public TinTriangleCursor SearchTriangles( 
   TinTriangleFilter filter
)

// search all "inside" nodes
using (ArcGIS.Core.Data.Analyst3D.TinNodeCursor nodeCursor = tinLayer.SearchNodes(null))
{
  while (nodeCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.TinNode node = nodeCursor.Current)
    {

    }
  }
}

// search "inside" nodes with an extent
ArcGIS.Core.Data.Analyst3D.TinNodeFilter nodeFilter = new ArcGIS.Core.Data.Analyst3D.TinNodeFilter();
nodeFilter.FilterEnvelope = envelope;
using (ArcGIS.Core.Data.Analyst3D.TinNodeCursor nodeCursor = tinLayer.SearchNodes(nodeFilter))
{
  while (nodeCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.TinNode node = nodeCursor.Current)
    {

    }
  }
}

// search for super nodes only
var supernodeFilter = new ArcGIS.Core.Data.Analyst3D.TinNodeFilter();
supernodeFilter.FilterEnvelope = tinDataset.GetSuperNodeExtent();
supernodeFilter.DataElementsOnly = false;
supernodeFilter.SuperNode = true;
using (ArcGIS.Core.Data.Analyst3D.TinNodeCursor nodeCursor = tinLayer.SearchNodes(nodeFilter))
{
  while (nodeCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.TinNode node = nodeCursor.Current)
    {

    }
  }
}


// search all edges within an extent
//    this could include outside or edges attached to super nodes depending upon the extent
ArcGIS.Core.Data.Analyst3D.TinEdgeFilter edgeFilterAll = new ArcGIS.Core.Data.Analyst3D.TinEdgeFilter();
edgeFilterAll.FilterEnvelope = envelope;
edgeFilterAll.DataElementsOnly = false;
using (ArcGIS.Core.Data.Analyst3D.TinEdgeCursor edgeCursor = tinLayer.SearchEdges(edgeFilterAll))
{
  while (edgeCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.TinEdge edge = edgeCursor.Current)
    {
    }
  }
}


// search for hard edges in the TIN
var edgeFilter = new ArcGIS.Core.Data.Analyst3D.TinEdgeFilter();
edgeFilter.FilterByEdgeType = true;
edgeFilter.EdgeType = ArcGIS.Core.Data.Analyst3D.TinEdgeType.HardEdge;
using (ArcGIS.Core.Data.Analyst3D.TinEdgeCursor edgeCursor = tinLayer.SearchEdges(edgeFilter))
{
  while (edgeCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.TinEdge edge = edgeCursor.Current)
    {

    }
  }
}


// search for "inside" triangles in an extent
ArcGIS.Core.Data.Analyst3D.TinTriangleFilter triangleFilter = new ArcGIS.Core.Data.Analyst3D.TinTriangleFilter();
triangleFilter.FilterEnvelope = envelope;
triangleFilter.DataElementsOnly = true;
using (ArcGIS.Core.Data.Analyst3D.TinTriangleCursor triangleCursor = tinLayer.SearchTriangles(triangleFilter))
{
  while (triangleCursor.MoveNext())
  {
    using (ArcGIS.Core.Data.Analyst3D.TinTriangle triangle = triangleCursor.Current)
    {
    }
  }
}