particles rotation problem

[blackchicken]

Hello I have problem with particles rotation after they start moving by field. there is example. How I could fix it? I try rotation pop but I`m realy confused of them.Houdini help didnt help me too much to. Any idea? Thanks a lot.

feathers_bad_rotation.mov

little hip

feather_02.hip

[anim]

the copy SOP is using "v" attribute to orient copies

that's why they rotate when they start moving

in rotation POP you can put your expression to Angle param and to axis Y just 1

but it would result in all feathers rotating around Y the same speed

you can use Angular Velocity POP for more controled rotation behavior, like according to speed you can increase angular velocity too

with some randomization on axis, or whatever you want

no matter what you use to rotate particles, you'll get "rot" attribute which is like relative offset to "v" for copy sop, so it won't help you much

but you can rename it to "orient" after POP network to get stable orientation of copies

look at the example

you can also just delete/rename "v" and "N" attributes if present

then "rot" will behave as expected

but you maybe need "v" for motion blur so the first solution is better i think

feather_02_fix.hip

[blackchicken]

Thats briliant, thanks, you help me a lot. Little bit more understanding of particle rotations.

[tomhanks]

the copy SOP is using "v" attribute to orient copies

that's why they rotate when they start moving

in rotation POP you can put your expression to Angle param and to axis Y just 1

but it would result in all feathers rotating around Y the same speed

you can use Angular Velocity POP for more controled rotation behavior, like according to speed you can increase angular velocity too

with some randomization on axis, or whatever you want

no matter what you use to rotate particles, you'll get "rot" attribute which is like relative offset to "v" for copy sop, so it won't help you much

but you can rename it to "orient" after POP network to get stable orientation of copies

look at the example

you can also just delete/rename "v" and "N" attributes if present

then "rot" will behave as expected

but you maybe need "v" for motion blur so the first solution is better i think

Thanks for this information and for the file, with that I´ve learned more about the rotation too but I got a little confused about the orient attribute, I tried to look for the manual to see the difference between the orient and the rot attribute but I didn't find anything the could clear this, can you?

thanks

[anim]

according to my experience it seems that:

"rot" acts like offset from rotation computed from "v" or "N" and "up" or "orient"

if "orient" is present, "v", "N", "up" are ignored and "orient" sets the whole rotation

if "orient" and "rot" are both present then "orient" sets the base rotation and "rot" acts like offset on top

[tomhanks]

Thank you very much, it clarifies a lot.

I just think that the manual should have a more detailed description about attributes like that.

Thanks again and sorry for the bad English.