Respectfully gentlemen, Error of Closure means little. E of C should reveal large blunders. Other than that, it means little.
As for explaining the process to the client, you should first ask why they want to know. If it was an idle remark thrown in to avoid silence while you work, most any explanation will do. If it was a serious question you are being given an opportunity to give a serious answer and create a loyal client. (See my post below about creating value. This is one way to do so. Helping the client understand what and why we do things the way we do has value to come clients.
Larry P
I think Norman is correct. Concidering:
B.In residential or commercial subdivisions where the length of lines does not exceed 300 ft, the area of tracts does not exceed 2 acres, and there is no plan for zero lot line construction, the allowable closure error is 1:10,000 and the allowable positional error is plus or minus 0.25 feet.
the 1-10,000 are paper points anyway.:-)
Yes JB, Why Would You Adjust It ?
The closure error is much less than any of your setup errors, so it is as good as "dead on". To go into an uneccessary adjustment routine is to give your computer/data collector an opportunity to mess everything up.
I definitely know how to adjust, but more importantly I know why and when to adjust. More often than not, I do not.
Your client appears to know better than you.
Assuming you did a perfect 1 acre lot and traversed through the 4 corners for a traverse length of 834.84' / 95,655 your distance error is 0.008', which could easily be at only one point or in one line. If you did not measure the distance in both directions you have no statistical justidication to adjust distnces. If the error was all in the angle it could be 8" at any one corner. If you used a 5" gun and did not do 2D & 2R at all 4 corners you have no statistical justification in adjusting the angles.
Paul in PA
I'm with you JB. Seems to me the better the closure, the more justified the adjustment. If the closure is within the range of your equipment and procedures then it indicates you only have random error and so can adjust it if you choose. One should not have to perform a least squares analysis each and every time (at least with conventional equipment). You should have already done statistical analysis in order to know what your equipment and procedures should be returning. If closure is outside the range of your equipment and procedures, then one should test the equipment and look at procedures to tighten up.
The point is that the beginning/ending point is not two differing places. All of the points are in slightly different places than observed. Tell the client to make a triangle with thumbs and index fingers, hold at arms length, look at on object through the triangle, close right eye and what is seen, close left eye and what is seen. It's magic. Things are not necessarily where they seem to be. Of course this isn't really the explaination, but it's fun and the client will think they now understand.
> The point is that the beginning/ending point is not two differing places. All of the points are in slightly different places than observed. Tell the client to make a triangle with thumbs and index fingers, hold at arms length, look at on object through the triangle, close right eye and what is seen, close left eye and what is seen. It's magic. Things are not necessarily where they seem to be. Of course this isn't really the explaination, but it's fun and the client will think they now understand.
To me, it seems much more natural to explain survey measurement adjustment from the standpoint of no survey measurement being absolutely perfect. They all contain small errors and, while to a layman may be so small as to be negligible, there is very good likelihood that a small error is present in any actual survey measurements. Adjusting a traverse amounts to making very small corrections to the survey measurements that are well within the expected ordinary errors in the measurements so that the result is a somewhat better reflection of reality and more useful for surveying purposes.
A good analogy would be adding or subtracting a number of sums of money such as deposits and withdrawals from a bank account, all of which had all been rounded to the nearest ten cents, but with an ending balance known to be exactly the same as the beginning balance. The analogous problem there would be to estimate the actual account balance after each transaction. An intelligent layperson with some numerical sense who can't appreciate that one is unlikely to be able to do much with any technical explanation of survey measurement adjustment.
> The point is that the beginning/ending point is not two differing places.
This is right on. The reason we adjust has nothing to do with statistics or our technical abilities. It comes from the legal perspective. A boundary must end at the exact point it begins to be a "correct" description. From a technical perspective a misclosure of .01'ft in 5000' is right on, but from a legal perspective it is lacking.
For those that argue that they want to report exactly what they measured. Remember you don’t exactly measure anything. The measurements your total station give you have a +/- after them. If your adjustment is larger than your +/- something is wrong. Also, often you do not traverse through the corners at all, and your reported distances where not measured at all.
> > The point is that the beginning/ending point is not two differing places.
>
> This is right on. The reason we adjust has nothing to do with statistics or our technical abilities.
Actually, any professional adjustment of survey measurements should be intimately connected with the nature of the errors inherent in the measurements. Those are the product of the technical means by with the measurements are made and without statistics to characterize the random errors in the measurement processes, nothing very meaningful can be said about important results of the measurements such as the relative positions of things connected by survey measurements.
>It comes from the legal perspective. A boundary must end at the exact point it begins to be a "correct" description. From a technical perspective a misclosure of .01'ft in 5000' is right on, but from a legal perspective it is lacking.
I'd be curious to know in what jurisdiction that would be true. It certainly wouldn't be in Texas where the main test of the sufficiency of a description is whether the land may be identified upon the ground by a competent surveyor.
I agree, but one should note that all of our measurements are always wrong...
It seems to me that some surveyor who actually believes that adjusting survey measurements somehow inevitably makes them more incorrect than had they not been would be obligated not to take the mean of repeated measurements. The mean is, after all, an elementary adjusted result that by his or her logic is somehow inferior to the measurements from which it was taken.
"THENCE N16°14'36"W or N16°14'48"W, a distance of either 648.32 ft. or 648.34 ft. ..."
Well put. You end up on the same point you begin at, and your "traverse" data should end up at the same point. I like that analogy.
I do it out of habit as my results are not usually this good!
