How to follow a 3d object to a panning shot?

[Y13oi]

Hi,

Sorry if my wording is incorrect or confusing. New to AE and I'm trying to understand how to get a 3D object to follow the movement and match the perspective of a panning shot. For example:

If somebody is throwing a knife across the room and the camera pans to follow the knife.

Is this something I could use the 3D camera tracker for? I understand how to stick things like text or images onto surfaces but getting something to fly across the screen is confusing me. Thanks for any help!

[Rick Gerard]

A camera pan has no parallax shift, so you get no depth information from a Camera Track. There are as many ways to get that kind of composite as there are ways to shoot a camera pan. The most efficient workflow depends entirely on the shot. If you already have a shot and can share it, we can give you a step-by-step for that specific shot. From your description, it sounds like just setting some keyframes for a position on the knife layer would do it. No tracking invoiced. Another option may be to motion stabilize the shot so there is no camera movement, then animate the knife, then put the motion back in the shot and add the camera move to the knife layer. 

[Y13oi]

Hi, Thanks so much for the quick reply. I've seen plenty of videos about throwing objects towards the lens or just flying past the lens but I haven't seen anything where the person throws an object and the cameraa pans and follows the object. I understand just animating the object by hand but I was wondering if there was something to do with the camera tracker to help automate the process.

I haven't actually filmed it yet. I was looking at ideas and trying to see how to do things so I can figure out my limitations but for reference, here is Captain America throwing his shield and the camera follows it. Starts at 0:16 seconds. Thank you again for any help Rick!

[Rick Gerard]

The camera tracker only gives you references to fixed geometry in the shot. That's all. 

If your shot is a pan from the thrower to the target, you set the first position keyframe when the object leaves the thrower's hand; then, you set the second keyframe when the object hits the target. If the camera is close enough to the motion path of the object that is thrown, you'll also need to scale the object layer at the beginning, middle, and end of the shot. You can eyeball this very quickly and easily. Check the preview at about 50% or even 25% magnification ratio and real-time. That will give you a very good idea if the timing and the scaling are correct. Unless the actor throws a prop that you can motion track, everything in this kind of composite shot is done by eye.

[Y13oi]

Amazing, thank you for the detailed explanation. I was going out of my mind trying to figure out how to use the camera tracker for this because I thought it would help.