Modeling of a Sample Scene

Our concluding example demonstrates the simulation of a complex plant scene. Here we applied some of the previously discussed instancing methods, in par-

ticular the approximate instancing procedure, whereby the terrain from Fig. 7.7 serves as a basis.

Подпись:The parameterized data base of different species is generated using the Xfrog modeling system (see Fig. 8.15). In the scene shown below, the production of the apple tree model took several hours. All other objects were created more quickly, partially they could be extracted from other scenes.

Modeling of a Sample Scene

Figure 8.15

Sample models for a complex plant scene: (a) stinging nettle; (b) reed; (c) apple tree


(a) (b) (c)


Modeling of a Sample Scene

Подпись: (a) (b) Modeling of a Sample Scene Подпись: Figure 8.16 Simulation of a population of the stinging-nettle: (a) height image of the terrain; (b) image of the planned creek; (c) density function of the population; (d) generated plant position
Modeling of a Sample Scene

For the rendering of the plant population, density functions were specified graphically. The stinging-nettle population in Fig. 8.16 serves here as an exam­ple. To parameterize the growth rate in this illustration, the height image was used, so that the specimens located in the lower river valley reflect a higher growth rate than those that are situated in comparatively dry regions on the small hills. Large objects, such as the apple trees, were added manually into the scene.

The already mentioned approximate instancing was applied to the completed populations. For each species a different number of representatives was se­lected. The values are indicated in the table of Fig. 8.17. The number of poly­gons without instancing amounts to 16.6 million for the scene; with instancing there are only one million. Thus, all in all, a reduction factor of 16.6:1 is ob­tained.

If further reducing the representatives, the reduction factor can be improved. In isolated cases, one representative is sufficient, so that the expenditure for the production of a scene is confined to the modeling and simulation of only one plant.

All in all, instancing procedures provide a good basis for the handling of geo­metrical data in natural scenes. The remaining data typically is of a size that is also manageable with standard computers.

Подпись: Plant Representative instances Apple 1 4 Grass 15 2577 Reed 140 140 Stinging nettle 10 430 Dandelion 10 55 Buttercup 10 2751 Figure 8.17 Number of representatives and instances in the example scene

In the next chapter, we will introduce procedures for rendering the geomet­ric data. in this context there are also approaches to additionally reducing the data with so-called level-of-detail modeling methods. While these approaches do not facilitate data reductions for the geometrical models of the representa­tives, they do, however, significantly reduce the data to be generated per image. We will demonstrate that this kind of methodology allows us the rendering of complex ecosystems in near real time.

Figure 8.18 Complete scene consisting of six species. The image resolution is 2560x 1720, the time for loading of geometries and for rendering is ca. 75 min.


Modeling of a Sample Scene