Edge Selection by Angle in Maya

This Python script is a utility for Autodesk Maya that allows users to select edges between two faces if the angle between those faces is above a given threshold.

Function

The script contains one primary function, selectEdgesByAngle(angle), which takes a single argument: the angle threshold in degrees. It selects edges between two faces in Maya if the angle between those faces is below the given threshold.

How to use

1. Save the script as selectEdgesByAngle.py in your Maya scripts folder. The default location for the scripts folder is:

   • Windows: C:\Users\<username>\Documents\maya\<version>\scripts
   • macOS: ~/Library/Preferences/Autodesk/maya/<version>/scripts
   • Linux: ~/maya/<version>/scripts

   Replace <username>, <version> with your username and your Maya version, respectively.

2. Open Autodesk Maya, and open the Script Editor by navigating to Windows > General Editors > Script Editor.

3. In the Script Editor, switch to the Python tab.

4. Import the script and call the selectEdgesByAngle(angle) function with the desired angle threshold in degrees:

   import selectEdgesByAngle
   
   selectEdgesByAngle.main(30)

5. Execute the script by selecting the lines you just entered and pressing the Execute button or the Enter/Return key on your keyboard while holding the Ctrl key (Windows/Linux) or Cmd key (macOS).

How it works

The script calculates the angle between two connected faces using the following math:

1. Convert the angle threshold from degrees to radians: radians = math.radians(angle)
2. Compute the dot product of the two face normals, v1 and v2: deg = v1.angle(v2)
3. Check if the computed angle deg is greater than or equal to the given threshold in radians: if deg >= radians:

The angle between two vectors v1 and v2 can be calculated as:

$$c=\alpha_f(c_f \cdot c_f) + (1 - \alpha_f) c_b$$

Here, $\theta$ is the angle between the two vectors $\mathbf{v_1}$ and $\mathbf{v_2}$, $\mathbf{v_1} \cdot \mathbf{v_2}$ is the dot product of the vectors, and $||\mathbf{v_1}||$ and $||\mathbf{v_2}||$ are the magnitudes of the vectors.

The script uses Maya's API to interact with the scene, selecting the edges that meet the angle criteria.

Additional notes

• The script avoids selecting edges with non-manifold topology or border edges by checking the length of the connected faces: if len(faces) != 2:
• The resulting edge selection is stored in a new selection list, which is then set as the active selection in Maya: om.MGlobal.setActiveSelectionList(newSelList)