Building geometry¶

Choose a kernel (geo or occ), construct entities, then synchronize().

Built-in `geo` kernel¶

The geo kernel builds a boundary representation bottom-up.

gmsh.model.add('lshape');

const lc = 0.05;
const pts = [
  [0, 0], [2, 0], [2, 1], [1, 1], [1, 2], [0, 2],
].map(([x, y]) => gmsh.model.geo.addPoint(x, y, 0, lc));

const lines = pts.map((_, i) =>
  gmsh.model.geo.addLine(pts[i], pts[(i + 1) % pts.length]));

const loop = gmsh.model.geo.addCurveLoop(lines);
const surf = gmsh.model.geo.addPlaneSurface([loop]);

gmsh.model.geo.synchronize();

Common geo constructors (see the reference):

Method	Purpose
`addPoint(x, y, z, meshSize?, tag?)`	a geometric point; `meshSize` sets local element size
`addLine(start, end, tag?)`	a straight segment between two points
`addCircleArc(start, center, end, tag?)`	a circular arc
`addCurveLoop(curveTags[], tag?, reorient?)`	a closed loop of curves
`addPlaneSurface(wireTags[], tag?)`	a plane surface bounded by loops (first = outer, rest = holes)
`addSurfaceLoop(surfaceTags[], tag?)`	a shell
`addVolume(shellTags[], tag?)`	a volume bounded by shells
`extrude(dimTags[], dx, dy, dz, ...)`	extrude entities

Holes¶

The first curve loop of a plane surface is the outer boundary; subsequent loops are holes:

const outer = gmsh.model.geo.addCurveLoop(outerLines);
const hole = gmsh.model.geo.addCurveLoop(holeLines);
gmsh.model.geo.addPlaneSurface([outer, hole]);

OpenCASCADE `occ` kernel¶

The occ kernel offers CAD primitives and boolean operations.

gmsh.model.add('part');

const box = gmsh.model.occ.addBox(0, 0, 0, 1, 1, 1);
const cyl = gmsh.model.occ.addCylinder(0.5, 0.5, -0.1, 0, 0, 1.2, 0.2);

// subtract the cylinder from the box
gmsh.model.occ.cut([[3, box]], [[3, cyl]]);

gmsh.model.occ.synchronize();
gmsh.model.mesh.generate(3);

Selected occ operations (see the reference):

Method	Purpose
`addBox / addCylinder / addSphere / addCone / addTorus`	primitives
`addWedge / addRectangle / addDisk`	more primitives
`fuse(objects, tools)`	boolean union
`cut(objects, tools)`	boolean difference
`intersect(objects, tools)`	boolean intersection
`fragment(objects, tools)`	general fragmentation (shared interfaces)
`fillet / chamfer`	edge blends
`importShapes(fileName)`	import STEP / IGES / BREP — see File I/O

Boolean operations take and return flat (dim, tag) arrays:

const out = gmsh.model.occ.fuse([[3, a]], [[3, b]]);
// out.outDimTags: [3, newTag, ...]

Physical groups¶

Tag entities for export / boundary conditions:

const g = gmsh.model.addPhysicalGroup(2, [surf], -1, 'plate');
gmsh.model.setPhysicalName(2, g, 'plate');

Mesh size control¶

Per-point size via the meshSize argument of addPoint.
Global bounds: gmsh.option.setNumber('Mesh.MeshSizeMin', 0.01) / 'Mesh.MeshSizeMax'.
Size fields (gmsh.model.mesh.field.*) for distance-based and threshold sizing. See Meshing.