Making the most of AutoCAD when using Revit
One of the most common things that engineers and architects do not understand is that their existing standard AutoCAD details can be used in a Revit Architecture, Revit Structure and Revit MEP project.
Additionally, those that do try and use them often explode them to try and make them appear visually consistent with their Revit Details and in doing do create additional model complexities for themselves down the road.
General guidelines for using DWG data in any Revit project
Link Instead of Import Wherever Possible
There are many reasons for this school of thought, ranging from limiting the size of your Revit model to reducing the amount of clutter that exists due to all the imported data that gets added to the Object and Line styles.
Suppose you use AutoCAD to generate a DWG file that contains external references (xrefs). When you import or link the DWG file, Revit Architecture displays the geometry from the nested xrefs. The decision to import or link a file to a Revit project affects what you can do with the xref information:
If you import the file, you can explode the nested xrefs to Revit elements. However, if the xref file is updated after the import, Revit Architecture will not automatically reflect changes to the xref file.
If you link the file, Revit Architecture automatically updates the geometry to reflect changes to the xref files. However, you cannot explode the nested xrefs to Revit elements.
Current View Only
Always use this option when importing a DWG files unless absolutely necessary. If this option is not selected, the linked file will be visible in ALL other views including 3D views. If not, you will eventually hear this question “What’s that multi-colored line in my section?.” and the answer will be “It is your linked floor plan!”
Layer / Level Colors
Use black and white in most cases; there is really no need for colors once the import lineweights are set correctly.
Setting the Origin Option
Always a source of debate, here are some thoughts on what option to select for the origin of linked in DWG files.
Plan Views / Civil Data Involved – Use Shared Coordinates
Import the 2D DWG plans into a working plan view and use Current View Only and Center to Center options. Then use Tools > Shared Coordinates > Acquire Coordinates and pick the imported DWG to align Revit’s shared coordinates with the World Coordinate System of the DWG file. All subsequent DWG imports can then use the By Shared Coordinates import option. They will be exactly aligned with the
first plan linked into Revit.
Plan Views / No Civil Data Involved – Link Origin to Origin
If there are no Civil drawings involved using coordinate systems, like Lat Long of State Planes, then use the origin to origin option. In most cases, this is the simplest option to use and will keep the resulting DWG’s oriented. We will use this option for our purposes later.
Detail Views – Link Center to Center
When all you are doing is referencing in a detail drawing or like information from AutoCAD, then you can use the default option of Origin to Origin.
And finally, remember this tip about DWG Origins. Keep for reference a clean AutoCAD drawing file with a simple “X” at 0,0,0 with the +X a little longer than the others. When you are questioning where the origin might be, simple insert this drawing file using one of the above option to confirm where the origin is.
Scaling and Import Units
In most cases, Auto-Detect will work just fine. Once again, in the case of a Civil drawing you might have to apply a custom scale to get things to work correctly.
Using standard details from AutoCAD and referencing them with a Revit callout
Although this is a fairly straightforward procedure, a vast majority of structural firms do not necessarily know the concept.
1. Create a drafting view.
2. Link in the AutoCAD Detail File.
3. Create a call out and reference it to the drafting view.
4. Place the view on a sheet.
Here are some additional guidelines for system settings to control lines weights and fonts:
Import Line Weight Settings – Line weights in the AutoCAD drawing file can be
controlled by one of three methods
Create and Import Settings File.
If your DWG data is consistent and well-controlled, this is the simplest option. In Revit, go to File > Import/Export Settings > Import Line Weights DWG/DXF and create a firm standard file for importing line weights. This is a simple table where you simply map a Revit line weight to an AutoCAD Color and the settings will be applied to linked and imported geometry.
Apply Settings After the Import.
If you have Geometry that is not on a strict CAD standard, and for ‘one-off’ items that you might need to control, you can use a combination of Visibility Graphics and the Query Tool to control the lineweights of the linked-in file after the file has been imported.
Note: Using Visibility Graphics you can change the line weight of one layer in the
AutoCAD DWG file.
Respect AutoCAD Line weights
If the AutoCAD file to be imported has already used assigned line weights, either by object or by layer, Revit will respect these line weights on Import.
Font Mapping – This is a very critical aspect to understand about Revit. Revit does not utilize shape-based font files (SHX) like AutoCAD, rather it uses True Type fonts (TTF). When you are importing DWG data with text, Revit attempts to map whatever SHX-style fonts it finds to an equivalent TTF using a file called shxfontmap.txt which is located in the Data subfolder under Revit’s installation folder. This file is customizable and follows a simple format:
Filename.shx <tab> Fontname
For example: ROMANS.SHX <tab> Arial Narrow
Once this file has been correctly set up for your firm, imported files should look much
better.
Important fact: In a larger office, it is critical to standardize this file and ensure it is distributed to all Revit users. When used in a worksharing environment where several users are working on local copies of a central file, if one user has a different version of the shxfontmap file, the font mappings within all linked DWG files for the Revit project will be affected when that person opens, works on and saves to central.
