temporal vs spatial curves

[Brian Jones]

if we are dealing with the position XYZ curves then the slope of the curve gives you the speed between keyframes. But you can’t move any of the keyframes position (up and down) or the point in space changes for that keyframe. You can move a keyframe left and right and that won’t change the position only the timing – the object gets there faster or slower). If you don’t move the keyframes at all then the slope handles are the control you have steeper is faster, flatter is slower, but given an object has to make it from ‘here to there’ in this many frames if you make it move faster in one part it has to move slower to compensate at some point.
More simply – you can’t move the keyframes up and down in the timeline if the position of a keyframe can’t change.

[Adam Trachtenberg]

Regular keys represent a specific value — X position for example — at a particular time. If you adjust an fcurve point up or down you are setting a different position at the same time. If you move a point right or left you are changing the time that the object arrives at the same position.

If you want to keep the same motion and only adjust the timing, then the time track is what you want. Time tracks are very powerful.

[Manojit Ghose]

thanks for the responses.

i understand. however i wanted to know something regarding the curve tangents.

i mean to i assumed changing the tangent in the time line only would change the in-between keyframes’ spacing. however when i manipulate them in the timeline the object trajectory changes rather than in-between keyframe spacing.

this does not happen until i select the key-frames in the timeline and make them “zero angle/length”

it would be ideal if i could manipulate the trajectory (in the editor view) and the animation speed (in the timeline view) independently and interactively.

does it mean if i change the keyframes to “zero angle/length” i loose the option of manipulating the animation speed altogether. and i have to resort to the time curve?

hope i was able to explain my problem.

MG

[Adam Trachtenberg]

The shape of the position curve reflects the shape of the trajectory. If you change it then you are changing the trajectory.

[Manojit Ghose]

hi adam, thanks again, i’ve already realized that.
i am seeking an answer to:
in the timeline, why the behavior of tangents manipulation effects spatial interpolation along with temporal? (it ends up manipulating the trajectory of the object, while all i seek is to manipulate the speed only) is there a way to manipulate them independently?
(i am not talking about the time curve solution)

thanks

[Manojit Ghose]

here are a couple of post i found but doesnt tell a lot on what i was looking for..

https://forums.cgsociety.org/archive/index.php/t-1103608.html

https://www.c4dcafe.com/ipb/topic/79853-velocity-curves-in-cinema-4d/

MG

[Adam Trachtenberg]

Again, the answer is no — there is no way to adjust the shape of a position f-curve without affecting the position. If you want to leave the position unaffected but adjust the timing, the way to do that is with a time track.

[Manojit Ghose]

thanks for the definitive answer adam.

MG