Polyline Join Evaluation Using Raster Approximation

The main subject of spatial joins are polygons and polylines. The processing of spatial joins can be greatly improved by the use of filters that reduce the need for examining the exact geometry of spatial objects in order to find the intersecting ones. Approximations of candidate pairs of spatial objects are examined using such filters. As a result, three possible sets of answers are identified: the positive one, composed of intersecting pairs; the negative one, composed of non-intersecting pairs; and the inconclusive one, composed of the remaining pairs of candidates. To identify all the intersecting pairs of spatial objects with inconclusive answers, it is necessary to have access to their representation so that an exact geometry test can take place. This is true for both polygons and polylines. There are many approximations designed for polygons, but few are suitable for approximating polylines. This article presents a join implementation based on the MSQP architecture [BRIN94] using the Five Color Direction Raster Signature (5CDRS) [ZSMA00] as a filter in the second step, which is polyline approximation. The performance was evaluated with real world data sets. The results showed that our approach, when compared to other approaches presented in the related literature, reduced the inconclusive answers by a factor of more than two. As a result, the need for retrieving the representation of polylines and carrying out exact geometry tests is reduced by a factor of more than two, consequently also reducing the overall time by a factor of more than two, since this step is the most time consuming.