• Adobe After Effects Expressions

  Distance Travelled Expression

  Posted by Christopher Johnstone on February 1, 2013 at 10:08 am

  I am trying to generate an accumulation for distance travelled.

  Knowing that Time x Speed = Distance

  The code attached is successful in accumulating my speed but I now need to add a valueAtTime multiplier to get my distance.

  Can anyone help shine a light?

  Many thanks in advance – Chris

  // time x speed = distance //

  spd = comp("- CNTL - MPH -").layer("- MPH -").effect("MPH")("Slider");

  accum = 0;
  for (f = timeToFrames(inPoint); f <= timeToFrames(); f++){
  accum += spd.valueAtTime(framesToTime(f));
  }
  s = value + accum;

  [s]


  Christopher Johnstone

  Christopher Johnstone replied 13 years, 7 months ago 2 Members · 6 Replies
• 6 Replies

• 

  Dan Ebberts

  February 2, 2013 at 4:26 am

  Try multiplying your accum variable by (time-inPoint). That should give you the distance traveled in the units of your speed control (pixels?)
• 

  Christopher Johnstone

  February 5, 2013 at 3:14 pm

  Hi Dan,

  Im stumped. Would you mind breaking that down for me.

  Many thanks – Chris

  Christopher Johnstone
• 

  Dan Ebberts

  February 5, 2013 at 3:46 pm

  It’s hard to get very specific without seeing how you have things set up, but I think that your accumulator should already be proportional to the distance traveled. You might need to multiply by some factor (not elapsed time as I originally suggested). So something like this (assuming it’s a position expression) would give you movement in the x direction:

  
spd = comp("- CNTL - MPH -").layer("- MPH -").effect("MPH")("Slider");
mult = .1;
accum = 0;
for (f = timeToFrames(inPoint); f <= timeToFrames(time); f++){
accum += spd.valueAtTime(framesToTime(f));
}

  value + [accum*mult,0]


  Dan
• 

  Christopher Johnstone

  February 5, 2013 at 4:32 pm

  Well it is all pretty basic my end.
  I am using a slider with some key frames to drive a number for MPH.
  This MPH is represented by a text number is in a digital dash readout.

  That is what this bit is:
  comp(“- CNTL – MPH -“).layer(“- MPH -“).effect(“MPH”)(“Slider”);

  I am trying to generate an accurate distance travelled number within my driving simulation given that at frame 0 my speed and distance is zero.

  I am unsure if I have to use the multiplier 0.1 in your example.

  Hope this makes a little more sense?
  Let me know what you think.

  Cheers – Chris

  Christopher Johnstone
• 

  Dan Ebberts

  February 5, 2013 at 5:51 pm

  If your speed control is miles per hour and you want your text layer to display miles traveled, I think this is what you want:

  
spd = comp("- CNTL - MPH -").layer("- MPH -").effect("MPH")("Slider");
accum = 0;
for (f = timeToFrames(inPoint); f <= timeToFrames(time); f++){
accum += spd.valueAtTime(framesToTime(f));
}
accum*thisComp.frameDuration/3600


  Dan
• 

  Christopher Johnstone

  February 6, 2013 at 10:23 am

  Lovely Dan,

  just what the doctor ordered – this works perfectly.

  Could you explain a little how the accum function works?
  I have tried to explain it to a friend a little and found myself a little unsure.

  Many thanks – Chris

  Christopher Johnstone

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