Particle Collision Problems

[melc92]

Hi,

 

I have tried to make rain in Houdini using source particles and I have managed to get them to collide with an alembic file that I have exported from Maya, however there's a problem because the collisions seem to be happening above the actual objects instead of on them so the particles are floating above?

 

I have no idea how to fix this as I am very new to Houdini, any help would be great!

[Nick da Silva]

What does your collision geometry look like? Can you attach the hip file?

[Sierra62]

Assuming you are using bullet collision try switching it from Convex Hull to Concave. 

[Farmfield]

In the solver for your collision object, you have the option to visualize the collision geometry, that will allow you to see if that is the problem or something else. As an example, I've done setups where I moved something at object level creating gaps without there actually being gaps in the simulation itself.

 

And if the problem is the collision geometry, you have all the optins in there for correcting the creation of that to match your actual geometry better, among other things using convex hulls.

[melc92]

Thanks for responding! I managed to fix it

[melc92]

I was wondering if anyone could help me again, I have the rain colliding with the objects and I have the style that I want but I want the particles to split when they collide with the ground and other objects in the scene.

 

I have tried using the 'POPreplicate' node but that makes the rain split the entire time, I'm guessing this may have something to do with where I am placing the node, but I'm not 100% sure where it should go.

 

I have attached an image of my setup, any help would be great!

 

This is also what I'm using for reference for the style of the rain, https://www.pinterest.com/pin/501588477227078883/

 

[Tyfx567]

Hey! I have attached a scene file in here. I explain everything in the scene file. But to explain it in here the biggest thing is your totalhit attribute. In your pop solver you can add attributes as the particle collides. There's one called hit total. This just tells you how many times it has hit obviously. But in your presolve in your pop solver, you can make an attribute that stores the hittotal on the previous frame, that way, in your group (in the post-solve), you can just say:

if(@previoushittotal != @hittotal) { ingroup = 1; } that way it only creates the group when it hits the ground. 

 

For the rain making it look the way you want, just maybe have them emit radially from the particle they emit from or just add a noise to them. And if you do noise be sure to say @v.y = abs(@v.y); that way they don't go through the ground

Split based on collisions.hiplc

Edited August 15, 2015 by Tyfx567

[melc92]

Thanks a lot for sending me this, but I can't seem to open the file :/

Edited August 17, 2015 by melc92

[Tyfx567]

Hmm that's strange. Well did what I say work and make sense at least?

 

 

Edit: Ok I have updated the file. It may have been because I had a gallery file to store my point vop that I use often to add turbulence to stuff. So I removed it. Hopefully it will work now

Split based on collisions_fixed.hiplc

Edited August 18, 2015 by Tyfx567

[melc92]

Ah, it might be a conversion problem because the file still won't open for me. The PC's don't seem to like 'hiplc' files, only 'hip' files.

 

But thanks for trying again and how you explained it on the earlier post made sense and I'll give it a try, so thank you!

Edited August 18, 2015 by melc92