I could go on for hours and hours talking about this subject as there are so many different scenarios which lead to different best practice methods for either linking or importing CAD Data. Instead, this post discusses the key considerations when linking CAD data into a Project.
Linked File Storage
- Take a copy of your Original CAD Data and store it in a separate location (suggest a folder such as …
BIMLinked Data). It’s important to do this as you will often need to clean up a sub-consultants drawing and remove unwanted links, blocks etc (and you don’t want to destroy the original file they sent you!). Its also good to be able to see and manage all linked information from one folder location.
Linked File Preparation
- Clean up the copy to make sure you are only linking in ‘the information you need’ i.e. If you are using an OS Plan to trace the outline of a house, don’t load in half of London! Similarly, if you only need the building outline, dont load in all the spot levels, hatching etc which will really slow down the performance of your model.
- Use the OVERKILL command in AutoCAD to remove duplicate lines (thanks for this tip J)
- Purge, Delete, Bind any Xref information in the CAD file and Audit it.
- Finally you need to consider the coordinates of the CAD Data. If you are importing Site Plan information, this is often located a large distance from the 0,0 origin. Revit used to have a limit of 2 miles. Anything over this limit would cause errors in graphical display. In 2011 this has been increased to 20 miles. You can read more about this here on the Autodesk Website
So if your CAD data is a large distance from 0,0 you may have to move the geometry in AutoCAD nearer to 0,0 (by whatever method you decide – too many options to post here). This isn’t an issue once inside Revit as the coordinate system is set retrospectively inside the model (I will post a separate discussion about site coordinates, True North/Project North etc…)
- Create a dedicated workset in Revit for the linked CAD file making sure you uncheck ‘visible by default in all views’. (if your not using central files ignore this part).
- Make this it the ‘Active’ workset.
- Decide which Level, Elevation, View, Reference Plane you would like to link the file into/onto and make it current (in my example this will be Level 0).
- Under visibility graphics, make sure the link is visible in the required view (remember this is turned off in all views by default as noted above). Note the interface has changed slightly in2011 as shown below (now a drop down instead of a check box).
- From the Insert Tab choose Link CAD (Avoid using the Import CAD option)
- Browse to locate your CAD file
- Make sure ‘Current View Only’ is Unchecked (the workset takes care of this issue). Note: If your not using worksets you may want to consider using this to restrict the CAD data to one view only.
- Colours & Layers are user specific but make sure you set the units to match the drawing (don’t rely on the ‘Auto’ option).
- ‘Positioning’, ‘Place at’ and ‘Orient to View’ are user specific.
- You can now link your CAD file into your project.
Remember, if you want to see your CAD file in other views, you will need to open the view and set the visibility graphics to show the CAD workset created earlier.