Hi everyone.
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Let's say this sentences are true.
Resection is a sample.
I want to perform it with control over sigma values along the project.
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What is an acceptable sigma value for topographical roads survey??ÿ
Where can I find this info ??ÿ
Thanks a lot. ^^
What is an acceptable sigma value for topographical roads survey?
Where can I find this info ?
Resections are less common on corridor projects in general due to the linear nature of the target area...but there's not a single number that is "acceptable" across all applications.
Usually contract specifications (what is the goal of the work) and the task at hand dictate the acceptable standard error for a resection (or any setup for that matter).
We do corridor/route surveys for a variety of purposes; some of them need sub-cm precision across the entire project, others can be as loose as a decimeter depending on what we're doing that day.
Just spit balling here, but I'd say a good root means squared error (RMSE) return at the 2 sigma (95%) confidence level should be less than .04' for northing, easting, and elevation of you're using a prism pole with a bipod to set control and backside.?ÿ If you're running three tripods, them RMSEs should be less than .01'.
@murphy Hum, intresting . I ll have to give it a try and see what are the outcomes on my topo.
If it's a DOT job be sure and review the surveying handbook. It may be that resection isn't allowed.?ÿ
It may be that resection isn't allowed.?ÿ
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Angles-only resection can have pretty bad error accumulation if proper care isn't taken, and that is probably why it isn't allowed by some.
When measuring angles and distances it is far easier to get good results. This is often called free stationing rather than resection.
If people understand the likely error of a procedure they can make an informed decision on whether it does the job. Least squares analysis is the best tool for understanding the errors.
This is often called free stationing rather than resection.
Free station used to be what I'd call it because I started on Geodimeters.?ÿ I've had many field guys look at me funny when I used that term.?ÿ Most around here are raised on Trimble and they call it resection.
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Resection is a sample.
I want to perform it with control over sigma values along the project.
What is an acceptable sigma value for topographical roads survey??ÿ
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How good are your control numbers?
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@bill93 @jim.cox Y??all must be on the same wavelength lol. Before doing a resection or free stationing one should already know 1. How good the control is they are coming off of the uncertainty error and such is always a great thing to know before if possible. 2. What the project specs requirements are. Y??all both nailed this. Now I realize one might also do a resection to tie or help strengthen some control for a least squares and not know yet. But in the context of the OP. Theoretically primary control would be completed at this point.?ÿ
Always good to see wise folks teaching and sharing on this site ?ÿjust a fantastic place ?ÿit has helped me begin to get the cobwebs out of my head as i am getting back to private se surveying for sure .
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Also critical is how many control points you include in your resection/free station, and how the software handles the calculations.?ÿ ?ÿI always like to have control marks (on poles or buildings)?ÿ and a few that I could put a tripod/prism on so that I was free to set the instrument up wherever I needed for the particular task at hand.?ÿ ?ÿ
@jimcox Well my daughter points them out every night. She is 8 and is counting them and I don??t know what multiple she is using but it??s happening at an outrageous rate lol.
@jimcox my traverse is one in 20000.
What I wanted to know is , given the trav accuracy , adjusted the stations, can I use resection with my TS shooting at those ST's ?
If so , what sigma should I have to not be looked as an alien??ÿ
@enri-f my traverse is one in 20000.
What I wanted to know is , given the trav accuracy , adjusted the stations, can I use resection with my TS shooting at those ST's ?
Sure, you can absolutely resect off of traverse-adjusted control.?ÿ
However, traverse closure is not an indicator of precision, merely a blunder check and an indicator of whether the observations should be accepted or further scrutinized before running a properly weighted LSA. Traverses assume that all observations are equal, and those base control pair(s) are perfect, which is not the case in real life.
If so , what sigma should I have to not be looked as an alien?
Without proper error estimates of the control network points it is difficult to pin a hard number on the cutoff for rejecting a resection.
That being said, as a general rule, if there are no blunders in the traverse I would expect to see no more than double the amount by which those traverse points are checking with each other (single-backsight).
In other words, if my single-backsight setups on traverse points are checking within 5mm, I would be concerned about anything more than 10mm resect off of those points.
