A lot of the survey control that I set in my current role is inside of existing buildings, often times up multiple floors, in buildings that don't have line of site to the ground through any window openings or rooftop access. Imagine a typical 4-10+ story office building. We do a lot of terrestrial scanning as-builts for design of future renovations.
My current workflow is to traverse up and down stairwells, using common points whenever possible. Besides being time consuming, the impact of such short backsights is not lost on me. We close our traverses as much as possible by utilizing multiple stairwells throughout the building but I am searching for a way to increase both accuracy and efficiently.
In the past when transferring control up & down through large vertical distances separated by short horizontal distances, I have used plumb lasers ( https://geo-laser.de/product/plumb-laser-plummet-ll-90l/). The project where I found this used most effectively was in a 300' vertical shaft with a 30' diameter where I set 6 control points around the circumference of the shaft & projected their horizontal coordinates to the base of the shaft around the exterior with the lasers and was able to do a resection below. Of course, when I was at the base of the shaft I couldn't rely on my orientation too heavily as again I was using short observations to perform this resection while I was setup in the middle of the shaft but it was an effective way to get a position where I could then supplement my orientation with use of a gyro total station if required.
What I am imagining for bringing this methodology to the stairwell example is running my ground floor & exterior building traverse into several stairwells, setting a point in the gap that typically exists between landings and projecting that point up vertically through the landing gap. Then on each floors traverse, tying into that projected laser point by making some sort of bracket that can clamp onto a handrail and hold the translucent target plate that comes with the plumb laser by means of using a peanut prism on top of the mounted plate centered over the projected laser beam. Then there is still the matter of transferring elevations up, but using a differential level for this would be fairly pain free and accurate.
Any thoughts? Has someone already found a better method or possibly employs something similar? We have some projects on the horizon that are up to 30 floors and would like to figure out a better methodology than what I'm currently doing, if possible.
Great topic!
Following this for sure....
T. Nelson - SAM
In the 90’s I did this and it was non robotic total stations. If you need to carry elevations instrument and rod heights become very very critical. We ran levels. Traversing back then re ran parallel traverse in and out up and down. Used steel tape for distance parallel to each station. StarNet was used for least squares. So we could use the taped distances as well as the edm along the haul ways. We mapped everything old school no scanner a lot of taping in the rooms etc. Now I would probably use a laser tracker to run the control transferring it a software for metrology using least squares. This means you do not have to set up over points nor be plumb and level. You can mount it anywhere upside down sideways upright etc. no looking through an eye piece etc. I will remember the name of the software at some point. I can’t recall it now. Your prisms will be SMR and this has been a proven solution doing what you are in ships. Up and down those stairs all over. These laser trackers are extremely precise. Do very well indoors. You can even map corners and doorways etc very quickly. I would say faster than a laser scanner and not have to extract that linework it’s done. You also do not have to set a point necessarily for your control. You can use planes to reference or any other objects. A bolt nut sprinkler head or even the floor on a specific tile etc. but I would also think if you are using a laser scanner I would imagine should be able to achieve a good registration if you scan inside and out and such.
edited the software is called spatial analyzer. As soon as I hit send it popped in the brain. The company is based in Williamsburg VA and do training and it’s good. They would also be someone you should reach out to to explain what you are trying to achieve and they know laser scanners as well.
I’m going a bit old school here, but perhaps this methodology could be adapted to your endeavor. Over the years, I’ve worked on numerous projects in the heavy construction and mining industries. One particularly complex and challenging project that stands out was during the 1990s on the Central Artery/Tunnel Project (Big Dig) in Boston. Our task involved a specific section where we had to excavate two 25-foot square shafts (east and west), each 175 feet deep and approximately 150 feet apart, running parallel to the existing 125-year-old Red Line trolley tunnel.
The new I-93 northbound highway was designed to cross underneath this old Red Line tunnel, passing between the two shafts at a lower elevation at specified depths within each shaft and below the Red line, we also had to construct two horizontal tunnels, each about 200 feet long, running parallel to and on either side of the new highway alignment. To support the old Red Line tunnel during construction, an additional series of 10 smaller cross-tunnels was built, connecting the two horizontal tunnels directly underneath the old Red Line tunnel.
Control for this project needed to be extremely precise. To achieve this, we fabricated and welded brackets made from 2-inch metal tubing, attaching them at four points around the top of each shaft. Heavy plumb bobs (10–15 lbs) were suspended from these brackets using piano wire, with the bobs submerged in 5-gallon buckets of oil at the bottom of the shafts. The oil dampened any movement, ensuring the plumb line remained vertical.
Horizontal control was established by precisely locating the piano wires at the top of the shaft using ground control points from the project. We then again at bottom of shaft located the piano wire and utilizing the Weisbach triangle method, we established horizontal control at the shaft base, verifying it with a Least Squares Resection. You will find if done correctly that control at top of shaft will match the control at bottom of shaft within thousands. For vertical control, we simply dropped a steel tape down the shaft. When we extended control through the parallel tunnels and cross-tunnels, horizontal and vertical discrepancies were minimal, typically within 0.02 feet.
If this method is adaptable to your work in the stairwell of a building, it’s a proven approach with a track record of reliability. You could reverse the process, establishing control by locating the wires at the bottom of the stairwell and working upward, transferring control floor by floor.
At the time, we also considered using a laser plummet for vertical alignment, but the options available had limitations, such as wide beams and less-than-ideal precision. I’m confident that laser plummet technology has significantly improved since then and could offer a viable alternative today.
Best of luck with your project...
@jms66 piano wire was my go to on building anchor bolt templates to make for was alignment and layout. But you can cut your hands very quickly if you are not careful.
Spads. That's the answer.
@holy-cow hats what the sprinkler heads in the ceiling are for lol.
Thanks for all the replies so far.
i can’t imagine we’d get approval to buy a laser tracker given how little we’d use it, even considering how much I would love to get my hands on one.
JMS66, correct me if I’m wrong but the method you’re describing is the same as what I mentioned in my initial post but using wire instead of a laser. Yea it’s a great method for sure. If nothing else comes of this thread I’ll figure out a way to incorporate a version of this method.
@bc-surveyor depending on your budget you can rent a laser tracker as well as they do come in on certain projects and set up your control for you. Just keep in mind they are not surveyors. But that team does great work and have worked with surveyors before. I have no idea what they charge. I know they do everything from factories to ships and other things in between. NGS has utilized the systems for certain ties. But it could be over kill for what you are actually trying to achieve. Now that software will also run a total station so that one can not do conventional types of control. That might help in building your network as you go utilizing different techniques than conventional types of traversing. The heavy plumb bobs and piano wire are great tools. Remember you can establish control that you don’t have to occupy. Think of multiple resections and least squares. Locating things like sprinkler heads aka spare a tack in ceiling and marks on floors walls taking measurements of angles and distance in any combination will allow for a least squares adjustment. Use all your tools triangulation tri literation but since you are in close quarters think full 3d up down sideways etc. you can hang a smaller plumb bob from a ceiling for line. And I have used a old coffee can with a bit of used oil in it so the tip of the plumb bobs steadies out that makes for a line of sight from anywhere as you go down a hall way etc. always turning angles to it from each set up as a extra redundancy etc.