Connect the nodes into a Delaunay tetrahedral or triangle grid. The Delaunay criterion requires that the circumsphere (circumcircle) defined by each tetrahedron (triangle) contains no mesh nodes in its interior. If the target simulator is one that uses two-point flux approximation and Voronoi control volumes (FEHM, PFLOTRAN, TOUGH2), use connect to create the mesh, then dump/stor to compute and output geometric coefficients file.

Click here for a description of Delaunay

Click here for more details on the connect algorithm


connect/[ delaunay/ ifirst,ilast,istride / big_tet_coordinates ]

connect / noadd

connect / check_interface


delaunay is the default algorithm and requires that a “big tet” be constructed that contains all nodes in its interior. For mesh points with multi-materials (imt with multi-values), connect will detect material interfaces and will look for edges that intersect the interfaces.  connect will add points at these intersections to create a conforming mesh, note that mesh quality may be impacted.  

ifirst,ilast,istride The user has the option of selecting a subset of nodes to connect.

big_tet_coordinates The user has the option of providing the coordinates of this “big tet”.

noadd This option will turn off material interface detection.

check_interface option does a more exhaustive job of making sure there are no edges of the mesh that cross a material boundary.


For 2D and connecting points on a planar surface, the mesh must have ndimensions_topo=2 and ndimensions_geom=2. This command will create a mesh object with settings appropriate for the connect command.

cmo/create/ cmotri / triplane

The connect command does not filter out coincident vertices (sqrt[(xi-xj)2 + (yi-yj)2 + (zi-zj)2] < epsilon). Use the following commands before connect to remove duplicate points.

filter/ 1,0,0

For better precision where large coordinate numbers are being used, translate the points close to zero before using connect. The following will move points, connect, then translate back to original position.

trans 1,0,0 /XBIG,YBIG,ZBIG/ 0. 0. 0./
trans 1,0,0 / 0. 0. 0./ XBIG,YBIG,ZBIG

The connect algorithm creates a triangulation or tetrahedralization of the convex hull. If the domain to be meshed is not convex, there is no guarantee that all of its faces and edges will be within the specified mesh boundary. Connections will be formed across non-convex boundaries.

A convex geometry is not guaranteed. A point distribution over a large region where spacing varies from very small to very large can result in high aspect ratios with small concavities formed on mesh boundaries. You can mitigate the impact by adjusting the mesh resolution. Generally high aspect ratio tets (long dimension along the external boundary) are more of a problem. This means that mesh refinement that brings the mesh closer to unit aspect ratio will help.

The connect command may refuse to add nodes that will result in near zero-volume tetahedra. The volume tests are based on the mesh object epsilons. To ensure that these epsilons are based on the geometry, issue a setsize command before setpts. Expert users may adjust the epsilons with the cmo/setatt command. 

The connect command will report if it is successful, check to see if there are any problems. For instance, connect may finish but may not be able to include all points due to a non-convex boundary or a poor point distribution. For instance:

 Dudding      7181 points that have no associated tetrahedra.

 The mesh is complete but could not include all points.                         
 Number of points that could not be connected:       7181                       
LaGriT FINISH: connect        



These two commands are the same, they create the Delaunay tetrahedral connectivity of all nodes in the mesh. Add nodes to break multi-material connections.

cmo / create / mo_tri / / / triplane
createpts / xyz / 4 4 1 / 0. 0. 0. / 1. 1. 0. / 1 1 1
cmo / setatt / mo_tri / imt / 1 0 0 / 1
cmo / setatt / mo_tri / itetclr / 1 0 0 / 1
resetpts / itp

Create a triplane mesh object (ndimensions_topo=2 and ndimensions_geom=2) with 4 x 4 points on plane with Z = 0. Connect into triangles and set node and element materials to 1. The resetpts/itp command will define the boundary nodes for this mesh.


connect/1,0,0/ 0.,0.,0./1000.,0.,0./500.,1000.,0./500.,500.,10./noadd

connect/delaunay/1,0,0/ 0.,0.,0./1000.,0.,0./500.,1000.,0./500.,500.,10./noadd


Create the Delaunay tetrahedral connectivity of all nodes in the mesh and specify explicitly the coordinates of the enclosing tetrahedron.

connect /pset, get, mypoints

Create the Delaunay tetrahedral connectivity of a subset of nodes with the name mypoints.


Create the Delaunay tetrahedral connectivity of  all nodes in the mesh and disregard material interfaces.

# create a 2D triangle mesh
cmo / create / mo_tri / / / triplane

# Make some points at the four corners
createpts / xyz / 5 5 1 / 0. 0. 0. / 1. 1. 0. / 1 1 1

# Add some random points and delete duplicate points
createpts / random / xyz / 0.4 / 0.1 0.1 0. / 0.9 0.9 0.
filter / 1 0 0
rmpoint / compress

# set some defaults for the connect routine
cmo / setatt / mo_tri / imt / 1 0 0 / 1
cmo / setatt / mo_tri / itp / 1 0 0 / 0


# set default materials and boundary tags
cmo / setatt / mo_tri / itetclr / 1 0 0 / 1
resetpts / itp

Create a simple 2D triangle mesh. Set defaults for material and boundary tags for nice behavior. This starts with points at the corner of a box and fills with random points. The connect command will create the triangulation and the result is a single material mesh with inside/outside boundary points tagged with the itp attribute.


Create the Delaunay tetrahedral connectivity of  all nodes in the mesh with added checking of edges that have both nodes tagged as itp=’intrface’ to be sure that the edge does not cross a material interface. This option is more expensive but may fix situations where multi-material edges do not get refined because they connect an ‘intrface’ node to an ‘intrface’ node.

Click here for 2D demos

Click here for 3D demos

The connect command replaces the LaGriT V1 command search/delaunay.