public LasPointFilter()

// search all points
using (ArcGIS.Core.Data.Analyst3D.LasPointCursor ptCursor = lasDataset.SearchPoints(null))
{
  while (ptCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.LasPoint point = ptCursor.Current)
    {

    }
  }
}

// search within an extent
ArcGIS.Core.Data.Analyst3D.LasPointFilter pointFilter = new ArcGIS.Core.Data.Analyst3D.LasPointFilter();
pointFilter.FilterGeometry = envelope;
using (ArcGIS.Core.Data.Analyst3D.LasPointCursor ptCursor = lasDataset.SearchPoints(pointFilter))
{
  while (ptCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.LasPoint point = ptCursor.Current)
    {

    }
  }
}

// search within an extent and limited to specific classsification codes
pointFilter = new ArcGIS.Core.Data.Analyst3D.LasPointFilter();
pointFilter.FilterGeometry = envelope;
pointFilter.ClassCodes = new List<int> { 4, 5 };
using (ArcGIS.Core.Data.Analyst3D.LasPointCursor ptCursor = lasDataset.SearchPoints(pointFilter))
{
  while (ptCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.LasPoint point = ptCursor.Current)
    {

    }
  }
}
// 

// searching on the LasDatasetLayer will honor any LasPointDisplayFilter

// search all points
using (ArcGIS.Core.Data.Analyst3D.LasPointCursor ptCursor = lasDatasetLayer.SearchPoints(null))
{
  while (ptCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.LasPoint point = ptCursor.Current)
    {

    }
  }
}

// search within an extent
ArcGIS.Core.Data.Analyst3D.LasPointFilter pointFilter = new ArcGIS.Core.Data.Analyst3D.LasPointFilter();
pointFilter.FilterGeometry = envelope;
using (ArcGIS.Core.Data.Analyst3D.LasPointCursor ptCursor = lasDatasetLayer.SearchPoints(pointFilter))
{
  while (ptCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.LasPoint point = ptCursor.Current)
    {

    }
  }
}

// search within an extent and limited to specific classsification codes
pointFilter = new ArcGIS.Core.Data.Analyst3D.LasPointFilter();
pointFilter.FilterGeometry = envelope;
pointFilter.ClassCodes = new List<int> { 4, 5 };
using (ArcGIS.Core.Data.Analyst3D.LasPointCursor ptCursor = lasDatasetLayer.SearchPoints(pointFilter))
{
  while (ptCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.LasPoint point = ptCursor.Current)
    {

    }
  }
}