Multiple motion tracking points

[Milesl2@mac.com]

Are you needing a 3d solution or just the xy coordinates?

[Andrew Shanks]

Okay, this is for when you are just wanting to do a basic 2D track (not corner pin or anything). With the setup you’ve got, track the tracker that is going to stay in shot the longest first (we’ll say its tracker 1). When tracker 1 moves out of frame, ALT-drag the tracker box to the next available tracking point, ….the tracker target (little cross on the screen) should not move, …then start the track going again. In theory you can just keep repeating this, then apply it to a null (or a layer, …I prefer the null way, cause then you can parent multiple elements to that one null, and if you want to make master changes to the move, it can all be handled by that one null, everything else will follow it). In practice After Effects has a bug with its tracker (that I keep complaining about, …anyone from adobe hearing me out there?!!) in that if the target cross happens to have moved off screen into the grey pasteboard area, when you do the ALT drag trick, you can find your tracker target resets to the centre of the screen, thus a jump in animation, ….damn annoying. So in practice you’ll probably get one alt drag before it resets due to this bug. The work around is to do a bit of precomping, placing your source footage for the tracking in a much larger sized composition (maybe 2k or bigger, will depend on how much your camera moves), tracking the data in that using the Alt-drag trick (due to the larger composition area you won’t have the little cross leaving the comp area, and hence the bug won’t occur), applying it to a null, then copying that null into your main composition where you can parent your layers to it. All should be fine.
…let me know if I’ve screwed up a step there, its been a while since I did it, …but yeah, we had a ton of sky replacements we had to track in that way, with trackable objects not staying in frame long. It was a pain to use the workaround, but it worked.

Please Adobe, this bug has been there since v6, …fix it for v7 huh? …its a great 2D tracker thats marred by that small bug.

Other alternative is to use Boujou, Matchmover Pro or Syntheyes (they’re all good, Boujou being the king of auto tracking (most expensive), Matchmover being the king of supervised tracking (medium price), but the latter is the one I use most, …its the most affordable by a mile and gives you a ton more bang for your buck than the others, ….but the learning curve is steaper than the likes of Boujou). From the matchmove software, solve the move in 3D, and export a maya (.ma) file, …import this to After Effects, and if you place the layer you want to have moving locked with your camera in 3D space you will be away laughing. Please note that AE uses a bit of a modified .ma file (I think it might just be an older flavour of the maya format), Syntheyes allows for this, but I can’t speak for the others (as I’ve only used them for solving for 3D apps.

Goodluck!!!

andrew

[Mark Underkofler]

Andrew,

Thanks for the ALT trick. It worked as long as the tracking dot I was ‘leaving’ didn’t move off screen before I ALT moved the cursor to the next tracking point.

I didn’t have any hiccups and it translated great!

Sincerely,
Mark

[Merlin65]

Hi,

I tried this method with two tracker points ( one for position and the other for rotation). The image still jumps. What could be the problem?