AddPolyline

from scriptcontext import doc
import rhinoscriptsyntax as rs
from Rhino.Geometry import *
from Rhino.Input import *
from Rhino.DocObjects import *
from Rhino.Commands import *
from System.Collections.Generic import *

def RunCommand():
  rc, obj_ref = RhinoGet.GetOneObject(
    "Select surface to split", True, ObjectType.Surface)
  if rc != Result.Success:
    return rc
  brep_face = obj_ref.Surface()
  if brep_face == None:
    return Result.Failure

  rc, obj_ref = RhinoGet.GetOneObject(
    "Select cutting curve", True, ObjectType.Curve)
  if rc != Result.Success:
    return rc
  curve = obj_ref.Curve()
  if curve == None:
    return Result.Failure

  curves = List[Curve]([curve])
  split_brep = brep_face.Split(
    curves, doc.ModelAbsoluteTolerance)

  if split_brep == None:
    RhinoApp.WriteLine("Unable to split surface.")
    return Result.Nothing

  meshes = Mesh.CreateFromBrep(split_brep)
  print type(meshes)
  for mesh in meshes:
    bbox = mesh.GetBoundingBox(True)
    bbox_type = bbox.IsDegenerate(doc.ModelAbsoluteTolerance)
    if bbox_type == 1: # rectangle
        # box with 8 corners flattened to rectangle with 4 corners
        box_corners = bbox.GetCorners()
        rectangle_corners = []
        for corner_point in box_corners:
          if corner_point not in rectangle_corners:
              rectangle_corners.append(corner_point)
        # add 1st point as last to close the loop
        rectangle_corners.append(rectangle_corners[0])
        doc.Objects.AddPolyline(rectangle_corners)
        doc.Views.Redraw()
    elif bbox_type == 0: # box
        brep_box = Box(bbox).ToBrep()
        doc.Objects.AddBrep(brep_box)
        doc.Views.Redraw()
    else: # bbox invalid, point, or line
      return Result.Failure

  return Result.Success

if __name__ == "__main__":
  RunCommand()

Imports Rhino
Imports Rhino.Commands
Imports System.Linq
Imports Rhino.Geometry
Imports Rhino.Input
Imports Rhino.DocObjects
Imports System.Collections.Generic

Namespace examples_vb
  Public Class TightBoundingBoxCommand
    Inherits Command
    Public Overrides ReadOnly Property EnglishName() As String
      Get
        Return "vbTightBoundingBox"
      End Get
    End Property

    Protected Overrides Function RunCommand(doc As RhinoDoc, mode As RunMode) As Result
      Dim obj_ref As ObjRef = Nothing
      Dim rc = RhinoGet.GetOneObject("Select surface to split", True, ObjectType.Surface, obj_ref)
      If rc <> Result.Success Then
        Return rc
      End If
      Dim surface = obj_ref.Surface()
      If surface Is Nothing Then
        Return Result.Failure
      End If

      obj_ref = Nothing
      rc = RhinoGet.GetOneObject("Select cutting curve", True, ObjectType.Curve, obj_ref)
      If rc <> Result.Success Then
        Return rc
      End If
      Dim curve = obj_ref.Curve()
      If curve Is Nothing Then
        Return Result.Failure
      End If

      Dim brep_face = TryCast(surface, BrepFace)
      If brep_face Is Nothing Then
        Return Result.Failure
      End If

      Dim split_brep = brep_face.Split(New List(Of Curve)() From { _
        curve _
      }, doc.ModelAbsoluteTolerance)
      If split_brep Is Nothing Then
        RhinoApp.WriteLine("Unable to split surface.")
        Return Result.[Nothing]
      End If

      Dim meshes = Mesh.CreateFromBrep(split_brep)

      For Each mesh__1 As Mesh In meshes
        Dim bbox = mesh__1.GetBoundingBox(True)
        Select Case bbox.IsDegenerate(doc.ModelAbsoluteTolerance)
          Case 3, 2
            Return Result.Failure
            Exit Select
          Case 1
            ' rectangle
            ' box with 8 corners flattened to rectangle with 4 corners
            Dim rectangle_corners = bbox.GetCorners().Distinct().ToList()
            ' add 1st point as last to close the loop
            rectangle_corners.Add(rectangle_corners(0))
            doc.Objects.AddPolyline(rectangle_corners)
            doc.Views.Redraw()
            Exit Select
          Case 0
            ' box
            Dim brep_box = New Box(bbox).ToBrep()
            doc.Objects.AddBrep(brep_box)
            doc.Views.Redraw()
            Exit Select
        End Select
      Next

      Return Result.Success
    End Function
  End Class
End Namespace