Sorry if this seems like something kinda dumb, but I am trying to figure out how to calculate the speed of my animated object.

i realize i can throw down a trail sop and compute my velocity that way, but my problem is that i want to calculate just the global animation of the object at OBJ level and no local motion.. so i just want the velocity of my animation curves in X, Y, Z at OBJ. the only thing i could think of is taking the derivative of the position curve but have no idea how i would go about that in houdini.

Also, i am really having a bad day math wise and am fighting with myself on how to calculate the speed (float) from the velocity (vector). i'm thinking it's the vector's length, but still not sure… is it sqrt(x^2 + y^2 + z^2)?


any help on this would be appreciated… thanks..

Sounds like a job for the “Slope” chop.

The slope chop takes 1st, 2nd, and 3rd order derivatives of incoming channels and is super-duper handy.

assuming that your input channels are positional data:

1st derivative = velocity
2nd derivative = acceleration
3rd derivative = jerk (rate of change of acceleration with respect to time)

Another good one to have in the back pocket is the “Area” chop,

Which reverses the process by integrating an incoming channel.

Hope this help,

Cheers,

G

You could also create a single point (via the add SOP), and from another object, object-merge that point (transform via /obj/World (which you'd leave at the origin)) and then trail SOP it.

– Antoine

ahh you guys are life savers..

im kinda suprised they would have those calculations via a slope and area chop. why not just have multiple order derivative and integral capabilities in the function chop or math chop? it'd also be kinda nice to have them in the expresion library, so i could just do something like deriv(ch(“/obj/geo1/tx”)) .

anyways, both those methods will work splendedly..

thanks you guys,

dave q

deecue
ahh you guys are life savers..

im kinda suprised they would have those calculations via a slope and area chop. why not just have multiple order derivative and integral capabilities in the function chop or math chop?

Maybe because CHOPs is sample based, so the accuracy of the integral or derivative is very much dependent on how many samples you have.

it'd also be kinda nice to have them in the expresion library, so i could just do something like deriv(ch(“/obj/geo1/tx”)) .

You can do this by doing:

ch(“/obj/geo1/tx”)-chf(“/obj/geo1/tx”,$F-1)


– Antoine