Drawing a line in real world via after effects

[jacobs24706348]

Hello world.

I haven't found the inspiration this time around to solve my problem with creating the path/line in a city-video. I am by no means a skilled editor, but I like to play around with it.

I have created a video to explain my troubles:

help - YouTube

Maybe you have a good guess as to how I can go about my idea? Maybe it differs from my take?

Thank you for taking a look and sorry about the bad sound.

[Theodoros Tziatzios]

If you insist on using the CC Particle System II:

• first create a Solid layer (do not make it a 3D layer)
• apply the CC Particle System II
• on the timeline, twirl open the properties of the Solid layer you just created, twirl open the Effects, CC Particle Systems II and finally twirl open the Producer
• on your Track Null 1 layer, twirl open the Transform -> Position
• now pick whip (lasso) the Producer Position property of the CC Particle Systems II on the Solid layer and connect it to the Position of the Track Null 1

Now, the CC Particle System II should follow your Track Null 1.

[jacobs24706348]

Thank you!

I really dont insist on anything, other than succeeding at creating an orange line that rests in the sky following the road. My best guess was to use CC particle system, but this is by no means an educated guess.

So again, thank you for the walkthrough, I will try it out. And if you do have any other way of doing it, I would not be angry our hold it against you if you shared your thoughts

Regards.

EDIT:

My issue persists

Help 2 - YouTube

[Theodoros Tziatzios · Accepted solution]

You're right. That's why I was skeptical about CC Particle II.

This next solution is going to be a little tricky to set up. Let's start over:

• first create a Solid layer (do not make it a 3D layer)
• apply the CC Particle World
• on the timeline, twirl open the properties of the Solid layer you just created, twirl open the Effects, CC Particle Word and finally twirl open the Producer
• Now the difficult part. Unfortunately, the CC Particle World Producer's X,Y,Z, coordinates are based on a ratio of the producer's position in relation to the composition size. So we have to do a little bit of math to convert pixels to a ratio with expressions.
  
  Alt+click on the stopwatch in front of the Position X of the Producer, delete whatever is filled and copy/paste the following code:
  (thisComp.layer("Track Null 1").position[0]-(width/2))/width
  
  Do the same with the Producer Y:
  (thisComp.layer("Track Null 1").position[1]-(height/2))/width
  
  and the Producer Z:
  thisComp.layer("Track Null 1").position[2]/width

All done.

(this code works only if the Null you want to follow is named "Track Null 1". If you want to follow a different Null adjust the code accordingly)

[jacobs24706348]

Holy crap I love you!

Now I just have to adjust the actual particle, easy peasy. You sir are a life saver.

If you ever happen to come around Aarhus in Denmark, you can pick up a beer on my tap

Regards Jacob.

[Mike_Abbott]

Jacob - I can see that Theodoros has given you a good answer. Yes doing this with CC Particle World is a little tricky as AE does not have a 'unified 3D space'. So some effects - including CC Particle World - define their own independent simulated 3D space. Hence the need for the translation given above.

- but the main reason for posting was to say well done on posting such a clear and well explained question! That very much helps those of us on this forum to give a good answer.

One other thing to note: You'll find that the AE camera tracker - like most camera trackers, calculate 3D position by analysing parallax in a shot - ie the relative shift between forground and background objects. When a camera is doing a tripod based pan (a 'nodal pan') there is no, or minimal, parallax. Hence these shots can't usually be tracked in terms of depth - note the 'No depth from a nodal pan solve' message in your video. This doesn't matter in your particular shot - but in many it will. Ironically a shot where the camera is moving (in location) will typically be easier to solve!