Large-scale unstructured point cloud scenes can be quickly visualized without prior reconstruction by utilizing levels-of-detail structures to load an appropriate subset from out-of-core storage for rendering the current view. However, as soon as we need structures within the point cloud, e.g., for interactions between objects, the construction of state-of-the-art data structures requires O(NlogN) time for N points, which is not feasible in real time for millions of points that are possibly updated in each frame. Therefore, we propose to use a surface representation structure which trades off the (here negligible) disadvantage of single-frame use for both output-dominated and near-linear construction time in practice, exploiting the inherent 2D property of sampled surfaces in 3D. This structure tightly encompasses the assumed surface of unstructured points in a set of bounding depth intervals for each cell of a discrete 2D grid. The sorted depth samples in the structure permit fast surface queries, and on top of that an occlusion graph for the scene comes almost for free. This graph enables novel real-time user operations such as revealing partially occluded objects, or scrolling through layers of occluding objects, e.g., walls in a building. As an example application we showcase a 3D scene exploration framework that enables fast, more sophisticated interactions with point clouds rendered in real time.

通过利用细节层次结构从核外存储加载适当的子集以渲染当前视图，无需事先重建即可快速可视化大规模非结构化点云场景。然而，一旦我们需要点云中的结构，例如，用于对象之间的交互，构建最先进的数据结构需要N个点的O ( NlogN ) 时间，这对于实时来说是不可行的每帧中可能更新的数百万个点。因此，我们建议使用表面表示结构，以在实践中权衡单帧使用的（这里可以忽略不计的）缺点，以实现输出主导和接近线性的构建时间，利用 3D 中采样表面的固有 2D 属性。这种结构紧密地包含了离散二维网格的每个单元的一组边界深度间隔中的非结构化点的假定表面。结构中的排序深度样本允许快速表面查询，最重要的是，场景的遮挡图几乎是免费的。该图实现了新颖的实时用户操作，例如显示部分遮挡的对象，或滚动浏览遮挡对象的层，例如建筑物中的墙壁。作为一个示例应用程序，我们展示了一个 3D 场景探索框架，该框架可以与实时渲染的点云进行快速、更复杂的交互。