When I was doing cell phone towers, this is how we would get the elevations to the top of towers, some more than 500' tall:
First we would run static GPS, usually on two (hopefully inter-visable) points at about 3 times the distance as the tower is high away from the tower, with the points and the tower forming something close to a right angle triangle, with the tower at the right angle.
Second, while the GPS was cooking, we would set a random 3rd point near the tower, and using assumed coordinates, a compass bearing to one of the GPS points as a back site, and topo the tower site and turn a set of angles and distances to the second GPS point.
Third, we would set up on the GPS points, and turn angles, both horizontal and vertical, direct and reverse, to all the pertinent features on the tower. I never did find a data collector which would let me record just angles, so we just entered them into an excel spreadsheet. One guy at the gun, the other in the truck with the window down, computer on his lap. (of course we would also turn a set to the 3rd point)
The rest was done in the office. It was pretty simple using the spread sheet to get mean angles, both horizontal and vertical to each feature, then using cad do bearing bearing intersections for horizontal locations, then using the horizontal locations to compute distances, use the vertical angles to compute elevation, and since we had two sets of vertical angles, we could compare the elevations to each feature, usually less than a tenth of a foot difference. Although we were not there to determine how vertically plumb the tower was, I was often curious, and amazed that most were pretty damn plumb!
> Just out of curiosity, what are they going to do if it isnt?
Look for the contractor who built it I guess. Ha ha ha, seriously though I think they suspectednsomething is wrong with the tower hence the resurvey. Tried to get more info from the site engineer but he kept on mentioning some NDA that he signed.
I think I will suggest the intersection method as rhe outer edges of the tower are difficult to access at regular intervals. Prismless would be another option.
Thanks for all the inputs.
I like this solution....would you also suggest doing it on all four faces of the tower?
:good:
The shims are funny, but not that far off.
The bases of the monopole and three legged lattice towers I've ever been around during construction all rested on nuts on the anchor bolts rather than directly on the concrete foundation. Obviously this gives them the ability to fine tune the tower before they grout the space between the foundation and the base plates. I've never seen it done, but I'd bet that they could remove the grout and re-level one if they had to.
I did a quick test in CAD. For a 180 foot tall monopole tower with a 6 foot diameter base, being 1 inch out of level at the base would cause the top of the tower to shift 2.4 feet.
The few times I needed to check plumb, I did it on two sides, but if you got the room it is a quick simple proceedure.