Why does my mask path change position when pasting it on a position parameter?

[AceLegacy]

https://community.adobe.com/t5/after-effects/why-does-my-mask-path-change-position-when-pasting-it-o...

I'm sorry but I'm about to lose my mind over this. I still haven't found a solution to this problem that works with me (yes, I marked the original post as solved, however, looking back at it now, I can't solve this again).

[Rick Gerard · Accepted solution]

The technique in the link you posted is an inefficient workaround presented by someone that does not fully understand the reason that a motion path does not precisely follow a vector (mask or shape) path. Let me explain the problem and give you the solution.

Mask paths are always created in layer space before any layer transformations. If you want a motion path to follow a mask path precisely then the layer with the mask or the shape layer with the path cannot have any changes to the Layer>Transform>Position, Scale, or Rotation properties*. It's as simple as that. Reset all of the Layer>Transform properties, draw a path on the layer (or shape layer) then copy and paste and the motion path will always line up on top of the vector path.

*If the layer is 3D you can rotate it in X or Y but never in Z.

The solution is to use a solid or a new shape layer, draw your path on the layer before you move or scale it, then copy the path and paste it to any parameter that has a position value.  The motion path will always be in the XY plane even if the layer is 3D. There is a workaround if you need the motion path to be on a different plane. All you have to do is paste the motion path to a 3D layer's position property, add a 3D null, parent the moving 3D layer to the null, then rotate the null. 

Some folks think this is an extra step but when I am going to copy a path and paste it to a motion path I always set a path keyframe, cut the keyframe (Ctrl/Cmnd + x) then select the layer I want to move and press Alt/Option + p to set a position keyframe and immediately paste Ctrl/Cmnd + v. Using this technique you will never have a problem turning the vector path into a motion path.

Here's a quick tutorial I did a long time ago that shows how to draw a vector path on a 3D layer and then turn that into a motion path for a camera. Notice that the reference layer that I rotated in X was not scaled or rotated in Z. That's why the technique works.

https://youtu.be/YyPMYK7ROYU

[AceLegacy]

Sorry, I still have a doubt. Now that I reset the transform properties, what should I do? The star is too big on the main composition. Would I need to create a null, solid or shape and draw a path and then scale it down? Just to make things clear. Thanks

[defaulttpks2s2fjmdr]

Hi, I came here looking for the same solution - Rick's answer works a treat.

I made a new solid layer named motion paths (which is automatically reset parameters, so I didn't need to change anything about the layer I was moving, which I think is where you're having an issue?) I drew a pen mask path, then copied than mask path and pasted it into the position of my layer that I wanted to move.  I've kept the solid in the project as as a guide layer where I can keep drawing mask paths and cutting them out.

Actually specifically for me, I was animating a mask, so there were a couple more steps (I don't know if this is 'correct' but it worked) I made my mask shape on a solid layer. then centred my anchor point in masked content and moved the shape to where I wanted it to start. This was an important step for getting everything to be where it should! Then I copied the mask path from the other layer into the position of the layer. I like using masks instead of shapes for their feather/expand options.