I am tracking motions with blender, and adding motion trails to tracked objects. With hq slow motion footage, just attaching an empty vert with a particle effect to my track works very well. However, when the frame rate is not very high, the tracker will be quite far apart frame to frame and I end up with what looks like a dotted line because the emitter jumps from one tracker location to the next. I would like to bridge the gap either with more particles or just a line. How can I distribute more particles between the current and previous/next tracker location? Maybe I have to convert the track into a path or a line (I can't figure out how)? Basically what i want to achieve is a smooth gap-less motion trail even when the tracked object moves quite a bit between frames. Grateful for any advice, thank you.
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$\begingroup$ Thanks. I think this is a good and practical solution for shorter paths, however mine was a bit too long and complex to manually add and shape a beveled curve on top of it. $\endgroup$– Sina ToadstoolCommented Jul 4, 2020 at 19:04
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$\begingroup$ Thanks for your reply. I've only recently pulled that link down but it's back again as a new one. Take a look, you might be surprised how effective it is. New link - dropbox.com/s/qi2r3adoz661noq/Trail.gif?dl=0 $\endgroup$– Edgel3DCommented Jul 6, 2020 at 1:49
2 Answers
You can do this with Animall (Addon, has lots of presets), but I always found it a bit wonky and it's not really migrated to 2.8 yet.
With a little more effort you can use Animation Nodes for that, in the end you have way more control over the behaviour of your path. Here's a screenshot of my Nodetree, note that the dotted line is just the visualized motion path of the empty, the selected curve is the actual offset. I moved it to the side, so you can distinguish between them.
You can probably clean the tree, or not use a loop, but this way works. Note that if you have more than just location keyframes on your object, the list indices might change.
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$\begingroup$ Thanks! I'm still working on it and generally understand what you're doing here. I managed to recreate your node tree, and now I'm trying to use it properly. Things that I'm still unsure about: Is it correct that this 'program' runs in advance to set up the path for the lines or particles? (as opposed to extending the curve frame by frame as the img sequence plays). Your example would be able to set up a 25 frame animation? (25 iterations) Is it correct that the Empty object that is the input should be a child of my tracker? I'm not able to manipulate a bezier curve (output) yet. $\endgroup$ Commented Mar 28, 2020 at 17:51
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$\begingroup$ It took me a while, but I found a solution based on this. I struggle with nodes, so I sort of translated this network into a python script. It took me a while to properly create the keyframes and connect my objects to what the node network is doing. But in the end I think I ended up with pretty much the script version of this. $\endgroup$ Commented Jul 4, 2020 at 19:12
Tracking information creates a constraint.
To convert constraints into keyframes, open the constraint section of the properties window and press Constraint to f-Curve
The tracking information will be converted to keyframes, the curves for those keyframes can be displayed and manipulated on the Graph Editor.
There are a few built in tools to clean up curves in the key menu of the Graph Editor.
Here's the same motion path after applying the "Clean Keyframes" function:
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$\begingroup$ Thanks, this was definitely a missing step in my failed attempts! $\endgroup$ Commented Jul 4, 2020 at 19:07