I'm trying to make realistic snow in Houdini with particles and metaballs. But i've discovered some problems... I don't know how to make metaballs smaller at the end of branches...



So, i need in good advices how to change metaball's radius towards the ends of branches I'm thinking how i can use bounding objects...
Here is my latest test (rendered in 3dmax):



How to make snow fluffy (larger metaballs) in the areas where i have many particles? And smaller metaballs near branch borders?

Nice



Maybe you can measure the polygon area and use it to modify the size.

not sure about getting smaller metaballs at the ends of branches...been a long day...

but from the above image I don't think you really need to worry about it...that's what this kind of heavy wet snow looks like on spruce/pine etc...
a better improvement might be to figure out a way to knock chunks off from random areas...

keep up the good work

Gr8 start.Like it.

this was just a quick test but you can somewhat scale the metaballs with the stamp func from copy with $BBX

Snx for help I think that measure SOP can't help me - actually i have very different polygon's areas, for example - long and thin one.
I'm thinking about Bounding Box - but how to use this variables with rounded trees? With pine, spruce etc. So, i'm currently thinking about making low-poly envelope around my tree (bounding object) and calculating distance from this envelope to particles. For example - if particle located near my envelope (how to check this?) then metaball's radius has to be smaller.
Another idea - to make envelope around main branches, group particles inside/outside and use this groups to modify the size.

It all depends on how you generate your base geometry.
though it might be possible i cannot reverse engineer this from your network screenshot.

I'd try to isolate the branches as lines to scale the metaballs based on $PT.
But this doesn't explain the popnetwork - does it "grow your snow"?
Maybe there is something inside the popnet that can be used too.

Georg

I'm importing trees as meshes from Onyx TreeStorm Unfortunately i have only mesh.

attrib transfer red from a simple geometry to your tree.
use blend width and distance to control falloff.
copystamp up the red to your metaball.
use fit01 to remap red to your min and max metaball size.

Great thanks! I made it!!!

Nice work
I like it.

Another question! For example i have grid object, how i can procedurally select border's point or edges?

Use the divide SOP with Remove Shared Edges turned on? Got that from the On the spot book, (it's great by the way).

Snx! And the last (i hope) question - i have small volumes of metabolls - how to delete them? Or delete small pieces of polygons? (i'm growing metabolls over them)

I used Fuse SOP after Convert Meta to remove undesirable points

Small udate

good stuff!
now lets see a forest!

And a Mantra render!

yea.. definitely a mantra version of this!!!
I would like to see how far it can go.

Rendering in mantra takes near 20 min! Its terrible! But i don't know how to improve render time, i'm novice in mantra
In this scene i have 1.3 million vertices, raytraced shadows and Global Illumination (full irradiance, 32 samples)
If i do renders with Global Illumination Matra renders 2 frames - 1st something white 256x256 and 2nd goes my picture. After turning off Global Illumination mantra doesn't render 1st white frame...

Really? That doesn't sound great. Any chance you could zip up this geometry and let us give it a try?

Yes, but later, i'm slightly busy

Have you checked "irradiance caching" and played with the settings?
Of course you are likely to achieve the cleanest result with irradiance caching off and something like 256 samples but I'm not sure if it is worth it

Also, if your geometry is imported it's all very heavy. If you'd use curves with witdh attribute instead of polys, rendertime and memory usage would be much more efficient and you could try rendering a forest. Thad should leave any MR/Vray far behind.

Here is my scene - 11 mb - scene

I noticed one thing that was kinda bugging me - it's a bug in the snow shader (which is a Simple Displacement material from the palette) - where it's adding some bad looking displacement to the polygons (offsetting each polygon individually, thereby making it look kinda faceted), giving it a rather crappy look. I've reported this bug to SESI.

You're probably better off just creating your own little noisy displacement shader in VOPs until they fix it.

This, I think, was also the reason for the slower render times. Raytracing against displaced surfaces is a bit slower and heavier than simple polygons. If you're really after some bump detail you could try add the "True Displacement" property to your shader, object or ROP and switch it off. This will simply bump the normals and your render shouldn't be any slower.

I've also found that using irradiance caching and using pure Raytracing can lead to quicker renders on this scene (I instanced 250 of your trees around the place to test)

man 41mb unzipped file. i manage to open it but every attempt to jumpback to obj level causes me fatal errors. would like to dig in this hip.

Here is that forest of 250 point instanced trees. I think this took about 45 minutes, I'm not sure - I forgot to time it. I could've rendered a better image too... but anyway.

Good news, snx!

This is looking way cool, tnx for scene file, can-t wait to have a look how you did this when i get home from work

I someone have this sceen, if can send me ona igorzcg@gmail.com
Thanks in advanced...