Your workflow is flawed as is your understanding of how parenting and auto orient work.
Here are a couple of things to consider. Generally you want your camera to move in the X Z plane. This prevents things like gimbal lock and other problems and helps you arrange your set. Motion paths from mask paths always end up in the X Y plane so you need to fix that.
A good workflow is to work just as you would in the real world. Arrange your layers to create your set generally on an X, Z plane so when you look at the set pieces without a camera in the scene they are arranged the way you want them. Next, add a 3D solid layer that is going to be the ground plane, rotate the ground plane layer 90º in X. This layer does not need to be big enough to cover your entire set and should not be scaled. Now draw the motion path on the ground layer using the pen tool starting at the desired beginning camera position. The path can extend beyond the layer boundaries.
When you have your motion path set a single keyframe for the motion path and copy.
Now create two 3D nulls. Name one motion null, and name the other temp null. Select the motion path null and create a single position keyframe and then paste. You will now have a motion path on the X Y plane. Parent this null to the temp null and rotate the temp null 90º in X. The path of the null should match the path you drew on the ground plane. Grab the last position keyframe and drag it to the point on the timeline where you want the motion to end. You can now delete the temp null. The last part of the setup is to reset the orientation of the motion path to 0, 0, 0 so that you may properly use the motion null as a parent for the camera.
Now position the camera close to the starting point of first position of the motion null and parent the camera to the null. The easiest way to do this is to copy the position keyframes for the motion null and paste them to the camera then delete the camera position keyframes.
The camera will now follow the path and everything should work as you expect. You can then animate or adjust the Y position of the camera to have it boom up or down, animate the point of interest to have the camera point to various objects as it moves along the path, or even use an expression to have the point of interest look ahead of the camera path for very movement. That's what you do when you are driving, you look ahead of the turns to anticipate the turn. It's easy to make a camera do this with an expression.
Parenting a camera to a moving null at the point of interest of the camera and then turning on any kind of auto orientation will just result in a mess. If you think about it for a moment you'll figure out why.
Really! appreciate your detailed elaboration.
I should make clear the Mask > Path > Shape keyframes i referred to are from a single mask Rotoscoped thru footage, it is Not nor is it meant be used as a motion path to orient the camera along.
You wrote: "Motion paths from mask paths always end up in the X Y plane so you need to fix that..."
Then subsequently wrote: "..Next, add a 3D solid layer that is going to be the ground plane, rotate the ground plane layer 90º in X."
I assume this last is the "fix" you referred to?
Next: "..Now draw the motion path on the ground layer using the pen tool starting at the desired beginning camera position.."
and this is where our motion sources differ: as written, my motion source is Path Shape keyframes pre-determined by Rotoscoping.
So rather than drawing the null motion path how do i utilize my roto's Keyframes to target its Anchor Point(center) as the Null\Camera Point of Interest?, (without the Velocity and other errors mentioned)
How did you do your roto???
Also, animated paths do not work as motion paths. You can only use the data from a single keyframe as a motion path.
I would think you want to use tracking. I'm not sure I understand what you are trying to do.
I think what you want to do is to track the footage using AE's point tracker or Mocha to track geometry.
Does this help: (sorry, there's no audio)
"How did you do your roto???"
- Roto Brush and KeyTweak.
Mocha and SihouetteSFX track more automatically using their Planar Trackers, but neither work as well as After Effects when using Animated footage (with typically low texture density)
"I'm not sure I understand what you are trying to do."
- Its actually very simple, esp. if you've seen the "Stabilize" view button work in Mocha: it allows a path or selection etc. to remain centered and zoomed in the center of the view window and thereby allow its edit without going offscreen.
I've had quick manual success using a few 3d camera keyframes manually aligning its Pos.\P.O.Interest with a then magnified roto or feature target thru the footage. But i hoped to learn an automatic way to target a roto (path) using a camera's P.O.Interest or any other effective methods?
"..Also, animated paths do not work as motion paths. You can only use the data from a single keyframe as a motion path.."
- good to know, and explains much of my current problems pasting multiple motion keyframes as well as the limited success pasting a single key, although in this latter case the camera is oriented perpendicular to the path verticies its POI is connected to.
I'm still not visualizing what you are trying to do by animating a camera's point of interest with a motion path from a mask... A screenshot of your project with a flow chart and some stated goals like I want the camera to follow the girls face. (see my example above) would help.
If I clearly understood what you were trying to achieve I could probably give you a solution. The only thing I know for sure that tying a motion path to an orbit null is going to create some pretty wild camera movements if the null is rotating.
For an exact visual example see Mocha's "Stabilize" view button which can be seen in their manual, YouTube vids and their trial version. So its real easy to see it in action, and your familiar with Mocha having suggested i use it to track geometry.
I also wrote: "..Mocha(Stabilize button): it allows a path or selection etc. to remain centered and zoomed in the center of the view window thereby allowing its edit without going offscreen."
But to put it in your terms: I want the camera to keep the girls face in the center of the view thru out the footage.
If this is still too difficult don't worry about it i'm satisfied with the camera keyframes i'm using now.