Streamlining Revit and DWG Collaboration for AEC Teams

This ndr-bim guide outlines essential workflows for seamless collaboration between Revit (BIM) and DWG (2D CAD) environments within the Architecture, Engineering, and Construction (AEC) industry.

Core Principle: Link, Don't Import (Most of the Time)

The fundamental distinction between linking and importing DWG files into Revit is crucial for model health and collaboration efficiency.

Linking (Recommended):

• Establishes a live connection to the original DWG file, similar to XREFs in AutoCAD.

• Updates to the source DWG can be reflected in Revit by reloading the link.

• Keeps Revit model size smaller, improving performance and simplifying file management via the "Manage Links" dialog.

• Promotes integration and minimizes redundant data.

Importing (Limited Use):

• Embeds DWG data directly into the Revit project, breaking the connection to the original file.

• Updates require manual removal and re-import, which is inefficient and increases Revit file size.

• Suitable only for static content that will not change or for creating detail components within Revit families where linking is not an option.

• Prioritizing linking is recommended to maintain system integrity.

Preparing DWG Files for Revit (The Foundation for Success)

Meticulous DWG file preparation before linking is crucial to prevent performance issues, display errors, and clutter in the Revit model. This proactive step embodies the "Structure" pillar.

1. Clean Up the DWG: Open in AutoCAD and use PURGE to remove unused items and AUDIT to check for errors.

2. Remove Unnecessary Data: Delete non-essential elements like hatch patterns, layouts, text, dimensions, and annotations not critical for the Revit model. For large site plans (over 1 MB), remove extraneous site information.

3. Bind XREFs: Bind all external references to the host file to consolidate geometry and prevent duplicate layers.

4. Simplify Geometry: Explode all blocks and intelligent AEC objects down to basic AutoCAD entities (lines, circles, arcs). Place all relevant geometry on Layer 0. Avoid exploding DWG files directly in Revit to prevent file size inflation.

5. Verify Coordinates and Origin: Check the DWG's origin (BASE point). Elements excessively far from 0,0,0 can cause "geometry extents greater than 20 miles" errors in Revit. Move elements closer to 0,0,0 if necessary.

6. Standardize Text and Proxy Graphics: Change all text to Arial. Set PROXYGRAPHICS to 1.

7. Save a Clean Copy: Save a cleaned and optimized copy in a dedicated "CAD Links" subfolder within the Revit project directory, keeping the original for reference.

   These steps empower users with control over incoming data.

Smart Linking Settings in Revit (Seamless Integration)

Careful configuration within Revit ensures optimal integration of clean DWG files, providing clarity for accurate model alignment and performance.

When using "Link CAD" from the "Insert" tab:

• Positioning:

  • Auto - By Shared Coordinates: Ideal for georeferenced DWGs and multidisciplinary projects for precise alignment.

  • Auto - Origin to Internal Origin or Center to Center: Use for initial placement if shared coordinates are not established, but be prepared for manual adjustments.

  • Manual - Center/Origin: Offers flexibility for interactive placement during linking.

• Current View Only: Activate if the DWG is only needed in a specific view to prevent clutter and improve model performance.

• Colors: Change to "Black and White" for improved visibility and a consistent aesthetic with Revit elements.

• Layers: Set to "Visible" to link only layers that are not hidden or frozen in AutoCAD, or choose "Specify" to manually select layers.

• Import Units: Always select the correct units to prevent scaling issues.

Consistent application of these settings minimizes errors and maximizes project efficiency.

Managing Linked DWGs for Ongoing Collaboration (Keeping Your Model Healthy)

Effective management of linked DWG files is essential for sustained collaboration in workshared environments, empowering teams and maintaining a healthy Revit model.

• Worksets: In workshared projects, dedicate a new workset specifically for DWG links. This workset can be set to be non-visible by default, allowing individual team members to control its visibility.

• Visibility Controls: Use Revit's "Visibility/Graphics Overrides" (VV or VG) to manage DWG layer display. Under "Imported Categories," selectively turn layers on/off or adjust line weights, colors, and patterns.

• Consistent File Structure and Naming: Implement a standardized folder hierarchy and naming convention for DWG files to simplify management, path referencing, and accessibility.

• Relative Pathing: Employ relative paths when linking DWG files to minimize issues if project files are moved.

• Regular Updates: Encourage regular updates of linked DWG files. Use the "Manage Links" dialog to "Reload" or "Reload From" updated DWGs.

• Shared Coordinates: Establish and maintain a shared coordinate system across all linked models (Revit and DWG) for precise alignment, especially for site plans and multidisciplinary projects. Coordinates can be acquired from a linked DWG or published to other linked models.

Exporting from Revit to DWG (When the Flow Reverses)

Exporting Revit models to DWG for consultants is common and presents its own challenges, requiring careful preparation for data quality.

Common Export Challenges:

• Data Loss: Revit's intelligent BIM data is often simplified to basic AutoCAD entities.

• Geometric Inaccuracies: Consultants may receive DWGs with broken, non-continuous, or overlapping lines.

• Clutter and File Size: Unnecessary elements can lead to heavy and cluttered DWG files.

• Layering and Standards: Translating Revit categories into correctly named AutoCAD layers requires careful setup.

Solutions and Best Practices for Exporting:

1. Prepare the Revit Model Thoroughly:

   • Audit and Purge: Open a duplicated project file with "Audit" enabled and purge all unused elements.

   • Remove Links: Remove all links (CAD, DWF, Point Clouds, PDF, Image) from the duplicated file.

   • Simplify Views: Hide unnecessary elements in views intended for export. Ensure views are scaled and detailed appropriately.

   • Save to Central: Save to central to ensure the most recent version of the model is used.

2. Optimize Export Settings:

   • Custom Export Setup: Define and save optimal export settings within Revit projects or templates for consistency.

   • Layer Mapping: Use or create a custom template to map Revit categories to AutoCAD layers.

   • Control Visual Elements: Precisely control colors, line weights, hatch patterns, and fonts to match CAD standards. Change all fonts to Arial.

   • Address Coincident Lines: Utilize "Merge collinear wall lines" during export. The OVERKILL command in AutoCAD can further clean overlapping lines.

   • Coordinate Systems: Correctly set the export origin (shared coordinates vs. internal origin) for proper alignment.

   • Export Specific Views: Only export necessary views (floor plans, elevations, sections).

3. Export Process and Location:

   • Export Locally: Export to a local drive and then upload to avoid corruption risks associated with cloud-based folders.

   • Backward Compatibility: Consider backward compatibility for older software versions used by consultants.

   • Alternative: IFC Format: For less data loss and better BIM interoperability, consider exporting to the Industry Foundation Classes (IFC) format, which retains Revit property sets and data.

These strategies provide a structured process for clarity and precision when delivering information to DWG users.

Beyond Basic Linking: Advanced Collaboration & Troubleshooting (Proactive Problem Solving)

Effective collaboration involves proactive coordination and efficient troubleshooting, empowering teams with a clear system.

Common Issues and Solutions:

• DWG Not Visible/Incorrect Position: Check Visibility/Graphics overrides (Imported Categories), view range, crop region, and the DWG's internal origin/coordinates. Type "ZF" (Zoom to Fit) in Revit.

• "Geometry has extents greater than 20 miles" Error: Resolve by cleaning the DWG in AutoCAD, copying needed geometry to a new file, and pasting it near 0,0,0.

• Lines Shifting When Zooming: Often due to elements far from 0,0,0 in the DWG. Cleaning the DWG and pasting it to the origin in a new AutoCAD file typically resolves this.

• DWG Not Cutting Correctly: If linked CAD data (especially 3D geometry) isn't cutting as expected, consider importing the cleaned DWG into a detail item family. Note: this prevents direct reloading of updates from the original CAD file.

Cloud Collaboration Platforms:

Leverage platforms like Autodesk Docs and BIM Collaborate Pro for advanced, multidisciplinary collaboration.

• Centralized Environment: These platforms allow sharing of DWG files and their XREFs, version management, change comparison, and issue tracking in a common data environment.

• Design Collaboration: Use tools within Autodesk Construction Cloud (ACC) Design Collaboration to create and consume packages of DWG files.

• Bridge Tool: The Bridge tool within ACC facilitates sharing design data, including DWGs, across different projects.

These strategies provide clear guidance and foster system over chaos, integrating all aspects of project collaboration.

Empower Your AEC Workflows with Clarity and Structure

By implementing these structured workflows, from DWG preparation and linking settings to management, exporting, and troubleshooting, teams are empowered with clarity and consistency. ndr-bim champions the integration of diverse tools through thoughtful processes to enhance project efficiency and foster a more collaborative, less error-prone environment.

For more resources on BIM best practices, visit ndr-bim.com.