Staking out from another surveyor's station co-ordinates or mine?
I'm doing a stakeout job next week which will be ongoing for a while. A topographical survey by another survey firm was carried out on the site 2 years ago and I've manage to find 5 of the 6 Mag nails used.
The construction firm got me to check the existing stations before I stake out any points. All the staking out drawings are done and are based on the local grid and station co-ordinates from that original survey.
So I set up over a station of known co-ordinates from the original survey and use an azimuth worked out from a backsight station also of know co-ordinates from the original survey. And then I works my way round the stations checking them all. My accuracy was really tight but I found 4 of the original station co-ordinates to differ from mine by 1/8 inch up to 3/8 inch.
So now I have checked the original stations as requested by the foreman. Who's co-ordinates do I use for setting out? ........ or is it not an issue with the magnitude of the differences I've discovered. The site is roughly 300 foot by 150 foot.
Not enough info, it would need to be something very tight for me to worry about 1/8".
3/8" vertically would get a bit of attention from me, but probably not horizontally unless like I say above something very tight.
Yeah, need more info.
I you are staking out limits of a temporary stockpile, probably OK. High-rise - maybe not.
Whats the job?
JA, PLS SoCal
I rarely have control check that well, especially with any time lapse. If I were staking a job out and it were started out on a local coordinate system based on recoverable monuments, I would stick with the local control. An alternative to sitting on their control is to set out in the middle of the site and do a resection on all of the points, providing you with a least squares average of the original control. Then re-shoot the control and call it "100-A", "101-A" etc. An 1/8' would not get me excited enough to do that though.
How good is your total station?
The S6 I use is rated to 3mm for distances - that's your 1/8 right there.
Not to mention any plumbing or prism constant errors
The design was done using the original control - and I would be staking based on that.
Changing the numbers opens you up to a huge liability when something goes wrong.