Resections and their accuracy
Resections and their accuracy
(OP)
Howdy all
I am an municipal engineer that does a lot of site and set-out surveying with a Set 5 Sokkia instrument and SDR 33 data recorder. It is often impossible for me to set up over a known point during construction and I am wondering what the accuracies of doing a resection are. I generally only do a 2 point resection but am beginning to think that I should be using at least 3 points. The way our boys off-set the points I give them probably doesn't warrant me being overly accurate but it would be nice to know if i am doing the right thing!
Cheers
I am an municipal engineer that does a lot of site and set-out surveying with a Set 5 Sokkia instrument and SDR 33 data recorder. It is often impossible for me to set up over a known point during construction and I am wondering what the accuracies of doing a resection are. I generally only do a 2 point resection but am beginning to think that I should be using at least 3 points. The way our boys off-set the points I give them probably doesn't warrant me being overly accurate but it would be nice to know if i am doing the right thing!
Cheers





RE: Resections and their accuracy
The best benchmarks can be the top of existing manhole covers, hydrants or survey monuments (in an urban area) and trees, power poles (spiked) or other immobile objects in open fields.
With these benchmarks, the original topo must be referenced and shot and then the resections or cross sections of construction can then be shot, plotted and compared. Any benchmark placed MUST be protected from disturbance. I hope I understood your query correctly.
KRS Services
www.krs-services.com
RE: Resections and their accuracy
RE: Resections and their accuracy
I tend to avoid manhole covers, hydrants, water valves, etc. Even though they are relatively solid, they can be removed and replaced without to much disturbance to the surrounds, making it difficult to see if the level has changed. They are also susceptible to moving when ran over by trucks (generally rotation).
kampho,
Act like a surveyor, check, check and recheck your work. Do your normal 2 shot method, then do an independant measure between points that have been placed by resection. This need only be a quick tape measure check to make sure distances are OK.
regards
sc
RE: Resections and their accuracy
KRS Services
www.krs-services.com
RE: Resections and their accuracy
regards
sc
RE: Resections and their accuracy
I generally agree with all your comments but warn against using two points only as you will get a seemngly valid result from two points but if one has been tampered with the consequences can be dire so check and check again three undisturbed points or benchmarks are advisable. Manholes have been rebuilt and shifted in the past so I avoid them too.On sites that need frequent revisits I have now resorted to use adhesive targets - see elsewhere on this forum.If you have enough of them on site they can be very useful to establish position from any convenient setup.
RE: Resections and their accuracy
I also use a Set 5 but only the on board data collection.
Rick Kitson MBA P.Eng
Construction Project Management
From conception to completion
www.kitsonengineering.com