public sealed class SurfaceConstraint 

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;
}

var activeSurfaceConstraints = lasDatasetLayer.GetActiveSurfaceConstraints();

// clear all surface constraints (i.e. none are active)
lasDatasetLayer.SetActiveSurfaceConstraints(null);

// set all surface constraints active
using (var lasDataset = lasDatasetLayer.GetLasDataset())
{
  var surfaceConstraints = lasDataset.GetSurfaceConstraints();
  var names = surfaceConstraints.Select(sc => sc.DataSourceName).ToList();
  lasDatasetLayer.SetActiveSurfaceConstraints(names);
}