I likely won't get much agreement on this topic, but I have personally seen a shift in measuring abilities with the use of GPS. Two surveyors using EDM's (with correct PPM corrections applied) will generally more closely match each other than a surveyor coming along later using RTK to compare to a measured EDM distance. There are too many younger surveyors now in the field measuring who have never used a steel tape, EDM, along with RTK. Unless I am doing long static observations between two points, I would prefer to use an EDM that is in proper adjustment and with the correct PPM to measure the correct distance between two visible points whether they be 200' or 2000' apart. There are many surveyors using RTK for lot surveys where trees, buildings, and fences are issues, but still record the positions and state on their plat that another surveyor's point if "off".
I will agree 100% with that!
SHG
There are many surveyors using RTK for lot surveys where trees, buildings, and fences are issues, but still record the positions and state on their plat that another surveyor's point if "off".
Amen!
And staking blue tops, curb, manholes, catch basins, ect.
The right tool for the job is not always GPS.
Staking a building with GPS (I've seen it done) makes no sense.
Perfect example of "A little knowledge ...
... is a dangerous thing."
It's fun to see the light bulbs "light up" in class when I explain that the precision that they used for establishing TBMs is different from what they need to observe for cross-sections for dirt work.
Amen and Amen
GPS (whether RTK or static) is another tool in the toolbox, albeit a wonderful tool. It should not be relied upon exclusively even when one understands the strengths and weaknesses of the observations. Good field procedures require one to be knowledgeable of the tools availble and the strengths and weaknesses of each. When staking building corners I may turn 90, pull or shoot the distances, BUT I will also check those diagonals just as a check.
Andy
Vectors and subsequent locations determined by any method other than a 'measurement' are merely calculations. Although surveyors have relied heavily on calculated positions over the years, the act of verifying and proving those locations is the true definition of our profession.
I always school my employees to know the difference between two calc'd points and an observed measurement between those points.
It hasn't happened yet with anything that I've been associated, but someday soon in depositions I'd like to hear a surveyor explain how he actually determined a 'measurement' between two points that were only located by GPS, or triangulation etc.
I believe we have dumbed down our ability to measure accurate distances in the exchangement for speed. At some point we each have to determine what is our own acceptable tolerance whether that be 0.001' or 0.100'. Then we have to have the mindframe and knowhow to achieve that tolerance.
A few years ago I researched and wrote an article about the USC&GS "Ice Bar" that was used to measure triangulation baselines around the year 1900. I came to the conclusion that things started to progress downhill after that. A surveyor later wrote to me and asked how the USC&GS baseline distance measured with the Ice Bar compared to a modern GPS distance between the two end points of the baseline. He wanted to know how far off the 1900 surveyors were in their measurement. I told him the 1900 surveyors were as close to anything that could ever be achieved. (They used microscopes). He argued with my statement and was stuck on the assumption that GPS was more accurate. I could not convince him otherwise.
Ice Bar article:
http://www.amerisurv.com/PDF/TheAmericanSurveyor_Penry-WoodwardIceBar_April2007.pdf
I know a very qualified and well respected surveyor who will not do any boundary work with GPS. Control yes, but not placement of corners.
His rational is that a GPS "measurement" can not be defended in court, because you DID NOT measure the true line. He is correct IMHO. But then again how many corners have been set with conventional instruments by radial methods. Is that any better?
Kind of like building a shed or a deck. You have all them tools in your box, and know what you want it to look like. What do you do - "measure twice, cut once". The corollary is "..no matter how many times I cut that board, it's still too short...".
But in defense of GPS I always feel a bit better when my bearings match whatever the other guy came up with. Many times within a couple seconds, with no adjustments. Usually the distances are close too. Whether that means we both got it wrong, or we both got it right sometimes remains to be seen? I guess that's why we get the big bucks, eh...
That was a very interesting article when I read it a few years back.
JRL
I would prefer to use an EDM that is in proper adjustment and with the correct PPM to measure the correct distance between two visible points whether they be 200' or 2000' apart.
No problem with that but I would prefer to use RTK that is in proper adjustment and with the correct PPM to measure the correct distance between two points whether they be 10000' or 20000' apart. 😉
Knowing the right tool for the job is often overlooked. Knowing your tool and its measurements standard errors and achievable accuracy as well as your survey accuracy requirements, sometimes is rarely considered.
I have seen someone try to make cabinets with a chainsaw and axe too…. 🙂 It is never pretty. Or easy. Or what the customer wanted.
Chains, compasses, theodolites, EDM, various GPS techniqes ... they give you measurements, and they all have systematic errors and random probable errors (temperature coeff, centering, PDOP, etc etc). Nothing wrong with including GPS in this list, because it gives you measurements, too.
Any combination of measurements that gives you redundancy for a check, and a probable error in the result that is suitable for the job is a good combination to use.
If you don't know the probable error in the result, and haven't gotten redundancy, then it isn't a good enough set of measurements no matter which tools you used.
> I believe we have dumbed down our ability to measure accurate distances in the exchangement for speed. At some point we each have to determine what is our own acceptable tolerance whether that be 0.001' or 0.100'. Then we have to have the mindframe and knowhow to achieve that tolerance.
>
> A few years ago I researched and wrote an article about the USC&GS "Ice Bar" that was used to measure triangulation baselines around the year 1900. I came to the conclusion that things started to progress downhill after that. A surveyor later wrote to me and asked how the USC&GS baseline distance measured with the Ice Bar compared to a modern GPS distance between the two end points of the baseline. He wanted to know how far off the 1900 surveyors were in their measurement. I told him the 1900 surveyors were as close to anything that could ever be achieved. (They used microscopes). He argued with my statement and was stuck on the assumption that GPS was more accurate. I could not convince him otherwise.
>
> Ice Bar article:
>
>> http://www.amerisurv.com/PDF/TheAmericanSurveyor_Penry-WoodwardIceBar_April2007.pdfbr >
This whole thread is missing the point. In a court of law the "monument holds". The discussion will be where is the boundary line not where is the measurement. All surveyors measure differently. The Courts hold to this because they don't want to get into a theoretical discussion in court about who measures the most precise. Whether you measure with a compass and chain, EDM or GPS all measurements will be valid if you find the true corner.
> His rational is that a GPS "measurement" can not be defended in court, because you DID NOT measure the true line.
I'd be interested in hearing him defend an EDM measurement, because he doesn't "measure the true line" with that, either. He pushes a button on a machine that generates electromagnetic waves and compares the phase relationships between the internal transmission and the reflected external transmission, does a whole bunch of calculations, applies some corrections and conversions, and spits out a distance value. It's pretty much the same principle as GPS, except that the measured ranges are shorter, the number of wavelengths (integer fix) isn't generally an issue, and there's one less step involved (GPS station-to-station distance is derived from an inverse between 2 calculated positions).
One method is no less valid than the other, you just have to know how to determine the error associated with each.
Yesterday i watched in amazement as a county employee set tow control points using VRS.
Hand held, 5 sec of data and that was it. No tripod, 3 minutes of data or even a mention of returning 4 hours later, to collect 3 minutes more of data and averaging the two values.
I am confident in saying they have no clue.
Gary
Come on Gary
> Yesterday i watched in amazement as a county employee set tow control points using VRS.
>
> Hand held, 5 sec of data and that was it. No tripod, 3 minutes of data or even a mention of returning 4 hours later, to collect 3 minutes more of data and averaging the two values.
>
> I am confident in saying they have no clue.
>
>
> Gary
You know the preferred datum around here is "Maryland State Plane-ish"; hold one GPS point and the direction toward another 😉
BTW your website address is misspelled in your profile (you left out the "a" in "professional")
Jim
