2D position coordinates of a 3D layer

[Steve Roberts]

I think it’s like this: it’s like tying a lens flare’s position to an object’s 3D position. The lens flare has to be in 2D, but its X and Y values wouldn’t numerically match those of the 3D object.

Maybe this would help. It allows you to make a lens flare follow a 3D light, but hey, position is position.

[Mike Park]

If I understand you correctly, you want a 2d layer to appear to be either on top or below the 3d layer, but not have it in 3d space. Basically, mirror the x,y movement of the 3d layer with no z translation. It is really not that easy. The problem is perspective. You cannot simply take the x,y position of the 3d layer as the change in z value will change the perception of x,y position of the center of the 3d layer on a flat plane. You could do some unit vector calculations, but that would only move the 2d layer on the same vector from the viewing point to the 3d layer, not match the screen coordinates of the 3d layer. To do what you want will require a calculation of the change in xyz space of the 3d layer and build in an offset in 2d space of the 2d layer for the change in z space of the 3d layer. Basically, you must compensate for the change in perspective of the 3d layer.

Somewhat easy to conceptualize, a little more difficult to pull off. However, if anyone can, it will be the prior poster, the expression master, Mr. LaRonde.

Wish I could be more help. Sorry if I made your head hurt. Actually, I am sorry I made my head hurt.

Best of luck

PS, you may be better off precomposing the 3d layer and motion tracking to a null, then parenting your 2d layer.

[Jan Sherlink]

paste this in you 2D layers position:

this_comp.layer(“your3Dlayername”).to_comp([0,0])

cya,

Jan

[Darby Edelen]

[mike park] “Basically, you must compensate for the change in perspective of the 3d layer.”

There are Layer Space Transform methods in AE that allow you to do this very easily using expressions:


l = thisComp.layer("My3DLayer");
l.toComp(l.anchorPoint);


If you apply the above to the 2D layer’s position property then its anchor point will follow the 3D layer’s anchor point exactly in 2D.

Darby Edelen

[Christian Tanner]

hope this is compliant with the forums curse policy – but HOLY CRAP – thanx for all the help guys. i’m overwhelmed.

the expression was exactly what i was looking for. that piece of code was simply too sophisticated for my level of education on expressions…

i wasn’t kidding – i’m seriously overwhelmed…

tanner

[Jan Sherlink]

Glad to help,

if you’re interested in learning expressions;
jjgifford.com is a good place to start.

have fun !

cya,

Jan

[Christian Tanner]

thanx for the tip.
tanner

[Tim Parsons]

Zombie thread! What if the object isn’t what’s moving, but the camera is?what if I have a 3D object just sitting there, and the camera is the thing moving around, and I want a 2D position (like a lens flare or something) to follow it??

[Tim Parsons]

This post is just to set the email notifications…. OK, set.

[Jan Sherlink]

That would result in the same,
paste this_comp.layer(“your3Dlayername”).to_comp([0,0]) in the 2D position of your lens-flare.

cya,

Jan