Survey Requirements

Well, you might do the job, and in fact only do it to a standard of + - 0.05' horizontal, and + - 0.04' vertical.

THEN, let them tell you you are wrong! (how are they gonna do that?)

I'm just playing the devils advocate here.

N

> Well, you might do the job, and in fact only do it to a standard of + - 0.05' horizontal, and + - 0.04' vertical.
>
> THEN, let them tell you you are wrong! (how are they gonna do that?)
>
> I'm just playing the devils advocate here.
>
>
> N

My thoughts exactly! I got a chuckle when I read the required accuracy and precision.

I am trying to envision the exact difference between 0.01' and 1/8". Pretty darn close.

Accurate related to what?

And how much do the barges move? You would probably need to attach instruments to the trusses themselves. And how are the trusses supported, with resulting flexing?

That is what an RFI is for. If you cannot meet the job specs, then you should pass on the job. The last thing you want to do is take the job, without knowing exactly what you are doing, only to find you are over the specs 3-4 times and the steel does not fit properly.

The last DOT contract I did had requirement of 1:10,000

The Head Engineer would not let us on the job unless we used a 1sec gun

We complied but I never was able to explain to him the overkill.

> Given this information only, how would you respond?
I'd propose to perform this survey with a scanner that does not rely on the instrument being plumbed and level to work, and set said scanner on the barge with the truss.

I can't see how you can set up an ordinary instrument on a floating barge, and if you set the instrument up on solid ground ashore the barges are going to be moving as you measure.

Besides that, the specs are pretty clearly written by someone with little idea of what is reasonable. I'd propose to provide accuracies that I can actually provide.

I would respond with an outline of what I felt the standards would be to which I could certify and which I believed adequate for the project. And I would make it clear that no further certification would be signed (or agreed to). No, I could not guarantee the tolerances you've cited.

I would respond with an RFI. Detailed drawings, etc.

There are firms and equipment that do this. We do it all the time in positioning precise equipment.

This is the difference between a boundary surveyor and other types of work and why I believe more and more that a surveying license should be limited to boundary only work and why surveyors in other states should be allowed to work in others without a license when doing precise work.

Its pretty easy to obtain 0.01' accuracy when you know what you are doing...

A 550' long truss span being assembled on 4 barges that are afloat does NOT constitute "precise equipment"!

I do see your point in that and missed that they are floating..

> Could you meet the accuracy stated below?
>
> "Survey Accuracy: Make precise measurements of horizontal and vertical locations to within +/- 0.01 ft accuracy vertically and +/- 1/8” in the horizontal plane.

> Given this information only, how would you respond?

I think I'd want to find out whether it would be feasible to set up an instrument on one of the middle barges on a bracket attached to the truss. The rest is probably doable with a total station if the vertical angle compensator is turned off.

Basically, you'd establish fixed reference planes and measure horizontal and vertical angles in relation to them (not worrying about whether the zenith angles were measured in relation to actual zenith or not) as well as slope distances. Then you'd compute X,Y,Z coordinates in some arbitrary system and transform them to some more convenient system to make the spreadsheet computations.

I recall reading several years ago about ship building with total stations. They turned off the level compensation, since the floating ship was constantly swaying relative to gravitational normal, and they would, each day, set up the gun on a pillar and sight two other points to establish the plane, which defined "horizontal on the ship. I'm sure they checked into other points as well, but the leveling was done by lining the cross hairs on a target at a particular vertical angle.

yep.

> I am trying to envision the exact difference between 0.01' and 1/8". Pretty darn close.

They're talking about 1/8 of a second on the horizontal plate? Most instruments don't have that level of precision. (It looks like you're thinking of 1/8 of an inch.)

Accuracies requests have gotten ridiculous.

JOB 1
We had a required accuracy of a high school sports track to layout the two controlling monuments (radius pts) to 0.005 feet.

I explained there was no surveyors within 120 miles that would be able to do that. (There are probably some high accuracy guys in Seattle that have done light rail or turbine layout that have that know how).

I explained I can layout the marks to 0.01 foot accuracy between themselves, and 0.02 accuracy across the entire project, and they were fine with that.

JOB 2
Have a current project for the military. We signed an non-disclosure agreement, so I cannot tell you what we are doing, but suffice it to say, it involves things that go rat-tat-tat-tat-tat.

Required accuracy for specific "targets" over 2 miles are 0.02 feet. So given those specs, we do a massive traverse, multiple observations, take all the observations, plug it into a computer, process and adjust, run levels to check the instrument work........ and the prime contractor checks our work with RTK.

....sigh.

Josh

When I drove by and saw those being assembled the other day, I wondered why they aren't doing that work in the staging area.

My guess is the cranes on the barges make it easier to move than assembling them on the dry land.

Do you know the reason?

I know it isn't much to some of the guys on this site, but that looks like some massive chunks of steel!!