I went out on what should've been a slam-dunk house stake-out on a 75' x 170' lot this evening. I kicked up all four corners plus one for the next lot over on the front. A few quick inverses had me scratching my head. All of the distances work pin to pin but diagonals are off by feet. If I hold the pins along the street the rear pins are both exactly 4' too far to the right. It's like someone took the whole section of the subdivision and racked it in a way that all of the distances remain the same but the angles are all off. I'll locate more pins tomorrow to determine the extent of the goof but I'm positive that these are the original undisturbed pins.
I've seen this a few times over the years, but I've never figured out the mechanics of how someone could screw up the office work or the field work in a way that would create this effect. I've attached a pdf below that shows what I'm talking about. The thin lines and bearings are per the subdivision plat, and the heavier lines are where the pins are in the field. Any ideas on how someone could make this goof?
What's the date on the original layout? Was it prior to the time radial stakeout became common?
Rankin_File, post: 390925, member: 101 wrote: What's the date on the original layout? Was it prior to the time radial shakeout became common?
No, this one is from 2004. Likely done radially with a total station but RTK could have been used.
Knowing the date of the subdivision would be helpful. I don't know about your locality, but at one time subdivisions were laid out in the field using just rough preliminary plans, and those measurements were transferred to the plat that was prepared for record. This was quite different than the contemporary method of generating a numerically perfect picture to be then laid out by some means.
Edit: 2004 would pretty much rule out the earlier method, I'd think. Could just be another RTK FUBAR.
Kent McMillan, post: 390928, member: 3 wrote: Knowing the date of the subdivision would be helpful. I don't know about your locality, but at one time subdivisions were laid out in the field using just rough preliminary plans, and those measurements were transferred to the plat that was prepared for record. This was quite different than the contemporary method of generating a numerically perfect picture to be then laid out by some means.
Edit: 2004 would pretty much rule out the earlier method, I'd think. Could just be another RTK FUBAR.
I've suspected RTK with a bad initialization but these rear pins are several feet into mature forest. I would think that the odds of getting a bad initialization that would shift everything so that the distances are all correct would be like winning the lottery.
Left handed cigarettes.
It's what happens when "Our Lady of Assumption" (Patron Saint of Lazy Persons) uses a tape only, to set corners. And, what they are taping off of is bad. Kent's comment above only reveals his lack of knowledge of how those things work.
Kent McMillan, post: 390928, member: 3 wrote: Knowing the date of the subdivision would be helpful. I don't know about your locality, but at one time subdivisions were laid out in the field using just rough preliminary plans, and those measurements were transferred to the plat that was prepared for record. This was quite different than the contemporary method of generating a numerically perfect picture to be then laid out by some means.
Edit: 2004 would pretty much rule out the earlier method, I'd think. Could just be another RTK FUBAR.
Nice try Kent. I would rule out RTK error because of its random nature, and this error appears to have it's own geometry separate from the plat. Looks like someone blew it (pilot error) hand entering the bearing from front to rear. Possibly 53d20'48" instead of the correct 52d30'48".
paden cash, post: 390941, member: 20 wrote: Nice try Kent. I would rule out RTK error because of its random nature, and this error appears to have it's own geometry separate from the plat. Looks like someone blew it (pilot error) hand entering the bearing from front to rear. Possibly 53d20'48" instead of the correct 52d30'48".
Agree - I would suspect a blown angle, either from poor fieldwork or a bust on the plat. Regardless it is what it is. Sounds like you got lucky and that surveyor 1 told the same lie throughout the entire block.
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I'm with you.....I don't even know how this happens? They're 90 degree angles anyway....I don't think I would bother typing in the bearings. I would probably use the bearing for the front line and then use station and offset for the pins. That's just my preference though. I find it to be the fastest and easiest way and allows for the fewest places to make a mistake (typo or otherwise).
The front pins may have been replaced by Quickie Dickey Surveyors by assuming the right of way is based on the road center line and measuring along the lot frontages so many feet from the curb from a pin set by another mortgage surveyor or a goat stake. In accordance with their business plan, Quickie Dickey Surveyors does not measure sidelines and why bother as they found the back pins. I confronted a local surveyor some years back about a similar procedure that resulted in a chain link fence being over the line. His reply was " so I have to pay for a few fences every year, no big deal".:mad:
lmbrls, post: 390948, member: 6823 wrote: His reply was " so I have to pay for a few fences every year, no big deal".
what a jackass......shouldn't be practicing.
Poor RTK procedures could actually be the culprit. If someone set the base up autonomous when staking the front, then used a different autonomous position when they staked the back. All session points would be relative, but between sessions there would be a substantial error. This can be caught by checking into a point from the previous session before getting started.
Another possibility is that RTK pairs were established for total station stake out and were not properly created. The likelihood of two points being perfectly shifted by the same amount is extremely unlikely, unless there is a bad initialization and each of the pair were collected within a matter of seconds of each other. Checking the backsight horizontal and vertical difference between total station and the RTK would catch a bad initialization on one of the points, but perhaps not if they were both based on the same bad initialization (astronomically unlikely occurrence). Repeating the observation on the two points would catch that.
I would say that in either case, poor procedure is the culprit and not the technology itself. Discussions like this are important. Surveyors need to be more aware of the entire system of measurement and be able to identify where things can get sideways so that they can build the necessary checks to make sure they catch blunders. Everything starts at the beginning and proceeds from there. Where are the weak links from the outer boundary survey to the final lot stake? Where are the vulnerabilities in your process? Failure to keep a critical view of your procedures is where things can get sideways very quickly.
My guess would be the CAD file used to stake the subdivision was revised but the map which got filed was an old version of the subdivision CAD file.
If they are into the trees, I doubt it was RTK. I can imaging someone creating points in a data collector by using "point in direction" or a similar function. One bad distance, and the rest of the line if wrong. Of course that would still mean poor procedures because they didn't check in at the end.
I have seen this in subdivisions around the lake. Rural area that was developed without any recording requirements or oversight and done before GPS or Total Stations.
The backlot points were done from one traverse. The points along the road were done from another, probably following a dozer. The only thing I could do was to re-establish the back corners based on adjacent back corners and re-establish the road points from additional points along the road. The side lot lines will never match the record.
James
I'm positive that these are original pins. 4 of the 5 still have their caps identifying the original surveyor. I'll be surveying the rest of the neighborhood this afternoon so I'll post more detail when I have it.
FWIW, I've spoken to the original surveyor (no longer with the same firm due to the economy) he doesn't have access to the files and doesn't remember any re-plats or redesigns that could have set the stage for an error like this.
JaRo, post: 390960, member: 292 wrote: I have seen this in subdivisions around the lake. Rural area that was developed without any recording requirements or oversight and done before GPS or Total Stations.
The backlot points were done from one traverse. The points along the road were done from another, probably following a dozer. The only thing I could do was to re-establish the back corners based on adjacent back corners and re-establish the road points from additional points along the road. The side lot lines will never match the record.
James
Those make sense because the front works and the rear works, but the angles and distances are off on the sidelines. This is different in that all of the distances work on each lot, only the angles are screwy.
Dave Karoly, post: 390954, member: 94 wrote: My guess would be the CAD file used to stake the subdivision was revised but the map which got filed was an old version of the subdivision CAD file.
This was my first thought also.
Stephen Ward, post: 390929, member: 1206 wrote: I've suspected RTK with a bad initialization but these rear pins are several feet into mature forest. I would think that the odds of getting a bad initialization that would shift everything so that the distances are all correct would be like winning the lottery.
Is any of the site clear enough so that RTK could have been used to set control for stakeout? What about street widths? Is there reason to think that a street could have been revised after layout, but boundary markers not reset on the back line?