Points of intertersection for circumfernce measurement on human body and use of convex hull

Hello, I’m new to Three.js, and I am using React Three Fiber for my project. My main task is to implement a plane intersection with a mesh algorithm and compute the convex hull of the intersection points for circumference measurement on the human body. I am working on it but got stuck. Can you help me figure out what I am doing wrong? I want to only get points that intersect the plane in a convex shape.

const setPointOfIntersection=(line, plane, pointsOfIntersection)=> {
        const pointOfIntersection = plane?.intersectLine(line, new Vector3());
        if (pointOfIntersection) {

  function calculateIntersections(plane, mesh) {
        var a = new Vector3(),
            b = new Vector3(),
            c = new Vector3();
        var planePointA = new Vector3(),
            planePointB = new Vector3(),
            planePointC = new Vector3();
        var lineAB = new Line3(),
            lineBC = new Line3(),
            lineCA = new Line3();

        // var pointOfIntersection = new Vector3();

        var mathPlane = new Plane();

        const positionAttribute = plane.geometry.getAttribute('position');

        const localVertex = new Vector3();

        localVertex.fromBufferAttribute(positionAttribute, 0);
        localVertex.fromBufferAttribute(positionAttribute, 1);
        localVertex.fromBufferAttribute(positionAttribute, 2);
        mathPlane.setFromCoplanarPoints(planePointA, planePointB, planePointC);

        var pointsOfIntersection = [];

        const dodecaPositionAttribute = mesh.geometry.getAttribute('position');
        for (let vertexIndex = 0; vertexIndex < dodecaPositionAttribute.count; vertexIndex += 3) {

            localVertex.fromBufferAttribute(dodecaPositionAttribute, vertexIndex);
            localVertex.fromBufferAttribute(dodecaPositionAttribute, vertexIndex + 1);
            localVertex.fromBufferAttribute(dodecaPositionAttribute, vertexIndex) + 2

            lineAB = new Line3(a, b);
            lineBC = new Line3(b, c);
            lineCA = new Line3(c, a);

            setPointOfIntersection(lineAB, mathPlane, pointsOfIntersection);
            setPointOfIntersection(lineBC, mathPlane, pointsOfIntersection);
            setPointOfIntersection(lineCA, mathPlane, pointsOfIntersection);
        return pointsOfIntersection;
        // return positions;
      //   pointsOfIntersection.setAttribute(
      //     'position',
      //     new BufferAttribute(new Float32Array(positions), 3));

      // var pointsMaterial = new PointsMaterial({
      //     size: 0.01,
      //     color: "red"
      // });

      // var points = new Points(pointsOfIntersection, pointsMaterial);
      // mesh.add(points);


  const addPlaneToMesh = () => {
    if (!obj) return;

    const mesh = obj.children[0];

    if (mesh.isMesh) {
        //const randomIndex = 1327
        const plane = new Mesh(new PlaneGeometry(1, 1), new MeshBasicMaterial({ color: "lightgray", transparent: true, opacity: 0.425, side: DoubleSide }));
        plane.rotateX(-Math.PI / 2);

        const intersectionPoints = calculateIntersections(plane, mesh);
        // console.log("intersectionPoints",intersectionPoints);
        const convexHullPoints = computeConvexHull(intersectionPoints);

        const pointsGeometry = new BufferGeometry().setFromPoints(intersectionPoints);
        let pointsMaterial = new PointsMaterial({
          size: .1,
          color: "red"
        let points = new Points(pointsGeometry, pointsMaterial);

function computeConvexHull(points) {
  const geometry = new ConvexGeometry(points);
  const positions = geometry.attributes.position.array;
  const vertices = [];

    for (let i = 0; i < geometry.attributes.position.count; i += 3) {
        vertices.push(new Vector3(positions[i], positions[i + 1], positions[i + 2]));

  return vertices;

@Mugen87 @prisoner849 Can you help me with my problem? That would be appreciated.

I didn’t get this phrase. A convex hull of a set of coplanar points is a flat figure :thinking:

@prisoner849 Thanks for your answer. The code is copied from one of the answers on Three.js, and I don’t know much about setcoplaner . Can you guide me? I just want to get all points that intersect with the plane. That is currently my objective. I am using the positions attribute for that. Let me share an image of what these will be used for. I want to calculate the distance between these points for circumference measurement.

You can start with this: Three-mesh-bvh: A plugin for fast geometry raycasting and spatial queries! - #18 by gkjohnson
@gkjohnson’s solution is way faster than the original mine.

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