[Sidefx-houdini-list] pop previous velocity
luca at cinesite.co.uk
Tue Apr 17 12:17:21 EDT 2007
It would most definitely work but it wouldn't be very efficient
(increased disk access times). I guess the trail sop would be an overall
I tested velocity minus acceleration but it gives me wrong oldVel values
(in the range of 4 times what I expected).
I've also tried to create an attribute oldVel at the end of the popNet
(using current velocity as values) and to cache the popnet outside by
using the rop driver node; but oldVel and vel seem to still be the same.
Any ideas ?
Thanks a lot for your help
Ben Schrijvers wrote:
> I would say that when you add some Attribute POP's at the end of the
> chain to create an oldVel or prevAge attribute.
> Just set it to $VX,$VY,$VZ.
> Then next frame that attribute should be the previous frame velocity
> or age.
> In fact I believe that while at the current frame you always access
> the previous frame attributes.
> So really you are talking about the one before the previous... but
> let's forget about that as it makes thinking more complicated.
> Another way to get previous velocity is to subtract the acceleration
> from the velocity. oldVel = velocity - acceleration
> Acceleration is the change in velocity and so is the difference
> between the velocity and previous velocity.
> In the same way you could calculate the previous age as you know the
> duration of a frame.
> oldAge = Age - ( (1/$FPS) / ch("../oversample") )
> Luca Zappala wrote:
>> Ok, I found a decent solution by storing the v to n, use the trail (1
>> frame) and compute velocity, copy v to oldVel, copy n back to v. This
>> way I get correct oldVel except for the last frame before the
>> particle dies, but I can live with that.
>> Now I'm getting stuck with the particle Age (life): I would also
>> like to store the previous frame's particle Age. :)
>> Any ideas?
>> I guess this would be an interested topic on how to store simulation
>> variables at a different time from current time.
>> Luca Zappala wrote:
>>> Hello there,
>>> I'm trying to cache the particle oldVel (velocity at the previous
>>> I read the upvector node should create a previousVelocity local
>>> variable (PV) but this doesn't seem to be working properly, in fact
>>> PV is the same as V.
>>> Do you have any other idea on how to store the oldVel as well?
>>> thanks a lot
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