Join Brian Bradley for an in-depth discussion in this video Working with irradiance mapping, part 1, part of SketchUp: Rendering with V-Ray 3.
- [Instructor] Because global illumination is such an important part of the rendering for Visualization Toolkit we're going to spend this chapter examining the GI engines that are available in VRay for SketchUp 3. In fact, for the first two videos we're going to focus entirely on using VRay's irradiance mapping engine testing out how good it is at creating a basic GI solution for an interior shot. Now we've chosen an interior setting to test the engines because this presents by far and away the biggest challenge when it comes to getting a clean, believable looking lighting solution.
In fact we're making things even harder than they need to be here by blocking light entry from the skylights in our geometry. The plain gray material that we're using on most of the objects will also add to the difficulty as it will show up any noise or blotchiness that is produced by the GI solution. Now it does have to be said that with just the default GI settings in place a new SketchUp scene using VRay does provide a pretty decent GI setup that can straight out of the box produce some very nice daylight illumination.
If I open up the Asset Editor we can see that when using those defaults Brute Force is setup as the primary ray engine whilst Light Cache takes care of the secondary bouncers. But the problem with this setup on an interior such as we have here is that getting a really clean render even from a setup with materials as simple as these can be quite a time consuming process. Assuming we don't have such time available let's set our primary ray engine to Irradiance Mapping, and set the secondary balance engine to None meaning that any bounced light that we do get in this scene will be coming from just the default irradiance map settings.
If we take a render then we can see how this works as VRay runs through a number of irradiance map passes with each pass refining the solution, and adding irradiance samples to the map being built as and when they are needed. Finally we get a finished GI render from the system. Now one of the nice things about the irradiance map system is that we do get to see the irradiance solution as it is being calculated meaning we instantly get an opportunity to evaluate lighting, and exposure levels, and if the setup isn't really working for us we can quickly cancel the render, make some tweaks, and then render again.
Now clearly what we currently have in the Frame Buffer window is a fairly blotchy solution that really isn't working for us. The question then is how do we go about improving things? Well one thing we could do is give the irradiance mapping engine a bit of a helping hand by making use of some sky portals in this scene. A sky portal being an operating mode of the VRay rectangle light. One that provides us with a mechanism for essentially pointing a GI engine to the areas of the scene from which direct light is coming.
This in turn helps VRay make more intelligent decisions regarding its use of the available irradiance samples. In the Layers rollout then let's un-hide the Sky Portals layer that we have there. Now whilst I have already added the rectangle lights that we will be using, and positioned them appropriately so as to function as portals I haven't, as of yet, gone ahead, and enabled that functionality. To have the plain light function as a sky portal we need to first of all turn the light itself on then enable the portal option, and then decide what type of portal we want to use.
Now if we had no geometry sitting behind the portal lights in the scene we could make use of the simple option which basically tells the light to sample in just a single direction that is inwards toward the interior which, in turn, would save a little bit on calculation time. As we do have geometry sitting behind the portals though, and because that will affect our lighting levels it would be best if we stick to using the accurate option. With that done the color and multiplier parameters of the lights now will be ignored, and they will instead take their color, and intensity values from the environment that is sitting behind them.
As these lights are all instances that single change affects them all, and so let's save what we have to history, and take another render. If we compare now we can see that we do indeed have quite a different lighting result both in terms of illumination levels, and, as regards to quality, of the irradiance mapping solution. Well whilst we have made a start at getting a basic irradiance map solution in place what we haven't as of yet managed to do is get a clean high quality final solution from the system.
Something that we would be happy to use in a production situation. In the next exercise then we can spend some time working with the irradiance map controls in order to clean up the GI, and produce something that we deem more acceptable as a final lighting solution.
- Gamma handling in V-Ray 3 for SketchUp
- Working with interactive rendering
- V-Ray light types
- Working with irradiance mapping
- Rendering animations
- Working with the V-Ray camera
- Using the Materials UI
- V-Ray FX tools
- Stereoscopic 3D rendering
- Using V-Ray objects