Hello everybody,
I'm new in the surveying field and want to hear from the experts;
First: I want to know the error tolerance in surveying works related to properties boundaries "I'm recently hired to work in local municipality and receive maps from various surveying offices when I compare between them some times I found shifts up to 10 cm sometimes even more what I mean is that the maps are almost identical but there is a shift Is that too hard to get the exact coordinates "
Second:I live in a developing countries ,my municipality still new to this method of work we have two Total-stations Foucs8 2" what can I do to get the most precision out of it (special I want to avoid coordinate shifting) and if there any tips helping me to develop the work here"
thanks a lotĀ
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Hi Khalid-Elejla:
I am working in the United Sates. The state in which I practice the profession of Land Surveying has the following requirements relating to the precision and accuracy required for Property Line (Boundary) Surveys.
Better than 1:10,000 closure for Rural Surveys and Ā 1:20,000 closure for Urban Surveys.
With a modern Total Station in good adjustment, Tribrachs and Prisms in good adjustment, and reasonable care and attention to the work, a 2" instrument should be able to produce a closed traverse considerably better than these requirements. Ā When you speak of shifts of 10cm in coordinates values, I perceive that you are getting hung up on the "truth" of coordinates rather than the "truth" of the physical markers that define the boundary of the the property. Ā I suggest that you compute the 'metes&bounds' (the bearings and distances) around your property description and determine the misclosure of the description first and see how well that meets the requirement in your jurisdiction for the closure of surveys related to property boundaries. Old descriptions can be remarkably poor in closure due to the old methods and equipment used to measure the boundaries, together with mistakes in the writing and subsequent transcribing of the descriptions themselves. Do not get tunnel-vision on the coordinates ~ always consider the physical evidence of the "Calls" that are in the description of the property in question. Ā If the Deed states that a 32 inch (830mm) diameter Tamarind Tree is the corner, then that is the corner, regardless of where your GPS coordinates say the corner should be.
There is a recent update to the requirements for a particular type of Boundary Survey here in the United States. Ā The sections at the beginning that relate to the technical requirements for measuring Property Boundaries may be a very good guide for you to contemplate, in general terms. Ā You will see that the technical requirements are not excessively difficult to Ā achieve ~ the skill and judgement comes in evaluating the evidence that one finds in the field at the project site, and in the research of the legal documents provided or discovered in the Land Records of your jurisdiction. Ā Please refer to this link:
Minimum Standard Detail Requirements for ALTA NSPS Land Title Surveys A 2016
Good Luck in your endeavours
Thanks every one this was very helpful
but I think I wasn't so clear
My department is concerned about organization and urban design , we adopted projected coordinate system and planted several reference points with known coordinates then we receive surveys from surveying offices according to the adopted Coordinate system , when comparing the boundaries of two neighbor properties we found some interfaces because it didn't came from the same surveyor another thing when we applying the survey of an existing house to the organization line "a line that represent the street boundary"in AutoCAD some times we found that the building is passing the line and when we assigned another office surprisingly the building isn't passing the line or passed it in different way so when this shift accepted and second how to train those surveyors or giving them tips . Are there any tips for precise survey with total station
Pardon me for asking too many questions it's because that the whole new thing is adopted recently and we faces a lot of problem
Dear Khalid:
Step by step:
- Have you got any idea how these surveys nave been made? For example, if they were taken by GPS, it is quite difficult to get the exact position of one house, as the GPS canĀ“t reach to the corner, so depending of the surveyor, it will consider a theoretical offset (thatĀ“s why usually you can get cross on the CAD drawings) or he wonĀ“t consider it at all, and then, everything fits. Same history with a total station, but the offset is smaller, so the deviation should be less. One method to avoid that is to make mandatory to survey benchmarks and kerbs (top and bottom), so you will see the differerences between surveyors. Maybe it is not an issue of a shift on the coordinates, and it is an issue of a "bad surveyor" or one guy that didnĀ“t take care of his job. In order to avoid that, it is always a good practise to survey some linear elements that can be regular (as kerbs) to see the diferrences on coordinates an levels.
- Regarding the total station, it is more than enough to make a good job. With this equipment you can reach easily to an accuracy on 1mm/km. Do a precise survey? First methodology: Closed traverse with partial closing... You will begin on benchmark 1 to benchmark to to benchmark 3... until you arrive at the end of the corridor you are traversing, and then you return from benchmar n to benchmark n-1', benchmark n-2'... until benchmark 2' closing on benchmark 1. You should survey, during the traverse, a few benchmarks without " ' ", so you can make partial closing, and if something were wrong, then you can reobserve. Another system, compensation through networks on Least Square, another one, CCMC... there are many, but you should have some idea on how this systems works. I can recommend you CCMC as it never fails and it shows youif there is any error on observations. And you should take a lot of care regarding observations: calibrated T.S., weekly calibration by your own, use tripods for observations, not rods, use the T.S. in order to level the levelling bases, make visuals on similar distances... If you are new on Survey, you should look for any book in order to have an idea of how to do a properly traverse. I never recommend that, as you are assuming to much risk and you should have some experience on that.
On my last project at Western Australia, we should stake out and check 5000+ anchor bolts on 1mm error (total error of 1mm, not 1mm on each coordinate) on position on an area of 1.5x2.0km... None of them reach to this 1mm error, ussually, 0.6-0.8 mm. But ussing CCMC and no traverses, weekly checking, fixed benchmarks...
If you need some help, please send me some more information and I will try to help you. Personal email: [email protected]
Regards and Welcome!!!
Be Careful! Especially if you are new to the work and the people whose work you are comparing are experienced licensed professionals.
Precision is a good thing to have in measurements. However, in most boundaries the measurements are accessories to the ACTUAL location of boundaries and their monuments.
Often you will see differences between two surveys,but if done correctly, the surveyors measured to the same monuments. The (undisturbed original) monuments are perfect. They are accurate. The measurements cannot be without some error. Furthermore, calculations based on those measurements such as the area of a property has even less dignity.
Best wishes in your new career.
JAC