Efficient Mining and Exploration of Multiple AxisAligned Intersecting Objects Identifying and quantifying the size of multiple intersections among a large number of axisaligned geometric objects is an essential computational geometry problem. The ability to solve this problem can effectively inform a number of spatial data mining methods and can provide support in decision making for a variety of applications. Currently, the stateoftheart approach for addressing such intersection problems resorts to an algorithmic paradigm, collectively known as the sweepline algorithm. However, its application on specific instances of the problem inherits a number of limitations. With that mind, we design and implement a novel, exact, fast and scalable yet versatile, sweepline based algorithm, named SLIG. Our algorithm can be employed in a number of problems and applications involving the efficient computation of numerous axisaligned object intersection problems in multiple dimensions. The key idea of our algorithm lies in constructing an auxiliary data structure when the sweep line algorithm is applied, an intersection graph. This graph can effectively be used to provide connectivity properties among overlapping objects, as well as to inform the much harder problem of finding the location and size of the common area defined by multiple overlapping objects. A thorough experimental evaluation on synthetic data of various characteristics and sizes, demonstrates that SLIG performs significantly faster than classic sweepline based algorithms. SLIG is not only faster and more versatile, but also provides a suite of powerful querying capabilities. To support the reproducibility of our methods, we make source code and datasets available.

Hierarchical Filter and Refinement System Over Large Polygonal Datasets on CPUGPU In this paper, we introduce our hierarchical filter and refinement technique that we have developed for parallel geometric intersection operations involving large polygons and polylines. The inputs are two layers of large polygonal datasets and the computations are spatial intersection on a pair of crosslayer polygons. These intersections are the computeintensive spatial data analytic kernels in spatial join and map overlay computations. We have extended the classical filter and refine algorithms using PolySketch Filter to improve the performance of geospatial computations. In addition to filtering polygons by their Minimum Bounding Rectangle (MBR), our hierarchical approach explores further filtering using tiles (smaller MBRs) to increase the effectiveness of filtering and decrease the computational workload in the refinement phase. We have implemented this filter and refine system on CPU and GPU by using OpenMP and OpenACC. After using Rtree, on average, our filter technique can still discard 69% of polygon pairs which do not have segment intersection points. PolySketch filter reduces on average 99.77% of the workload of finding line segment intersections. PNP based task reduction and Striping algorithms filter out on average 95.84% of the workload of PointinPolygon tests. Our CPUGPU system performs spatial join on two shapefiles, namely USA Water Bodies and USA Block Group Boundaries with 683K polygons in about 10 seconds using NVidia Titan V and Titan Xp GPU.