Motion Tracking & Object Tracking inside Cinema 4D: Trimming Tracks

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Trimming, is a way to tell the Tracking algorithm to ignore a tracker for a specific number of frames, rather than risking the tracker "picking up" a random pattern by mistake.

Trimming, is a way to tell the Tracking algorithm to ignore a tracker for a specific number of frames, rather than risking the tracker "picking up" a random pattern by mistake. Let's see how this is done.

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Very often, especially during manual tracking, you may need to trim your tracks. Trimming is a way to tell the tracking algorithm to ignore a feature for a specific number of frames rather than risking the track of picking up on a random pattern by mistake. Trimming occurs naturally when a feature exits a frame or hides behind another object but sometimes it's something we need to manually. Now, again, we are in our camera solved scene. I'm going to get rid of my cubes and get rid of my constraints just for clarity. Select this. And let's go and see an example of trimming. So let's go and select a feature where we lose along the way. There you go. So, if I want to track this little feature here, you can see that at some point, it disappears completely behind another feature. So we don't really know if it's here or here, or here, or here and that may create some issue with the solving if we do that. But with trimming, we can solve this problem. So let's go to a frame where we can actually see it and press Cmd+left click, or Ctrl+left click to create our new manual tracker. I'm going to place it here and of course, bring up my Motion Graph View. Fantastic. And what else do I need to do? Yes, dock this. Excellent and then rip off the menu. Now, if I press H here, you would see that we see everything. So, I'm going to select all Auto Tracks and hide Selected and press H so we have our nice little key frame here. So, let me select it and of course, Track Bi-directional. So, let's wait for this to process. It will take a couple of seconds. Fantastic, let me Lock the View on Tracks and see what happens. This is exactly what we want to avoid. Although it seems to be a good tracker, if I go here and press H, you will see the error is high but it seems to be active and then, it deactivates over here. And let's go the other way and this happens again. Okay, let's fix it for this part, for the forwards motion. So, Insert Key Track Position and it's going to automatically update the tracks and move forwards. Excellent, and Insert Key at Track Position and move forwards and Insert Key at Track Position and move forwards but it doesn't really work. So, what I'm going to do here is go to the last frame I consider valid which is this one over here. And let's go and see what the Graph View says. It does give us a relatively good solve up to this point. That's where it jumps. Good, so I want to tell the tracker to ignore this particular feature from here onwards. All you have to do in this frame, you right click and you say Trim Track and it has that little scissors icon. If you Trim Track, what it does...it trims towards a direction where we don't have a keyframe. So, from this point onwards, this particular manual track will be ignored for the solve. Let's go and see if it appears again clearly. In the future, it doesn't so we can ignore it in that direction. Let's go backwards now and do the same thing for the backwards motion. Let's go. Oops, there it jumps. Excellent, let's go and Insert Key at Track Position. Let it calculate. A bit more, a bit more. Oops, there you go. I think this is the best frame to go and trim it. So, as we are now, we can go here and right click and Trim the Track. So you can see, now we have two trims, one on this side, one on that side. And again, the choice is made based on where we have a keyframe. Let me show you how to recover. Now, what I'm going to do is move backwards and see if at any point this particular feature appears again and is useful to us and let's assume that... Yes, here it is. All you have to do is go here and move your invalid tracker to a valid position. And you can see the calculation resumes and if we look at this, what you will see is that it does the bi-directional tracking as it should. And there you go. At this point, I don't want to calculate between this and this. Right click and Trim, and automatically, the algorithm is going to identify the area between the two trims and is going to ignore that feature. Excellent, so now what we have here is... Let's rewind. We have this feature that is tracked up to this point. Then, it gets ignored. Just forget about where the ignored tracker is. It's red so we don't get... And it picks up, again. So this is the way you are going to use the track trims to define areas of features where we don't know exactly where they are and so they don't interfere with our calculations we just tell them to ignore it. And that is trimming tracks.
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