Hierarchical representations of 3-dimensional objects are both time and space efficient. They typically consist of trees whose branches represent bounding volumes and whose terminal nodes represent primitive object elements (usually polygons). This paper describes a method whereby the object space is represented entirely by a hierarchical data structure consisting of bounding volumes, with no other form of representation. This homogencity allows the visible surface rendering to be performed simply and efficiently.
The bounding volumes selected for this algorithm are parallelepipeds oriented to minimize their size. With this representation, any surface can be rendered since in the limit the bounding volumes make up a point representation of the object. The advantage is that the visibility calculations consist only of a search through the data structure to determine the correspondence between terminal level bounding volumes and the current pixel. For ray tracing algorithms, this means thata simplified operation will produce the point of intersection of each ray with the bounding volumes.
Memory requirements are minimized by expanding or fetching the lower levels of the hierarchy only when required. Because the viewing process has a single operation and primitive type, the software or hardware chosen to implement the search can be highly optimized for very fast execution.
3维对象的层次表示既节省时间又节省空间。它们通常由树组成,这些树的分支表示边界体积,并且其终端节点表示原始对象元素(通常是多边形)。本文介绍了一种方法,其中对象空间完全由包含边界体积的分层数据结构表示,没有其他形式的表示。这种均匀性使得可见表面的渲染变得简单而有效。 P>
为此算法选择的包围体为平行六面体,以最大程度地减小其大小。通过这种表示,可以绘制任何表面,因为在限定范围内,包围体积构成了对象的点表示。优点是可见性计算仅包括对数据结构的搜索以确定终端级边界量与当前像素之间的对应关系。对于光线跟踪算法,这意味着简化的操作将产生每个光线与边界体积的交点。 P>
仅在需要时才通过扩展或获取层次结构的较低级别来最大程度地减少内存需求。由于查看过程具有单一的操作和原始类型,因此可以高度优化选择用于实现搜索的软件或硬件,以实现非常快速的执行。 P>
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