Author Topic: Accurate As-Fitted models  (Read 3877 times)

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  • SuperMod
  • Seagull
  • Posts: 15568
Accurate As-Fitted models
« on: September 01, 2021, 04:52:00 AM »
Hi all

Long-time no speak.  Iím looking for some advice.

I work for an MEP company who design/install. Part of our contract on jobs are to provide accurate As Fitted models (within 50mm tolerance). I was just wondering how others picked up changes made on site to amend in the model?  Getting accurately marked up drawings from site on a timely basis (eg before floors go down etc) is quite difficult.

Anyone else gone through this stage in modelling and what did you do to overcome it?  Any processes you are comfortable sharing? Any lessons learned etc.

Thanks in advance.
T :)
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  • Newt
  • Posts: 167
Re: Accurate As-Fitted models
« Reply #1 on: September 01, 2021, 09:58:25 AM »
AutoCAD or Revit? Workflow has to change a little in either case but in AutoCAD we use the compare command. In Revit the bim site really helps for version control. When we are in steel structure our tolerance is 1/32" per 60' or some such nonsense.


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  • Seagull
  • Posts: 10572
Re: Accurate As-Fitted models
« Reply #2 on: September 01, 2021, 10:59:30 AM »
Bluebeam studio (which is just a PDF, in a cloud, which many people can all view and markup) was used a lot at the last contractor I worked for. But I have a friend who had me do some weekend consulting for him a bit back and it looks like they used Procore in their office. I did some looking at what Procore was and it's essentially a hub for all information to flow through so the office/field can generate FOs (filed orders), CO (change orders), and RFI (request for info) easier and faster. Seemed like a good idea; the filed foreman can just use their tablet where ever they are instead of walking down to the trailer and back again. (serving the CAD community since 2003)
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  • Water Moccasin
  • Posts: 2437
Re: Accurate As-Fitted models
« Reply #3 on: September 17, 2021, 02:55:21 PM »
Laser scanning to point cloud, full color scan with panoramic images, unified and transformed to match project (rather than site or survey) coordinates/orientation.  There really is no substitute when field conditions are rarely straight, true, and/or plumb (which is what any as-built CAD models will be).  Can't always count on photos from field trips either as there's always a corner or backside of a building that someone forgets to get a picture of.

While larger sites will need the full real-deal $70k+ system plus a trained operator to create, there's now a number of small scale scanners on the market which can handle smaller projects at a reasonable price.
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  • SuperMod
  • Seagull
  • Posts: 15568
Re: Accurate As-Fitted models
« Reply #4 on: September 29, 2021, 06:17:22 AM »
Thanks everyone for their input so far. (sorry for the delayed reply)

The markups we get back from site are lacking in most of the information needed to create a full accurate 3D model. Often missing vital information for our coordinated revit models, such as height or distances away from walls. And often late so its almost impossible to verify what has actually been installed as pipework or ductwork is covered by ceilings, floors or walls. 

I know the fitters out on site have a busy time installing to a schedule, but in the BIM world we need to know what they have fitted, where etc (if they have deviated from the model) is very important when the contracts specify what accuracy our final models need to be.

I guess I was just hoping to copy/adapt some other company's workflow that works in a BIM world to ensure the models we produce and send to our clients are as accurate as can be expected.

I will have a look at the options mentioned above, thank you :)
Thanks for explaining the word "many" to me, it means a lot.