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Disadvantages to running resection vs normal setup
a-harris replied 7 years, 4 months ago 41 Members · 93 Replies
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elkboarder, post: 421851, member: 12485 wrote: Well that’s just it… my previous comments I was talking about how his control is sometimes off by as much as .06′. I don’t disagree with his methods but they are not working anymore and it’s taking him 2 hours to perform a layout that should take a half hour if done the way I’ve (politely) suggested. This causes work to get backed up and I’ll give you one guess who ends up doing it. I’ll give you an example of one of his setups… set up, backsites 800′ performs his work which is only 50′ closer than his backsite. So he’s shooting 750′. I’m very suspect of this because our transits “drift”. he does not set up a permanent backsite to check for this so he’s putting all his trust on the level screen. I’ve explained that the level screen often says you’re fine but when you stake out your backsite I’ve seen as much as .12 off. (This literally just happened today to me.) For me this doesn’t affect my layout because I’m 30′ away from what I’m laying out because I can get that close because I’m doing a resection…so the error remains very small. It may be .12 900′ away but it is negligible when I’m that close. I’ve tested this numerous times and actually just did it today. Set something, checked my backsite and it was .12 out, re leveled, ran my resection again and hit the same thing I just laid out by .005. His problems all arrive by him not listening to me and even going as far as subtly mocking me for running resections so often. I’ve overhead carpenters talking about how we will tell them to move something .04 only to tell them to move it back .04 the next day
“because our transits “drift”.”
Transits? I sure hope you are using something more precise.
Paul in PA
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Paul in PA, post: 421937, member: 236 wrote: “because our transits “drift”.”
Transits? I sure hope you are using something more precise.
Paul in PA
Wow thanks Paul in pa.. your insight has been very helpful. I wasn’t aware this forum was going to contain so many people looking to stroke their egos than actually help but hey whatever helps you think you’re the smartest in the room
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Where I went to school, I don’t care who the Chief was, if the crewmember with the most experience says “Somethin’ don’t look right”. Ya need to listen. That being said, maybe he doesn’t understand resections? Mr. Charles Elam (God rest his soul) developed “freestationing” and some solar programs (remember SMI) that are probably still built in to many DC programs. The man understood every in and out of resection. Old timer or not, the proof is in the dirt (credit to Uncle Phil for that one).
Freedom is just another word for nothing left to lose -
I used to do more resections than I do now, but I am not afraid to do them. It sounds like the other chief doesn’t trust them for some reason. I would stay away from 2 point resections though. There’s no check. And be careful about your trig elevations so far from the target.
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I was totally opposed to my crews doing Resections until the economy tanked and I was back in the field. It just goes to show that too much time in the office can cause one to lose touch with the field.
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I think one reason some of us “more experienced” surveyors don’t use resection is that before field computers it would have been too tedious to calculate in the field. SurvCE makes it very easy to use and understand the errors. One thing I recently realized is that the LS solution gives the same weight to varying distances, I think. When setting up between 2 points, one close and one much farther, I would like to proportion the errors to the distances. Can I do this? Am I missing something?
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Staking a cluster of points that require tight relative accuracy and that are a close proximity to each other, like a building, from a long distance away is foolish. Each stake point has random error associated with it. Some of that error is increased as a function of distance which causes the relative accuracy between the points to get worse. I believe you when you say he’s 4-6 hundredths off if he’s staking from 800 feet away.
Sounds like he may have 1 year’s experience 15 times. A room full of kindergartners has 20-30 years of experience too.
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With the invent of application of prismless TS, resection became a priceless tool to orient and start looking for stuff.
Simply drive to the vicinity of what you are looking for, turn to anything that has been located before and you are close enough to start looking for the real control.
I us resection, “free station or whatever is is called on your particular DC”, all the time instead of getting the tape out and waking around in “chinese firedrill style” to get started.
0.02
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imaudigger, post: 421844, member: 7286 wrote: You didn’t mention any problems caused by your fellow crew chief such as lawsuits, claims, damages, lost work, ect. ect.
If he has been successfully doing construction staking for 15 years, it sounds like he has established a proven method. That’s worth a lot in the high liability construction staking business.If your employer is happy with his work, and the contractor isn’t complaining…
I don’t think this is the proper way to handle the dilemma. It doesn’t seem to make much sense to wait for a lawsuit or the client to become unhappy before suggesting he change his procedure. The control he sets is off… that’s all the evidence I need. I was put in charge not because of the number of years of experience I have, it was because I care a lot about my profession and am constantly trying to improve and whatever goes wrong on site is in a way a reflection on myself for not nipping something in the bud
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In my I-man days, I had a chief that always wanted to resection a lot survey. He would resection from two found lot corners and try to stake to and “check” the other corners. There were varying “closure” results. Back in the office, the result was not a true measurement of the points resected from. Only the bearing and distance from the plat was shown, the LS had to recreate the measurements to the initial points from the raw file. After, having to dig through the data, he said “Don’t do it again”. This was with SMI.
That being said, I will resect from my own control points for construction stake out, but only when I have no another option. -
Resection is our go to orientation method when doing precise layout or as-built with or track trolley. Resections are nice because there is zero centering and measure up error for the instrument and the instrument can be setup where it is most needed for the task at hand. Typically for this type of project we have a great deal of permanent control that is tied together in a strong network. In most cases, prisms are directly attached to the monument thus eliminating any setup error on the known control. We use a minimum of four (4) up to eight (8) prisms for the resections (we carry about 10 prisms for these type of projects). We also take at least one set of direct and reverse readings to each prism. With these procedures minimize the effect of setup and orientation in our error budget.
I would never recommend relying on 2 known points for anything other than dirt work and while 250m to the control is great for horizontal control it is way to much for vertical. With only 2 knowns all you have to work with is 2 distances and an angle. And I would never trust an elevation from non-reciprocated measurement over 150m for anything more that dirt. If you are going to rely on resection on a project you need to plan for it. Set up an abundant amount of control throughout the site to allow for ties to at least three (3) known points and if needed transfer your elevation from the closer control. -
elkboarder, post: 421973, member: 12485 wrote: I don’t think this is the proper way to handle the dilemma. It doesn’t seem to make much sense to wait for a lawsuit or the client to become unhappy before suggesting he change his procedure. The control he sets is off… that’s all the evidence I need. I was put in charge not because of the number of years of experience I have, it was because I care a lot about my profession and am constantly trying to improve and whatever goes wrong on site is in a way a reflection on myself for not nipping something in the bud
I’m sorry, I didn’t catch that you were responsible for this party chief’s work.
In that case, I’d simply have a tailgate meeting and describe how the work will be carried out, and spend some time going through the process to determine acceptable geometry for a resection, the quality control statistics that will be recorded with each resection, the acceptable residuals, min. checks…ect
No need to convince the guy of the error in his ways, just tell him how you want the control work done. You might catch a little grief from him for a short while, but you will have better results if everybody is following the same protocol. -
Sometimes you have to be the boss instead of a friend. Nothing wrong with have an organized method of doing things.
Surveyors come in many different flavors…but I have found that there are generally 3 groups of surveyors..Those that…
1.) Strive to exceed the required min. accuracy – even if it’s not required for the task at hand.
2.) Do just enough to get the job done without problems.
3.) It’s just a matter of time before something hits the fan. -
Sounds like the real issue isn’t the merits and limitations of doing resections, but who is actually in charge. Unless you want to drive this guy off the job I suggest you have a little Pow Wow with your chief and those above you to get it worked out before somebody’s blood pressure redlines and you find yourself short an experienced chief. Little disagreements can morph into something that makes your present woes seem trivial. To me this sounds like as much an issue of egos as acceptable procedure. Two captains on a ship usually doesn’t end well. Good luck.
Willy -
John Putnam, post: 421978, member: 1188 wrote: If you are going to rely on resection on a project you need to plan for it.
Plan:
1) Develop technical acumen needed to understand methodology and control networks sufficient to meet needs of project.
2) Develop control network sufficient to support operations.
3) Develop protocol regarding positional accuracy and procedure and communicate them to affected staff.This plan and it’s implementation to be directed from the management level of the organization.
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Mark Indzeris, post: 421975, member: 1019 wrote: In my I-man days, I had a chief that always wanted to resection a lot survey. He would resection from two found lot corners and try to stake to and “check” the other corners. There were varying “closure” results. Back in the office, the result was not a true measurement of the points resected from. Only the bearing and distance from the plat was shown, the LS had to recreate the measurements to the initial points from the raw file. After, having to dig through the data, he said “Don’t do it again”. This was with SMI.
That being said, I will resect from my own control points for construction stake out, but only when I have no another option.Wrong use of the program. I use SMI’s 2 point free station on as many projects as possible. While the initial shots are saved in the raw data file, I do not rely on them. I set up to occupy the free station point and backsight my 2PFS “A” shot, then shoot it as a side shot. I then change my backsight to the sideshot point number and shoot the “B” point. Now I have stored coordinates for my shots that I can then translate and rotate as my data collection continues.
What I see here today are surveyors complaining about a survey technique that they have failed to understand and use appropriately.
BTW, how many of you actually write in your field book the 2PFS Precision. On my traverse points I have exceeded 1/100,000 and have gotten useful information from as low as 1/30 numbers. When I survey with another surveyor, I shout out the precision, he replies with a value for the point to point comparison, all done in his head.
I have a point numbering preference. If I am starting out with a 2PFS I always use an even number, say 100. If I am occupying a precalculated found corner it is an odd number, say 101. That way I can always look at my filed number point file and know how it was initially derived.
Elkboarder, I am not the smartest in the room, but I am able to learn from even the dumbest. Thanks for educating me.
Paul in PA
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When I resect I then “setup” again on the newly resected point, backsight to previous point used and then read and store my points previously used in a resection setup.
I also call the setup station with “Resect” as description end. “IRod Resect” etc.
That way I always have an easier way to adjust a stuff up.
Also I prefer that for later use if I need to read the raw data.
I’m talking Field Genius, not sure how SurveCe shows this in raw data file.I’m also wary of building up control by using resected points to do further resections from.
Being in control of your own work and with an understanding of process and issues I feel comfortable in using resections with confidence and for accurate work. -
Paul in PA, post: 422069, member: 236 wrote: Wrong use of the program. I use SMI’s 2 point free station on as many projects as possible. While the initial shots are saved in the raw data file, I do not rely on them. I set up to occupy the free station point and backsight my 2PFS “A” shot, then shoot it as a side shot. I then change my backsight to the sideshot point number and shoot the “B” point. Now I have stored coordinates for my shots that I can then translate and rotate as my data collection continues.
What I see here today are surveyors complaining about a survey technique that they have failed to understand and use appropriately.
BTW, how many of you actually write in your field book the 2PFS Precision. On my traverse points I have exceeded 1/100,000 and have gotten useful information from as low as 1/30 numbers. When I survey with another surveyor, I shout out the precision, he replies with a value for the point to point comparison, all done in his head.
I have a point numbering preference. If I am starting out with a 2PFS I always use an even number, say 100. If I am occupying a precalculated found corner it is an odd number, say 101. That way I can always look at my filed number point file and know how it was initially derived.
Elkboarder, I am not the smartest in the room, but I am able to learn from even the dumbest. Thanks for educating me.
Paul in PA
Paul in PA,
Thanks for the kind words. If I didn’t understand or know how to apply this method then I highly doubt anchor bolts I set 5 months ago would be staking out never more than a hundredth off after each resection I do. One post I read the gentleman said he sets up 8 backsites for his resection. I’d love to work on a project where you have the time to set up 8 backsites and run that kind of resection. I do what works with the time allotted and from what I’ve seen a 2 point resection and then checking to control on site/ to previous bolts I’ve set is working hence why this post started. I wasn’t looking for a lesson in terminology. Our survey manager calls a TS a transit and it just stuck. I know it’s wrong. Another one of our guys calls GPS “a satellite” we know he doesn’t actually think he’s carrying a satellite around but we also don’t call him dumb or correct him because that would be pompous and douchey. I’ve learned there is a certain way to carry yourself in this business and acting the way you do is not the answer. Anyone can throw big words around but in my humble opinion, being able to teach in layman’s terms shows a much deeper understanding of the subject. I once had a math teacher who could teach calculus to a 4th grader because of the way he spoke. That’s the real test of intelligence. Also… signing your name at the end of your posts shows that subconsciously you don’t think people are smart enough to remember that it’s you posting by the time they finish reading… given your name is at the top of the post.
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Elkboarder,
I just wanted to clarify some things from my post. First, I would not normally use 8 known control points for a resection on a normal job site. The scenario I was describing is for fixed in place rail that needs to be constructed within 3mm. We set control down both sides of the grade on short intervals. For these projects we have a significant control budget. And as a clarification, we are not setting up back sights up over our control. The prisms are directly attached to a specialized monument with the prism center being the true control point. My main points were that a 2 point resection is very week and that you can not get reliable vertical information with a total station from a shot more that 150m without shooting the line from both directions. -
Thanks for the clarification John, I do agree that I should be running at least 3 point resections. I’ve been thinking about putting some targets up around site but just haven’t had the time to find good spots. Tower cranes would be awesome if they didn’t sway so much. I’m thinking a couple telephone poles lower on the pole may have to do. The congestion on site is so bad sometimes it is hard enough to set up to see two of my control points. 90% of the time we use digital levels for any elevations we set. We have a good number of benchmarks scattered around site so the other 10% of the time I am usually benching in with my TS from one of those, it’s never more than a 100′ shot. Side note…if anyone is in the market for a digital level I highly recommend the Leica Sprinter 250m. It closes tighter than any human can. (The guy I work with who I first mentioned in this post also firmly disagrees with me on this) I don’t really know how he can read 5.027 on a level rod from 75′ away because I know I sure as hell can’t. The Sprinter however… not only does this but also takes 3 readings and automatically averages them. But that’s for another discussion.
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