Camera movement

Willy2

I wanted to do a simple animation, with a character moving in a straight line.
I wished to film him with the camera in front of him, and quite close.
I used 180 frames, with 30 frames per second.
My character moves 8 meters and the camera I created travels the same distance, on the same axis.

To my surprise, I realized, while watching the movie, that the camera was never at the same distance from the character.
Indeed, the camera moves in a perfectly linear fashion, which is not the case with the character.
The linear speed of the character is slightly sinusoidal. As its center of gravity rises, its speed slows down. Conversely, when the height of its center of gravity decreases, its speed increases.

Thus, for a walking cycle, during half of the cycle the speed of the character is slightly lower than that of the camera, and during the other half of the cycle it is the reverse.
This produces a concertina effect which can be fun to watch at close range, but which is annoying if shooting the character from a long distance.
It is obvious that if we film the character without placing the camera too close to him, or if we film him from the side, this effect is less visible.

In view of this problem, I would like to know if we can attach the camera to the character so that it can have the same instantaneous speed, or if there is another method.

 

Richard Haseltine

How are you moving the character, by the hip bone or the figure? If he is essentially walking in place, with the figure handling the horizontal displacement, then parenting the camera to the figure will track movement without bouncing up and down. If, on the other hand, you want to keep the character's head in the same position in the frame then parent the camera to the head. If you want to link the camera to some, but not all, of the motions of a node (e.g. if the hip is both moving up and down and handling the forward motion) then you would probably want to use the Property Hierarchy pane to make the x/z translations of the camera match those of the bone while keeping the y independent.

Willy2

Thanks for your answer, Richard.
I am using an animation that I didn't create. So I don't know how the character is animated.
Following your directions, I tried to parent the camera with the body parts.
It's the parenting with the head which keeps a fixed distance, and a regular framing.
But the problem with this method is that the horizon line behind the character is moving slowly from side to side. However, I can cut out the character and put a background behind it, which will temporarily fix this problem.
When I have free time, I will analyze the bvh file in detail in order to better understand the movement of the bones, to properly configure the camera. This file corresponds to a sexy walk, with a fairly pronounced movement of pelvis, which complicates the problem ( we could ask women to walk more simply, but that's another topic ! )