Create List in C#

[laurent_delrieu]

The documentation is clear here
https://developer.rhino3d.com/wip/api/RhinoCommon/html/M_Rhino_Geometry_Collections_MeshTopologyEdgeList_GetConnectedFaces.htm

public int GetConnectedFaces( int topologyEdgeIndex)

It is an array of int which are faces index.

If you are in Mesh Topology
dont’ use GetTopologicalIndenticalVertices, it doesn’t work
Use instead mesh.TopologyVertices.TopologyVertexIndex

cf.

Mesh topological identical vertices

When does mesh.Vertices.GetTopologicalIndenticalVertices(vertexID); returns null? File and simple mesh attached. http://developer.rhino3d.com/api/RhinoCommon/html/M_Rhino_Geometry_Collections_MeshVertexList_GetTopologicalIndenticalVertices.htm [identical]TopologicalIndeticalVertices.gh (7.7 KB)