FLIP sourcing from VDB

[Waasha]

Hello, I'd like to ask what is wrong with sourcing initial velocity from VDB field..

 

Attached I have a scene, which is working fine with sourcing from fluid source node, but is not working with the same field created as VDB fields.

 

To see the VDB version, switch the switcher in the AutoDopNetwork from 0 to 1.

 

Thanks for any idea why it's not working..

init_vel_from_VDB_V01.hipnc

[anim]

FLIP uses particle v attribute as the velocity, so sourcing to vel field, will not help as it will be wiped and populated from v attribute, unless you plug source to Volume Velocity input of FLIP solver

on top of that you didn't set any velocity operation nor specified the vel field in the Source Volume parms, so your vel field would not add anything even if plugged correctly

 

for FLIP is the easiest to keep v as an attribute so either attribtransfer v to source points or sample v from your vel volume before sending source to DOPs

[Waasha]

Thanks for such a quick reply, anim!

 

I am aware, that I didn't specify the vel field in the source Volume parms, but neither I did for the "classic" way of sourcing the velocity and it works.. I tried to mimic all the field just the way the "classic" fluid source node sets them, so if you carefully look in the emitor, you will see, that I have particles there, and I have both the surface and the vel field, just like with the "shelf tool" situation.. There is no difference in the source concerning the data.. Yet with the shelf tool it works and with the data prepared from VDB it doesn't work..

 

I just don't understand why?

 

And also I know I can plug source to volume velocity input of the FLIP solver, but that would act as a velocity emission, but not as the initial velocity of the particles, if you know what I mean. You can see the difference in the color of particles at the first frame. If they have initial velocity, they are already lighter (they have some velocity when they are born)..

 

I have some ways to solve it differently, I just wanted to understand, why the same data are not working when made from VDB (try to middle click on both OUT nulls in the emitor geometry, they have the same parameters and fields..)

 

Thanks a lot!

[anim]

as I mentioned before, FLIP uses v attribute from source particles for velocity, source vel field is ignored

 

and if you notice the difference between the shelf setup and your source is exactly v attribute containing initial velocity being present on shelf source, but your's doesn't have any v, therefore no initial velocity in DOPs

Edited September 17, 2014 by anim

[Waasha]

Ooh, ok... That's right... I was so focused on replicating all the volumes (there is a surface and a vel volume created by the Fluid Source node in the emitor), that I didn't notice a simple fact, that all the points have a v attribute, that is NOT transferred to the points created by the "points_from_volume" node...

 

Sorry for my ignorance.. I just thought the initial velocity for the "shelf" example is working because of all the volumes, but there doesn't have to be any volume at all to source particles with some initial velocity...

 

Thanks again, you made it quite clear for me..