Technical details

Technical details: metadata search

The metadata search consists of a database where metadata is stored, as well as a search and an API which enables the metadata to be requested and perused and guarantees integration in the geodata4edu.ch website. The entire stack of the metadata search is operated in the SWITCHengines Cloud.

The metadata is structured based on a metadata scheme, which is negotiated among the project partners and can be adjusted in important cases. The metadata elements defined within are geared to the metadata search. A metadata set is required for every geodata set to find it in the search. The metadata is entered by the person responsible from the two access services. GeoVITe uses a CSW interface. The metadata of the HSR web services is entered via elements of the rest interface and an entry interface.

The search contains search algorithms to transform the contents of the metadatabase into an easily searchable form (search database), which can be searched using a defined search syntax (this search syntax is documented in a search guide). The search also uses two tools to improve the results. Firstly, a stemming in the corresponding language of the entries is conducted, which enables the word stems to be recognised. Words are therefore found independently of the gender or number. Secondly, there is a list of the most important technical and data terms with translations in German, English and French (e.g. Wald – forest – forêt) and the corresponding synonyms (e.g. forest – wood – copse). In a search request, the search term entered is automatically supplemented with the corresponding translations and synonyms in the background. The list of translations and synonyms is operated and constantly supplemented by the data officers from the two access services.

The API for integration on the geodata4edu.ch website provides a REST interface, which accepts the search terms and search information, returns the search results in a relevant form and, if need be, allows straightforward access to the metadatabase via the established and current interface.

Technical details: web services

The HSR web services enable a GIS-specialised user to access licensed geodata from federal offices and cantons directly with the proprietary user software ArcGIS for Desktop and OpenSource user software, e.g. QGIS. Authentication with the SWITCHaai Identity Provider guarantees that only authorised users from research and students from Switzerland gain access to the licensed data.

The technical infrastructure is based on the SWITCHengines Windows Server 2012 R2. The vector and raster data is saved in the backend in an ArcSDE/MS SQL database and a FileStorage server, and published as map, feature and image services via the REST API interface of an Esri ArcGIS server. These web services hosted on the ArcGIS server are organised by Esri via a federation portal for ArcGIS for further usage and made available for visualisation purposes and processing. For the integration of the web services in the desktop client, the user connects following a successful registration via “Portal for ArcGIS” on the ArcGIS server and loads the web services into the corresponding desktop user software.

Technical details: download service

GeoVITe (Geodata Versatile Information Transfer environment), which is providing the download functionality of the Geodata4EDU national service, is based on a three-tier architecture, with a clear separation between the data (managed by a back-end data management layer), the application (consisting of server-side geo-services) and the presentation (front-end; client-side user interface).

The available vector and raster datasets are managed in back-end systems such as PostgreSQL geodatabases and Network Attached Storage (NAS) shares. The server-side application layer was developed around servers hosting geoprocessing and view services based on well-known open source software and libraries such as QGIS Server, GDAL/OGR and GeoTools, and enhanced by several Java servlets creating an Application Programming Interface (API) around the data management layer. The portal’s Graphical User Interface (GUI) is built using well-known Web technologies such as HyperText Markup Language (HTML), Cascading Style Sheets (CSS) and JavaScript (JS) on top of GeoAdmin3 and OpenLayers3 frameworks. The entire GeoVITe GUI is also wrapped by Java server technologies such as Java servlets and Java Server Pages (JSP) in order to enforce authentication and proper communication with the server-side application layer. As a consequence, the “thin” Web-based interface in GeoVITe handles the majority of user interactions by sending requests and listening to responses from the server-side application layer. In turn, the geo-services access the data in the back-end, do the necessary data processing (for viewing or downloading) and return the corresponding responses back to the user interface.

The GeoVITe technologies support the implementation of academic spatial data infrastructures (SDIs) and geoportals that are interoperable with commonly used open source and proprietary GIS software such as QGIS or ESRI ArcGIS. The GeoVITe portal and services also serve as the corporate SDI of ETH Zurich, which is now part of the comprehensive national service offered to the Geodata4EDU consortium members.