[Sidefx-houdini-list] pop previous velocity

Luca Zappala luca at cinesite.co.uk
Tue Apr 17 12:17:21 EDT 2007


@Pablo
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 
faster solution.

@Ben
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
Luca



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") )
>
> succes,
> benS
>
>
> 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[0]): 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.
>> thanks
>> Luca
>>
>> Luca Zappala wrote:
>>> Hello there,
>>>
>>> I'm trying to cache the particle oldVel (velocity at the previous 
>>> frame).
>>> 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
>>> Luca
>>>
>>>
>>>
>>> _______________________________________________
>>> Sidefx-houdini-list mailing list
>>> Sidefx-houdini-list at sidefx.com
>>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>>
>>
>> _______________________________________________
>> Sidefx-houdini-list mailing list
>> Sidefx-houdini-list at sidefx.com
>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>
>
> _______________________________________________
> Sidefx-houdini-list mailing list
> Sidefx-houdini-list at sidefx.com
> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>




More information about the Sidefx-houdini-list mailing list