Simple Motion Tracking Offset?

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Old 09 September 2012   #1
Simple Motion Tracking Offset?

Hey guys,

I'm trying to put a flare in a sky with Optical Flares (running CS6). Since there is nothing in-focus in the sky to track, I instead tracked a building a bit lower and to the side of the frame to determine the movement of the camera. Applying the tracked XY data from the building corner to a null object then locks the null to that corner of the building.

That's all fine and dandy--but now when I pick-whip the 'Position XY' of the flare to the position parameter of the null object (pinned to the corner of the building...), then my flare is also pinned to the corner of the building. I'd like for the pick-whip to maintain its original offset, but can't figure out how to do it! Am I missing something easy?

I've tried changing the code, but also don't quite know what I'm doing there. Adding a "+740" to the end of "thisComp.layer("Null 1").transform.position" (so it reads "thisComp.layer("Null 1").transform.position+740") does offset the flare's Position XY on the X-axis as I'd expect, but for the life of me I can't figure out how to affect the Y-axis.

Any help would be super appreciated! I seem to remember pick-whipping not actually affecting the location of the parameter being pick whipped in the past, so its offset used to be maintained? Is this a change, or am I going crazy?

-Tim Bubb

+kyrie eleison+
Old 09 September 2012   #2
It's very simple: Instead of adding just one number to the expression ("+740") you have to add the X and Y values in square brackets:

thisComp.layer("Null 1").transform.position+[740,150]

This will offset the point 740 pixels on the X axis and 150 pixels on the Y axis. Of course you can also use negative values:

thisComp.layer("Null 1").transform.position+[740,-150]
What would be even more flexible would be to add "Point Control" effect (under Effects -> Expression Controls) to the Null object (or the flare layer, doesn't really mtter), and pickwhip that:

thisComp.layer("Null 1").transform.position+(pickwhip the point expression here)

That way you can change the offset just by changing that point controller.

Last edited by Laserschwert : 09 September 2012 at 07:49 AM.
Old 10 October 2012   #3
Excellent, thank you so much!
-Tim Bubb

+kyrie eleison+
Old 10 October 2012   #4
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