I must be doing something wrong! Tracking problem

This is a test for a job.
I need to track the little girl so I can replace her by an other kid. Each time I do so, my “surface” spline don’t track correctly. There is something that I do wrong but what is it???
Here what I did:
At first I made a spline (photo #1) - Min % pixels used = 50 / Motion Translation,Scale, Rotation, Shear, Perspective.
That is my tracker spline - so I rendered it (Tracked it)
Then after I did a second spline (photo #2)
I linked my second spline to my first spline
Then I played it - The surface spline don’t follow the shape (especially in the face and shoulders)…
What the … am I doing wrong???
I use mocha AE for CS5.5 Version 2.3

Without seeing the camera motion, my suggestion would be to break the object into multiple tracks and rotos. For example, draw a shape only around the girl’s face, track and and use that to link a roto shape around her head. Same for the body.
One large shape is probably not specific enough. Sine mocha is a planar tracker, think about the body being made up of multiple plans. If the movement on multiple plans competes too much, you won’t get a track that is useable for roto.
You might want to watch a few of the roto videos found here:

I would start with “Learn mocha: Chapter 5. Rotoscoping” and you will see how Steve Wright uses multiple track shapes for various parts of a roto.
Hope this helps.
-R

Without seeing the camera motion, my suggestion would be to break the object into multiple tracks and rotos. For example, draw a shape only around the girl’s face, track and and use that to link a roto shape around her head. Same for the body.

One large shape is probably not specific enough. Sine mocha is a planar tracker, think about the body being made up of multiple plans. If the movement on multiple plans competes too much, you won’t get a track that is useable for roto.

You might want to watch a few of the roto videos found here:

I would start with “Learn mocha: Chapter 5. Rotoscoping” and you will see how Steve Wright uses multiple track shapes for various parts of a roto.

Hope this helps.
-R

This is a test for a job.

I need to track the little girl so I can replace her by an other kid. Each time I do so, my “surface” spline don’t track correctly. There is something that I do wrong but what is it???

Here what I did:

At first I made a spline (photo #1) - Min % pixels used = 50 / Motion Translation,Scale, Rotation, Shear, Perspective.
That is my tracker spline - so I rendered it (Tracked it)

Then after I did a second spline (photo #2)

I linked my second spline to my first spline

Then I played it - The surface spline don’t follow the shape (especially in the face and shoulders)…

What the … am I doing wrong???

I use mocha AE for CS5.5 Version 2.3