Transfer rotoscope path to different layer

Question

A novice rotoscoper, I got a little confused from having read and watched tutorials with several diffeent styles of rotoscoping.
Some said to use a layer in between path and actual subject layer with the eyeball turned off.  Then lock the actual target layer so as not to move it around inadvertantly.
I may have that confused a bit... if so, it not the tutorials doing but mine.
Cutting to the chase; I have a solid light grey layer with the opacity turned down to 1. above a footage layer of my great grandson doing his first zombie walk.
I spent a lot of time getting a mask to follow his little head in his trek across the floor.  Now I wanted to transfer the mask path points over to the target footage layer.  I clicked the footage layer with the pen tool to get a mask started, then with focus on the grey layer/Mask/mask path (all the points are lit up so selected) and copy... then to the footage layer Mask/Mask path - paste.  So far so good.
But somehow I must have moved either the grey solid layer or the footage layer sometime during all the pulling and hauling.so the mask misses the head in a perfect offset all the way thru.  The attached screen shot illustrates it well.  The first one shows the mask on the grey layer, the second on the footage layer.
I tried lining up the layers by setting the `position' parameters the same, also by just eyeballing the crosshair thing that shows the center of each layer.
Trouble is I can't find a way to see the crosshair from the one layer as soon as I focus on the other to move it.  Ditto for the path itself.  Soon as focus changes the path does to.  I may be going the opposite way of what I should, but tried it both ways with both layers and am just not getting how to get it right.
I know I can just do it over, and that isn't really a problem since I can clearly use the practice.  But I feel like there must be a a clearcut way to match up a layers position to a path.
At this point I've thoroughly confused the heck out of myself and would like to hear someone lay out how to get two layers to match up

Answer 1

Haa, the footage layer is turned on but the solid layer above was
set to 1% opacity.. with the eyeball off. cranking that up 100 fixed
it.  Now I can see the babies head, and the rest is masked out as
expected.
You'd
think the opacity setting on the solid layer would not matter if the
layer eyeball is off anyway, but apparently it does.  If I scroll the
opacity up and down with the layer eyeball off,  the babies head
appears at higher percentages and disappears below 10 or so.
If you think about it, it makes sense.
A track matte set to "alpha" applies the opacity value of each pixel in the layer directly above to current layer. So, if Opacity for that layer is 1 per cent, that affects the opacity value of all pixels. Leaving it at 100 per cent, means that fully opaque pixels are applied as fully opaque, and fully transparent pxiels as fully transparent.
The visibily control (eyeball) for the layer above is turned off aumatically (if it's not already off) as soon as you set a track matte mode. So, the layer is "seen" for the operation regardless of the visibiliy status.
The column is headed with `T'  and when you check it, it says `preserve transparency'.  I don't quite get what that is for.
That's called "Preserve Underlying Transparency", and it's a very convenient option... but I am surprised by how many people enable it without knowing what it does. It's not the first time someone gets bitten by it
And what it does is... this layer (the one with the switch turned on) only exists in areas that are not transparent, when taking into account the combination of all layers below. Example: if you have three circles placed in different places, and then create a large text layer and enable this switch, text will only exist in places that match the circles underneath.
More info in Preserve underlying transparency during compositing, in After Effects Help on the web.
Another aspect of this:  I wanted to rotoscope the whole body... so as to be able to insert it on differnet backgrounds.
I
could use some ideas on that too.  I started with just the head to get
an idea of how its done... but I'm guessing it might be easiest done by
taking several masks to enclose various chunks of the babies body.   Is
that how its done?
There are many valid approaches, and whatever works for you is fine. But you can be happy to learn that many experienced roto artists suggest doing exactly as you just described
I really recommend Mark Christiansen's book After Effects CS4 Visual Effects and Compositing Studio Techniques. It has a lot of useful information on roto work with AE.