determined at some time in the past for each of those controlling corners?

Time is not the determining factor. I am saying once I leave a site, evidence begins to change. It is my duty to investigate that to whatever level I must in order to certify the new survey.
I've seen surveys where it appears the only thing different is part of the title block and seal. This despite right of way takes and a new subdivision next door. The first survey was fine. The second borders on fraud.
We all have to decide for ourselves what we will certify. Taking my old survey and certifying it as current without checking is not something I would do...

Around here the surveyors add the note "not visited this survey" The latest one I reviewed, the nearest I could tell, the surveyor hadn’t been to the controlling corners in 25 years and on this particular survey he was placing two new monuments on a line formed by those non-visited corners, go figure. I do recognize that the measurements are the easy part now, and in most cases when I revisit a point it is nothing more than a check (no real measuring error to deal with) and I think that now that we have the ability to repeat our measurements so closely we do need to implement new practices. So if you plan to use statements such as "not visited this survey" then your published survey (that you did visit the controlling monuments) should show well monumented control points and traverse closures or properly done lease squares adjustments tied to the controlling monuments in a survey network that any or all surveyors can use and work with. My 2 cents, Jp

A related question

Anyone ever get a different set of coordinates for the exact same monument? Little issues like canopy in July versus canopy in January or three satellites versus 13 satellites or totally unexplainable but it happened anyway or any other possible excuse?

I'm thinking there have reports on this excellent site from numerous surveyors having encountered some variation of said problem.

A related question

When following post-processing procedures, never. When using RTK under canopy, several times (caught when point had also been observed with static).

A related question

We do 30 by 30 RTK with a second set under a different constellation. I've had the second set show up feet different using Topcon Hyper V in a clear environment. It happens. My concern wouldn't be so much a change in coordinates, but a change in circumstances and evidence...

A related question

> ... My concern wouldn't be so much a change in coordinates, but a change in circumstances and evidence...

Yes, as long as you can confirm this.

Steve

"Per the Minimum Standards of your State you should locate certain controlling monuments, indicate which ones you found and used for control on your plat, then develop your plan to set new monuments."

That pretty much says it all to me. Nothing ambiguous there.

I think that you need to go out and touch those monuments. You need to confirm that they still exist and are undisturbed. You can use your previously determined coordinates presuming that the check shot you get confirms that those coordinates are correct within some tolerance.

RTK does not produce magic coordinates. It measures vectors between the base and the rover. The coordinates are a byproduct. The vector data will include quality control metadata, which should be evaluated.

BTW - checking and editing a map prepared by a draftsman, without also checking the underlying data, is putting lipstick on a pig.

Yes...with a few depends for certain scenarios.

If you cannot rely on your previous research and survey work as a professional, then who else should rely on it.
As far as the coordinates are concerned, they would have to tied to a physical monument and the monument would control. Proper metadata of the previous work is necessary for reference.
Listen GPS or magicskyblackbox as you choose to call it has been in practice for precise positioning for a quarter of a century or more. It is only a tool that others have constantly reiterated here in discussions. But some like to label others the 'expert measurers' to discredit use of GPS in boundary determinations.
I think Kent has previously demonstrated the comparison of early GPS measurements to current work that was does in Texas.
If one can not review other's work where that have used GNSS than they need to get up to speed or hire someone who is capable to review the work for them.
carry on

I guess the best answer I have for you is the stand by "It Depends" (which we so routinely come back to, it seems).

Here's a for instance:

We surveyed 26 acres in 1998 with about 15 corners, before we were using GPS.

In 2003, we cut out 5 acres from this tract. Even though this 5 acre tract was out of a corner, we observed enough of our original traverse with static GPS to have a great relation to Geodetic Coordinates (in this case we were using State Plane, NAD83 HARN).

In intervening years we have surveyed two adjoining tracts with independent GPS observations confirming our 2003 observations/transformation.

Two months ago, we were hired to divide the 21 acre residue in to halves. Now equipped with RTK, we observed directly most every monument to verify its position. We exposed all corners and flagged them. Those corners that did not lend themselves to precise RTK positions, we verified by offset/taping (not terribly precise, but good enough to prove the position). Then we staked the division line. We were able to do this in a long afternoon.

Technically speaking we didn't "locate" the controlling corners again. We navigated to them. Sometimes precisely, sometimes loosely. Professional judgment dictated that the points were all substantially in the same position as found in 1998 and so the 1998 geometry was held (if rotated now to reflect GPS derived directions). We've been doing this for years. GPS has actually made this process easier than before, the only way to do this would be to rerun the traverse.

I will add this. If I find an original land grant corner (your version of a section corner) in a distant, remote location and determine accurate coordinates on this monument, I will happily state "Found 2 inch iron pipe on South bank of river (found by Shawn Billings July 2007) bearing N 12°34'56" E, 7654.32 feet". I feel no need to remeasure to that monument or even verify it's there today. I've told you when I found it. No fraudulent claims there.

> RTK does not produce magic coordinates. It measures vectors between the base and the rover. The coordinates are a byproduct. The vector data will include quality control metadata, which should be evaluated.

Actually, I'd be willing to wager that the commonest use of RTK GPS is just to generate coordinates, with no use of the vector data being the norm. It's bizarre and scary, but likely true.

> Actually, I'd be willing to wager that the commonest use of RTK GPS is just to generate coordinates, with no use of the vector data being the norm. It's bizarre and scary, but likely true.
I agree. If the data is correct it takes 5 minutes to run a day's data through StarNet and generate coordinates. If it isn't correct you may never know it - until it is too late - if you don't. There is no better way to combine and analyse multiple observations in a meaningful way.

That's your decision...

You'll certainly never find an error or new monuments someone else has set, nor be able to tell the judge that you "walked the line" if you don't check all controlling monuments every time.