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I am using the following function to have a globe rotate a point on its surface to face the global Z toward the camera. This works fine, but after each rotation the Y axis seen as a green line is not vertically aligned.

I believe this is how slerp between two unit vectors works, it takes the shortest path.

I would like to know how can I achieve this rotation whilst getting the globe to rotate itself so that Y is at least parallel to the global Y?

        function rotateToHub(continent){
            var speed = 2000;
            var z = new THREE.Vector3(0, 0, 1);

            point = continent.position.clone().normalize();

            var q = new THREE.Quaternion();
            q.setFromUnitVectors(point, z);

            var duration = {t: 0};
            var tween = new TWEEN.Tween(duration)
                .to({t: 1}, speed)
                .onStart(function(){
                    slerp = true;
                })
                .onUpdate(function(){
                    earthContainer.quaternion.slerp(q, this.t);
                })
                .onComplete(function(){
                    slerp = false;
                    update();
                })
                .start();
        }

globe

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  • \$\begingroup\$ Do not cross-post between SE sites. \$\endgroup\$ – Almo Dec 19 '15 at 21:11
  • \$\begingroup\$ I will delete from SO and keep the question here \$\endgroup\$ – Neil Dec 19 '15 at 21:11
  • \$\begingroup\$ Well, I don't know about THREE js but I think you are rotating target vector to Z (0,0,1) that making it like this. Just my guess, what would happen if you try q.setFromUnitVectors(point, new THREE.Vector3(0, point.y, 1)); and sorry in advance if I did any syntax or spelling mistake \$\endgroup\$ – Hamza Hasan Dec 19 '15 at 21:43
  • \$\begingroup\$ @HamzaHasan thanks for the suggestion, unfortunately that moves my point away from centring on the Z and goes further to the Y axis up the globe. \$\endgroup\$ – Neil Dec 19 '15 at 21:53
  • \$\begingroup\$ I think both cases would be applicable at the same time. Either you will get your desired point at exact front and aligned to Z axis, or freeze the Y axis, I don't think both can be true at a time. What you say? \$\endgroup\$ – Hamza Hasan Dec 19 '15 at 21:56

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