Question

我在场景中有一个给定的矢量V.矢量由世界坐标（VWx，VWy，VWz）定义。请注意，它是方向向量而非位置向量。

在场景中我还有一个随机方向（和位置）的Object3D。

我希望找到方向向量V的局部（即相对于Object3D）坐标（VLx，VLy，VLz）。

我尝试了以下代码（从this question中的WestLangley的回答中推断出来），但它似乎没有给出正确的结果。

var VW = new THREE.Vector3(10,20,30); 
var VL = new THREE.Vector3(0,0,0); 

givenObject.updateMatrixWorld();

var ob_WorldQuaternion = new THREE.Quaternion(); 
ob_WorldQuaternion  = givenObject.getWorldQuaternion();

var ob_InvWorldQuaternion = new THREE.Quaternion(); 
ob_InvWorldQuaternion = ob_WorldQuaternion.inverse();

VL = VW.applyQuaternion( ob_InvWorldQuaternion);

编辑（1）请注意，THREE.js Object3D方法.worldToLocal（矢量）不适用，因为它仅用于转换位置矢量，而不是方向矢量。

EIDT（2）This jsfiddle说明了一个示例应用程序。绿色圆锥是绿色框的孩子。该应用程序试图保持绿色圆锥指向与白色世界锥相同的世界方向。

Answer 1

（我之前回答的改进版本）。

This jsfiddle说明了3种对齐儿童视锥的方法。

红色圆锥相对于其父框具有固定的方向。

绿锥对齐，以便它的＆＃39; z轴与白色世界锥对齐。

蓝锥有它的＆＃39; XYZ轴与白色世界锥的XYZ轴共同对齐。

CODE（来自init函数）： -

cone_geometry = new THREE.CylinderGeometry(3, 40, 120, 40, 10, false);

//... The following mod is as recommended by WestLangley's answer at:-
//... http://stackoverflow.com/questions/13757483/three-js-lookat-seems-to-be-flipped
//... cone.LookAt(PosX) will then point the cone Z-axis towards PosX
//... (assuming cone.position and PosX are relative to the same coordinate system).

cone_geometry.applyMatrix( new THREE.Matrix4().makeRotationX( Math.PI / 2 ) );

核心代码（来自更新/动画功能）： -

    worldCone.lookAt(target.position); 

    var worldVec =  new THREE.Vector3();
    worldVec.copy(target.position).sub(worldCone.position);

    worldBox.rotation.x += 0.01;
    worldBox.rotation.y += 0.03;
    worldBox.rotation.z += 0.02;

    var localVec =  new THREE.Vector3();
    localVec = F_get_LocalDirectionVector_relativeTo_Object3D_of_WorldDirectionVector 
( worldBox, worldVec, localVec) ;

    //=================================================================
    function F_get_LocalDirectionVector_relativeTo_Object3D_of_WorldDirectionVector 
( givenObject, WDV, LDV)
          {
              givenObject.updateMatrixWorld(); 

             //FLABBY method: - works but verbose and excessive object creation
             /*
              var ob_InvWorldQuaternion = new THREE.Quaternion(); 
              ob_InvWorldQuaternion = ob_WorldQuaternion.inverse(); 
              LDV.copy( WDV ).applyQuaternion( ob_InvWorldQuaternion );        
              */

              //LEAN method: copies WDV value into LDV 
              //then applies inverse world quaternion of givenObject.

              LDV.copy( WDV )
              .applyQuaternion( 
              givenObject.getWorldQuaternion().inverse() 
              );  

              return LDV;
      } 
      //=================================================================

//... Apply localVec 
//... Get the localCone_G to point in the direction of the LocalVec

 var localCone_G_target_pos = new THREE.Vector3();

 //... LHS becomes sum of two RHS vectors
 localCone_G_target_pos.addVectors( localCone_G.position, localVec );

//... ORIENT THE CHILD CONES

//...Cone_R has fixed orientation relative to parent cube
localCone_R.lookAt(1,0,0); 

//... Cone_G has z-vector pointing in the same direction as world cone
localCone_G.lookAt(localCone_G_target_pos); 

//... Cone_B has its' xyz axes aligned with the world cone
localCone_B.lookAt(1,0,0);
localCone_B.quaternion.multiply( worldBox.getWorldQuaternion().inverse()  ); 
localCone_B.quaternion.multiply( worldCone.quaternion );

Three.js获取具有给定世界方向坐标的场景矢量的对象相对局部方向

1 个答案: