Blackmagic Forum

Hy,
I want to track a flashlight held by a man.
This man simply walks left to right
but in the middle of the sequence he stops, looks back (so the flashlight is obscured by his body for 2sec), and then resumes his walk until the end.

I can track the flashlight before or after his looking back.
But I don't know how to track those 2 parts with the same tracker and obtain a coherent path.
(I searched the manual and several online tuto without solution)

Here my workflow :
I track the first part until the flashlight gets obscured
Then I check the "Track center (append)" mode
I go 2sec later in the timeline
I reposition the tracker on the flashlight
I track the 2nd part from this frame to the end of the sequence.

My problem is that the 2 different parts of the tracker's path are offset and I don't know how to correct it.

I Would just need to select all the tracker's position points of the 2nd part and offset them on the correct flashlight position...
But I just don't know how to do it.
The only keys I see are the "displacement" keys in spline editor.
How could I edit the X and Y tracker's position ?
Any help ?

Fabrice

Right-click in the Viewer with the Tracker selected, choose the Polyline Path > Convert to XYPath.

That will convert the Displacement parameter of the PolyLine to X and Y coordinates in your spline editor.

You can change the default spline type that a Tracker produces in the Preferences somewhere.

Thanks a lot Brian!

You're welcome! If you ever need to, you can convert an XY path back to a polyline the same way.

Hi Fabrice,

Even though Bryan's tips are very good, in your case the trouble lies with your approach.
The 'Track center append' method is to create a consistent track when the object you're tracking is leaving the frame (or is obscured). But this is for stationary trackers i.e. items that do not move.
For example you want to track dot 1, next to that dot is dot 2, that you don't want to track, but when dot 1 is obscured you can use dot 2 in Append Mode to continue to track dot 1. The track will pretend it continues from where it left off.

In your case all you are after is the exact position of the flashlight when it's visible, right?
So just ignore the fact that your track goes haywire when the flashlight is obscured, just follow your original steps WITHOUT selecting 'Track center append' and you should be fine.

But it is possible without too much trouble to fix what you have done, because the keys are not only visible in the Spline Editor, they are right there in your view. Just select the keys from the second part of your track in the view (box select them) and use the arrow keys to move them all back in place to match up with your flashlight. Since you've tracked the flashlight the keyframes will all end up at the correct position after that. It's less work to fix it than for me to type this.

No need to convert anything to anything.

Thanks for the precisions Sander.
Converting to XY maybe usefull sometime.
But your workflow fits my needs, no need to use the append mode in that case.