In general the trick is to add the clouds (either an image or a node) to the physical sky “Haze” value as Master Zap indicated in his blog.
To achive that in Maya you will need the following.
Maya nodes = noise, multiplyDivide and luminance.
Connect as follow
noise out color > multiplyDivide input
multiplyDivide output > luminance input
luminance out value > mia_physicalsky haze.
The noise node will serve as the clouds in the sky, which can be animated easily.
Once rendered you will hardly notice any clouds.
This where the multiply/divide nodes comes in.
Increase “Input 2″ to be 20, 0, 0
Now you will have more prominent clouds.
Since the haze parameter accept only ONE value.
The RGB > Luminance node can be useful in this connection, since it will convert the 3 out values of RGB to 1 value which is luminance.
In the Noise node, you can animate the time value to get the animated clouds in your render.
Note: The Noise node can be replaced with a texture file or any other Maya nodes.
To achieve more realistic result, add an envBall node to the shading network, this will give the sky roundness effect rather than just a flat image.
From here you can start building more complicated network to get more realistic look.
Note: to get rid of these artifacts that you see on the cone object, one needs to examine the network connection closely.
The clouds were connected to the “haze” parameter, however that “Sky haze” is already connected to the “Sun haze”
The following image reminds me with Alias Power Animator Sky system.
If you know what I’m talking about , then you are old.