Resections vary based on your software, My software does not have a resection option, it uses a "2 point free station" option that is more geometrically precise. I have the option of direct and reverse observations, which I always use if I need an elevation. Only once was I displeased with my first result and I then shot my 2 control points in reverse order. I meaned those 2 positions and met my tolerances for a traverse.
Paul in PA
Resections from solid control and good geometry is more precise than traverse from two control points as the instrument setup error is completely removed. In a traverse there are at least two times that instrument setup error is introduced into the system. There are also more target setups in traverse than resection, adding more sources of error.
If more than 2 points are used in the resection then the observation and target setup errors are dispersed in the solution.
Traverse is much less dependent on geometry, the backsight should be longer than or equal to the foresight. But beyond that resection is superior to traverse in terms of accuracy and speed in most cases.
I like to draw a comparison of GPS to Resection. Similar in that you are establishing your location from observations of multiple known remote positions. That being said, good geometry and good control on multiple points will yield the best solution.
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I agree, my errors are generally very low. As a check once I am finished occupying that station I will check it with our gps to make sure everything is hitting. I never have a problem where we have staked a couple of his points using his method and they have been off almost 3/4" for me it just seems all around better to occupy 2 or more points. (my errors are always very low using 2) l just thought maybe I was missing something
elkboarder, post: 421717, member: 12485 wrote: I agree, my errors are generally very low. As a check once I am finished occupying that station I will check it with our gps to make sure everything is hitting. I never have a problem where we have staked a couple of his points using his method and they have been off almost 3/4" for me it just seems all around better to occupy 2 or more points. (my errors are always very low using 2) l just thought maybe I was missing something
Unadjusted, open traverse will extrapolate errors in the system while resections interpolate errors in the system.
jim.cox, post: 421699, member: 93 wrote: I also use resections on a daily basis
But ALWAYS with at least three points and good geometry
I only skimmed but it seemed like reactions from 3 or more are better.
We do a good amount of roadworks on rural roads with 1st floors. We set control with the GPS, level through, then resection from 3 points to tag 1st floor and monuments. Then we reprocess everything in the office. It is pretty tight.
Honestly as far as control this site has gotten so busy and so crowded that in a pinch I will "burn" a point in with gps, set up on that and sometimes even burn in a point to backsite. My method for doing this is shooting it 100 times, losing fix, turning 180 and shooting another 100 and then averaging. Distance always hits under an 8th which I find very impressive. Always checks tight to other control too
In my experience a resectionat at 900 feet is too far for vertical, maybe not for dirt work but for buildings, I would use a level. I would also beware of doing more than one resection on the same building. It doesn't mean much if one building is a little off from another but within the same building it does. I would set the daily control with the GPS just as you mentioned, occupy a point and backsight another and use that for each building. That's one thing I miss about using Leica, being able to shoot the same point multiple times.
Please don't mention inches on this site
I'm not using a 900' site for vertical.. I'm benching in from one of several benchmarks we have down on site.. (adjusting rod height up or down .01 to read our benchmark elevation.) I work very closely with carpenters, iron workers etc who only speak in terms of inches, that arrogant comment is not why I signed up for this site and I'll mention it all I want
Scanned the posts and looks like some good advice. I can not imagine being a 1 man survey outfit and not using resections! Especially during construction staking. Seems like a waste of money on an expensive robot. Some guys will buy the equipment but use it like old school equipment. Just like anything, have good checks. Jp
Thanks for all the comments guys, I appreciate it
I accidentally hit some button and I don't know what was that. Whatever it was, just forget it please.
If properly done, resection is better for me. It works for me all the time.
billvhill, post: 421725, member: 8398 wrote: In my experience a resection at at 900 feet is too far for verticaI....
Who said anything about 900'? If resection is going to be used then the control needs to be set with that in mind.
billvhill, post: 421725, member: 8398 wrote: ...... I would set the daily control with the GPS just as you mentioned, occupy a point and backsight another and use that for each building.
I think that method would be less precise than resection even with very long shots to control.
The layout of the site is all of the work is being done further to the north. There is a ridge (basically they created the ridge by drilling and blasting down to their starting elevation, was just a gentle sloping hill. So now the ridge sits about 30 feet above the work area and I have been using this to my advantage by setting control all along this ridge. Then when I first get to site in the AM I set up my two -35mm backsite kits on two of my ridge points and am able to do a pretty substantial amount of work bouncing around. I've made a habit of hiking back up to the ridge when I complete a layout to 1, check to make sure they are still level and 2 turn the glass if need be.
Mark Mayer, post: 421794, member: 424 wrote: I think that method would be less precise than resection even with very long shots to control.
Very little difference, and you can populate an area with control much faster then doing multiple resections/setups
elkboarder, post: 421786, member: 12485 wrote: that arrogant comment is not why I signed up for this site and I'll mention it all I want
Sorry, I wasn't trying to be arrogant, just a reminder you are talking to Surveyors.
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...
One of the main things I've taken away from this project is the surprising precision that our Trimble rtk achieves. When we first got out to site we were setting the base up on coordinates set from another company until we got our zephyr installed. This was when it was all earth work. But once the base was installed we set two points a good distance apart (700/800') and ran our traverse from those two points. Well first we occupied one, backsited the other and then shot it DR depending on how the distance checked. This gave us a good baseline. I was always taught not to deviate from the traverse and only set one point off the traverse at a time. From what I've experienced, I would go as far as to say it is at least as good to burn control in as you go rather than setting up and throwing a point where you need it. The reason I've been pushing my guys towards doing resections is because you're killing two birds with one stone. You're setting up for your layout and at the same time establishing some pretty tight control. With a project as demanding as this every little trick helps because you need to save time where you can in order to work longer on the more important things. The client is one of the most demanding I've ever worked for. We have three crews up there with a helper for each guy and we all go non stop from 7-6 6 days a week.
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...
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