Last resort only because my boss feels the same as some on here do about resections. I figure if I only use them when it is clearly the better option than whatever my alternative is..and then do several checks to prove it was good...then he won't complain about it.?ÿ
I set up as close to the middle of where I'm working as possible and shoot points in several directions. If I only have 2 points I make sure they're 90 degrees apart.?ÿ
Originally I only used them to find control points buried in the snow or under dirt or for staking for excavation (0.100m tolerance for those). That gave me the chance to see how well they worked on multiple occasions before actually using one for anything that needed to be very accurate.?ÿ
@350rocketmike?ÿ
Few things...
1st: Calculating traverses and resections by hand, using pencil/paper and formulas (not a programed solution) in college proved to me that resections are mathematically robust.
2nd: efficiency and production is improved with an understanding and use of resection.
3rd: doing what your boss tells you to do is probably a good idea.
@tim-v-pls until your resection goes wrong.?ÿ I have seen it happen more than a few times.?ÿ My crews do not resect unless it's a last resort.
@norman-oklahoma I work on large commercial and school construction projects routinely.?ÿ I've been on several sites for two years after the walls have gone up and rarely, if ever, use resectioning.?ÿ Resectioning is only as good the geometry it employs, just like a floating circle with weak satellite geometry.
If you plan your control network carefully at the start of a project you should have almost full access to anything you need.?ÿ When walls go up and hard surfaces start being poured, expand your control for complete coverage with points that should last for years to come.?ÿ?ÿ
getting back to your original question... some suggestions:
don't be shy about watching and learning from the other trades on the project. I've learned as much about layout from carpenters, iron workers, glazers, etc. as from surveyors.
Be part of the team. Be there for stretch/flex 1st thing in the morning, try to have lunch and breaks with the other trades. Same goes for the construction management group. Stop in to them for coffee. As a team member, others are much more forgiving about mistakes/timeliness and such. Being looked at as not on the same team isn't fun.
Others might argue against this but here's a thing I always do for large building projects: rotate the control and building grids so that you have your grid line axis north/south, east/west. Then pre-calc every grid intersection.
This method lets you set any grid line offset you need. For example: Carpenter says "can you give me the layout for this wall?" No, but I can give you a grid offset that you can pull from.
@norman-oklahoma imagine something going wrong with a resection, causing something to be built incorrectly.?ÿ When you are sued and explain the standard of care that you employed as being based off a resection, how do you think that will fly?
We are going to have to agree to disagree on the virtues of resectioning, Chris. Nevertheless, we do agree on the virtue of carefully planned control, and that resectioning is only as good as the control geometry. I don't see that as a negative.?ÿ
I can't think of a single time in the last 20 years where resection was a problem. Tons of other things created problems, but not resection.
"I got 99 problems, but resect ain't one of 'em"
Modern-day field software will compute and display any and all residual information, and allow one to add or remove points in real-time, until satisfied with the solution, and then allow the user to observe a check on any point they wish to, before commencing with the task at hand.
The method is sound, the computation equations are not new, and there are plenty of ways to verify the setup.
It's odd to me that a basic textbook problem in 100/200 level survey courses, and which has been around forever, is shunned by a significant percentage of practicing surveyors.
The ways of the screwup are many, and varied. Suffice to say that I've seen plenty in simple traversing, too.?ÿ
I always use at least 3 points in my resections, retain the data, record check shots, etc. etc. Sometimes the results of a resection are not great, it is true. But the statistics that my dc returns on a resection actually give me more information about coordinate quality than I get by other means, not less, so I know it on the spot. I'm using at least 3 controls, all of which have to be correct, not just 1 and a BS.?ÿ I'd be very confident going into whatever court I might need to with my resectioning data.?ÿ ?ÿ ?ÿ?ÿ
imagine something going wrong with a resection, causing something to be built incorrectly.?ÿ When you are sued and explain the standard of care that you employed as being based off a resection, how do you think that will fly?
You say that as if a resection is somehow inherently "less than" a typical single-backsight setup. I would be very interested if someone - anyone - on this board can tell me exactly how a properly performed resection is less defensible than a single-backsight setup.
We employ resections, keep all our raw data and field notes, check our work in the office, and don't lose any sleep at night. I've had to prove out stake points from resected setups multiple times. Across five employers in sixteen years I can't ever recall an instance where someone attempted to backcharge us or take legal action based upon our choice of setup. It's our responsibility to choose procedures that enable us to place stakes correctly. If they turn out to be wrong, no one cares why they're wrong, and I would never argue that my choice of setup might relieve me of that responsibility.
I've personally only seen bad results when it was clearly not going to work well...I was just using it to find a control point. Like shooting 2 points no where near 90 degrees apart and staking out a control point a ways away from me just to get close enough to find it with the metal detector. I always tried to make a habit of seeing how far off it was before moving the robot to it.?ÿ
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@rover83 Just like anything else, the software is only as good as the people using it.?ÿ If you don't understand what you are seeing it falls back to the age old statement, garbage in, garbage out!
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@norman-oklahoma but you have the time in to understand the math behind it and enough knowledge to accept or reject.?ÿ You have the time and experience in to know when something just looks or smells wrong.?ÿ That's a different ball game compared to what companies are doing now, out of need to keep the work flow going they are making newbees PCs in a matter of a year or two.
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@rover83 "Properly performed".?ÿ I'm 38 years in and have so many horror stories from 6 different places that I have worked.?ÿ I have had to put the emergency breaks on far more than once and sound the alarm because a short cut that somebody tried to save their efforts in the field went south.?ÿ There is nothing more humiliating to a PLS than calling the contractor and telling them not to use the stakes your crew set because they are wrong.
@350rocketmike that's a valid use if you are not staking critical construction points.
But that really doesn't make a difference whether or not it was a resection they screwed up right??ÿ
I know of an instance where a crew at our other office occupied the wrong point and backsighted, got less than 1cm error and didn't do a check. There were 2 points both basically the same distance from the backsight and they assumed they were good and laid stuff out like a meter off.?ÿ
I'll never do any layout or tie in anything without a check, either way. But if you're saying no resections because you don't trust your guys to do them right....you must also have specific instructions for them about how to backsight and check as far as good geometry goes?
As to a standard of care, it is a question of not being negligent.?ÿ?ÿDid your equipment, methods, and procedures fit the work at hand??ÿ I can do the math to calculate the errors in my measurements.?ÿ With a resection I can see the residuals of my calculation.?ÿ I do not believe that I would have a problem explaining a resection, I am making redundant observations to multiple control points.?ÿ I have also used StarNet to adjust my control network using appropriate errors and weighting.?ÿ This will again yield a report with error ellipses and testing results.?ÿ Is radial stakeout an inappropriate method to layout a building, no. ?ÿIs that how I would layout an entire building, no.?ÿ Can things go wrong, sure.?ÿ Did things go wrong when the tools were a 20? transit and a steel tape, yes.?ÿ Like it was said you can never have enough control, additionally you can never enough checks.?ÿ It is about being competent and knowing your work.?ÿ
@350rocketmike?ÿ
the ??resections only as a last resort? tells me you have been at this game for a while. I was also taught that, and it comes from old school resections determined from angular values only. Assuming the geometry is good (ie: not inline or acute angles) a 4 or 5 point resection is generally really good. Modern software packages can even isolate bad control points within the resection and recalculate your position, much like GPS calibration (localization) procedures.