nate, and jeff if you are sacker2, i have to disagree.
it is my belief that this practice came from decades ago when the math was often done from trig tables in large books and computed from hand. in this case, a long corridor survey, measured with steel tape and theodolite, would have issues with 'alignment', or orientation. keep in mind that steel taping had a limited accuracy, so maintaining distance control was already difficult. couple that problem with the sine of angles close to zero and one eighty changing quickly with only small variations, and your network is going to have a hard time closing well.
this is why the older surveyors wanted some deflection in angles of a corridor traverse.
in short, it was mostly a computation problem, not a measurement problem. now i have a rain day project. i will mock up a couple scenarios to try to prove my theory.
does this make sense to anyone?
You might start with the example I posted late in this thread when we argued about this topic a little over a year ago.
[msg=45467] https://surveyorconnect.com/index.php?mode=thread&id=45467#p45531 [/msg]
This is known as Strength of Figure and you are correct, the dislike of very small and very large angles comes from the days of triangulation surveys. You can look at the trig tables in a field book and see why... as you approach those angles the differences of the sine of sequential anges increases exponentially.
Obtaining the distance with an EDM virtually eliminates the need to favor 60° angles and other strength of figure concerns.
Stephen
Put The Least Weight On GPS And The Angles Will All Do Fine
Even if you called for 1" maximum error LS will find a solution.
Please cite the survey text that calls a 180° traverse angle weak. You are miss stating the truth.
Paul in PA
Just checked that thread. All good stuff. I have found that the strength or weakness of the "180" angle still holds even with our more precise equipment, but not all traverses are the same... just sayin'...
> The problem: After coming off the northern pair and traversing into the southern pair there was an angular error of 46”. We were told to hold the coordinates of the first setup and to throw the angular error into the first angle turned (not to hold the BS as 00-00-00). After this was done the linear error was about 0.08’.
>
Re-occupy/observe the "GPS" pairs a second day for some feel good...
But, if it is me, I hold my original backsighted member of the first "GPS" pair as my basis of position, and rotate holding the last shot member of the second "GPS" pair as my basis of bearing.
I end up with what is essentially a route traverse between two "known" points. If you want to let Starnet massage it, all the better.
Then, I check the over all distance and how the rotated traverse hits each "GPS" point. If I want to feel even better, I would shoot one in the middle with my GPS.
All In All Opinion, GPS Vs. Instrument
With less than minimal input which was not of optimum quality, you will get a reasonable result.
Do not be fooled that you are good, it may just be a result of "Gross errors canceling out." That is a direct quote from my surveying professors, about 41 years ago.
Paul in PA
:good:
> Boy that sounds like famous last words!;-)
The original post speaks of 0.08' misclose in a 4300' traverse. That's better than 1 in 50,000. I repeat, there is no bust worthy of re-running here.
EXACTLY RIGHT!!! 🙂
> EXACTLY RIGHT!!! 🙂
I guess I didn't quite grasp the meaning in your emoticon the first time.
