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copied!<p>Here are my working assumptions:</p> <ul> <li>The coordinate system (x,y,z) is such that positive x is to the right, positive y is down, and z is the remaining direction. In particular, y=0 is the ground plane.</li> <li>An object at (0,0,0) currently facing towards (0,0,1) is being turned to face towards (x,y,z).</li> <li>In order to accomplish this, there will be a rotation about the x-axis followed by one around the y-axis. Finally, there is a rotation about the z-axis in order to have things upright.</li> </ul> <p>(The terminology yaw, pitch, and roll can be confusing, so I'd like to avoid using it, but roughly speaking the correspondence is x=pitch, y=yaw, z=roll.)</p> <p>Here is my attempt to solve your problem given this setup:</p> <pre><code>rotx = Math.atan2( y, z ) roty = Math.atan2( x * Math.cos(rotx), z ) rotz = Math.atan2( Math.cos(rotx), Math.sin(rotx) * Math.sin(roty) ) </code></pre> <p>Hopefully this is correct up to signs. I think the easiest way to fix the signs is by trial and error. Indeed, you appear to have gotten the signs on <code>rotx</code> and <code>roty</code> correct -- including a subtle issue with regards to z -- so you only need to fix the sign on <code>rotz</code>.</p> <p>I expect this to be nontrivial (possibly depending on which octant you're in), but please try a few possibilities before saying it's wrong. Good luck!</p> <hr> <p>Here is the code that finally worked for me.</p> <p>I noticed a "flip" effect that occurred when the object moved from any front quadrant (positive Z) to any back quadrant. In the front quadrants the <strong>front</strong> of the object would always face the point. In the back quadrants the <strong>back</strong> of the object always faces the point.</p> <p>This code corrects the flip effect so the front of the object <strong>always</strong> faces the point. I encountered it through trial-and-error so I don't really know what's happening!</p> <pre><code> rotx = Math.atan2( y, z ); if (z >= 0) { roty = -Math.atan2( x * Math.cos(rotx), z ); }else{ roty = Math.atan2( x * Math.cos(rotx), -z ); } </code></pre>

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