I have a flock of helicopters using particles, how can I simulate the helicopter-like orientation based on their velocity/acceleration? Either during the POP-sim or post-sim inside SOP level. So far, I am using their velocity direction as N to have them facing forward. Is there any way to rotate points in VOPs?

You can't really “rotate” a point - it's just a position in space. It has no orientation.

You can, however, rotate a vector attribute that you have attached to the point. You can also rotate a sprite that you've attached to the point. Is that what you want to do?

It sounds like you already have what you need - the normal vector pointing in the direction of the velocity. That's your ‘helicopter orientation’ right there. 8)

KMcNamara thanks for the reply, velocity gives me the main orientation but there secondary rotation in an helicopter based on its acceleration, when goes faster is leaning forward on x axis, when its changes direction by making a turn leaning sideways on z axis based on which direction . Maybe I can use an up vector but how I will combine the up vector with the N which gives me the main orientation?

Ah, I see.

You could probably do this quite easily with CHOPs using the lag node. The idea would be that you have a second particle dragging behind the first, as if being dragged on a rope. The vector between the two particles will always be the helicopter's up vector. This should capture the leaning forward as well as the tilting sideways to make a turn.

Have a look at this tutorial - should give you all of the information that you need. I can try to whip up an example later if this doesn't make sense

https://vimeo.com/6930074 [vimeo.com]

I havent done CHOPS before but this seam clear enough, the problem is that with one object or point which has few keyframes will be propably fast. I am thinking that with 100s of points coming from a particles sim, which means every frame there is an in point of animation in CHOPs will be slow. But even if thats not the case and I get the up vector from CHOPs as an attribute attached to the original points, how I will use it in combination with velocity's direction to rotate each instance object attached the points?

I will create a simple hip and post it soon

here is the hip


regarding my question for the up vector with normal vector… I gave the answer myself, it was a stupid question. I am getting close with vops but still missing few bits.