You may not use all of those commands for getting your model ready for the further steps with Grasshopper. On the other hand, there are other difficulties and ways of reaching your goal. If you need an other Rhino command regarding meshes, please visit this site.

• Import
  • Use the Import command for importing your 3D scan (.stl file) into Rhino.
  • Hint: If you can't see anything after importing, check the Zoom extents button in the tool bar.

•  MeshSplit
  • You need a surface to cut a mesh. Use the Surface command to do this.

  • The MeshSplit command divides meshes into parts with another object, in this case your surface.
    
    

• ReduceMesh
  
  • If you haven't scanned an object but downloaded a high res 3d object / mesh, you can simplify this. You'll probably need a simpler mesh later when working with Grasshopper.

  • The ReduceMesh command decreases the polygon mesh face count while minimizing geometric and texture distortion.

• ShowEdges
  • To make edges – respectively holes – visible, use the ShowEdges command.
  • You can then either use MatchMeshEdge for smaller openings or manually select those with FillMeshHole.
    
    

• MatchMeshEdge

  • The MatchMeshEdge command moves face edges of an open mesh to meet adjacent face edges.
    
    

• Check
  • …
    
  • If still holes, use Explode.

• Explode
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• FillMeshHoles
  • If you have openings in your mesh which you'd like to close, use the FillMeshHole command.
    
    
• MeshToNURB
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