So, just imagine that you’ve got an object parented to a NULL and the object is also moving. If you show the position properties you’ll notice that its perimeters are relative to the NULL.
Here is where a problem occurs …
Suppose you want to have a particle emitter’s position at that parented object. You wont be able to quick whip the two position parameters and get the right results. Here is how you go about finding the the objects position on the stage to connect the particle emitter’s X/Y to the object.
myVar = thisComp.layer(quick whip position parameter);
Here is an example of it being used on an image of a wheel that was parented to a NULL object. This code was placed in the Position XY of Trapcode Particular.
fw = thisComp.layer("front wheel");
If you don’t have or use Trapcode Particular I urge you to pick it up today. http://www.redgiantsoftware.com/products/all/trapcode-particular/