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Use motion tracking data to generate a path/stroke - how?

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James MartinUse motion tracking data to generate a path/stroke - how?
by on May 13, 2013 at 1:08:28 pm

I've googled the heck out of this and asked more knowledgable colleagues, but continue to draw a blank.

Ive tracked the motion of an object, and and want to generate a stroke along the motion-tracking path, as the object travels. I.e. it travls from A to B and I want to reveal the path of where it has already been.... a bit like hawkeye in tennis!

Now I know I could just draw the path by hand, key-framing it, but as I have a dozen shots to do this to, I' looking for a quicker way, hopefully using the motion-tracking data.

Any help will be greatly appreciated.


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Tim VaughanRe: Use motion tracking data to generate a path/stroke - how?
by on May 13, 2013 at 2:12:28 pm

That's a darn good question. It can be done somewhat easily in C4d and probably other 3d programs, but I'm not sure about in Ae. Maybe using trapcode 3d stroke and/or echospace? Sorry I couldn't be much help...

Tim
Apple XRAID, XServe, 2008 2x3 GHz Quad-Core MacPro, Macbook Pro, XSAN, Dell Studio xps PC's
FCP Studio (7), AVID Media Composer, Adobe Production Premium, Maxon Cinema 4d, AJA Kona 3, Flanders Scientific Monitors, Panasonic HPX250's, Kessler Crane, Glidecam.....
Beer fridge fully loaded.


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Dave LaRondeRe: Use motion tracking data to generate a path/stroke - how?
by on May 13, 2013 at 2:20:16 pm

Is this a 2D or 3D motion track? There's a BIG Difference.

Dave LaRonde
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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James MartinRe: Use motion tracking data to generate a path/stroke - how?
by on May 13, 2013 at 3:15:27 pm

Hi Dave, it's a 2D (x & y) motion track. I'm hoping that makes things simpler!


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Dave LaRondeRe: Use motion tracking data to generate a path/stroke - how?
by on May 13, 2013 at 3:30:00 pm

It should. Is it AE's built-in motion tracker?

Dave LaRonde
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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James MartinRe: Use motion tracking data to generate a path/stroke - how?
by on May 13, 2013 at 3:32:13 pm

Yes, it is.


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Dave LaRondeRe: Use motion tracking data to generate a path/stroke - how?
by on May 13, 2013 at 4:29:52 pm

Good. Don't use Stroke; instead, use AE's Write On effect. Here's what you do:
  • Got a good motion track? Great. Close the lay window for the tracked layer.
  • Highlight the tracked layer in the comp and hit the u key to reveal the animating properties.
  • Go to the first keyframe of the Attach Point keyframes. Highlight the actual name Attach Point at the far left; it highlights all the keyframes. Copy them.
  • Create a solid that has the exact same horizontal & vertical dimensions and pixel aspect ratio as the tracked layer. Apply the Write On effect to the solid.
  • Set the effect to write on over transparent: you'll find it in there.
  • Make sure the timeline cursor is at the same time as the first Attach Point keyframe.
  • Click on the stopwatch for the Brush Position property.
  • In the timeline, highlight the now-invisible solid and hit the u key to reveal the animating properties. There's only one, the brush position. Highlight it.
  • Paste the Attach Point keyframe data into the Brush Position keyframe.
  • Tweak the write on colors, sizes, etc. to taste
.
You should be good to go.

Dave LaRonde
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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James MartinRe: Use motion tracking data to generate a path/stroke - how?
by on May 13, 2013 at 4:32:38 pm

Dave, you are a gentleman and a scholar. I will give this a go tomorrow - it certainly looks like a robust solution. Many thanks.


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Matthew KeaneRe: Use motion tracking data to generate a path/stroke - how?
by on May 14, 2013 at 11:07:05 am

An alternative suggestion to Dave's method: If you already have your tracking data applied to a Null, then you could use it as an emitter for Trapcode Particular, with no copying or pasting of data necessary. Just add a new solid with Particular, link the Emitter position to the Null, and then tweak the particle size to taste. If you set all the velocity and physics options to zero, the particles will stay where they were emitted and draw a line. If you want the line to fade off, play with the settings for particle life time and opacity over life.

Matthew Keane

Freelancer based in Paris, France
- Motion Graphics, Video Editing & Effects, Watchout Programming & Live Operation.


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James MartinRe: Use motion tracking data to generate a path/stroke - how?
by on May 15, 2013 at 11:39:14 am

Great suggestion, but alas I don't have trapcode. It might be of use to others though should they find this thread when they're stumped.


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James MartinRe: Use motion tracking data to generate a path/stroke - how?
by on May 15, 2013 at 11:37:57 am

Dave, you are a gentleman and a scholar. I will give this a go tomorrow - it certainly looks like a robust solution. Many thanks.

EDIT - this worked a treat - many thanks for such a clear set of instructions.


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Dave LaRondeRe: Use motion tracking data to generate a path/stroke - how?
by on May 15, 2013 at 2:44:55 pm

You are welcome, sir,

Dave LaRonde
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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