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Motion 5 - Motion Tracking - Offset Track problems

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Greg Merkes
Motion 5 - Motion Tracking - Offset Track problems
on Oct 11, 2013 at 7:47:27 pm

Hello,
Is anyone else having trouble with motion tracking? I am attempting to track an object that gets temporarily covered up by the foreground. In the Motion Manual it says to use Offset Track to pick a separate track reference point - then start the analyze again. I have tried this many times and am having much difficulty. Does anyone know how to do it? Any help would be greatly appreciated.
Thank you.
Greg Merkes
Salty Dog Films

Its easier to ask for forgiveness. . .


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Sandeep Sajeev
Re: Motion 5 - Motion Tracking - Offset Track problems
on Oct 12, 2013 at 7:45:37 am

Hi,

can you expand on your issue a bit? What exactly is happening once you check Offset Track and Analyze? If you can post a screengrab it might be helpful.

Sandeep.


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Greg Merkes
Re: Motion 5 - Motion Tracking - Offset Track problems
on Oct 13, 2013 at 6:12:43 pm

Hi Sandeep,

Here are a few screen grabs.

I am attempting to track the background as the camera pans from right to left. On the first track I am tracking the white water bottle cap on the bottom right and it tracks fine until the image goes off screen.


In the second track I select the "offset track" box and move the original track location to a new track point - in this case I moved it to the high-contrast of the chair with the white behind it. Then I select analyze again and it seems to track it but it adds all the key-frames way outside of the tracked area - as you can see the second track key-frames. I have somewhat fixed the issue by selecting the key-frames and manually moving them to around the same curve as the original track, but there is a movement between my "moved frames" and the original track. It seems that Motion should compute the offset of the two tracks and automatically move the second track key-frames to link up to the first track?

I could be doing something wrong as I have not done this before.


Thanks in advance for any help or feedback.
Greg Merkes
Salty Dog Films

Its easier to ask for forgiveness. . .


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Sandeep Sajeev
Re: Motion 5 - Motion Tracking - Offset Track problems
on Oct 13, 2013 at 8:10:19 pm

When you pick an offset, the Tracker continues from that point onwards. It does automatically calculate the offset.

One way to check that the offset is working correctly is to watch the Tracker Preview window in the Inspector. You will see the reference point switch from the last trackable frame of the water bottle to the offset point that you have selected. This should happen immediately - i.e one frame after the last water bottle frame.

Is this happening? Is it holding on to your offset feature? If it's not then clear out your track and start over. Try choosing the yellow dot inside the white thing in the background or the athlete's eye. Those will probably be better points.





Let me know if that helps. You're planning on match-moving something on to this shot right?


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Greg Merkes
Re: Motion 5 - Motion Tracking - Offset Track problems
on Oct 14, 2013 at 2:59:53 pm

Hi Sandeep,

I am attempting to layer a font on the wall behind the athlete. I was hoping to track the back wall then roto-key/mask the athlete over the foreground.

My attempt at motion tracking is not working as well as yours. I noticed that when you have the second pass of the motion track that you get 2 green keyframe strings in you keyframe editor but the original keyframe string looks uninterrupted? Are the two green strings the "offset track" and are they transparent in the actual move but calculated keyframes on the original track?

When you select the second track "track point" do you just simply drag the yellow "target" on the canvas to the new track point? Or is there another way to do this? Also, what is the "tracker preview window"?

I have tried multiple times to delete the entire "analyze motion" layer and start over. I have also tried to do this on multiple clips with no luck. I think I am doing something drastically wrong.

Thank you very much for your input.
Greg Merkes

Its easier to ask for forgiveness. . .


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Sandeep Sajeev
Re: Motion 5 - Motion Tracking - Offset Track problems
on Oct 14, 2013 at 5:17:03 pm

Hi Greg,

Yes the green curves are the offset curves. You can see the difference between yours and mine is that my offset curves follow the general shape of the original Tracker Reference Curve and there isn't a huge value jump.

A good rule of thumb is that you should pick an offset on the same plane as the original track point.

The Tracker Preview Window is the box in your Inspector that's labelled Tracker Preview - it's visible in the screenshots you've posted.

[Greg Merkes] "When you select the second track "track point" do you just simply drag the yellow "target" on the canvas to the new track point?"

Yes, Pick your bottle cap as your start point and Analyze. When the bottle cap goes off frame the Tracker will automatically stop and wait for an offset. Then you check offset track and drag the cross hair to your offset reference point, and click Analyze. Once it's done, play your clip back and watch the Tracker Preview Window to see if the hand off is correct. Then take a look at your curves and if you see something like the one in your screenshots then it's probably not going to work.

The easiest way to check is to add a Text layer to your Timeline, drop a MatchMove Behavior on it, point it to your tracked layer and see if it tracks properly.

If you find you are unable to get a decent one-point track (remember that a 1-point track only deals with position) then you should add a tracker and do a 2 point track. A 2 point track will track scale and rotation as well, so depending on the movement in your shot you should choose the appropriate tracking method.

To do a 2 point track, select your reference point as normal, and then click add tracker. At the bottom of the Inspector window you'll now see a Track 2 button. Click to select it and you'll see a second cross hair on screen. Drag that to another good tracking point. You'll see that your first cross hair hasn't moved. Then click analyze. And go from there. If you need to offset, click the appropriate track in the Inspector before checking the offset track box. Then as normal drag your cross hair to the offset point.

So if a 1 point is failing, or if there is more to your shot than just a horizontal/vertical move then you should try a 2 point track.

Hope that helps?

Sandeep.


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