Line Trails Stuck To The Ground

Question

ive been given a brief recently which has given me quite a bit of grief in the past. it seems easy on the surface, but have always found it very time consuming, I think I’ve been going about it in the wrong way all along.

So one of my clients is a race car brand, and they often give me long shots where the cam is following a car, and I need to put trails behind it, which are left on the ground behind it and stay there afterwards for the duration of the shot.

So I’ve been doing it with paths, going towards the end of the clip, and seeing where the dirt trails are that the car has left, putting the paths with the pen tool, then manually keyframing those points every 10 frames to make sure things stay stuck to the ground ( I do this by looking at identifiable pieces of the ground and making sure points are close to them at all times).

I know this sounds insane, and it kinda is, but I had to resort to doing this because 3D camera tracking these shots just isn’t working for me. The path always ends up jittering, often the path will be really solid in one location, then for example in the distance it’ll be jittering a lot. I think this is because they’re long clips and the path is in view throughout?

If 3D paths were a thing in AE this would be a lot easier for me as I’d be able to map the points a lot easier, but as it stands it’s a bit of a nightmare.

Oh also, I’ve tried points to nulls, but it means I can’t then edit the bezier curves at all, which I need to do.

Can anyone suggest another workflow for this? Even another software? Plugins etc?

Thanks a lot.

Rob

Rick Gerard · Answer

I have done a fair amount of this kind of shot. The workflow depends on the shot. Generally, you have to motion stabilize the shot so the ground (the road) does not move. That requires eliminating the background motion so the ground does not move. It is not Camera Tracking. Mocha may be used to freeze the highway if the camera is only panning. If the camera is moving, like a shot from a drone or a helicopter, the workflow is much more complicated.

The idea is then to tie the tracked data from the car in the stabilized shot to a shape layer path that sticks to the ground, then put the motion back into the original shot and motion path layer at the same time.

If you can provide some sample footage, I can take a look and give you a more step-by-step approach. The time it takes to set up the comps and do the tracking depends on the amount of camera movement in the shot. I've done 3-second shots that take about 15 minutes and other 3-second shots that took 3 hours.

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