Consistent Queries over Cardinal Directions across Different Levels
of Detail
Roop Goyal and
Max Egenhofer 11th International Workshop on Database and Expert Systems Applications, Greenwich, U.K.,
A.M. Tjoa, R. Wagner, and A. Al-Zobaidie (eds.), pp. 876-880, September 2000.
Abstract
Current models for cardinal directions, such as north and
northeast, are either point-based or region-based, but no
models exist that apply equally, independent of the geometric data
types (be it points, lines, or polygons). To allow users to
formulate queries such as "Find all towns in Maine that are
northeast of Augusta" without pondering about the cities'
geometric data types, we extend the model of the model of the
direction-relation matrix to handle arbitrary pairs of
points, lines, and polygons. This new model, called the deep
direction-relation matrix, retains the 3x3 structure of the
direction-relation matrix with empty and non-empty tiles, while it
records additionally neighbor codes for empty tiles to capture
whether the tiles' boundaries are empty or not. This extension
covers all intricacies imposed by line and point objects, yielding
a unifying and consistent model for cardinal directions. It enables
the use of cardinal directions in spatial query languages
independent of the objects' geometric data types.
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Roop Goyal and
Max Egenhofer