Modules | TS

Intersect

Compute intersection curves between meshes and scalar field isocontours.

The Intersect module computes intersection curves between geometric objects and extracts isocontour curves from scalar fields.

Intersection Curves

Compute intersection curves between two 3D meshes:

import * as tf from "@polydera/trueform";

const mesh1 = tf.readStl("mesh1.stl");
const mesh2 = tf.readStl("mesh2.stl");

// Compute intersection curves
const curves = tf.intersectionCurves(mesh1, mesh2);

console.log(`Number of curves: ${curves.length}`);
console.log(`Total curve points: ${curves.points.length}`);

// Access individual curve paths
for (let i = 0; i < curves.length; i++) {
  const pathIds = curves.paths.at(i);
  console.log(`Curve ${i}: ${pathIds.length} points`);
}

The function returns a Curves object with:

paths — OffsetBlockedBuffer where each element contains indices into points, representing one curve
points — NDArrayFloat32 of shape [N, 3] containing all curve vertices
length — number of curves

Requirements:

Both meshes must be 3D
Works with both triangle meshes and polygon meshes

Self-Intersection Curves

Find curves where a mesh intersects itself.

To embed self-intersection curves into mesh topology, use tf.embeddedSelfIntersectionCurves from the Cut module.

import * as tf from "@polydera/trueform";

const mesh = tf.readStl("mesh.stl");

// Find self-intersection curves
const curves = tf.selfIntersectionCurves(mesh);

console.log(`Found ${curves.length} self-intersection curve(s)`);

Isocontours

Extract isocontour curves from scalar fields on meshes.

To cut meshes into regions using isocontours, use tf.isobands from the Cut module.

import * as tf from "@polydera/trueform";

const mesh = tf.readStl("terrain.stl");

// Create scalar field (one value per vertex)
const plane = tf.plane([0, 0, 1], 0.0);
const scalars = tf.distance(tf.point(mesh.points), plane);

// Extract isocontours at a single threshold
const curves = tf.isocontours(mesh, scalars, 0.0);

console.log(`Number of contours: ${curves.length}`);

Multiple Thresholds

Extract isocontours at several threshold values in a single call:

// Extract contours at multiple thresholds
const thresholds = new Float32Array([0.0, 0.5, 1.0]);
const curves = tf.isocontours(mesh, scalars, thresholds);

for (let i = 0; i < curves.length; i++) {
  const pathIds = curves.paths.at(i);
  console.log(`Contour ${i}: ${pathIds.length} points`);
}

Parameter	Type	Description
`mesh`	`Mesh`	Mesh to extract isocontours from
`scalars`	`NDArrayFloat32`	Scalar field with one value per vertex
`threshold`	`number \| Float32Array`	Single threshold value or array of thresholds

Use cases:

Extracting elevation contours from terrain data
Visualizing level sets of physical quantities (temperature, pressure, etc.)
Creating contour lines from implicit functions
Analyzing stress distributions in FEA results

Async

All intersect functions are available as async variants via tf.async for off-main-thread execution:

const curves = await tf.async.intersectionCurves(mesh1, mesh2);
const self   = await tf.async.selfIntersectionCurves(mesh);
const iso    = await tf.async.isocontours(mesh, scalars, 0.0);

For implementation details and low-level intersection access, see the C++ Intersect documentation.

Remesh

Decimation and isotropic remeshing.

Cut

Mesh booleans and scalar field cutting operations.