T.P.M. Tijssen

About Invalid, Valid and Clean Polygons

Spatial models are often based on polygons both in 2D and 3D. Many Geo-ICT products support spatial data types, such as the polygon, based on the OpenGIS ‘simple Features Specification’. OpenGIS and ISO have agreed to harmonize their specifications and standards. In this paper we discuss the relevant aspects related to polygons in these standards and compare several implementations. A quite exhaustive set of test polygons (with holes) has been developed. The test results reveal significant differences in the implementations, which causes interoperability problems. Part of these differences can be explained by different interpretations (definitions) of the OpenGIS and ISO standards (do not have an equal polygon definition). Another part of these differences is due to typical implementation issues, such as alternative methods for handling tolerances. Based on these experiences we propose an unambiguous definition for polygons, which makes polygons again the stable foundation it is supposed to be in spatial modelling and analysis. Valid polygons are well defined, but as they may still cause problems during data transfer, also the concept of (valid) clean polygons is defined.

Benchmarking and improving point cloud data management in MonetDB

The popularity, availability and sizes of point cloud data sets are increasing, thus raising interesting data management and processing challenges. Various software solutions are available for the management of point cloud data. A benchmark for point cloud data management systems was defined and it was executed for several solutions. In this paper we focus on the solutions based on the column-store MonetDB, the generic out-of-the-box approach is compared with two alternative approaches that exploit the spatial coherence of the data to improve the data access and to minimize the storage requirements.

Validating a 3D topological structure of a 3D space partition

The goal of this research is to develop a 3D topological structure to represent a 3D space partition with validation functionality and support for conversions from topological to geometrical primitives. Several 3D topological structures have been presented in the past, mainly by researchers. The technical (implementation) model developed in this paper is based on the conceptual model of the ISO 19107 ‘spatial schema’ standard and consists of four topological primitives: node, edge, face, and volume, which are related to each other via their (co)boundary relationships. In our setting, only linear primitives (no curves) are supported and no isolated and dangling primitives are allowed. In our model, the rings, the shells, and the orientation play key roles within the topological structure and the functions that implement the geometrical realization.

Realistic Benchmarks for Point Cloud Data Management Systems

Lidar, photogrammetry, and various other survey technologies enable the collection of massive point clouds. Faced with hundreds of billions or trillions of points the traditional solutions for handling point clouds usually under-perform even for classical loading and retrieving operations. To obtain insight in the features affecting performance the authors carried out single-user tests with different storage models on various systems, including Oracle Spatial and Graph, PostgreSQL-PostGIS, MonetDB and LAStools (during the second half of 2014). In the summer of 2015, the tests are further extended with the latest developments of the systems, including the new version of Point Data Abstraction Library (PDAL) with efficient compression. Web services based on point cloud data are becoming popular and they have requirements that most of the available point cloud data management systems can not fulfil. This means that specific custom-made solutions are constructed. We identify the requirements of these web services and propose a realistic benchmark extension, including multi-user and level-of-detail queries. This helps in defining the future lines of work for more generic point cloud data management systems, supporting such increasingly demanded web services.