• Adobe After Effects

  PFTrack 5 – Very Long Scene Geometry Inquiry

  Posted by Andrew Spirk on May 19, 2009 at 12:31 pm

  I know this isn’t related to AE, but when I posted a Mocha/AE question last time, I got fantastic advice for a problem I wracked my brain trying to figure out.

  The shot:
  Pretty simple shot with a JVC-HD110u locked down on a tripod from within a jeep. The camera is aimed out of the back right window, and driven next to a sidewalk slowly, following a subject. The angle of the shot is forward, with the front of the subject concealed as he walks down the sidewalk, but the side and back visible. It’s a long shot, so the sidewalk is in view, but angled. Also, about 3 feet from the subject there is a wall along the sidewalk. We shot on an overcast day to avoid major shadows. The shot is around 650 frames long. PFTrack had no problem tracking and solving the footage.

  Okay, so down to the problem.

  So, I have a 3-day trial for PFTrack that I got this morning as I have a shot that Boujou is having a horrible time with, so I figured I would try an alternative. I’m really impressed with PFTrack, it tracks and solves incredibly well, and after cleaning up a bit, I managed to get a very solid track.

  The problem comes down to scene geometry; I can’t figure out how to strap the plane to the sidewalk along the entire path. I’m guessing I’ll have to split the scene up into separate cameras and then import those into AE (I can do that with boujou) but it would be really, really nice to get the plane to stick to the entire length of sidewalk.

  Does anyone have any suggestions, preferably towards PFTrack, but ideas with Boujou are more than welcome.

  In the end result, the data is going into After Effects, if that helps.

  Thanks!

  -Andrew

  Dan Prostak replied 15 years, 7 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Andrew Spirk

  May 19, 2009 at 5:07 pm

  Thanks for the quick response Dave!

  PFTrack does indeed export to After Effects, it spits out a nice .ma file with a comp and null objects on the specific points I specify. Just like Boujou or Syntheyes, when I track a shot in PFTrack it first gives me a ton of feature points via an autotrack function. After that, I run a camera solve which interprets all those little points (hundreds of them) and is able to accurately solve where the camera was in relation to the footage. You probably knew all that, but just wanted to specify where my problem is.

  I can pick out these solved points which appear in Boujou/PFTrack, and export them to AE, once they’re in AE I can drop my footage in and just copy and paste the position data from the null objects that correspond to the points I picked, make it a 3D layer, and just like that I have it following the null object in 3D space.

  The problem arises in a crucial part of this process where PFTrack/Boujou needs to assign what amounts to an origin point, x/y/z information to determine where the ground in the scene is. AE uses that information to make all the points stick where they’re supposed to be. Without that information, the camera solve is no good as it doesn’t know what is up/down/left/right/depth in relation to the footage. At least that’s how I understand it.

  So to sum things up: PFTrack -> (feature track) -> (camera solve) -> (*scene geometry*) -> Export for AE

  Without the scene geometry, the null objects still track, but they float around the footage because they are using a ground plane determined in PFTrack/Boujou.

  This is all quite easy to do with a shot that pans from a relative position, and where all the items placed into the scene are on in the area of that shot. However, my shot is a long tracking shot as stated above, so if you pieced all the information together like a panorama, it would cover a city block.

  I’m sort of thinking that I may need to do what Andrew Kramer did, but adapted, and track say 40 frames, export camera, next 40, export camera, etc. Then use expressions to link those up.

  As I said, it would be really nice to just use one camera and assign a ground plane to that, but the more I think about it, the less that seems feasible.

  Any thoughts?

  Thanks,
  Andrew

  (I’ll post a few screen caps as soon as I get a chance tonight. As I’m using the trial version of PETrack, I can’t actually export the camera, but I only have 3 days to use it, so I wanted to make sure I have a steady workflow before it’s considered for future projects.)
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  Dan Prostak

  October 1, 2010 at 2:05 am

  I just started learning about PFTrack and very new at this but did you define your origin point?

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