View Full Version : Sky domes, reflections, and radiosity.

11-28-2003, 03:45 AM
I want to do a skydome type radiosity scene, but early experiments ran into trouble. As the render times are VERY high, I'd really appreciate some ideas before I start experimenting.

The scene is basically a coastline, with a water surface covering part of the land, and a hemisphere with a gradient providing the basis for the sky, with some HV clouds. Sky colours are strong. I get very close to the surface of the landscape (a couple of metres), and the farthest parts of this object are several kilometres away. So UV maps are right out.

I tried straight radiosity, but the problem was that the land acquired a strong bluish cast, presumably picked up from the sky. But I want the sky to be picked up by the reflection in the water, (and the HV clouds too).

So I guess what I am trying to say is that I want the current sky to be 'seen' by the water for the purposes of reflection, but not by anything or the purposes of radiosity. And I don't think reflection maps are an option, as I plan to have things moving low over the water at some point.

Anyone have any suggestions?:confused:

11-28-2003, 05:01 AM
hi starbase,
You can use a 'raytrace and spherical map' for the reflections at the same time.
Under the objects properties you can disable radiosity from effecting the sea object (per object setting, not per surface :( .
Try using 'backdrop only' mode for Radiosity to help speed up the renders (a lot).

11-28-2003, 10:34 AM
Sometimes you can get away with using pretty high settings as you can see below in my Hemispheric Lighting test.


11-28-2003, 10:47 AM
If you're only rendering a still, then the Interpolated mode of Global Illumination works pretty well and saves a lot of time. However, you can't use it during an animation because of the flickering that will occor.

I tend to use the spinning light trick. Eki's Plugpak is the one that I use and the differences between the spinning light rig and GI are hard to tell. Plus, it saves tons of rendering time.

As for your sky reflections in your water, if you are using Skytracer to make your skies, you can pre-render it to a dome or cube object. And also at the same time, you can save it in an HDR format so that your reflections have a much greater range on the surface of the water.

11-28-2003, 03:21 PM
Radiosity + Ray-trace Reflections + HV = Absurd render times ! They practically Multiply the render times when used together -

You don't really need ray-traced reflection at all, use a nice image of the sky as a reflection map, and in place of HV clouds - that's what the pros do...

11-29-2003, 07:37 AM
Thanks for all the sugestions guys, though I am not sure I have the answer I need...

I think I do need real reflections - the sky is very complex, (gradient dome as background, HV clouds in front, additive transparent solar haloes, big moons in the sky, and I want somethjing to sweep over the water eventually, reflected in it!

I tried spinning lights but still have very deep shadows, and ambient looks wrong, (as usual!).

I'll certainly give interpolated a go.

I don't think raytrace plus backdrop will wrk - you cant see the backdrop, the sky object is in the way!

I don't want to exclude an obect fropm RECEIVING radiosity, (though that will help cut own render times on water, thanks).

I want to exclude an object from contributing to it.

I'm coming to the conclusion that a big light array is about the only way to go...


In case it helps, here's what I am working on...

11-29-2003, 10:57 AM
That cool looking.

You might also render in passes then assemble everything in a compositing package. That way you have greater control over each element.

11-29-2003, 12:48 PM
oy! you want to render an animation with all that? It'll take a week just to test render!

Since it's an outdoor scene in direct sunlight, radiosity isn't even that neccessary - I would highly suggest an alternative, like area lights or, again, the spinning light trick ; try changing the color of the shadow and/or using shadow maps for more softness

As mentioned before this is a good candidate for compositing, especially if you still want to do radiosity - use 'Backdrop radiosity' with no skydome to get the shadows you want (especially if the skydome is adding too much color), then render a skydome/reflections pass separately.

The scene is looking really good already, I don't think you need to throw all the technology at it to get it looking great -