An alignment meta-model for the comparison of alignment product models

In this paper, an alignment meta-model is presented that can be used as a common basis to compare arbitrary alignment models. To this end, we describe how existing alignment product models can be mapped to the proposed meta-alignment model. In addition, we define quality metrics of a well-performing alignment model, which can be used to evaluate different design alternatives for alignment models. LandXML 1.2 Schema, Weak Point Typing, Case Inconsistencies, Name Optionality Inconsistency, etc. (Scarponcini 2013). The development on LandXML has suddenly stopped in 2009, while after 4 years of complete silence, in December 2013 suddenly an update on the LandXML.org webpage appeared. Right now it is not clear if the development of LandXML will be continued. A major problem is that the LandXML data format is currently not supported by a standard organization that guarantees its longevity. Besides this, some legal and organizational issues have to be clarified. For instance, it is not clear who owns the copyright of LandXML or who is the official maintainer of LandXML. The OpenSpatialGroup considered LandXML to integrate into their existing standards. Because of the many different problems described above (see also Scarponcini 2013) they decided against the integration of the LandXML standard. Instead they plan to create InfraGML, a standard that targets the same use cases (alignment, roads, drainage, parcels, etc.) as LandXML does. Right now InfraGML is in the requirement analysis phase and up to now there is no data model available. The German standard OKSTRA (Objektkatalog für das Straßenund Verkehrswesen) unifies the data description of objects from traffic engineering and also contains a data model for alignment data. It is owned by BASt (German Federal Highway Research Institute) and distributed under a free license. The main design goal of OKSTRA is the simple data exchange between different applications that implement the standard. The current OKSTRA standard (version 2.016) has been published in January 2014. In the past the OKSTRA standard has been delivered as an EXPRESS schema along with and XSD schema, while in the current version the data model is solely described as a XSD. Also the CTE data format (STEP based data format to store EXPRESS based instance files) was retired. In detail, the OKSTRA developers moved from EXPRESS to XSD, from NAIM Diagrams (similar to EXPRESS-G Diagram) to UML and from STEP to store instance files (also called CTE files within the OKSTRA standard) to XML. A similar transition from EXPRESS/EXPRESSG/STEP to XSD/UML/XML will also appear probable in the IFC standard, since UML, XSD and XML are better supported by tools than EXPRESS, STEP and EXPRESS-G (since 2001 ifcXML is available). OKSTRA uses several packages of the ISO harmonized model (maintained by ISO/TC 211 Geographic information/Geomatics). Table 1 gives an overview of the different used standards. Table 1. Overview of the different standards used by OKSTRA ______________________________________________ Standard name ______________________________________________ ISO 00639 Language Codes ISO 03166 Country Codes ISO 19103:2005 Schema Language ISO 19107:2003 Spatial Schema ISO 19108:2006 Temporal Schema ISO 19109 Application Schema ISO 19111 Referencing by Coordinates ISO 19115:2006 Metadata (Corrigendum) ISO 19136 GML ISO 19139 Metadata – XML Implementation ISO 19148 Linear Referencing ISO 19156:2011 Observations and Measurements _____________________________________________ The major problem of the OKSTRA standard is that it only targets the German market. In the provided XSD schema only identifiers in German language are used and the documentation is also only provided in German language hindering this standard to become a good candidate for an international standard. RoadXML (current version 2.4) is an open file format for the logical description of road networks (Chaplier et al. 2010) and targeted for vehicle driving simulations. It is based on XML and contains also and alignment data model. In contrast to OKSTRA it is a very lightweight standard (see Table 2). Its main goal is to enhance the interoperability between different driving simulators and traffic engineering applications. Currently RoadXML is maintained by the RoadXML Board which encompasses INRETS (French National Institute for Transport and Safety Research), OKTAL (French company that develops simulation software and systems for vehicles), PSA Peugeot Citroën (French vehicle manufacturer), Renault S.A. (French vehicle manufacturer), and the Thales Group (French provider for electrical systems and services for aerospace, defense, transportation and security). Table 2 gives an overview of the complexity of different described standards. Of course LandXML and OKSTRA are not only limited to alignments and have also other use cases like land acquisition or accident documentation. Lines of Code are not the best measurement for complexity, but they show at least a hint of how complex these data models are. Table 2. Complexity in Lines of Code ______________________________________________ (Pseudo) Standard XSD Lines of Code Last Update ______________________________________________ LandXML 1.2 4821 2008 OKSTRA 2.016 2840