Some problems with the clouds

[TopNub]

Hi, guys!

I have a serious challenge to create photorealistic clouds.

For example like this -

I seriously Explore the Internet and Houdini help on the clouds and I even managed to achieve some results.

My scene has fly camera, shader based on the blowysmoke and the geometry of clouds consisting of metaballs. Scene rendered from two nodes. This is a pass for light from the sky and sun light.

But now I have a few problems which I can not change:

1. My shader beautiful, but I'm not enough, I need like Rytm & Hues, or something similar to this picture - http://dobrochan.ru/src/jpg/1012/Clouds.jpg.

shader of my clouds do not have enough shape, flat shader. I want to make it more spherical. I tried to change the position of the sun and the value of ambient, but it's not much help.

2. Then I decided to way of change in geometry. I've done in my heap geometry is something akin to real clouds. To do this SOP, I convert the metaballs to the geometry, and then with the mountian and peak and make noise. But my shader is not working with geometry, he needs it the metaballs as volumetric. -> So I added to the bottom of the tree again my isoofset and volumemix. But it did not help, shader not repeat the form below.

3. To test a new form with the mountian I decided to take the standard blowysmoke and setup a little noise. Standard blowysmoke showed the shape of clouds, but as a whole look bad. Has no diversity, and transparency at the edges

4. An additional problem is that the edge of my geometry shader has a sharp boundary, but the standard has blowysmoke

Please see the my hip and tell me what is wrong:

http://depositfiles.com/files/xz75yk2i7

P.S. Sorry for my English, I used Google translator.

[lukeiamyourfather]

I'd start with reducing the density (either shader or volume).

[Macha]

I'd say, give your clouds some shape, like a flatter bottom ( nice and round is very pleasing, but this is a cloud and usually the base would indicate the point at which condensation starts, and that would usually have a different shape from the rest), a bit of updraft towering, and perhaps a little displacement noise. Also, some sense of directionality and layering would help. I also find them a little too grey. As if it was about to rain.

Edited March 1, 2011 by Macha

[Darric]

Not to cross post from General Chat, but incidentally, cmiVFX recently released a video on exactly this topic:

http://www.cmivfx.com/tutorials/view/280/Houdini+Fractals

[TopNub]

Another question. What are the methods of displacement with volumetrics? I got only change the fog on the edge. I used curlnoise

[Sven]

@Darric: I saw that tutorial and its realy great.

For the film "A-Team" they used a very similar approach. To bring in some variation and smooth out the edges they used advection: ". A few steps of advection by vector noise was used to soften the edges and create small, ragged, separated pieces of cloud near the larger cloud." PDF

I wonder if somebody knows a way to reproduce advection?

[old school]

Gas Advect DOP.

It has several parameters that you just fill in. The critical parameter is of course Velocity where you point it at the vel fields. There is a Field parameter where you supply the field to advect.

The idea is to isolate the edges of the cloud, add noise and then use that to advect density.

There are a few ways to do this btw.

[TopNub]

Gas Advect DOP.

It has several parameters that you just fill in. The critical parameter is of course Velocity where you point it at the vel fields. There is a Field parameter where you supply the field to advect.

The idea is to isolate the edges of the cloud, add noise and then use that to advect density.

There are a few ways to do this btw.

old school Please make a small example for me!

[Chris3D]

Just wanted to echo the cmivfx video is really very good. They even walk through a part of the lesson doing something like the 'bunny' that you see in the referenced A-Team cloud PDF.

[TopNub]

Hello again everyone!

Many thanks for the tip, the lesson of cmivfx really helped me. For example, I understood much about the volumes.

Right now, my pipeline is as follows:

1. I have a large and complex system of points on which I put metaballs.

2. Then node objectmerge import my metaballs and turns them into volume fog in isooffset

3. Twice baked isooffset to i3d

4. Work with noise for my two i3d

Now I prevent two serious problems:

1. I have a very strong shadow on the clouds below. Just when the camera flies into the clouds, the entire screen goes black. See picture. I tried to change the light, but it did not help. It seems that this darkness is obtained from the density of the clouds.

How and where can I fix it? Maybe you need to convert metaballs to geometry or here work only with shaders or something else?

2. I read the help, but did not understand how the two parameters in isooffset. This Sign Sweep threshold and Max Sweep Count. I just realized that if their values ​​are small, the volume can be torn apart by horizontal lines. so the field is broken? Can anybody tell about these options in detail?

Thanks, Ilya.

[andreu.lucio]

Hi Ilya,

Maybe your overall density is to high if you want to fly through. Adding another light from the bottom and lowering it´s shadow intensity may help to control the darkness off the clouds. Even with no shadows in this second light to act as a ambient light can work aswell. You can also tweak the shader but I think it´s much easier to control the look with the lights.

[TopNub]

putoparri

I do not think it's a good idea. I have a lot of places where the camera is all inside the clouds - clouds around the camera. So if I put the light source from the earth, the rays will not work better than my sun. I think I got this from even more problems

Maybe you can do selfillumination clouds? Does anyone know how to do this?

[andreu.lucio]

If the light has no shadow it works the same as selfilumination. You will have to lower the sun intensity because it will be more bright but it´s an easy way off faking selfilumination.

[pelos]

i watch the cmivfx tutorial, and is great, he explain the noise in a 2d first so you understand whats going on and then move to do it in 3D,

the thing i don't understand, is why he use CVEX at shop lvl instead doing everything in the volume vop any ideas?

=)

Hello again everyone!

Many thanks for the tip, the lesson of cmivfx really helped me. For example, I understood much about the volumes.

Right now, my pipeline is as follows:

1. I have a large and complex system of points on which I put metaballs.

2. Then node objectmerge import my metaballs and turns them into volume fog in isooffset

3. Twice baked isooffset to i3d

4. Work with noise for my two i3d

Now I prevent two serious problems:

1. I have a very strong shadow on the clouds below. Just when the camera flies into the clouds, the entire screen goes black. See picture. I tried to change the light, but it did not help. It seems that this darkness is obtained from the density of the clouds.

How and where can I fix it? Maybe you need to convert metaballs to geometry or here work only with shaders or something else?

2. I read the help, but did not understand how the two parameters in isooffset. This Sign Sweep threshold and Max Sweep Count. I just realized that if their values ​​are small, the volume can be torn apart by horizontal lines. so the field is broken? Can anybody tell about these options in detail?

Thanks, Ilya.

[pclaes]

i watch the cmivfx tutorial, and is great, he explain the noise in a 2d first so you understand whats going on and then move to do it in 3D,

the thing i don't understand, is why he use CVEX at shop lvl instead doing everything in the volume vop any ideas?

=)

I have not seen the video, but it's pretty obvious to use cvex, that way you can apply it as a shader at rendertime. It is much more memory efficient to do it at rendertime, rather than the limited volume divisions you would get in sops. The cvex shop "divisions" apply to the volume sample step size (on the mantra node on the "sample" tab). Which means you could in sops have a full volume (density=1) with 4x4x4 dimensions and in the shop you can do anything with that volume at much higher detail levels.

It needs to be density=1 though, density=0 does not get sampled by mantra, therefore your cvex code would not be evaluated. A lot of operations can be done in cvex, especially noise functions and pointcloud look ups are good fun to help shape a volume. Or the displacements they are doing in that other thread, should work well at rendertime too.

[TopNub]

hello again everyone!

I have achieved certain results in the light volumes by adding uniform sampling. But the noise that results from multiply 3d gradient and 3d texture is suitable only for the edge veil, I think. So now I want to come up with an asset for my cloud pipeline.

I quickly made about what I want with the cycle of three ligaments mountian + peak + subdivide. But asset with them get a very heavy! Also during extrusion geometry intersect each other (I think because of this slowdown are made).

The implementation of such extrusion using VEX displace do not think that would help, because I use real geometry to create a *. i3d ...

Does anyone have any ideas how to implement this asset, so that I could bloat the cloud of any shape?

Edited April 8, 2011 by TopNub