We have some survey magicians doing 50' x 130' lot surveys using GPS to bring in control from miles away.
John, an LS friend and I spoke yesterday and he told me that another surveyor called him up and told him his points were off. It seems that this other guy ignored existing tract monuments and brought in control from a mile away using GPS.
The job I just finished had another GPS situation. One line was staked three times. The surveyor told the client he brought in his control from four miles away. He also ignored existing monuments on site.
That GPS is surely amazing stuff!:-O
Sounds like.......
........more work coming up for guys like you.
There is definitely a benefit to having it all tied together. There are many places in Jacksonville where we have block after block tied together. Normally, you can't work block to block, but it's nice to see it all and has helped more than once.
All of downtown in Rusk is tied together, pre GPS. Now, I would use GPS to tie all of the jobs in suburbia together just to get a feel for how the work was done and if you see patterns emerge.
Ignoring monuments, well, that's just silly, but it's not the GPS' fault, that would be operator error.
> We have some survey magicians doing 50' x 130' lot surveys using GPS to bring in control from miles away.
>
> John, an LS friend and I spoke yesterday and he told me that another surveyor called him up and told him his points were off. It seems that this other guy ignored existing tract monuments and brought in control from a mile away using GPS.
>
> The job I just finished had another GPS situation. One line was staked three times. The surveyor told the client he brought in his control from four miles away. He also ignored existing monuments on site.
>
> That GPS is surely amazing stuff!:-O
Well, technically, using GPS is fine for most any boundary survey, given the field conditions allow for it. Those "surveyors" just didn't look hard enough for local monuments. You could survey it with compass and chain, or total station, but if you don't find local monuments to control, or look hard enough for them, then you're in trouble.
I've surveyed many small lots with GPS. Your XY control is miles away (CORS or NGS stations), but your boundary control is still the same no matter what method you use.
GPS for suburbia lots..Ryan
> .... Your XY control is miles away (CORS or NGS stations), but your boundary control is still the same no matter what method you use.
I am wondering if this surveyor did a bunch of record calcs and used a monument referenced on some map that was miles away. How would one use GPS to bring in control and stake a single family? The map has it's own local coordinate system...right? How would you tie the two systems together without at least three on site monuments tied to the map?
I do not see why any surveyor would use GPS on single family 50' x 130' lot when C/L control or sideline monuments are available. Thats TS work.
Why would go work so hard to bring in control from four miles away, when you have control tight there for you locally?
I have followed a few that come into this area that use other control to stake for monuments that are there and do not bother to get into the brush and find them.
I suppose that they are going with the odds that it will be beyond the limitation period before they are discovered.
GPS for suburbia lots..Ryan
I wouldn't do it without tieing into the monuments required to survey the boundary. It's all relative. Usually I work in a 10,000, 10,000 world. If I use GPS I tie to all of the monuments and tie to the XY control at State Plane. After processing you it is all on the same system, you can move it all to a local system at that point.
It's an option. I prefer TS on the small jobs.
GPS for suburbia lots..Ryan
GPS is a measuring tool just like a total station. If you have plenty of clear sky around your monuments then it works fine. If they are using it to bring in control from a long way aways, that is just as smart as using a total station to bring in control from miles away. It's abusing the tool. With either tool you must work within your lot and block to establish the subject lot.
GPS in the right hands.
GPS period is dangerous when in the wrong hands and a huge benefit when in the right hands. Not that anyone here needs to be told that, but good to keep the message going for those who do need to hear it.
In regards to the accuracy on a suburban lot, it would be hard to get a high order closure on such short distances between points, however each position could be fairly accurate, even with a base station or tied control point being several miles away. At least when the equipment and data processing is done in the right hands. I'm guessing the surveyor mentioned in your post is bringing in geodetic control from miles away, not boundary control. I don't see a problem with that, and I'm guessing that is the misunderstanding you are getting from the clients statement??
Up here in timber country, it is tempting to establish a couple of GPS points in an opening which may a couple of hundred feet apart, set up on one, backsight the other and then traverse a thousand feet or so to the point to be tied or established. I think this is becoming a very common practice in timbered lands and is some cause for concern as the practice may not be producing the accuracies the parties using them think they are getting. My experience is that why the positional accuracy of the GPS points are good, the directional accuracy of the traverse is often lacking and should be verified or corrected with an astronomic observation.
clearcut
>
> Up here in timber country, it is tempting to establish a couple of GPS points in an opening which may a couple of hundred feet apart, set up on one, backsight the other and then traverse a thousand feet or so to the point to be tied or established. I think this is becoming a very common practice in timbered lands and is some cause for concern as the practice may not be producing the accuracies the parties using them think they are getting. My experience is that why the positional accuracy of the GPS points are good, the directional accuracy of the traverse is often lacking and should be verified or corrected with an astronomic observation.
We do it all the time in the piney woods of East Texas. Works well if you observe the points a few times with RTK or have good static values on them.
The difference is we always run between pairs and never dead-head a point out there to stake in the boundary world without it. In the oil patch is a different critter when you consider the cellar of the well is a 6' tin horn. A tenth or two doesn't bother me there.
UNCLEAR ON THE CONCEPT
PLENTY OF FOLKS USE RTK FOR BOUNDARY.... NOT ME. TALK TO ALAN FRANKS (SOCAL SURVEYOR,LONG TIME GPS USER) AND SEE WHAT HE HAS TO SAY ON THE SUBJECT. ON REALLY SHORT LINES ONE CANNOT MET 1:10,000. MANY SPECS STATE UNDER IDEAL CONDITIONS AT A 68% CONFIDENCE ONE CAN EXPECT 1 CM PLUS A COUPLE OF PARTS PER MILLION.AT 95% CONFIDENCE,FOR PROJECT YOUR, UNDER PERFECT CONDITIONS WE ARE LOOKING AT PLUS OR MINUS 0.06'. THIS IS REALLY NOT VERY GOOD FOR SHORT LINE OF 30'. NOPE WRONG TOOL, FASTSTATIC MAYBE, UNDER PERFECT CONDITIONS......
Dane
That's why you re-observe critical points. Static seems counter-productive for lot surveys, unless you're just tying it together and do the lot with conventional methods.
For me, I don't use it much for lot surveys but it can be done to the nat's a$$ if you know what you're doing.
KRIS
AN RTK SHOT IS AN RTK SHOT,ONLY NETWORK ADJUSTABLE IN CERTAIN CIRCUMSTANCES, BUT MOST DO NOT ADJUST. WE ARE TALKING CMS V. MMS. YOU CANNOT GET MMS LEVEL WITHOUT ADJUSTMENT
Kris
Like I said, I have concern as I have uncovered errors in corner positions that were established by traverses that originated from GPS points a couple of hundred feet apart. In fact, I found one last week, where I shot the GPS points with a total station and came up with the same distance as an inverse between the GPS coordinates, however the bearing was off by 4 minutes when compared to a solar observation. The GPS points were 300' apart. Apparently the coordinates of the GPS points were derived from opposite sides of each points respective error ellipse.
UNCLEAR ON THE CONCEPT
> PLENTY OF FOLKS USE RTK FOR BOUNDARY.... NOT ME. TALK TO ALAN FRANKS (SOCAL SURVEYOR,LONG TIME GPS USER) AND SEE WHAT HE HAS TO SAY ON THE SUBJECT. ON REALLY SHORT LINES ONE CANNOT MET 1:10,000. MANY SPECS STATE UNDER IDEAL CONDITIONS AT A 68% CONFIDENCE ONE CAN EXPECT 1 CM PLUS A COUPLE OF PARTS PER MILLION.AT 95% CONFIDENCE,FOR PROJECT YOUR, UNDER PERFECT CONDITIONS WE ARE LOOKING AT PLUS OR MINUS 0.06'. THIS IS REALLY NOT VERY GOOD FOR SHORT LINE OF 30'. NOPE WRONG TOOL, FASTSTATIC MAYBE, UNDER PERFECT CONDITIONS......
I don't like RTK for boundary either. I have done FastStatic with 2 15 minute sessions per point at different times of the day with two bases running. This was to tie in a block corner on a hill with open sky, where it would have taken me a day just to traverse through it and back. You just need to tie in three or four of your already found points to tie it to the survey. I have also done the faststatic for lot corners and CL intersections, but it was for a large scale Caltrans R/W boundary survey with over 100 found mons over 6 miles long.
clearcut
No, that was a fluke, not an error elipse. 4' is 0.34 feet and not 0.03' like should have been generated. Your premise throws out the specs of the instrument.
More than likely they were getting points where they shouldn't have been.
I've gotten results from my submeter that match my total station, but I don't use them for anything but creeks and roads.
DANE
Bull$h!t! You can, but you need to re-observe the points and average them. You don't need to network adjust everything.
You can get repeatable RTK that is sub-centimeter. One shot won't cut it. Static will get the job done, but takes longer.
If you're not matching 0.02' or less, then re-observe the points more than once and find out which initialization is bad.
This isn't rocket science, it's just checking until you get the same answer three times.
We use GPS all the time for suburbia lots and more urban (downtown) areas; but only for the main control. It's nice to get a system that continues to build on itself. We always had problems with our large instrument based control systems in more urban settings-but with GPS there is little error across control networks. In fact we have tried to control all our small surveys with it. But once on site its the robot or TS.
We never use GPS to set property corners on small lots, layout a house, set curb and gutter stakes, blue tops, ect. But a lot and I mean a lot of other firms do.
I would never use GPS for surveying small tracts, like lot surveys. Like someone else said, its not accurate enough for short distances. Why use GPS to shoot a distance you could get a more accurate measurement with a steel tape?