Methods for Processing Moving Regions in Moving Objects Databases
Florian Heinz · 2021
Moving objects database systems are specialized to store and process data with spatiotemporal attributes. A simple object type in this context is a moving point, which can represent the motion of a pedestrian, car or airplane. Another, more complex, type of object is a moving region, which is a region that changes position and shape over time. This thesis discusses various aspects for handling moving regions. One topic in this thesis is the region interpolation problem, where snapshots of regions are interpolated to moving regions. This procedure can be performed in several ways with varying results. The goal is to achieve a high quality result, which means primarily that the database model should match the corresponding real world objects as accurately as possible. Another chapter presents a new, polyhedra based, model for moving regions. This has two advantages compared to the prevailing unit based models: Complex moving regions, especially the results of binary set operations as, for instance, “union” can be represented in a much more compact way. Furthermore, operations on moving regions can be mapped into geometrical operations on polyhedra, for which robust and efficient algorithms are available. Based on this new model, operations for spatiotemporal coverage analysis of moving regions are developed. This is a set of operations to determine which regions are covered for which time intervals by a given moving region. In the light of large forest fires in the world, a method for creating moving regions from earth satellite scan data is discussed, that has several advantages over the prevailing methods. Another topic is the decomposition of moving regions into smaller and less complex entities, to improve their manageability in moving objects databases. Finally, an alternative data model for moving regions is introduced, which is optimized for rigid objects. The class of moving regions supported by that model is unable to change shape, but in return rotational movement is modeled accurately. For this new data type, useful operations like “moving point inside”, “traversed area” and more are introduced. As a part of this work, reference implementations for all these topics are distributed in form of freely available C++ libraries, which can be easily integrated into existing moving objects database systems, as, for example, the DBMS Secondo developed at the FernUniversität in Hagen.