A review of forest visualization and forest fire simulation technology research

森林是生态环境系统的重要组成部分。随着气候变暖，恶劣气候气象条件造成全球森林火灾频繁发生，给国民经济和消防救援带来巨大挑战，森林火灾已成为全球主要的自然灾害。因此，森林场景可视化建模、3维场景仿真、林火模拟仿真、火场复现、预测和灾害评估成为林业虚拟仿真研究热点。本文对树木形态结构建模技术、森林场景大规模重建和实时渲染、森林场景可视化、林火模型和林火模拟仿真等前沿技术和算法进行综述。对相关的林木、植被的形态结构表达和真实感可视化建模方法进行归纳分类，并对不同可视化方法的算法优劣、复杂度、实时渲染效率和适用场景进行讨论。基于规则的林木建模方法和基于林分特征的真实场景重建方法对大规模森林场景重建技术进行分类，基于物理模型、经验模型和半经验模型对森林火灾的林火模型、单木林火、多木林火模拟和蔓延进行总结，对影响林火蔓延的不同环境气象因子（如地形地貌、湿度、可燃物等）和森林分布对林火发生、扩散和蔓延的影响进行分析，对不同算法的优劣进行对比、分析和讨论，对森林场景可视化和林火模拟仿真技术未来的发展方向、存在问题和挑战进行展望。本文为基于森林真实场景的森林火灾模拟仿真和数字孪生沉浸式互动模拟系统的构建提供了理论方法基础，该平台可以实现森林场景快速构建、不同火源林火模拟、火场蔓延模拟仿真以及不同气象影响条件的火场预测，可对森林火场救援指挥、火场灾害评估和火场复原提供可视化决策支持。;Forest is a sort of highly complex and important ecosystem and it is still challenged by such severe forest fires. To strengthen the information-driven ability of forest fire emergency management decision-making, it is required to build a forest fire virtual simulation platform in terms of virtual reality and visualization technology. Therefore, our review analysis is focused on a virtual reality and visualization-based forest fire virtual simulation platform for exploring the forest scene visualization and forest fire simulation technology, and it seeks to trace forest scenes, multi-source forest fire simulation, and its fire scene further. In order to provide visual decision-making support for fire rescue command and fire disaster assessment, information-driven forest fire emergency management decision-making is improved further. First, we discuss and analyze the highly realistic 3D visualization reconstruction technology of real forest landscapes, which is beneficial for a forest model library and realize highly realistic 3D visualization reconstruction of forest landscape areas. To establish a forest fire spread model and reflect the forest fire combustion process and pyrolysis-physical characteristics accurately and its combustion process-oriented real-time visual simulation, it is essential to develop the application of forest fire simulation technology and explore the mechanism of forest fire spread. The related methods are categorized into forest scene visualization and forest fire simulation technology, and the research growth of it is summarized as well. Forest scene visualization methods can be divided into mechanism-based tree modeling methods, including L system-based and custom sketch-based or interactive modeling methods, and forest stand characteristics-based natural scene reconstruction methods. That is, realworld forest stands feature data like images and point clouds are used to reconstruct forest trees. The two types of methods mentioned above are mostly used to construct single tree models as the theoretical basis for large-scale forest scene reconstruction. The mechanism-based tree modeling method can be used to balance the tree structure intuitively and flexibly, and it is more suitable for plant growth design, immersive creation, and other related fields;the forest stand characteristicsbased real scene reconstruction method has high fidelity, and it is suitable for vegetation quantification, small-scale ecosystem simulation, and its contexts. Forest fire simulation technology is divided into three categories:physical model, empirical model, and semi-empirical model. The physical model can be well used to illustrate the physical and chemical reactions in the burning process of the forest fire and show the changes in the flame. The empirical model is used for the relevant data obtained from the experiment for mathematical fitting, which can simulate the forest fire spreading status in some typical scenarios, and the accuracy of the direction and rate of forest fire spread is guaranteed. For the semi-empirical model, the physical and chemical reactions in the process of forest fire spread and the statistical analysis methods in specific experiments used are considered at the same time, which reduces the computing cost of physical simulation and enables real-time simulation further. In addition, forest fire simulation can be a key aspect of immersive forest fire simulation and interactive fire extinguishing simulation research, and real forest scene visualization is on the basis of other related research. Real-time generation of realistic forest scenes is beneficial for the simulation of the forest fire. The immersion of the corresponding senses can be improved by constructing real forest scenes to approach the real situation of forest fires, and complex terrain and meteorological conditions can be simulated and visualized as well. Experience and realistic scene roaming can be one of the application scenarios for forest scene visualization technology. We link researches of 1) the growth of forest scene visualization and the forest fire simulation technology, 2) an immersive three-dimensional visual simulation of forest fire scene, and various forest fire ignition methods related to forest fire spread, and 3) fire extinguishing simulation together. Furthermore, most researches are focused on the forest fire spread model coupled in relevance to atmospheric, ecological, and hydrological models since a real and credible forest fire cannot be completely simulated only by forest scene visualization and forest fire simulation technology. To aid fire departments to alleviate deployment decisions, both the forest scene visualization and forest fire simulation technologies can be applied in the field of forest firefighting, strategic planning, and resource allocation via simulation-based planning methods. Finally, we summarize the relevance of forest scene visualization and forest fire simulation technology. Three types of models of forest fire spreading, physical, empirical, and semi-empirical are introduced in detail, in which task-based forest scene visualization into tree modeling methods are related to forest stand characteristics-based reconstruction methods, and the theoretical basis, scope of application, pros and, cons of forest scene visualization and forest fire simulation technology are explained as well. At the same time, it is essential to resolve some application problems in terms of large-scale scene rendering technology and forest fire protection, and a virtual reality and visualization technology-driven basis are offered for future construction of forest fire virtual simulation. The development trend of forest scene visualization and forest fire simulation technology is predicted further.