public TinSurfaceType SurfaceType {get;}

var constraintCount = lasDataset.GetSurfaceConstraintCount();
IReadOnlyList<ArcGIS.Core.Data.Analyst3D.SurfaceConstraint> constraints = lasDataset.GetSurfaceConstraints();
foreach (var constraint in constraints)
{
  var dsName = constraint.DataSourceName;
  var wksPath = constraint.WorkspacePath;
  var heightField = constraint.HeightField;
  var surfaceType = constraint.SurfaceType;
}