Coordinates and planes - OpenGeometry

Every point and vector is an [x, y, z] array.
Model units are metres.
Y is up, as in Three.js.
Angles of primitives are in radians. Angles of transforms are in degrees.

The plane of a primitive

Each primitive is made on a plane. The plane option sets it:

Field	Default	Meaning
`origin`	`[0, 0, 0]`	Where the primitive’s centre or start goes
`normal`	`[0, 1, 0]`	The plane’s normal; an extrude goes this way
`xDirection`	`[1, 0, 0]`	The plane’s u axis

By default this is the ground plane through the origin. plane applies to primitives only, not to operations.

Where a profile point lands

A profile, a polyline in a profile, and the angles of an arc are given in the plane’s own [u, v] axes. The u axis is xDirection. The v axis is normal × xDirection. On the default ground plane, v runs along −Z. A point [u, v] lands at world (u, 0, −v). If you miss the sign, a D-shape comes out the wrong way round. With plane: { normal: [0, 0, 1], xDirection: [1, 0, 0] }, an upright plane facing +Z, a point [u, v] lands at (u, v, 0).

import { OpenGeometry, Wire, OG_PRIMITIVE_PROFILE } from 'opengeometry';

await OpenGeometry.create(
  { wasmURL: '/opengeometry_bg.wasm' },
  { workerURL: '/tessellation-worker.js' },
);

const upright = {
  normal: [0, 0, 1] as [number, number, number],
  xDirection: [1, 0, 0] as [number, number, number],
};
const triangle = new Wire(
  OG_PRIMITIVE_PROFILE,
  { start: [0, 0], segments: [{ to: [1, 0] }, { to: [0, 1] }, { to: [0, 0] }], closed: true },
  { plane: upright },
);
console.log(triangle.getBounds());

The bounds are about [0, 0, 0, 1, 1, 0]: the triangle stands in the XY plane.

Positive angles

A positive angle turns counter-clockwise, seen from the side that the plane normal points to. On the default ground plane that is seen from above, from +X towards −Z.

Placement

Each node has a placement: { origin, xDirection, normal, scale }. getPlacement() reads it relative to the parent. getWorldPlacement() reads it in the world. Change it with transform. See Transforms and assemblies. A body’s own coordinates are those of getBrep(), before its placement. classifyPoint, faceNormalAt, measure and mirror use them.

Tolerances

The geometric tolerance is 1e-8 m. The 2D region calls use OG_REGION_TOLERANCE, 1e-6 m. Sizes must be above four times the geometric tolerance.

​The plane of a primitive

​Where a profile point lands

​Positive angles

​Placement

​Tolerances

The plane of a primitive

Where a profile point lands

Positive angles

Placement

Tolerances