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

var tinLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<TinLayer>().FirstOrDefault();
await QueuedTask.Run(() =>
{
  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
  }

});

var tinLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<TinLayer>().FirstOrDefault();
await QueuedTask.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);
});

var tinLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<TinLayer>().FirstOrDefault();
await QueuedTask.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);
});

var tinLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<TinLayer>().FirstOrDefault();
await QueuedTask.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);
});