DWG Insertion Protocol

DWG insertion protocol

Content

Inserting DWG files in the model might be of help for certain modeling purposes. However, it is best to avoid inserting/linking reference geometry as it might induce geometric errors and inconsistencies.

The recommended approach is to follow guiding PDFs / DWGs as separate references, by looking at them on another screen or even in paper. Thus ensuring positioning of elements can be done as it would be in reality.

However, if inserting existing drawings is required, the following protocol should be followed to ensure model health.

General Rules

• Files should be LINKED rather than IMPORTED. This should be the default case.
• Reference files should be thoroughly cleaned before insertion, and should be inserted only in specific views. Always follow the steps below.
• DWG file extension should be under control. Beware of extremely large files.
• Beware of files with thousands of line-types as they might bloat your model file. Use DWG-PURGE extension from Autodesk Apps or use a Dynamo definition to clean the model.

DWG Preparation

If the file comes from Civil 3D, make sure that it has been exported using _EXPORTTOAUTOCAD command. If not, a message about proxy graphics will appear when opening the DWG file with autocad.  

1. Open desired DWG in AutoCAD
2. Go to Model Space
3. UCS > World
4. Erase all hatches. QuickSelect > Hatch / Select All > Erase
5. Delete all undesired blocks and explode the rest. QuickSelect > BlockReference / Select All > Explode.
6. Repeat step 4 and 5 till every block reference has disappeared.
7. Flatten the drawing. Select all elements > Flatten
8. Overkill lines. Select all elements > Overkill
9. Some elements will not be flattened with the command, so you may need to check it on elevation, select the ones that are not flatten by smaller groups, and Flatten again from plan view. If this does not work, you must select elements and manually put their Z coordinates at 0.
10. Purge the drawing. _Purge > PurgeAll
11. Purge all linetypes. You should use the DWG-Purge extension in AutoCAD.
12. Change all text to Arial (Revit cannot read line-based fonts such as RomanS). Properties > Style
13. Audit the file. Audit > Y
14. Copy the elements you want to insert into a new file > Ctrl+C > New document > PasteToOriginalCoordinates.
15. Save the file with the same name and a _cleaned suffix.

DWG Revit Link

1. Open the view in which we want to work with our drawing
2. Insert>Link CAD
3. Current View Only > ON
4. Colors > Preserve
5. Layers/Levels > Visible
6. Import Units > meters (default)
7. Correct Lines That Are Slightly Off Axis > OFF
8. Positioning > Auto- By Shared Coordinates (default)
9. Place at:> Revit level where the DWG will be placed
10. Select desired “cleaned” DWG
11. Click Open

If the DWG is 3D, the reference level selected in “9” will be considered as the origin of elevations for the imported CAD (Even when the positioning is by shared coordinates). To properly place the reference, select the CAD Link instance and set a negative “Base offset” equal to the absolute elevation of the level where it has been inserted.

REVIT may warn you that the model and the DWG do not share the same Shared Coordinates system and that it will be positioned using the world UCS. This is OK.

Conclusion

Do not link DWG files whenever possible. If it is strongly needed, follow these steps.