Client wants a survey of inside of lift core. How?

A real heavy plumb bob on a piano wire; dampened in a bucket of oil...

@scott-zelenak would know.

https://surveyorconnect.com/community/surveying-geomatics/super-tall-geodesy/#post-478012

When i first started, i used an optical plummet and a plex sheet with a 90degree bracket. Then after I started using laser scanning. Makes the job much easier both in the field and office. Where they want, i just cut a slice in the point cloud easy.?ÿ

Why would you use conventional methods when you could scan it?

@dougie That was a real interesting read! but what was his objective? to place a control point on the top of the building that matches the lobby?
Or was it to detemine the angle of deflection due to the earth? Much of that is unclear

I would love to get into that level of accuracy some day

@just-a-surveyor well im not sure how well i trust scan of a wall 60m away vertically at an incident angle of less than a few degrees to give me something within a 3mm horizontal ballpark. Have you done any checks with a scanner on this?

Hi @sireath! i replied to @just-a-surveyor below on using a scanner, honestly im not sure how well i trust scan of a wall more than 60m away vertically at an incident angle of less than a few degrees to give me something within a 3mm horizontal ballpark. (this is assuming you would setup at the base of the lift shooting upward?)

Have you done any comparison checks with a total station or otherwise on this?

I would consider just winging a couple of line marks at some even offset at the top inside of the form-work/concrete from there they can run a string and read a miss with a plumb bob. That combined with a tape or laser distance meter should get them?ÿ

It sounds like the sort of thing where they may just need a guiding hand to work with what they have, transferring control up the shaft sounds like overkill and likely to cause more problems than it solves.?ÿ

The whole give a man a fish metaphor and all that.

I have tried scanning in similar situations. All attempts were utter failures. To be fair it was likely the lack of expertise on the part of the 'expert' we hired to walk us through.?ÿ

If all you need is relative at key points the heavy bob makes the most sense. Keep it simple...

@akeane @just-a-surveyor When I scan, I do not scan from the lift pit only, i do take scans upwards of the shaft at other openings i am able to access and have targets to register into with TS to supply the coordinates. So I can double check in the office as well. It sounds like alot of work. But I find it easier than previous methods of optical plummet in the dark. 

@akeane

I personally don't do this kind of work so I'm not sure what he was trying to do, but I think it was to establish Geodetic control.

Scott hasn't posted here in a long time, I hope he's OK... I miss reading his posts.

With regard to laser plumb/levels - there are those you can pick up at the home center, quite suitable for residential construction. Then there are those you buy from a survey equipment dealer. 30 floors might be a bit much to go in one shot, but 10-15 up, and 10-15 down, may not be.

@norman-oklahoma

There are many accurate Laser plummets for both Zenith and Nadir(money).

+ or - 1mm in 100 meters.

No specifications as to accuracy were given in the post.

JOHN NOLTON

@john-nolton I had initially tried laser plummets but as the distance get further, the laser gets more diffused and harder to find the centre of the laser like reflectorless laser on TS. thus i initially used optical plummet. 

Ignorant hillbilly here, with no knowledge of highrise construction.?ÿ So take the following question for what it is worth.

?ÿ

Would it be possible to have something equivalent to the heavy plumb bob approach but replace the plumb bob with the instrument and lower it at a uniform (very slow) speed from top of shaft to bottom?

@sireath

I have only used optical plummets myself. On a job with NGS we would use a Kern (1/100,000) OP but the largest

Bilby tower on that job was  77 foot. This was about the same height where I used a Wild OP on another job. I always wanted to take

my Kern E2 Theodolite (electronic theodolite)  and try it with the diagonal eyepiece but never did. I wonder just how

high this job is?

JOHN NOLTON

@holy-cow sounds like youve worked in mining core hole logging before! I reckon there would be a market for such a device, something that scans as you lower it, though id wager the movement of the line would be more than a few mm and as high as 20-40mm.

But ill have to ask the boss if he'd let me test that with an old machine 😉 

@john-nolton sub 3mm is generally the accuracy i go for with core asbuilts

@akeane

Perhaps minimize the oscillation by determining the allowable weight of a plumb bob/weight at a reasonable length directly below the instrument.  Getting perfect alignment/balance could be a further challenge.

Just some wild thoughts.

Id forget the plumbs/zenith lasers etc.

Setup total station to the elevator pit and run upwards with a prism pole. Stick it inside elevator shaft at each floor and shoot 2 points from each wall. Connect the lines at the office and offset them out using the offset you had on the prism pole.

Id say this is the easiest, fastest and most accurate method. It eliminates most of the stationing errors as you station only once. You get allmost ready data, no need to draw tape measures clean.

It gets trickier if there are wooden work platforms at each floor blocking line of sight. Then you have to setup at each floor separately...