Merge Coplanar Mesh Faces in Rhino3D

Simplify and clean up mesh geometry by automatically merging adjacent coplanar faces into single n-gons. This custom Rhino script is designed to optimise mesh quality and readability, particularly useful when working with triangulated or imported geometries.

What Does the Script Do?

The Merge Coplanar Mesh Faces command allows you to:

• Select multiple mesh objects in the viewport.
• Combine them into a single mesh and fully weld them.
• Automatically detect and merge adjacent coplanar faces into clean n-gons based on a user-defined angle tolerance.

This process is especially helpful for reducing face complexity after import, retopologising geometry, or preparing meshes for clean presentation or fabrication.

Note: Requires Rhino 7 or later (due to AddPlanarNgons() support).

Why Use This Tool?

Rhino’s native tools do not provide an easy way to merge coplanar faces into n-gons. Triangulated or fragmented meshes can be difficult to work with, both visually and structurally. This script:

• Reduces mesh face count and improves legibility.
• Simplifies post-processing workflows.
• Helps with 3D printing and export to external software (e.g., Unreal, Blender, or Revit).

How to Use the Script

Load the Script in Rhino

Method 1:

1. Type _RunPythonScript in the command line.
2. Browse to the saved location of the script file and run it.

Method 2 Creating a Button or Alias for Easy Access (Optional)

Creating a Toolbar Button

1. Right-click an empty area of a toolbar and select New Button.

2. In the Button Editor:

   • Left Button Command:

     ! _-RunPythonScript "FullPathToYourScript\merge_coplanar_mesh_faces.py"
     

     Replace FullPathToYourScript with the actual script file path.

   • Tooltip: For example, Merge coplanar mesh faces into n-gons.

   • Icon (Optional): Assign a custom icon if desired.

Creating an Alias

1. Open Tools > Options, then go to the Aliases tab.

2. Create a New Alias:

   • Alias: e.g., meshmerge

   • Command Macro:

     _-RunPythonScript "FullPathToYourScript\merge_coplanar_mesh_faces.py"
     

Using the Command

1. Select one or more mesh objects when prompted.

2. Enter an angle tolerance in degrees. Adjacent faces within this angle will be considered coplanar.

3. The script will:

   • Combine all selected meshes.
   • Fully weld them at 180°.
   • Merge coplanar faces using AddPlanarNgons.
   • Replace the original meshes with a new optimised version.

Example Use Cases

• Cleaning up triangulated meshes from STL or OBJ imports.
• Preparing meshes for CNC or laser cutting.
• Reducing geometry complexity for viewport performance or mesh UV mapping.