TETRIUM

Model Regions:

 

A model is built from three nested volumes. The Core of Interest (COI) contains the target and carries the finest mesh, the Inner Padding (ROI) surrounds it, and the Outer Padding (POI) carries the mesh out to the model boundary. An Air region can be added above the topography for methods that require it, and a Sub-COI can be nested inside the core when a second level of detail is needed.

 

Each region is defined either as a rectilinear box from its coordinate ranges, or as an irregular shape read from an outline file, and each has its own tetrahedron edge size. The transitions between regions are controlled rather than abrupt: at every boundary you set a minimum and maximum cell size, a refinement radius and a transition factor, so cells grow from fine to coarse at a rate you choose instead of changing suddenly.

 

Topography:

 

Topography can be a constant elevation for a flat model, or a real surface read from a file. When a surface is supplied, TETRIUM interpolates it onto the mesh, sews it to the sides of each region, and splits the model into the volumes above and below it. Dense topography can be decimated on the way in by specifying a minimum separation distance, so a high-resolution surface does not force a mesh larger than the inversion can handle.

 

Mesh Refinement:

 

Refinement is set separately on the topography surface and inside the volume, and in both places it can be driven directly from the survey. Point TETRIUM at a node file of station locations and it refines the mesh around each observation point. Supply survey lines, loops or traverses and it refines along their length, treating them as discrete segments, continuous segments or closed loops as appropriate. Spherical refinement regions can also be placed around points anywhere inside the COI, ROI or Air volumes.

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Mesh Generation:

 

Two meshing methods are available. The standard method intersects surfaces where nodes and lines already exist, and is considerably faster on large meshes. The Boolean method lets Gmsh compute the intersections itself and generate nodes and lines where surfaces meet, which handles geometry the standard method cannot, and allows extra geometries to be imported into the model.

 

Because the Boolean workflow requires a decision partway through, TETRIUM includes a Boolean Assistant: a five-step guided panel covering the generation of the initial geometry, the discovery of volume identifiers, the removal of unwanted volumes, verification of the result, and the final mesh.

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Gmsh Controls:

 

The meshing options that would otherwise require editing a geometry file by hand are exposed directly in the interface. Nine 2D surface meshing algorithms and six 3D volume meshing algorithms are available, along with the mesh optimization level, the optimization threshold and the number of smoothing steps.

 

Interactive Tools:

 

The Region Outline viewer displays mesh files in two dimensions and allows outline points to be picked directly from the plot rather than entered as coordinates. A live execution log reports every command as it runs and shows the current stage of the pipeline. Complete configurations can be saved to and loaded from settings files, making a mesh reproducible and giving the next survey a starting point.

 

Output:

 

TETRIUM writes Gmsh `.msh` files and the TetGen format `.node` and `.ele` files that describe the mesh itself. Depending on the output option chosen, it will also produce cell neighbour information, boundary face and edge files with a boundary marker value of your choosing, and the connectivity files that map between tetrahedra, faces and edges. VTU files are written throughout for viewing in VISIUM (or ParaView). Intermediate files are removed at the end of a run by default, or kept if you want to inspect the stages or use Post-Run afterwards.

 

Requirements:

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Gmsh is used for the meshing itself but is not bundled with TETRIUM, for licensing reasons. The Gmsh SDK is available free from gmsh.info; once downloaded, the path to it is set once in the interface.

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