Meshing¶

After geometry is synchronized, generate a mesh up to a target dimension.

gmsh.model.mesh.generate(3); // 1D -> 2D -> 3D

generate(dim) runs all lower dimensions first, so generate(3) also produces the 1D and 2D meshes.

Reading the mesh¶

Nodes¶

const { nodeTags, coord } = gmsh.model.mesh.getNodes();
// nodeTags: number[]      — N node ids
// coord:    number[]      — 3N values, [x0,y0,z0, x1,y1,z1, ...]
for (let i = 0; i < nodeTags.length; i++) {
  const [x, y, z] = coord.slice(i * 3, i * 3 + 3);
}

Elements¶

const { elementTypes, elementTags, nodeTags } = gmsh.model.mesh.getElements();
// elementTypes: number[]    — one entry per element type present
// elementTags:  number[][]  — element ids, grouped by type
// nodeTags:     number[][]  — connectivity, grouped by type (flattened per element)

Common element type ids: 1 = 2-node line, 2 = 3-node triangle, 3 = 4-node quad, 4 = 4-node tetrahedron, 5 = 8-node hexahedron.

const triIdx = elementTypes.indexOf(2);
const numTriangles = triIdx >= 0 ? elementTags[triIdx].length : 0;

Algorithms and options¶

Set options before generate() with gmsh.option.setNumber.

Option	Meaning	Notable values
`Mesh.Algorithm`	2D algorithm	`1` MeshAdapt, `5` Delaunay, `6` Frontal-Delaunay (default), `8` Frontal-Quad
`Mesh.Algorithm3D`	3D algorithm	`1` Delaunay (default), `4` Frontal, `10` HXT
`Mesh.MeshSizeMin` / `Mesh.MeshSizeMax`	global size bounds
`Mesh.MeshSizeFactor`	scale all sizes
`Mesh.Optimize`	optimise tets	`0`/`1`
`Mesh.ElementOrder`	element order	`1` linear, `2` quadratic, ...
`General.Verbosity`	log level	`0` silent … `5` debug

gmsh.option.setNumber('Mesh.MeshSizeMax', 0.1);
gmsh.option.setNumber('Mesh.Algorithm3D', 4);
gmsh.model.mesh.generate(3);

Known issue — 3D Delaunay on re-imported CAD

In the WASM build, the default 3D Delaunay boundary recovery can fail (zero tetrahedra) when meshing geometry round-tripped through STEP/IGES import. Native occ/geo solids are unaffected. Workaround — use the Frontal algorithm:

gmsh.option.setNumber('Mesh.Algorithm3D', 4); // Frontal
gmsh.model.mesh.generate(3);

See Troubleshooting.

Higher-order and optimisation¶

gmsh.option.setNumber('Mesh.ElementOrder', 2);     // quadratic elements
gmsh.model.mesh.generate(3);
gmsh.model.mesh.optimize('Netgen');                // optimise

Size fields¶

For non-uniform sizing, use the field submodule:

const f = gmsh.model.mesh.field.add('Distance');
gmsh.model.mesh.field.setNumbers(f, 'PointsList', [p1, p2]);

const t = gmsh.model.mesh.field.add('Threshold');
gmsh.model.mesh.field.setNumber(t, 'InField', f);
gmsh.model.mesh.field.setNumber(t, 'SizeMin', 0.01);
gmsh.model.mesh.field.setNumber(t, 'SizeMax', 0.2);
gmsh.model.mesh.field.setNumber(t, 'DistMin', 0.1);
gmsh.model.mesh.field.setNumber(t, 'DistMax', 0.5);

gmsh.model.mesh.field.setAsBackgroundMesh(t);
gmsh.model.mesh.generate(2);

Threads¶

This build is OpenMP-enabled (pthreads). Gmsh still defaults to 1 thread; opt in per session:

gmsh.option.setNumber('General.NumThreads', 0); // 0 = all cores, or an explicit count

Per-stage limits are available via Mesh.MaxNumThreads1D, Mesh.MaxNumThreads2D and Mesh.MaxNumThreads3D. The OMP_NUM_THREADS environment variable does not exist in the browser (and is not read by the WASM module) — use the options.

In the browser, threads require a cross-origin-isolated page (COOP/COEP headers) — see Browser usage. Avoid setting the thread count above navigator.hardwareConcurrency: the pthread worker pool is sized to the core count, and oversubscribing it can deadlock the main thread.

The OpenMP-parallel 3D mesher is HXT (Mesh.Algorithm3D = 10). For CAD re-imported through STEP/IGES, Frontal (4) remains the recommended algorithm in this build (see Known issues); HXT under WASM threads should be considered experimental.