Have you ever needed to find the relative 2D point for a 3D layer? Well there is a simple expression to do just that: .toComp().To see this expression in action, check out this example clip.
To use toComp() in this manner, first, you must alt click on the position stopwatch of the 2D layer to open its expression editor. Pick-whip the 3D layer, then add .toComp([0,0]) to the end. (for example: thisComp.layer("3D Layer").toComp([0,0]); )The 2D layer will match up to the 3D position even if the compositions camera is moved.