I've recently been involved in staking out the anchor bolts for a relatively small one storey steel frame bulding (75x85m)and , to my surprise , I?ÿ found there a surveyor hired by the owner to check every set of bolts I install.?ÿ I usually welcome any kind of help I get when it makes me sleep better at night knowing that everything I?ÿ do is right, but in this case I?ÿ am having some reservations.?ÿ I have always used a scale factor of 1 when staking out a structure, however on this particular project?ÿ I had to use the same scale factor (0.999874) as the person who was checking me, or else our points wouldn't match. Using this scale factor the building would be around 10mm shorter, so?ÿ no big deal considering that the tolerance of 6mm between any 2 columns have been met.?ÿ The dimensions we both used were from the architectural drawings and there was nothing there that said those were grid distances.I have staked out buildings that were 800x300m?ÿ and never used a scale factor other than 1. Please feel free to comment on this.
So, you are employed by the contractor ?
Stick with scale factor 1, which I believe is correct based on your information, tell the contractor what you are doing and why.
Let the other surveyor explain to the owner why his checks are different.
I've never heard of changing the scale factor. Seems ridiculous. Distances on construction stakeout are always short so ...
Why would anyone be using grid instead of ground in this case??ÿ It makes no sense.
Never would I alter my measurements so I could match someone else's work.
The architect who designed the building, probably knows nothing about this scale factor. He probably used 1.000000
The surveyor may have to use this scale, for "grid to ground". Though it may be flipped over (1/x). Somebody could be functioning with an apple pie, with a piece removed. (Not whole story).
N
or, in this case, use any other scale factor besides 1.0000000000000000 ?????ÿ
I chased and wrestled with gremlins around one site for about 2 years. Multiple trips to site to recheck everything with GPS and bot.made it all work at a fantastic loss of time, but eventually discovered that my but was NOT set to 1, which I routinely do. That explained all the cussing.
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Was the other surveyor using the factor to account for a mapping grid versus surface distances, or for a temperature difference between steel fabrication versus layout?
I will have to interject the caveat that some programs will allow a scale factor to be applied around a point that brings a projection up to the surface.
If he is doing that to make his coordinates work on the surface then it's ok, if he is shrinking surface measured distances then it's not ok. The point is to make 100.000m measure 100.000m with the GPS, Total Station and tape, not 100.000m with a tape and 99.987m with GPS. 1.3cm in 100 meters is a large number when it's shoved into the project for no good reason other than it makes it easier for a button pusher.
The building will be 10 mm shorter?
Who's going to pay to shorten all the steel girders that are going to be 2 inches too long?
The building will be 10 mm shorter?
Who's going to pay to shorten all the steel girders that are going to be 2 inches too long?
10 mm ~= 0.4 inch
Another good case to complete all design work using Ground values.
You have a great point. The original survey that the design is based on may have been done on a projection of some sort. Then subsequently the new building needs to conform to tie-in points, statutory offsets, ect. He may feel he is stuck for reasons that override the 10mm error across the building footprint.
If I'm the building owner I would be expecting a full size functional building. Not a scale model.
