Change opacity of specific points in Points Cloud data

Question

I am loading some PCD data using the PCDLoader, after loading the PCD data successfully we get the Points to add to the scene. I have a circle on top of the PCD points that I created using the Three.js Line Geometry,

I am trying to reduce the opacity for all the points that lie outside of the Circle.

Here's my code which loads the PCD and draws a circle

this.loader = this.loader || new PCDLoader();
this.loader.load(pcdPath, (mesh: Points) => {

  mesh.name = `pcd-mesh`;
  (mesh.material as PointsMaterial).size = 1.5;
  (mesh.material as PointsMaterial).color.setHex(0xffffff);

  const circlePoints = [];
  const radius = 18;
  for (let i = 0; i <= 360; i++) {
    circlePoints.push(
      new Vector3(
        Math.sin(i * (Math.PI / 180)) * radius,
        Math.cos(i * (Math.PI / 180)) * radius,
        0
      )
    );
  }
  const circleLineGeo = new BufferGeometry().setFromPoints(circlePoints);

  const CircleLineMaterial = new LineBasicMaterial({
    color: 0xffff00,
    linewidth: 1.75,
  });

  const c = new Line(circleLineGeo, CircleLineMaterial);
  this.scene.add(c);

  this.renderView();
});

I know I can change the opacity of all the points using the ;(mesh.material as PointsMaterial).opacity = 0.5

but I don't want to change the opacity for all the points, I just want to change the opacity for all the points that Lie outside this yellow circle.

I've never done it with a Points mesh, but you should be able to set the material's vertexColors to true and add a 'color' attribute to the geometry. Not sure if it handles opacity, you might have to write your own shader for that. — Ethan Hermsey, Jun 08 '21 at 16:56

score 5 · Answer 1 · answered Jun 08 '21 at 18:13

Since r127 four-component vertex colors are supported by three.js. Meaning you can control the alpha value per vertex. Check out the following live example for more details:

let camera, scene, renderer;

init();
render();

function init() {

  camera = new THREE.PerspectiveCamera(70, window.innerWidth / window.innerHeight, 0.01, 10);
  camera.position.z = 4;

  scene = new THREE.Scene();

  const points = [
    new THREE.Vector3(-2, 0, 0),
    new THREE.Vector3(-1, 0, 0),
    new THREE.Vector3(0, 0, 0),
    new THREE.Vector3(1, 0, 0),
    new THREE.Vector3(2, 0, 0)
  ];

  const geometry = new THREE.BufferGeometry().setFromPoints(points);
  const material = new THREE.PointsMaterial({
    vertexColors: true,
    transparent: true
  });
  const pointCloud = new THREE.Points(geometry, material);
  scene.add(pointCloud);

  // add color data

  const colors = [
    1, 0, 0, 0, // r,g,b,a
    1, 0, 0, 0.25,
    1, 0, 0, 0.5,
    1, 0, 0, 0.75,
    1, 0, 0, 1
  ];

  geometry.setAttribute('color', new THREE.Float32BufferAttribute(colors, 4));

  renderer = new THREE.WebGLRenderer({
    antialias: true
  });
  renderer.setSize(window.innerWidth, window.innerHeight);
  document.body.appendChild(renderer.domElement);

}

function render() {

  renderer.render(scene, camera);

}

body {
  margin: 0;
}

<script src="https://cdn.jsdelivr.net/npm/three@0.129.0/build/three.min.js"></script>

Change opacity of specific points in Points Cloud data

1 Answers1

Linked