[Aaron Pozzer]

so, many months later the misaligned travelling dot comes back to haunt me!

turns out the client now wants the dot back. so to recap the above conversation your suggestions worked great, but when i rotate the camera, the dot no longer follows the line. there is no parenting or different in z space, so im wondering what is causing this.

any ideas?

[Aaron Pozzer]

you would think with 15 yrs of 3d experience this would make more sense to me!

regardless, thanks again for the help.

[Aaron Pozzer]

once again Dan, you got it. right off the bat i should have noticed that the layer was parented, but i overlooked it. the tweak to the expression fixed it.

so in this instance we use toWorld instead of position because toWorld sets the position based on where it is on screen?…where as if it was picking up position of the parented camera, it would think its somewhere that its not, as its inheriting the transforms of the parent? i havent gotten to that section of the book yet so im not quite sure what toWorld, toComp, fromWorld, etc, all do, haha.

[Aaron Pozzer]

that was actualy my first thought as well, but they are on the same z plane. both sitting right at 0, and neither are parented.

regardless, i talked with the client yesterday and we are NOT going to use the graphic afterall, just the line…. isnt that always the case!?

though, if you DO think of some reason they might have become misaligned after rotating the camera, it would still be good to know.

thanks!

[Aaron Pozzer]

hey Dan, just a bit of a curiosity. i was playing around with my map animation (the camera move) and decided to put some rotation on it so it was not just looking straight down at the map. it seems that when this happens, the graphic layer no longer follows the stroke… it jumps off into the lead and seems to get further and further ahead the longer it travels.

if im limited to looking straight down, thats fine, i just thought id ask why this is happening, and is there a way to correct it. if not, not a big deal.

thanks!

[Aaron Pozzer]

well it had been stretched out because when i was setting up the comp originally and i just had the linear motion, the animation still had to span the length of the comp, so i had stretched the keys out to match the keys of the stroke animation.

but, i understand now that it can be left at 2 seconds.

[Aaron Pozzer]

damn, confusing. its worse that time is in seconds, not in frames! oh well.

i do have lots of roving frames in my position channel between the 2 keys. it seems that no matter how long you stretch the 2nd key out to, the expression still works. were you aware of this? cause it seems like your math was based on the fact that you assumed the keys were spaced 2 seconds apart. either way it seems to work… so just fyi.

i got that book, After Effects Expressions, and im making my way through that. hopefully once im done this will make more sense.

thanks alot for you’re help Dan! im sure ill have more questions soon enough.

[Aaron Pozzer]

ok, so let me see if i understand this…

-valueAtTime, means: be this value (that we are about to calculate inside the brackets) right now?
-percent, well thats obvious.
-*key(numKeys), the number of keyframes, in this case 2.
-.time/100, the current time (frame #?) divided by 100?

this last part is what confuses me. is it numKeys x frame# / 100?

so, the path gets converted into 2 keyframes and into a linear animation, 0% at key1 and 100% at key2 (hence the /100 at the end?). every point on the path in between is just an interpolation so the graphic sticks to the path and maintains that constant linear speed. the shape of the path is not important, only that its getting from point A to B over a linear number of frames…?

so if it was frame 75, and the stroke was at 18%, it would be valueAtTime = (18x((2×75)/100))? so it would return a value of 27? meaning the graphic should be 27% way through its animation?

…am i on the right track here? 🙂

[Aaron Pozzer]

hey Dan. so, this works, but not quite off the bat, though i figured it out.

i have the Stroke start set to start animating at frame 25. the 1st key in the graphic layer position was also set at 25, so they would start together.

so i left the position keys alone, pasted in your expression, added a tweak via some additional keys in the Stroke start, and it did follow, but it was delayed by 23 frames.

on a hunch i set the 1st position key for the graphic back to frame 0, and now everything follows properly.

it would be great if you could explain to me how this expression works, in plain english. im tryin to learn expressions, and i’ve only been at it for a couple weeks. id love to be able to understand the logic of how it does what its doing.

thanks alot!

[Aaron Pozzer]

hmm, interesting. thanks dan. i will try this in the morning and let you know how it goes!