isoap: A software for isosurface extraction on arbitrary polyhedra

The implemented algorithm extracts, from discrete data, isosurfaces on arbitrary polyhedra, convex or non-convex, even with non-planar face boundaries. The software package also includes a user manual and routines for writing the geometry of polyhedra and isosurfaces in external files. Tests programs are included to extract isosurfaces on single polyhedral cells and grids of any type, either from implicit mathematical functions or discrete data such as volume fractions or signed distances to scanned surfaces. The proposed method for isosurface extraction on arbitrary polyhedra uses a general polygon tracing procedure, which can be applied to any convex or non-convex geometry, and produces consistent results even for ambiguous situations. The locations of the extracted isosurface points are approximately computed by interpolation. This procedure does not rely on predefined configurations and can be considered as an extension of the marching cubes technique to arbitrary polyhedra. The implemented routines can be used in FORTRAN or C, and, to speed up the operations performed over grids, the OpenMP application programming interface is used. The proposed algorithm can be used in multiple applications, including the visualization of surfaces in computer graphics or the reconstruction of interfaces in PLIC (piecewise linear interface calculation) VOF (volume of fluid) methods.本实现算法可从离散数据中提取任意多面体（包括凸多面体与非凸多面体，甚至含非平面面边界）的等值面（isosurface）。本软件包还附带用户手册，以及用于将多面体与等值面的几何信息写入外部文件的程序例程。本软件包含测试程序，可从隐式数学函数或离散数据（如体积分数、扫描曲面的有符号距离）中，在单个多面体单元与任意类型网格上提取等值面。本文提出的任意多面体等值面提取方法采用通用多边形追踪流程，可适用于任意凸/非凸几何结构，即便在模糊场景下也能生成一致的计算结果。提取得到的等值面顶点位置通过插值方式近似计算。该流程不依赖预定义配置，可视为移动立方体（marching cubes）技术向任意多面体场景的扩展。本实现的程序例程可在FORTRAN或C语言环境中调用；为加速网格相关运算，本软件采用了OpenMP应用程序编程接口。本提出的算法可应用于多种场景，包括计算机图形学中的曲面可视化，以及PLIC（piecewise linear interface calculation，分段线性界面计算）、VOF（volume of fluid，流体体积法）中的界面重构任务。