[Closed] how to calculate in/out tangent in tackview

no, no, no… not again. i remember… i’ve answered… i swear

alright i’ll try to go back to the old thread and try to figure out what I missed

atan2 outTangent 0.1875 

seems to give the appropriate answer, no idea why 0.1875 is the magic number.

What is the angle if you can zoom x and y independently, and In/Out tangent value doesn’t depend on next key position?
here is the same curve but different zoom:

the “reverse” would be

    outtangent = (y * 0.1875)/ (outlength  * delta_frames )

i may get there in the end?

the 0.1875 could relate to 4800 ticks per second somehow (other than being equal to * 900)

hmm didnt get the same results as using atan2

just to be sure y = y value in the track view ( the value of the next key) ? and delta frames the differences between the current frame and the next frames ( out tangent)

edit:outtangent = y value *.1875 / delta_frames seems to work.

I did get the desired tangent… I’ll do another test

SECOND EDIT: my second test seems to work although we should replace Y or Y value by delta Y ( see attachment) I used the out tangent value from the math and this is what I got ( and no matter how I zoom it stays the same

so outtangent = (delta_Y*.1875)/delta_frames

btw this is working with a .5 tangent length setting

y was the vertical offset to the handle from keyframe value

Hello gents,

I’m a newbie on CGTalk and I’m also digging up an old topic, but I think I’ve got answers for unresolved questions here. I’ve read numerous threads which never gave a proper solution, so here is mine.
I’ll try to be as clear as possible, though my mind is still pretty dazed. I’ll just start by saying, Mr denisT, .1875 is definitely NOT a magic number

I’m been working on an animation exporter for some days, finally facing the awful issues of bezier key tangents. I’ve spent like ten hours trying to figure out what was REALLY going on there, mostly on that .1875 value that I’ve found on every topic regarding those in/outTangent values. Fact is, this value stand as long as you don’t change your time configuration.

I’ve finally understood the logic, as the outTangentValue is a percentage of the distance between the following key and the current key – let’s call this distance, Delta. Delta is however a substraction between time values.
At this time, I understood that those tangent values relied on the frame rate. The frameRate value is linked to the ticksPerFrame value as ticksPerFrame * framerate = 4800. (cf. MAXScript help). And then, I’ve ended up finding our precious : .1875.

With a basic frame rate of 30fps, ticksperframe is therefore 4800./30 = 160.
BUT, here it comes : 30./160 = 0.1875.
This value will change if the frame rate change. For example, at 25fps, it’s 0.130208.

I’m not quite sure of how I ended up on this, but here’s the final & proper equation for an out tangent, which will give you the difference Y value between the key and the tangent point :

 OutTangent_Yvalue = (
  ( outTangent  * outTangentLength * Delta * ticksPerFrame ) / frameRate
)

Some trick here as Delta is the distance in frames between the current and the next keys. For instance, if the first key is on frame 5, and the second on frame 30, Delta equals 25. This calculation goes like this :

 Delta = (
  -- Gets the distance in frames between the keys as a Float value,
  -- as Animation keys time values are float values.
  -- A key can be set to a time like 19.5f.
  ( ( theKeys[i+1].time - theKeys[i].time ) as float / ticksPerFrame )
)

Hope I got it all right, once again I’m quite exhausted right now. Feel free to correct my points or explanations, but I’ll stand on my formula ! =)
Hope it’ll be useful to you all.