Yes your reasoning is correct,from the point of view of train the ball will travel in a tilted parabolic path as direction of apparent gravity will be different in the train and will not  end up in your hand

Throwing a ball upwards in an accelerating train
I am able to render a curve by bevelling it.

However, for a scientific visualisation that I am working on, this doesn't render the way I wish it to. I would like the curve to render as a fixed width line irrespective of the distance from the camera.

Currently, I have to adjust the bevelling amount based on camera distance, and also play with rendering samples to get a smooth looking line.

Is there a cleaner approach that I am missing?

I am currently using the "cycles" renderer, but I am open to suggestions for any other renderer. Thanks!

Clarification: This is an animated visualisation. Hence, the distance from camera varies continuously. Here's an example video of what I am trying to do. The comet orbit is the curve I am worried about.
