I have spent two nights trying to find a fix for this. Maybe someone has an idea.
I am looking to create a radar screen but also show a fantasy 3D view of the airspace. On a radar screen a Prediction Line shows the direction the target is traveling and it's length is proportionate to it's speed. I have use a fixed length, that's no problem. However the line has to follow the route, in 3D. But if I use a 1 px line and make it Auto-orient along path, when the camera rotates to it's side the line disappears (because it has no thickness and does not auto-orient to camera). The label itself is set to Auto-orient to camera, and to make the trail appear in 3D I used Trapcode Particular. However for the prediction line I have no idea.
you could try using a duplicate line that is parented to the respective line, but rotate the duplicate 90 degrees so that as the camera looks down, it will be invisible, but as the camera (or the scene) rotates to the side view, the duplicate line will be visible.
you could also try dan ebbert's auto-orient y only expression... i have a feeling that you will need to modify it to effect the x-axis, but i'm not sure of your setup. it may require further tweaks for your use, so if you are having problems with it, you might post questions about the expression in the ae expressions forum... dan is usually happy to help with his expressions.
You're a GENIUS :).
That's the best idea and it's easy as pie. Can't believe I hadn't thought of it before. Just tested your idea and it works - the one with rotation. I had given up and was going to do it manually.