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Airborne Light Detection and Ranging (LiDAR) topographic data provide highly accurate digital terrain information, which is used widely in applications like creating flood insurance rate maps, forest and tree studies, coastal change mapping, soil and landscape classification, 3D urban modeling, river bank management, agricultural crop studies, etc. In this paper, we focus mainly on the use of LiDAR data in terrain modeling/Digital Elevation Model (DEM) generation. Technological advancements in building LiDAR sensors have enabled highly accurate and highly dense LiDAR point clouds, which have made possible high resolution modeling of terrain surfaces. However, high density data result in massive data volumes, which pose computing issues. Computational time required for dissemination, processing and storage of these data is directly proportional to the volume of the data. We describe a novel technique based on the slope map of the terrain, which addresses the challenging problem in the area of spatial data analysis, of reducing this dense LiDAR data without sacrificing its accuracy. To the best of our knowledge, this is the first ever landscape-driven data reduction algorithm. We also perform an empirical study, which shows that there is no significant loss in accuracy for the DEM generated from a 52% reduced LiDAR dataset generated by our algorithm, compared to the DEM generated from an original, complete LiDAR dataset. For the accuracy of our statistical analysis, we perform Root Mean Square Error (RMSE) comparing all of the grid points of the original DEM to the DEM generated by reduced data, instead of comparing a few random control points. Besides, our multi-core data reduction algorithm is highly scalable. We also describe a modified parallel Inverse Distance Weighted (IDW) spatial interpolation method and show that the DEMs it generates are time-efficient and have better accuracy than the one's generated by the traditional IDW method.

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One of the most relevant and widely studied structural properties of networks is their community structure or clustering. Detecting communities is of great importance in various disciplines where systems are often represented as graphs. Different community detection algorithms have been introduced in the past few years, which look at the problem from different perspectives. Most of these algorithms, however, have expensive computational time that makes them impractical to use for large graphs found in the real world. Maintaining a good balance between the computational time and the quality of the communities discovered is a well-known open problem in this area. In this paper, we propose a multi-core multi-level (MCML) community detection algorithm based on the topology of the graph, which contributes towards solving the above problem. MCML algorithm on two benchmark datasets results in detection of accurate communities. We detect high modularity communities by applying MCML on Facebook Forum dataset to find users with similar interests and Amazon product dataset. We also show the scalability of MCML on these large datasets with 16 Xeon Phi cores.

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