Unlike bump and normal maps, a displacement map affects the geometry of a model. This means that the polygons are moved, displaced, from their original position. For example, if we have a model of a car, a displacement map can move the polygons in it to simulate the effect of a collision, or a rock hitting the side of the car.
The effect is achieved with a map that is very similar to the bump map. A grayscale texture that indicates positive or negative displacement at several points. The dark spots indicate dents, and the light spots in the map will move the geometry “up,” along the normals.
But that is not all. To make the geometry move with a displacement map, the mesh must have enough detail that the displacement can happen. For example, if we have a floor that is modeled with one single large polygons, then the displacement will not work. That is because a single polygon does not have anything “inside” that can be moved. The displacement happens at the vertex level. If we only have four vertices then we will be able to curve that polygon within the limits of the transformations that can be achieved by moving four point. We will not have enough geometric resolution to create more movements in the inner part of the floor. To do that we need to subdivide the polygons in smaller units.
Take, for example, the Reality’s water plane. Add it to a scene and switch to wireframe view. Here is a screenshot:
There is a human figure in the middle to give a scale reference. A plane with such high level of subdivision can displace easily, but we can give it even more resolution by increasing the level of subdivision in Reality. If we look in the Modifiers tab we see that there is a subdivision value.
Every time that value goes up, every polygon in the associated material is divided. The division happens along each side, so, in the case of a square/rectangle that polygon will be split in four smaller polygons. This makes it possible to create more subtle movements via the displacement map.
When we use subdivision in Reality, subdivision happens during rendering, it’s not applied to the geometry in Studio or Poser.
Displacement maps are a great way of adding detail to a model without having to sculpt such detail in the geometry. Because the displacement happens during rendering, there is no need to have highly-detailed geometry in action while we prepare the scene or pose the characters. This, in turn, requires less computation power and memory and therefore makes the handling of the model easier and faster.
Our own Marcel2586 has posted a great tutorial that covers bump maps, normal maps, and displacement maps all in one great example. He included several images demonstrating the effects of using the maps. Fuzzy70 added another example of displacement map that shows the effect quite dramatically.
Next week we will see how to take advantage of Light Emitting Materials, aka LEMs. Stay tuned!