Record Measurement Not matching Quandary

Skeeter1996, post: 454592, member: 9224 wrote: Just finished surveying a section of farmland. The Section was previously surveyed in 1996. There are aluminum caps at all the Section Corners. Should be an easy survey, but all my retracement inverse measurements differ from the 1996 survey by being 10 feet and a tenth or so more. I only did a site configuration to two points so no scale factor should have been introduced. I used a Trimble R10 system and I have no idea what was used on the 1996 survey. My only guess is the draft person clipped the lines on the symbol and then auto labeled the lines in the 1996 survey. I I've double checked by inverses and the all go to surveyed node points. It's strange that every measurement differs by 10 feet and a little bit more.
Anybody run into this before?

I've never seen anything like that. They are all aluminum caps. BTW, were they all set by the same surveyor, or do they vary?

Skeeter1996, post: 454592, member: 9224 wrote: Just finished surveying a section of farmland. The Section was previously surveyed in 1996. There are aluminum caps at all the Section Corners. Should be an easy survey, but all my retracement inverse measurements differ from the 1996 survey by being 10 feet and a tenth or so more. I only did a site configuration to two points so no scale factor should have been introduced. I used a Trimble R10 system and I have no idea what was used on the 1996 survey. My only guess is the draft person clipped the lines on the symbol and then auto labeled the lines in the 1996 survey. I I've double checked by inverses and the all go to surveyed node points. It's strange that every measurement differs by 10 feet and a little bit more.
Anybody run into this before?

What happens if you hold all 4 corners in your site calibration? Does 1 jump out as having a bogus distance against the '96 survey?

Could be a 10' prism offset error?

Paul in PA

How are the internal angles?

If you did a two point calibration then that needs to be looked at (you probably already have).

If you are using TBC you can inverse between points and see if the grid and ground distances are close. Also I would export the lat, long, hts that were collected and import them into a "clean" file and be sure that nothing weird is going on.

However, I would not calibrate that type of job, it is much better to LDP or SP it.

is your scale factor set to hold at ONE?

...My only guess is the draft person clipped the lines on the symbol and then auto labeled the lines in the 1996 survey...Anybody run into this before?

I have seen an entire subdivision plat prepared and initially filed for record that employed the very issue you raised- the draftsperson "trimmed" the boundary and lot line linework at the monument symbols so that the monument symbols were easier to "see" on the plat, then autolabeled the lines that were "left". Just about every one was incorrect and the plat had to be fixed and re-filed. Very frustrating problem, but you may indeed be onto something with the scenario you are facing based on your initial field findings.

Paul in PA, post: 454629, member: 236 wrote: Could be a 10' prism offset error?

Paul in PA

I should have entered the "tongue in cheek" emoji with the above.In reality such an error would effect lines as they are relative to the traverse.

I wholly agree with the thought that the lines were dimensioned in CAD rather than from point file, since I had done that once or twice myself, usually when showing an unmonumented PC or shallow angle point with an open circle rather than a solid ball. They did not go out the door because I learned from a surveyor that insisted that you always did a separate check survey closure independently using only the information on the paper map.

The more important question is how do you explain on your new map the difference from record map and how often?

Paul in PA

How does the map close? Unless the section were perfectly rectangular or a parallelogram, the map would no longer close under the theory that the lines were clipped by map symbols.

Paul in PA, post: 454684, member: 236 wrote: I should have entered the "tongue in cheek" emoji

yeah, that took a second to understand how many millimeters that would require to enter, and what the cutoff was for digit input

roger_LS, post: 454705, member: 11550 wrote: How does the map close? Unless the section were perfectly rectangular or a parallelogram, the map would no longer close under the theory that the lines were clipped by map symbols.

We'll both of our surveys close, now what? Each record leg differs from the measured leg by approximately 10 feet.

Hopefully the previous survey had referenced to some outside the box monuments that can be checked to see if the monuments you found are where they are suppose to be.
Crew have been caught placing monuments completely backasswards to where they belong from existing control.
There are the countless transposing of digits, had a PC that would often confuse 4s and 1s. His major blunder was turning a distance of 414.41 into 411.14 on a 2,500 acre boundary. I blame our boss for being too cheap to have DC.
Then there is the staking out and IMan says go 5ft and the rodman measures 5ft toward the IMan and drives monument and never does a SS or check.
Many things can cause this.
At least it was not what I found out on one project, some ancient original surveyor in the mid 1800s had added 100 varas to each end of the 4 boundaries.
Yep, each boundary was 200 varas longer than called for and patented.:scream:

A Harris, post: 454776, member: 81 wrote: Hopefully the previous survey had referenced to some outside the box monuments that can be checked to see if the monuments you found are where they are suppose to be.
Crew have been caught placing monuments completely backasswards to where they belong from existing control.
There are the countless transposing of digits, had a PC that would often confuse 4s and 1s. His major blunder was turning a distance of 414.41 into 411.14 on a 2,500 acre boundary. I blame our boss for being too cheap to have DC.
Then there is the staking out and IMan says go 5ft and the rodman measures 5ft toward the IMan and drives monument and never does a SS or check.
Many things can cause this.
At least it was not what I found out on one project, some ancient original surveyor in the mid 1800s had added 100 varas to each end of the 4 boundaries.
Yep, each boundary was 200 varas longer than called for and patented.:scream:

The consistency of the 10 foot difference concludes me to believe it's an office error and not a field error. All the quarter corners we're single porpotioned in so it is basically a box. I've only done a two point calibration so a scale factor should not be the problem. 10 feet is too large to be a grid ground difference. The old GLO measurements are around 40 feet different from both of us so they are of little use in trouble shooting the problem. I'm leaning heavily towards a draftsman induced error. The corner marker symbols are cute little Maltese crosses and the wider section line doesn't appear to extend to the center of the symbol.

Skeeter1996, post: 454775, member: 9224 wrote: We'll both of our surveys close, now what? Each record leg differs from the measured leg by approximately 10 feet.

Personally, I'd probably expand the survey further out to ensure that what he did was correct. Tie into the found monuments he had and redo the thing. Call the client and tell them you've encountered unexpected conflicts.

Skeeter1996, post: 454780, member: 9224 wrote: The consistency of the 10 foot difference concludes me to believe it's an office error and not a field error. All the quarter corners we're single porpotioned in so it is basically a box. I've only done a two point calibration so a scale factor should not be the problem. 10 feet is too large to be a grid ground difference. The old GLO measurements are around 40 feet different from both of us so they are of little use in trouble shooting the problem. I'm leaning heavily towards a draftsman induced error. The corner marker symbols are cute little Maltese crosses and the wider section line doesn't appear to extend to the center of the symbol.

A two point calibration would be exactly the type which would cause a 10/2640 error, I would be very sure using independent checking of your locations that it's not the issue. But I figure you are probably correct thinking its a CAD label error, wipeout is so much better than trimming.

MightyMoe, post: 454782, member: 700 wrote: A two point calibration would be exactly the type which would cause a 10/2640 error, I would be very sure using independent checking of your locations that it's not the issue. But I figure you are probably correct thinking its a CAD label error, wipeout is so much better than trimming.

How would a two point calibration cause a scalar error? I agree a three point calibration could definitely cause a scalar problem, but all a two point calibration does is translates and rotates. I only use three or four point calibrations when I'm laying out items. I want my distances to be my found distances when I'm doing a land survey. The only reason I even use a two point calibration is for searching corner purposes.

A two point calibration will hold two points and scale all measured distances between them, as well as rotating to those two points. If you specify within your software that you want to hold a scale factor of 1.00000, then it will not scale, and you will see residuals on your localization.

If you have a scale factor applied, you still will not see residuals with only two localization points as there aren't any; your localization has held the record locations as gospel and forced your observed points to match with no residual.

As to the larger question; what do other record maps say? The latest was 1996, but surely you have older maps in the file that would prove out a distance one way or another, or confirm that you're observing the correct monument.

I'd go back the site, locate the points you have already found on an LDP and compare results, if it were a CAD trim error of a monument symbol, the old map shouldn't close.

If you take a look at your measurements in SPC with no calibration applied, you could at least see whether your calibration is completely fubar and eliminate that as a factor. Even with the distortion in your SPC zone, you're only going to be seeing a foot or less per mile, not 10 feet.