[Sidefx-houdini-list] Grabbing velocity from dops

Louis Dunlevy ld at dneg.com
Thu Jun 28 05:31:26 EDT 2007


the dopfield expressions should do it for you although obviously you're 
only going to get the velocity of each individual piece rather than a 
varying attribute over the surface. I've been lazily putting a trail SOP 
down..

dopfield("../dopnet1", "myRbdObj_$CUSTOMID", "Position", "Options", 0, "vx")
or maybe
dopfield("../dopnet1", "myRbdObj_$CUSTOMID", "Position", "Options", 0, 
"velx")

or if you want to reference some custom data..
dopfield("../dopnet1", "myRbdObj_$FUNNYID", "BirthData", "Options", 0, 
"BirthFrame")

I have noticed that DOPs transforms vector3 attributes so you could try 
to pass v in and then suck it out and see what it looks like

something along the lines of (although this is definitely wrong)
dopfield("../dopnet1", "myRbdObj_$FUNNYID", "Geometry", "Options", 0, "vx")

Can you use the Dop Transform SOP in you're setup? That gives you velocity.

beeeeeeeeer, or mybe milk.. hmm I'm not too gone on milk
Louis

Rangi Sutton wrote:
> Hey folks,
>
> I'm fairly new to actually using dops.. so excuse me if this is obvious.
>
> I've got a whole bunch of rbd objects doing their thing, created from 
> groups as you do. I'm pulling them back into sops with an object merge 
> and /obj/dopnet:chunks*/Geometry, as I think is the way you should do.
>
> I want to render them with motion blur. I don't want to use a trail 
> sop because they're pretty heavy and I can see there is a value "vel" 
> for each object in the Position in dops. How would I go about getting 
> this onto my geometry as a point attribute? Do I need to stamp around 
> an expression per group or something? There must be an easy way for 
> this...
>
> Beers,
> r
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