Some advice please if anyone can help , say for setting out a building,Using a local grid, ?ÿchoosing an arbitrary north and an arbitrary east , starting with the origin in the bottom left of the building and assuming the coordinates of the 4 corners of the building to be set out.
what is the procedure to set up your control stations so that you can set out your chosen building using the total station from your local grid ??ÿ
Hire a surveyor.
As a civil engineer that does some survey, I'm embarking on such an exercise. I'm not in USA, rather the southern hemisphere. Anyway down here the local cadastral grid is a transverse mercator jobbie on WGS72, and with its false N and E, where land is, the coordinates are typically in the millions of meters. All the subdivisions use this, and are surveyed by the equivalent of a PLS - there they are called Registered Surveyors (RS), and this is a Statutory title.
I could set things out with either TS or RTK (or both) using the local grid, but after a lot of thought (there's many parameters to consider), have decided to use an arbitrary grid with 1000,1000 at one of the building centerline corners, and then all the numbers will be small. I could use 0,0 but then some numbers will be negative. The lot is only say 25m x 15m, and since the combined ground to grid scale factor is 1.0000735025909, over 50m that's a diff of 3.7mm, so if I use the TS with a SF of 1, set up on one of the lot corner pegs, then things will be ok, i.e. we're not going to be building in someone else's property.
However, at the corner pegs, that's where the fun starts. In the image below, the red numbers show what we have measured (by tape, TS and RTK). The main anomaly is in the NW corner where the measured distance between pegs is 1.38m whereas the RS plan says 1.21m. To cut a long story short, that means if the RS pegs are used our Lot 21 will be about 270mm (about 1 foot) short, and we loose 1% of an already small lot.?ÿ
The developer wont respond to emails, but verbally says "go by the pegs" or "get your own RS". We are getting our own RS, mainly because:
- It will give a second opinion.
- Only an RS can "move" the pegs.
- This may be a legal/liability case.
I think there's another recent thread here that says building setout is always "ground".
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I spent a few hours out there today trying to locate some control, and only found one possible out of 10, that being a 8mm dia screw head epoxied into a concrete lid of a sewer manhole. All other control appears to be under the tarseal road or concrete footpath, i.e. obliterated. Not sure what the RS is going to find.
a 8mm dia screw head epoxied into a concrete lid of a sewer manhole.
Hope you meant rim of a sewer manhole!
Some advice please if anyone can help , say for setting out a building,Using a local grid, ?ÿchoosing an arbitrary north and an arbitrary east , starting with the origin in the bottom left of the building and assuming the coordinates of the 4 corners of the building to be set out.
what is the procedure to set up your control stations so that you can set out your chosen building using the total station from your local grid ??ÿ
First of all make sure the confabulator on the total station is set to 10. Then proceed to obtain the chakra co-ordinates from the cad file. Once that is done the total station pretty much takes care of the rest.
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Assign coordinates to your building corners (ie. N (or Y):1000 ; E (or X):2000
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Decide where you want to orient the front face of your building
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Set a control point that will be a permanent corner of your front face of building. This could be a spike set solidly in the ground, a tent stake or anything that will not move easily and that you can plumb your total station over.
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Set another control point approximately at the second front face of the building. The key is to think in terms of the face of the building and not to worry about the exact distance between the two front corners.
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Set total station on first control point and backsight second control point. You will get a warning saying your distance is off, however, the direction of the face of the building will now be locked in.
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Stake out your second front face corner to the correct distance and proceed to set the remaining corners with the stakeout routine or using horizontal distance checks and turning angles.
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@totalsurv 10 is a good start. But in humid climates the confabulator works just as well on 12 or even 13.
Chakra co-ords normally run straight down the middle. He's talking about building corners. So they'll need to be put in at offsets.
