[Sidefx-houdini-list] Emitter velocity

Erik Zimmermann ezim at d2.com
Tue Oct 23 13:20:34 EDT 2007


Use a trail SOP to compute the velocity of the source/emitter geometry, 
and then set the source POP to "use inherited velocity" or "add to 
inherited velocity."  The global variables $VX,$VY,$VZ, or the point() 
expression can be used to access velocity elsewhere.  You can also 
calculate the magnitude (speed) of the velocity vector using 
length($VX,$VY,$VZ).  CHOPs can be used to calculate change in 
acceleration, etc.

-Erik


A ndras Ikladi wrote:
> Hi Andy,
>
> The simplest I can think of is a trailSOP then using point() sample a given
> point's velocity attribute.
> Alternatively feed the transform to CHOPs and derive the speed there..
> but then you need to take both rotation and translation into account.
>
> cheers,
> Andras
>
> ps: say hi to the guys at Axis, if you happen to head that way :)
>
> On 10/23/07, Andy Nicholas <andy at andynicholas.com> wrote:
>   
>> Hi,
>>
>> Can anyone tell me how I can get the velocity of an object into an
>> expression? I need to vary the direction of emission of some particles
>> based on their emitter's velocity.
>>
>> I'm sure there's a simple answer, but I haven't found it yet!
>>
>> Thanks
>>
>> Andy
>>
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-- 
erik zimmermann
effects artist
digital domain
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