partial class Examples
{
  static void SearchCallback(object sender, RTreeEventArgs e)
  {
    SearchData data = e.Tag as SearchData;
    if (data == null)
      return;
    data.HitCount = data.HitCount + 1;
    Point3f vertex = data.Mesh.Vertices[e.Id];
    double distance = data.Point.DistanceTo(vertex);
    if (data.Index == -1 || data.Distance > distance)
    {
      // shrink the sphere to help improve the test
      e.SearchSphere = new Sphere(data.Point, distance);
      data.Index = e.Id;
      data.Distance = distance;
    }
  }

  class SearchData
  {
    public SearchData(Mesh mesh, Point3d point)
    {
      Point = point;
      Mesh = mesh;
      HitCount = 0;
      Index = -1;
      Distance = 0;
    }

    public int HitCount { get; set; }
    public Point3d Point { get; private set; }
    public Mesh Mesh { get; private set; }
    public int Index { get; set; }
    public double Distance { get; set; }
  }

  public static Rhino.Commands.Result RTreeClosestPoint(RhinoDoc doc)
  {
    Rhino.DocObjects.ObjRef objref;
    var rc = Rhino.Input.RhinoGet.GetOneObject("select mesh", false, Rhino.DocObjects.ObjectType.Mesh, out objref);
    if (rc != Rhino.Commands.Result.Success)
      return rc;

    Mesh mesh = objref.Mesh();
    objref.Object().Select(false);
    doc.Views.Redraw();

    using (RTree tree = new RTree())
    {
      for (int i = 0; i < mesh.Vertices.Count; i++)
      {
        // we can make a C++ function that just builds an rtree from the
        // vertices in one quick shot, but for now...
        tree.Insert(mesh.Vertices[i], i);
      }

      while (true)
      {
        Point3d point;
        rc = Rhino.Input.RhinoGet.GetPoint("test point", false, out point);
        if (rc != Rhino.Commands.Result.Success)
          break;

        SearchData data = new SearchData(mesh, point);
        // Use the first vertex in the mesh to define a start sphere
        double distance = point.DistanceTo(mesh.Vertices[0]);
        Sphere sphere = new Sphere(point, distance * 1.1);
        if (tree.Search(sphere, SearchCallback, data))
        {
          doc.Objects.AddPoint(mesh.Vertices[data.Index]);
          doc.Views.Redraw();
          RhinoApp.WriteLine("Found point in {0} tests", data.HitCount);
        }
      }
    }
    return Rhino.Commands.Result.Success;
  }
}

import Rhino
import rhinoscriptsyntax as rs

# data passed to the RTree's SearchCallback function that
# we can use for recording what is going on
class SearchData:
    def __init__(self, mesh, point):
        self.HitCount = 0
        self.Mesh = mesh
        self.Point = point
        self.Index = -1
        self.Distance = 0

def SearchCallback(sender, e):
    data = e.Tag
    data.HitCount += 1
    vertex = data.Mesh.Vertices[e.Id]
    distance = data.Point.DistanceTo(vertex)
    if data.Index == -1 or data.Distance > distance:
        # shrink the sphere to help improve the test
        e.SearchSphere = Rhino.Geometry.Sphere(data.Point, distance)
        data.Index = e.Id
        data.Distance = distance

def RunSearch():
    id = rs.GetObject("select mesh", rs.filter.mesh)
    mesh = rs.coercemesh(id)
    if mesh:
        rs.UnselectObject(id)
        tree = Rhino.Geometry.RTree()
        # I can add a RhinoCommon function that just builds an rtree from the
        # vertices in one quick shot, but for now...
        for i,vertex in enumerate(mesh.Vertices): tree.Insert(vertex, i)

        while(True):
            point = rs.GetPoint("test point")
            if not point: break

            data = SearchData(mesh, point)
            # Use the first vertex in the mesh to define a start sphere
            distance = point.DistanceTo(mesh.Vertices[0])
            sphere = Rhino.Geometry.Sphere(point, distance * 1.1)
            if tree.Search(sphere, SearchCallback, data):
                rs.AddPoint(mesh.Vertices[data.Index])
                print("Found point in {0} tests".format(data.HitCount))

if __name__=="__main__":
    RunSearch()