public enum SurfaceInterpolationMethod : System.Enum, System.IComparable, System.IConvertible, System.IFormattable, System.ISpanFormattable  

{
  // Note: Needs QueuedTask to run
  // Note: Needs 3d Analyst license to run
  {
    ArcGIS.Core.Geometry.Geometry output = null;
    // interpolate z values for a geometry
    if (tinLayer.CanInterpolateShape(polyline))
      output = tinLayer.InterpolateShape(polyline, SurfaceInterpolationMethod.NaturalNeighbor);

    if (output != null)
    {
      // process the output
    }

    // densify the shape before interpolating
    if (tinLayer.CanInterpolateShape(polygon))
      output = tinLayer.InterpolateShape(polygon, SurfaceInterpolationMethod.Linear, 0.01, 0);

    if (output != null)
    {
      // process the output
    }
  }
}

{
  // Note: Needs QueuedTask to run
  // Note: Needs 3d Analyst license to run
  {
    // interpolate z values at the geometry vertices only
    Geometry output = tinLayer.InterpolateShapeVertices(polyline, SurfaceInterpolationMethod.NaturalNeighbor);
    if (output != null)
    {
      // process the output
    }

    // or use a different interpolation method
    output = tinLayer.InterpolateShapeVertices(polyline, SurfaceInterpolationMethod.Linear);
  }
}

{
  // Note: Needs QueuedTask to run
  // Note: Needs 3d Analyst license to run
  {
    // interpolate values at the specified x,y location
    double z = tinLayer.InterpolateZ(x, y, SurfaceInterpolationMethod.NaturalNeighborZNearest);

    // or use a different interpolation method
    z = tinLayer.InterpolateZ(x, y, SurfaceInterpolationMethod.Linear);
  }
}

{
  // Note: Needs QueuedTask to run
  {
    // interpolate heights and calculate the sum of 3D distances between the vertices
    double length3d = tinLayer.GetSurfaceLength(polygon, SurfaceInterpolationMethod.NaturalNeighbor);

    // or use a different interpolation method
    length3d = tinLayer.GetSurfaceLength(polyline, SurfaceInterpolationMethod.NaturalNeighborZNearest);

    // densify the shape before interpolating
    length3d = tinLayer.GetSurfaceLength(polygon, SurfaceInterpolationMethod.NaturalNeighbor, 0.01, 0);
  }
}