利用三维体素遍历和GPU进行辐射度加速计算——以虚拟植物冠层辐射模拟为例

辐射度模型是虚拟植物冠层内光分布模拟的主要算法之一，针对其形状因子计算量大，辐射能量计算效率低等问题，提出了一种辐射度计算加速方法。以虚拟枇杷冠层内光分布模拟为例，利用均匀体素剖分场景包围盒及三维体素遍历方法进行光源与树模型之间的遮挡判断，同时结合CUDA技术使辐射度算法的形状因子求解并行化。采用归约求和算法和共享内存实现植物模型接受辐射总能量的快速求解。该方法较CPU串行方法有150多倍的加速比。将太阳直射光合有效辐射（photosynthetically active radiation，PAR）分布模拟结果与光线跟踪模型、传统辐射度模型模拟结果进行对比，天空散射PAR分布模拟结果与龟型算法、传统辐射度模拟对比。计算所得PAR值接近，变化趋势一致，表明该方法有较好的精度保证。

Optimizing Radiosity Based on Three-Dimensional Voxel Traversal and GPU for Radiation Simulation Within Virtual Canopy

The radiosity is one of the popular algorithms for radiation simulation within a virtual canopy. However, owing to the complexity of plant architecture, enormous computation on computing the form factors has become a serious burden. Thus, a new optimized strategy of radiosity based on CUDA and 3D voxel traversal was developed to improve computation efficiency. Taking simulation of radiation transfer within a virtual Loquat canopy as an example, our proposal is based on uniform partition of bounding box and voxels traversing along a 3D line to identify occlusion between the light source and tree model facets, combining GPU to compute form factor in parallel using CUDA. Furthermore, we adopted reduction algorithm and shared memory to optimize the radiation flux calculation. Compared with serial implementation on CPU, the results are good in terms of execution times with speed-ups about 150. By comparative analysis with ray tracing and traditional radiosity model (progressive refinement radiosity algorithm), the simulation results of PAR distribution are similar and consistent. The results of comparison show that the new method not only improve computation efficiency, but also insure the accuracy.