三个js围绕球体旋转物体答案

【问题标题】：Three js rotation of objects around a sphere三个js围绕球体旋转物体
【发布时间】：2014-01-27 03:16:30
【问题描述】：

我正在使用粒子系统在球体上均匀分布点。这很好用。然后我将给定几何图形的实例放在这些点上。这部分也有效。我现在想旋转这些几何图形以匹配球体的表面角度。

这是目前的功能：

function placeGeometryAtPlatonicPoints (points) {
  var len = points.length -1,
    x, y, z,
    geometry,
    // subgroup a group to apply the rotations to
    subgroup = new THREE.Object3D(),
    mesh,
    material = new THREE.MeshLambertMaterial({
      color: 0x0992299
    }),
    r,
    theta,
    varphi;

  // I wait to append this group because I am waiting for the 
  // particles to settle into there positions
  scene.add(group);

  for (len; len >= 0; len -= 1) {
    // Geometry could be any geometry I am just using a cube to test.
    geometry = new THREE.CubeGeometry( 25, 25, 25, 1, 1, 1 );
    x = points[len].x;
    y = points[len].y;
    z = points[len].z;

    // Move the geometry to the point on the sphere. 
    geometry.applyMatrix( new THREE.Matrix4().makeTranslation(x, y, z) );

    mesh = new THREE.Mesh( geometry, material );
    subgroup.add(mesh);

    // This next portion is just some guess work about 
    // polar and azimuth coordinates
    r = Math.sqrt(Math.pow(x,2) + Math.pow(y,2) + Math.pow(z,2));
    theta = Math.acos(z/r);
    varphi = Math.atan(y/x);

    theta = theta * (180/Math.PI);
    varphi = varphi * (180/Math.PI);

    console.log({
      theta : theta,
      varphi : varphi
    });

    // This would be the implementation of the rotation degrees.
    subgroup.rotation.x = 0;
    subgroup.rotation.y = 0;
    subgroup.rotation.z = 0;

    group.add(subgroup);
  }
}

我是 Three js 的新手，所以如果有更好的方法来完成这一切，请告诉我。这是我的WIP。在渲染几何体之前，您必须稍等片刻才能正确放置粒子。我可以加快速度，但我喜欢动画:)

【问题讨论】：

标签： javascript math three.js geometry

【解决方案1】：

如果您希望旋转立方体以使其与球体相切，则可以将每个立方体想象成一根棍子的末端。

棒是位于原点的Object3D。立方体是位于( 0, 0, r ) 的棍子的子代。现在将摇杆旋转到您想要的位置。（但要避开北极和南极。）

var parent = new THREE.Object3D();
scene.add( parent );

var stick = new THREE.Object3D();
var point = new THREE.Vector3( x, y, z );
stick.lookAt( point );
parent.add( stick );

var geometry = new THREE.CubeGeometry( 25, 25, 25, 1, 1, 1 );
var mesh = new THREE.Mesh( geometry, material );
mesh.position.set( 0, 0, r );
stick.add( mesh );

three.js r.64

【讨论】：