In the popnet source node you can set the initial velocity of your particles under the attributes tab.

What I am trying to figure out is how to use that same velocity elsewhere like in another objects transform node so its movement is at the same rate as the particles velocity.

I've tried using a channel reference by dragging and dropping the velocity channel to the desired transform box eg. ch(“../../Tail_2/popnet/source_first_input/vely”).

Houdini doesn't complain ( no error messages ) when I do this but the object doesn't move.

I've looked in the Help file and there is much info about the pop velocity, however my level of Houdini knowledge is not yet high enough to make use of it in order to make an expression that works.

At the moment I've been guessing through trial and error using different values of $F * x to get it close to the particle velocity. I've tried using $F * x in the velocity entry but that seems to create a “mess”.

Any help is appreciated - thanks.

I assume, you dropped the reference to your location, right?

Then you you really should see nothing, because you set the position of your object at the value of your particle's speed. Maybe you missed the jump as you pasted the reference, or as a coincidence, object was at (eg.) loaction 0 and the speed was also at 0.

Speed is movement per time. So you would need to multiply that speed by time, to get a distance.

location = time * speed


If you just paste the reference, even though it is logically a speed, houdini does not really care about. It is just a referenced value, being used in a location parameter and so is interpreted as a location.

modify your “loaction” to like:
$FF*ch(“../../Tail_2/popnet/source_first_input/vely”)

Should be better then.

Best would be, if you would be able/allowed to provide at least a small *hip with what you set up.

Anyways, I hope this helps also a bit.

Hi WhoDjini,

Thanks for taking the time to answer.

So yeah like you suggested I had already tried that, but the object moves much more faster than the particles.

So I made a new file and reduced the components to the minimum.

So I have 2 objects.

One is a line which is emitting two streams of particles with its velocity parameter set at 0.25 in the x axis.

The second object is a sphere whose x translation is set to :

$FF * ch(“../Point_Emitter/popnet1/source1/velx”)

Thanks again for taking the time on this.

And just to clarify, I'm not necessarily looking for a solution to a particular setup I have.

I was just trying a tutorial when this idea of velocity in the popnet source node was introduced to set the particles speed.

And I was simply wondering if it was possible to set up a scene whereby a single or many separate objects could be moving about at the same rate that these particles being emitted were.