Hello,

I just finished watching the fog tutorial in compositing and I did everything that they said but it seems that my fog doesn't work. I got my fog to show up, but I couldn't get my fog to be at the ground level.

In the tutorial, under the “Layer” tab, I've changed Layered off to “Y Layered (below)” and Layer edge to “-0.9”. But that only diffused the fog.

I guess my question is, how would I create fog so that its only on the ground?


Brownies

For layered fog to work, you need to have a P (point) plane, which includes x,y and z information. Pz is the depth only, which won't include y information, and so layering in that direction won't work.

If that's not it, try reducing the layer falloff parameter to 0 - the falloff produces a gradual decrease from full fog to none; perhaps it's too large for your case. 0 will make a sharp transistion from fog to clear.

Finally, inspect your deep raster image's point plane (press ‘i’). Check the height of the floor and make sure it's close to your Layer edge.

The thing you said about having th P plane sounds like what I need. How would you do this?

I'm doing a short animation for my class and I want to add ground fog to make it look more mysterious. How would I render my animation so that it has the P plane?

When rendering through the mantra ROP, first make sure you're rendering to a .pic file. Switch to the ‘Deep Raster’ page and in the first parm named ‘VEX Variable’, use the button menu to select ‘P (surface position)’. Now render; mantra will place the P plane in the .pic file.

You can also render to a non-deep raster file, like TIFF, however the P plane will need to be written to a separate TIFF file, which makes the process a little more complicated (which is why I recommend using .pic files).

You can also render N (surface normal) in the same way, which will let you use the Lighting COP effectively. But it's not required for Fog.

there is a video tutorial here:
http://sidefx.vislab.usyd.edu.au/houdini_video/by_topic/compositing/index.html [sidefx.vislab.usyd.edu.au]
about using fog

Thanks for the feedbacks.

I got the fog working but there doesn't seem to be any fog in the center of the picture. It seems like that the fog is distributed in a circluar fashion from the center instead of horizontally. If you know what I mean…

If I increase the Fog Density, the outer edges is filled with the fog first leaving the center with no fog. All I want to do is to create fog on the ground.

And one more thing, I rendered about 10 frames of my animation to test the P plane. But the file seems to be huge (almost 1MB in a 320x243 resolution). Is this normal? Is there anything that I can to to decrease the size of the file so it won't have a long render time?