Shadow Simulation And Analysis Of Light Transmission Based On Virtual Forest Scene

With the rapid development of computer hardware and computer graphics, virtual reality technology is widely used in areas such as virtual simulation,3D games. In real life, where there is light there is shadow, shadow is an important factor to enhance the computer virtual reality, the shadow of virtual scenes can not only provide a lot of 3D space information, help to determine the relationship of the spatial relative position of objects, greatly enhance the realism of the scene; but also in plant intercropping or planting configuration, the shadow of upper plants have a certain impact on the amount of light which the lower plants achieve, and the light is just the most important resource to plant growth, as well as important ecological factors affecting the material production and the energy transformation. Therefore, analyzing the light transmission of the forest scene under the condition of different ages^ different plant row spacing help to explain effects of the upper to the lower plants in mechanism and provide reference for plant intercropping and planting configuration. The specific research work and results are summarized as follows:(1) Analyze the current research status at home and abroad of virtual forest environment shadow related techonology and light distribution in forest environment, focus on the related concept of shadow and the mainstream algorithm, and summarize the specific application scene and the advantages and disadvantages of each shadow algorithm.(2) Select Manglietia insignis and citrus as the modeling objects, and use ParaTree parametric individual plant modeling tools software and VisForest virtual forest scene visualization system which are developed by the research team respectively to build the real 3D individual plant model and a variety of forest scenes based on the measured data in the field.(3) Analyze the advantages and disadvantages of planar shadow algorithm> shadow map algorithm、variance shadow map algorithm and so on. For the problems of shadow algorithms, use Frame Buffer Object and GPU technologies to improve traditional shadow map algorithm, the self-shadow of trunk and the organ in geometric mesh model is simulated according to the dot product of texture normal and light source direction, and the sawtooth problem of shadow is improved by increasing resolution. Integrate the shadow algorithms above into the ParaTree software system and realize the shadow of individual plant model. Integrate shadow map algorithm and light space perspective shadow map algorithm into the VisForest software system, and realize the shadow effect of forest scene. Take the forest scene which is builded by Manglietia insignis and citrus as an example to simulate scene shadow.(4) According to the different ages of morphological parameters of Manglietia insignises, make different ages of real 3D models of Manglietia insignises, then form different forest scenes. Use ray tracing algorithm to simulate the phenomenon of light transmission in the forest scene, analyze the effects which different ages, different plant distance, row distance have on the light transmission in the forest scene. The results suggest that the greater the age, the smaller the light transmission in the same spacing condition, the reason is that as the age increases, the crown increases, causing the increase in the size of the shadow and the decrease of light transmission. Under the condition of the same age, the light transmission increases as the planting distance (or row spacing) increases, but amplification diminishes gradually, and the planting distance has a greater effect on the light transmission than the row spacing.