Construction of a large scale virtual world based on a map

要构建大规模的虚拟空间，需要对大量的空间对象进行有效的管理。在我们的项目中，一个有效的分层时空数据结构，称为PMD树，已于1996年开发。PMD树通过只保留PMD树生长过程中的差异，可以有效地管理时空数据。1997年，提出了利用地图在虚拟世界中构建空间对象的方法。在地图中，三维空间中的对象的俯视图被绘制为多边形或线段。如果给定从任意位置拍摄的具有任意视角方向的图片，则可以通过选择从给定视角和视角方向拍摄的图片来获得3D空间的场景。在我们的方法中，一个场景为一个给定的视点和视图方向是从多个图片构建。当给定视点和方向时，使用地图搜索视体积中的对象。然后找出包含目标的图片，选择最合适的部分进行投影变换。1998年，提出了一种面向移动对象的时空数据管理方法。对PMD树进行了扩展，并引入了时空包围盒的概念。

To construct a large scale virtual space, a large number of spatial objects should be managed efficiently. In our project, an efficient hierarchical spatio-temporal data structure, called the PMD-tree, has been developed in 1996. The PMD-tree can manage the spatio-temporal data efficiently by preserving only the differences among the growing processes of a PMD-tree. Spatial temporal searches with time and spatial intervals can be performed quickly In 1997, the method for constructing spatial objects in a virtual world using a map were proposed. In a map, top views of objects in a three dimensional space are drawn as polygons or line segments. If picture with any view direction taken from arbitrary positions are given, a scene of 3D space can be obtained by selecting the picture taken from a given view point and view direction. In our method, a scene for a given view point and view direction is constructed from an plural pictures. When a view point and a direction are given, objects in the view volume are searhed using a map. Then pictures in which the objects are contained are found. The most appropriate parts of pictures are selected and applied the projective transformation. In 1998, a spatio-temporal data management method for moving objects was proposed. The PMD-tree was expanded and an new idea of time space bounding box (TSBB) was introduced.