问题描述

[求助]这段球面算法无法理解

private function moveTweets():void {

    var newScale:Number=Scale(meshes.length,50,500,6,2);
    trace("new scale:"+newScale);

    var l:Number=this.meshes.length;
    var tweetMeshInstance:TweetMesh;
    var destx:Number;
    var desty:Number;
    var destz:Number;
    for (var i:Number=0;i<this.meshes.length;i++){

        tweetMeshInstance=meshes[i];

        var phi:Number = Math.acos( -1 + ( 2 * i ) / l );
        var theta:Number = Math.sqrt( l * Math.PI ) * phi;

        tweetMeshInstance.origX = (sphereRadius+5) * Math.cos( theta ) * Math.sin( phi );
        tweetMeshInstance.origY= (sphereRadius+5) * Math.sin( theta ) * Math.sin( phi );
        tweetMeshInstance.origZ = (sphereRadius+5) * Math.cos( phi );

        destx=sphereRadius * Math.cos( theta ) * Math.sin( phi );
        desty=sphereRadius * Math.sin( theta ) * Math.sin( phi );
        destz=sphereRadius * Math.cos( phi );

        tweetMeshInstance.lookAt(new Vector3D());

        TweenMax.to(tweetMeshInstance, 1, {scaleX:newScale,scaleY:newScale,x:destx,y:desty,z:destz,onUpdate:onLookAtTween, onUpdateParams:[tweetMeshInstance]});

    }

}
private function onLookAtTween(theMesh:TweetMesh):void {
    theMesh.lookAt(new Vector3D());
}

    其中 var theta:Number = Math.sqrt( l * Math.PI ) * phi; 我怎么算都推导不出来,请各位算法高手帮忙解释下