issues with 'geometry velocity blur'

[dpz]

hi.

i want to render an imported bgeo sequence with motion blur.

since the geometry has changing topology i have to turn on 'geo velocity blur' and add the velocity attribute manually.

i used the trail sop, switched it to 'compute velocity' and lowered the 'velocity scale' from 1 to 0.2.

and the result is a pretty messed up piece of something.

but check it out yourself ..

geovelblur.mov

so if anyone experienced something like this before and has a solution ... let me know.

thanks i advance.

cheers

-chris

[aracid]

Hey Chris

I think the point count may be changing over time, which makes it a problem for the trail sop to compute the velocity.

it compares point(1)'s position at frame X to point (1) position to frame X + 1,

The problem with that is, if the points's position can't be tracked by either their id or the order of the points, you have to come up with a funky solution.

where is the mesh generated?

[dpz]

well, the geometry was generated in houdini and i simply forgot to add the velocity attribute to the 'particle fluid surface' node.

and of course no velocity information was written to the geometry 'cause one has to define it manually ..

stupid me .. anyway, thx for your help. =)

but let's imagine i wouldn't have the chance to fix it as easy as this .. what would be such a funky solution u mentioned?

cheers,

-chris.

Edited September 6, 2010 by dpz

[Macha]

Are there volumes involved in the creation/simulation process? If yes, check if there is a velocity field, use that for your v attributes.

Otherwise, perhaps your underlying points that you use to create the fluid motion may contain v attributes.

I think there is a way to let mantra calculate the correct velocity if you are using metaballs. But I forgot where the setting is.

If all this fails, you can use mantra's standard motion blur (!=geometry v attributes).

As Brian says, the point count confuses velocity calculation.

Edited September 7, 2010 by Macha