Andrew Danner

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We consider the problem of extracting a river network and a watershed hierarchy from a terrain given as a set of irregularly spaced points. We describe TERRASTREAM, a "pipelined" solution that consists of four main stages: construction of a digital elevation model (DEM), hydrological conditioning, extraction of river networks, and construction of a(More)
We present an external planar point location data structure that is I/O-efficient both in theory and practice.The developed structure uses linear space and answers a query in optimal <i>O</i>(log <i><inf>B</inf>N</i>) I/Os, where <i>B</i> is the disk block size. It is based on a persistent B-tree, and all previously developed such structures assume a total(More)
We develop cache-oblivious data structures for orthogonal range searching, the problem of finding all <i>T</i> points in a set of <i>N</i> points in <i>IR<sup>d</sup></i> lying in a query hyper-rectangle. Cache-oblivious data structures are designed to be efficient in arbitrary memory hierarchies.We describe a dynamic linear-size data structure that answers(More)
In line with institutions across the United States, the Computer Science Department at Swarthmore College has faced the challenge of maintaining a demographic composition of students that matches the student body as a whole. To combat this trend, our department has made a concerted effort to revamp our introductory course sequence to both attract and retain(More)
Recent progress in remote sensing has made massive amounts of high resolution terrain data readily available. Often the data is distributed as regular grid terrain models where each grid cell is associated with a height. When terrain analysis applications process such massive terrain models, data movement between main memory and slow disk (I/O), rather than(More)
Bare Earth gridded digital elevation models (DEMs) are often used to extract hydrologic features such as rivers and watersheds. DEMs must be conditioned by removing spurious <i>sinks</i> (or depressions) which impede water flow in the model, but are not true hydrologic barriers. This conditioning process is designed to enforce proper drainage and connect(More)
Modern remote sensing methods such a laser altimetry (lidar) and Interferometric Synthetic Aperture Radar (IfSAR) produce georeferenced elevation data at unprecedented rates. Many Geographic Information System (GIS) algorithms designed for terrain modelling applications cannot process these massive data sets. The primary problem is that these data sets are(More)
The proliferation of lidar technology in remote sensing has resulted in extremely large, high resolution point clouds covering a wide variety of terrain. Constructing a grid digital elevation model (DEM) from these large data sets requires extensive computational resources and ample disk space. We propose a framework for leveraging modern computing(More)
We present an I/O-efficient algorithm that decomposes a grid-based terrain model into a hierarchy of watersheds. Each watershed gets a unique label, a Pfafstetter label, and each grid cell is labeled with the labels of all (nested) watersheds it belongs to. The algorithm runs in O(sort(T)) I/Os, where T is the total length of the computed cell labels. Our(More)