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BIM as built

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    BIM as built

    I'm working on a project and I'm coming from the field of geodesy. I have following problem:
    I have a dwg file of a builing which is built. There are uneven rooms, the angles are not necessarily orthogonal and so on. What is the best way to model the geometry of an existing builind which is that "uneven"?
    And when I eventually have modelled the builing what is the best way to compare the model with the exising dwg file? Is there a way to investigate the accuracy of the Revit model? Are there some common ways to detect the accuracy of the geometry in a statistical way?
    Thanks in advanced for your help!!

    Hi Lisa, interesting question! When you say "coming from the field of geodesy", do you mean you yourself are, or your question is?

    If the former; if you have the model already in .dwg why is there a need to have it in Revit at all? You'd be better off exploring point-cloud survey workflows (if the aim is to validate the .dwg original, and the building is around the survey)

    If the latter; then yes, but it's a bit can-can back and forth... In simple terms you'd model in Revit then re-export to the baseline originating format of .dwg to use a .dwg compare tool - which (depending on the elected tool) may or may not return the statistics you require (but will almost always require some finessing for reporting)

    [jumps gun]

    If the exercise is to work in Revit, then the argument stands you should not build off of another model (.dwg or otherwise) as there will almost certainly have been compromises made in it's creation (or maybe that's what you're investigating?) - do you have access to the original survey data? Even that's a compromise (itself an abstraction) but that's where one should at least to try to start if re-surveying is not an option.

    But since we are all generally quite cool with abstractions, caveats and legal-outs in this game - it pays to heed that:

    1. Revit ain't great for 1:1 accurate real-world conditions
    2. Those who model existing conditions will (should) always caveat their "levels of accuracy"
    3. For all the digital-dreaming, minutia will always get worked out on site

    [/puts gun away because guns are bad]
    Last edited by snowyweston; March 7, 2018, 11:58 AM.


      Hey Snowyweston,

      thanks for your quick answer. Well I am studying "Geodesy and Geoinformation" and for one part of my master thesis I have to analize how accurate it is possible to model a building in Revit which already exists. That's why I have to analyze the accuracy of the Revit model.
      Do you have any recommandations on how to deal with "as built" projects in Revit?

      Kind regards, Lisa


        Only to the extent of what I've learnt from those working in the field (surveyors and alike providing such services) - most of whom have survey-specification checklists (the more thorough of which explain, discuss and caveat their working accuracies).

        Since we don't seem to attract many of their kind to this site, you're perhaps best reaching out directly via LinkedIn and/or Twitter.

        But to not leave the conversation dead, (and kick a hornet's nest or two) - "as built" is a highly fractious phrase in itself, and one of much legal consternation. "we" (the industry) have far-more appropriate (than Revit) software (&hardware) tools available to capture survey data, one does wonder why "Revit" is even in question (?) unless your studies are extending beyond Revit alone (?) and you are attempting to also compare workflows against one another - which extends the remit of your OP well beyond the "comparing .dwg against .rvt" question - and (some might contest) well out of the context of this forum.
        Last edited by snowyweston; March 7, 2018, 12:38 PM.


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