Some questions about planning a TLS survey

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Re: Some questions about planning a TLS survey

Post by tadol »

While it’s probably obvious, I’d recommend spheres as well - ;)

Using a magnet base, In long hallways you can sometimes attach to the ceiling grid, but if there are light fixtures that hang down, they can interfere with visibility. You might be able to attach to steel door frames, but you should make sure that targets won’t get knocked off if doors get thrown open or slammed closed. You can also attach to glass, either by using steel washers attached to the glass with painters tape, or even using a secondary magnet on the back of the glass such that the glass is sandwiched. I would still add a tape bond, in case there is mechanical equipment in ceilings that might switch on and create vibrations. If you trust the paint quality, you can try using taped washers on the walls, but any dirt/grease (or if the paint is poorly applied) could quickly have or create other problems.

Another option in both hallways and stairwells are traffic cones with targets on top. These are extremely visible, relatively inexpensive, and very fast to set-up. If you have to allow employee access during or between scans, traffic cones in bright safety colors can keep people from tripping over standard tripod legs, and usually take up less floor space. They are available in multiple heights if you want to make sure your targets are on different planes.

Finally, my latest bases have a v-groove and hole that are built in along with the ⅝” survey thread. With a handful of zip-ties, you can very quickly and very solidly attach targets to pipes, conduit or - handrails. And agreed, so many stairwells are identical from top to bottom, so some printed targets which are very clearly numbered to identify the floor or landing can be extremely useful.

I’ve found that just having some spheres is not as important as having target spheres that have been thoughtfully designed and include the accessories necessary so they can be easily mounted or attached and used in the field. Otherwise, a ball is just a ball -
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Re: Some questions about planning a TLS survey

Post by VXGrid »

caskar wrote: Fri Jan 08, 2021 9:42 am [...]

Another question is about georeferencing. My thought is establishing a traverse from reference stations outside the building to the upper floors along the stairways. I won't extend the traverse down to the hallways. Then I will measure 4 - 5 targets on each floor close to the stairways. Would this plan work, or would I have a problem in georeferencing? Do I have to measure more targets with a total station throughout the whole floor?

Thank you so much!
The question is for what you want to use the measured geodetic points.
If it is "only" for georeferencing and getting your project somewhat in the right coordinate system (~0,5 meter), then a single connection between your global coordinate system and one scan position, where you measured 3 checkerboard targets is sufficient (just a 6 parameter transformation).

If you want to use the total station measurements to improve your registration, then your approach should be fine.

To me, it sounds like the accuracy and results you try to achieve, a SLAM based scanner would give you a lot faster the results you want to have, without the hassle to go scanning for 1-2 days.
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