Message-ID: <4EE88126.5060109@vucx.de>
Date: Wed, 14 Dec 2011 11:57:42 +0100
From: Sascha Gritz <s.gritz@vucx.de>
Organization: VUCX
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To: After Effects Mail List <ae-list@media-motion.tv>
Subject: Re: [AE] Fun bit of animation
References: <list-4549639@media-motion.tv>
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Dear list,
we  got the following problem:
we track a point and give the tracked position data (x,y) to a null 
object. What we want to do now is write an adjustable expression that 
compares the values of the tracked data from frame to frame that 
determines changes in position that are above a specific threshold. Only 
if a change in position is beyond this threshold, movement should take 
place.

We put the expression on the keyframed transform.position of our 
null-object.
but it seems it isn't working.

The error we get at this point is that valueAtTime(0) is undefined. 
Although there is a Keyframe at frame 0;
since we step from error to error, there must be another problem.

By the way, the smooth function on the other hand is not an option, 
because it produces, in regard to our footage, not a fitting movement.

here is what we tried:

------------------------------
CODE
------------------------------

p = transform.position;

//we go through the frames and determine if major changes has taken place

for (f = 0; f <= timeToFrames(); f++){

savepos = p.valueAtTime(0);  //error at this line!

if (timeToFrames(0) == 0){
lastpos = savepos;
}


// define two points in time to compare values of these two

now = framesToTime(f);
nextnow = framesToTime(f+1);

tempLoc1 = p.valueAtTime(now);
tempLoc2 = p.valueAtTime(nextnow);

tempX1 = tempLoc1[0];
tempX2 = tempLoc2[0];
tempY2 = tempLoc2[1];

threshold = 0.5;


// if there is a change that is big enough we set the new position, else 
it stays as before

if (tempX1 < tempX2+threshold){
lastpos = [tempX2,tempY2];
p = lastpos;

}else{

p = lastpos;

}

}


------------
END CODE
------------

Many thanks in advance,
Sascha


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