Problem with lookAt function and X rotation

[Airweb]

Hello,

I use the lookAt function to orient a text layer to a NULL layer position but I want to be able to rotate the text layer on the X axis too.

To look at the NULL layer correctly, I need to set the Y rotation to 270°

I think the problem is here, if I want to rotate on the X axis correctly, the Y rotation must be 0 or 180/-180.

I think that I need an expression to recalculate the Y and Z orientation with the X orientation set to 0.

And maybe an expression to set Y rotation value too.

 [ VIDEO ] 

Thanks in advance for any help!

[Dan Ebberts · Accepted solution]

Would it help to put the lookAt() expression on a 3D null and parent the text layer to that, so you could adjust the text layer's rotation independently?

[Airweb]

Yes Dan, thank you it's exactly what I want to do.

But is there a way to calculate the orientation?

[Dan Ebberts]

Probably, but unless it's trivial (which this may be, I don't know) things can get out of hand pretty quickly when you have to do 3D rotation matrix math...

[Mylenium]

http://www.motionscript.com/design-guide/auto-orient-y-only.html

Can easily be modified to work for a different axis. That and of course there's a ton of other "targeting" expressions out there that could be used as well.

Mylenium

[Airweb]

Thanks Mylenium,

The expression returns an angle

delta = toWorld(anchorPoint) - thisComp.activeCamera.toWorld([0,0,0]);
radiansToDegrees(Math.atan2(delta[0],delta[2]))

but I need to convert the original orientation from [X, Y, Z] to [0, Y, Z]

I tried to add or substract the angle but it doesn't work.

[Airweb]

Finaly, don't need to calculate the new orientation using Dan's trick, then 

just need to unparent or delete the new NULL layer to get the correct orientation.