Saturday, March 15, 2008

Revit to AutoCAD for Construction

It's been awhile since my last post as I had some problems with my Tablet PC and an offline blogging tool. Long story...I'll explain in a future post. In the meantime, I have been working very hard on a conversion process for one of our Revit-based projects. As I discovered through conversations with others at Autodesk University, it is not uncommon (from the Architect's perspective) to convert a Revit project to AutoCAD (DWG) for the construction phase of a project. The following will highlight some of the reasons why one would convert a project, aspects of DWG export from Revit and things to beware of in Revit if you might be exporting it later.


Why Convert?

The reasons are few, but simple and compelling. First, if a thorogh design development has been completed using Revit, very few design changes should be required during the course of construction. Second and probably most compelling is the staff during construction phase services. In many design firms a different - most often, more senior - team will handle a project in construction. These team members may not be familiar with Revit at all.


Aspects of Revit's DWG Export

Revit has the ability to export DWG, DGN, DXF and some other formats with a decent level of consistency; however, there are a few aspects to note before embarking on converting an entire project.
  • Revit does not export DWGs in STB plot style format. If you require this format, be prepared to use some scripts or custom programming to assign your standard named plot styles.
  • Revit assigns lineweight and linetype overrides at the entity level. Although there are other options to assign overrides to new layers or exclude overrides completely, they are not very useful. If you don't use overrides, you lose all lineweights and linetypes anyway and using new layers for overrides only complicates a clean conversion by creating layers such as A-WALL-1, A-WALL-2, A-WALL-3, etc. If your standard use of CAD dictates using a plot style table for defining plotted lineweights, again be prepared to do some work.
  • Using the "Shared" option for coordinates on exported files has no effect on plans when you're exporting sheets. Data in model space of exported sheets is positioned only in relation to the paper space viewports.

  • Lines within blocks are not on layer 0; they are on the layer of the category or sub-category of the entire component. This is particularly troublesome if families are made with confusing categorization. For example, an elevator door was made as a Specialty Equipment family, but with a sub-category called "Doors". When exported, the lines within the block were on A-DOOR, but the block itself was inserted on layer A-EQPM.

  • Text and Dimensions all export into the "Standard" style. There is no setting in Revit to modify this.

  • Hatches for columns are exported onto the same layer as the column.

Pre-Conversion Tips for Revit

If you happen to be working on a Revit project and know (or even think) you will be exporting to CAD format, be aware of these potential pitfalls.

  • Don't use solid white Fill Regions to mask model elements in any views. The latest versions of Revit have the new Masking Region tool which will behave as expected (like a wipeout) when exported.
  • Don't coverup unwanted text or dimensions with opaque background text. AutoCAD does not have an analogous object, so you end up with two, overlapping text elements in the exported CAD file.
  • Use appropriate sub-categories for custom families. If you have many custom families all under Generic Models, they will most likely be exported onto one layer.

  • Try not to 'fudge' a design by drawing it with Model Lines or Detail Lines. These will export as line layers, not as building layers such as walls, doors or windows.

  • Because unreferenced view tags cannot be hidden or removed during the exporting process, make it a habit to hide all temporary sections, callouts or elevations during your project. Hopefully, Autodesk will soon develop a way to mitigate this problem - perhaps by allowing visibility (on/off) access to the various view types within a project.

  • Protect your export layers template file. Every time you use it to export CAD formats from Revit, it is appended with any additional data which may be in the Revit file at the time - including all linked and imported CAD files. This is an additive process ONLY. The export template will not 'clean' itself when it is needed for the next project. I usually create a clean master template then ZIP the file so no one can accidentally use it in a live Revit project.

9 comments:

  1. We are CAD and BIM Solutions company and work mostly with all the flavours of Revit. Your tip will be of great use.
    Great!!
    Thanks
    Abhishek
    www.pinnaclecad.com

    ReplyDelete
  2. We are a CAD Solutions company working mostly with all the flavours of Revit. We also use AutoCAD. I just want to know what are effects to the layers after conversion.
    Thanks
    Abhishek
    www.pinnaclecad.com

    ReplyDelete
  3. Abhishek,

    Could you clarify your question? I'm not sure what you are asking.

    James

    ReplyDelete
  4. James,

    Very helpful entry. Ever tried to go from Revit to Microstation?

    Steve

    ReplyDelete
  5. Hello,
    I know we can convert Revit (*.rvt) file to AutoCAD (*.dwg) file one at a time, Like i have
    mentioned below
    File > Export > CAD Formats
    a dialog box pops up where we can select place to save the CAD file in required format..
    i.e., in save as option, i was selecting *.dwg & i use to select wire frame.
    Since i have to convert more number of files, I wanted to know is there any other options,
    software or scripts available to convert more numbers of Revit (*.rvt) files to AutoCAD (*.dwg)
    files at a time. Could anyone can help me in this regard.
    Any help is appreciated
    Sorry, If it is not right place to ask help

    Thanking You
    Prashanth

    ReplyDelete
  6. How would you export a Vectorworks file to Revit and vice versa? The geometry exports with IFC, but the 2D linework does not? Any suggestions?

    ReplyDelete
  7. This comment has been removed by the author.

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  8. Autocad is indeed helpful in architectural designing. An architect can address even the most minute details thoroughly, so there is minimal room for mistakes. It has made designing more comprehensive, efficient and versatile. That's technology at its finest.

    Jamie Shellman

    ReplyDelete