Three.js Get Camera lookAt Vector

Question

I'm looking to translate the camera along its lookAt vector. Once I have this vector, I can do scalar translation along it, use that point to move the camera position in global coordinates and re-render. The trick is getting the arbitrary lookAt vector? I've looked at several other questions and solutions but they don't seem to work for me.

See http://stackoverflow.com/questions/15696963/three-js-set-and-read-camera-look-vector/. Also, is `camera.translateZ( -1 )` what you mean? — WestLangley, May 13 '14 at 23:52

Kevin Kuyl · Accepted Answer · 2014-07-20T19:36:28.407

11

You can't get the lookAtVector from the camera itself, you can however create a new vector and apply the camera rotation to that.

var lookAtVector = new THREE.Vector3(0,0, -1);
lookAtVector.applyQuaternion(camera.quaternion);

edited Jul 20 '14 at 19:36

answered Jul 20 '14 at 15:39

Kevin Kuyl

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This answer is not correct. See http://stackoverflow.com/questions/15696963/three-js-set-and-read-camera-look-vector/15697227#15697227 – WestLangley Jul 20 '14 at 17:49
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so what exactly is the difference? :) – Kevin Kuyl Jul 20 '14 at 19:31
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The difference was the negative lookup vector, the answer has been edited. – Sjeiti Oct 09 '18 at 18:22

score 1 · Answer 2 · answered Oct 16 '15 at 19:38

The first choice should be cam.translateZ();

There is a second option as well. You can extract the lookAt vector from the matrix property of the camera object. You just need to take the elements corresponding to the local z-axis.

var lookAtVector = new THREE.Vector3(cam.matrix[8], cam.matrix[9], cam.matrix[10]);

Three.js Get Camera lookAt Vector

2 Answers2