Precision in Total Station

Welcome Khalid-Elejla,

I too ponder these questions:

"Is it too hard to get the exact coordinates?"

and

"What can I do to get the most precision out of my equipment?"

I am sure you will get a lot of fine advice.

Your question:
"I want to know the error tolerance in surveying works related to properties boundaries..."
The State of Arkansas' requirements can be found here:
Standards of Practice - Arkansas

Good luck,
DDSM

In New Hampshire, USA the minimum error standards are 1':300' for rural farmland ; 1': 5000' rural land; 1': 10,000' city or industrial, commercial property.
https://www.nh.gov/jtboard/lsrule.htm

Khalid-Elejla, post: 361123, member: 11397 wrote: 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 lot

Hi Hhalid-Elejla,
You are hitting on a much misunderstood topic I think. If there are "State Plane Coordinates", they coordinates reduced to a plane that is probably near zero elevation. Many surveyors "manipulate" those coordinates to get to a project coordinate basis. They should publish the information necessary for that transformation. This may result in what you are referring to a "shift" in coordinates. There are other issues as well, depending on datum used. It sounds like this is the sort of difference you are seeing. The important thing is the bearings and distances between points. If you have two different survey plats that have a common line, that is the line you want to match up. The local coordinate tables are just local for that job (probably).

It is hard to know exactly what you are looking at, and what the specific issue is, so it is hard to answer your specific question. You need to see coordinates reduced to "State Plane" in a common datum, and you should see fairly close coordinate values. Remember that the boundary points in the ground are your important information, and the coordinates are shown to help you find the monuments on the ground.

I hope my explanation helped somewhat.

Welcome to the board.

Howdy and glad you have found you way here.

It has been said "Grasshopper, become one with your instrument to achieve enlightenment".
Basically, simply know the limits of survey equipment apart from the mathematical precision quoted by calculations.
Precision is something that is attainable and repeatable thru proper training and proper procedures.
Location of a true monument is a physical place on the ground that holds a higher priority than either precision, calculation and measurement.

Above all, understand that practice and understanding can last a lifetime.

:gammon:

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

I can hear my professor at college when I read this saying "there is no such thing as an exact measurement, but we sure do like to get as close as possible" one of the biggest things taught to me is redundancy in measurements. measuring an angle multiple times and taking the average will improve precision compared to measuring once. having good adjusted and calibrated equipment with solid control will improve your accuracy. having closed loops and checking into known points is essential. depending on the standards used will greatly impact the results of a survey. if every surveyor is using low modern-day standards, the more the surveys will very from survey to survey. It is hard for me to understand the exact problem and produce good answer for you, every situation is different. many factors dictate a surveyors professional opinion on where a boundary line should be.

There's a good reason why every parcel based GIS has a disclaimer you must acknowledge before viewing the map.

Khalid-Elejla, post: 361123, member: 11397 wrote: Hello everybody,
I'm new in the surveying field and want to hear from the experts.....

You have asked 3 great questions, all of which deserve an extended and detailed answer - which I just don't have time this morning to write. Perhaps later in the week....

But, briefly, if you traverse around a 4 sided site which is 250m on a side and you close back to the beginning point to +/-0.10m you have a closure ratio of 1:10000. That is acceptable in most jurisdictions. Better is very possible, but 1:10000 is acceptable. That misclosure should be distributed among all the measurements instead of just left in that one last leg. If it took 10 traverse points to perform that traverse the misclosure should be distributed among them, so that instead of having 0.1m misclosure in 1 leg, you have 0.01m in each of the 10 legs. That procedure is called "adjusting" the traverse. There are various ways to do that. Some hi-tech, some can be done with a slide rule. If you don't adjust you will have what appears to be a big "bust", but is in reality just normal imperfection.

Khalid-Elejla, post: 361123, member: 11397 wrote: Hello everybody,
I'm new in the surveying field and want to hear from the experts;

Khalid-Elejla, you said you have set up a coordinate base and three control points. It also sounds as though you have set up the AutoCad equivalent of a Geographic Information System (GIS). Now you are trying to fit individual surveys into that system. It is very common to have problems when doing that. 10 cm or more would not be unusual.

As WGD said above, there is a reason why every parcel-based GIS has a disclaimer.

You ask about the error tolerance for boundary surveys. Do you mean the tolerance with respect to the coordinate system you have set up?

Most U. S. states have precision requirements for boundary surveys. The state requirements that I know of apply to precision within the survey itself, rather than with respect to an adopted coordinate system.

There may be places in the U. S. or in the world where there is a precision requirement with respect to established coordinate systems. If so, someone who posts on this board will likely know about them.

Your municipality could pass a regulation requiring a certain precision with respect to your coordinate system. However, that would probably not accomplish much. Some of your local surveyors might not follow the regulation. They might not know how, or they might not want to do the extra work.

It appears that you need to upgrade the skills and professionalism of your local surveyors, or some of them at least. You also need to gather accurate information for your GIS. Both these things can be done, and are well worth doing. But both will take time.

As you have suggested, you (and a few others in your agency) will need to learn more about surveying. That way you can better understand the work of your local surveyors. When you have learned more, you may be able to give advice to some of them, but that won't be possible for some time. And some of your local surveyors may already have very good skills.

You will find a lot of good information on SurveyorConnect. One thing that would be useful to you (if you don't already know) is learning how to run and adjust a traverse with a total station. Mark Mayer has given a good brief explanation of closure error above. Others will be able to explain the details of how to run a traverse in the field.

Once you know how to run and adjust a traverse, you could add some more control points to the three that you have. You could also tie in any surveys that are not fitting well into your GIS.

There are several ways you could get different locations for points.

A couple of major issues could be, if you have a common line with two different surveys on adjoining properties, where one surveyor came up with a legal interpretation of one property's deed, and another surveyor surveying the adjoiner's property came up with a different legal interpretation of where that line falls. Hopefully, if one surveyor sets monuments on the common line, and another surveyor finds those monuments, he will accept them instead of setting his corners in a slightly different position. The second surveyor might set his corners in a different location which would cause a discrepency, and/or he might accept the corner monuments found, but his coordinates might be based on his math on the legal description.

Another source of error might be what you are describing, where there is differences in precision of the equipment, and/or techniques. One surveyor might tie into your point 1 and turn sets of angles and distances into his property, and do a precision adjustment, and come up with his final adjusted coordinates. Another person might come from a different point, have different adjustment and minor precision errors and have a slightly different final coordinate for the same two points. In surveying, we come to understand the mathematical differences, and usually emphasize the monuments in the ground controlling over differences in coordinate values.

Yes, there are standards of equipment, and number of observations to take, and what outliers to throw out when getting differing measurements. There is a whole study of statistical error and precision that can bring the precision down. You may never get the coordinate system to be the final word, however, because of the need to accept legal principles and evidence on the ground, as well as other possible ambiguities that don't settle a boundary location until it's adjudicated. Further, if you do have a settlement by a court, the coordinate value of those points won't hold over the ground positions.

I may not have properly addressed your concerns. I did get the impression you are talking about property boundary, and if you are talking about a location of a physical item, that brings up a complete further discussion.

RPlumb314 and Tom Adams
the information you gave was very useful and I appreciate it