Bulens, J.D.

Kuyper, M.C.

Swol, R., van

Vanmeulebrouk, B.

Zevenbergen, J.

English

Name not available

Why new tools were developed for the “GeoPortal Network: Liberty United” project

van Swol, R.

NARCIS 

Wageningen Yield 

Why new tools were developed for the “GeoPortal Network: 
Liberty United” project 
 
Bas Vanmeulebrouk1, Rob van Swol2, Marjolijn Kuyper3, Jandirk Bulens4, Jaap 
Zevenbergen5 
1Centre for Geo Information, Wageningen University and Research Centre, 
bas.vanmeulebrouk@wur.nl 
2National Aerospace Laboratory, vanswol@nlr.nl 
3Centre for Geo Information, Wageningen University and Research Centre, 
marjolijn.kuyper@gmail.com 
4Centre for Geo Information, Wageningen University and Research Centre, 
jandirk.bulens@wur.nl 
5TU Delft-OTB j.a.zevenbergen@tudelft.nl 
 
Abstract 
As part of the national innovation co-funding scheme “Space for Geo-information” 
the project “GeoPortal Network: Liberty United” ran from late 2005 till the end of 
2008. Purpose of the project was to promote access to geo-spatial information via 
web services. To achieve this goal, a network of geo-portals that is governed by a 
minimum set of rules was developed. 
 
Several approaches for finding spatial data were investigated. Earlier experiences 
show that a top down approach as tried in the Dutch National Clearinghouse Geo-
Information does not work. Instead, it was decided to use a thematic approach for 
opening up metadata. Several thematic portals were created. In line with the 
INSPIRE principle the data are located and maintained at its source and the 
application of open standards allows everyone to contribute to the network. However, 
this is still a supply driven approach whereas a more demand driven approach seems 
more appropriate. Therefore, attention in the project shifted from the creation of 
thematic portals to the underlying web services and the creation of web applications 
developed with a specific purpose in mind.  
 
Initially, it was our intention to implement the network using existing software. 
However, as it turned out, not all the tools needed to implement the network outlined 
in this paper were available. Existing tools work really well for specific applications or 
in predefined environments, but a lot of the tools available do not strictly adhere to 
the open standards or do not use all possibilities offered by the standards. This 
prevents an adequate adaptation of interoperability standards. Innovations in the 
application domain are still a prerequisite to force these developments to take place. 
 
This led to development of a true OGC/ISO compliant CSW dubbed eXcat and a 
platform independent, extensible framework for the development of standards 
compliant internet GIS applications dubbed Luigi. Together with of the shelf tools, the 
newly developed tools provide the technical foundation of our network. It can 
therefore be concluded that software is not a barrier for the adoption of the principles 
laid down in the INPSIRE directive. It is now up to the owners of geo-spatial data to 
take the next step and make their data available using standards compliant web 
services. 
 
Keywords: OGC, open standards, INSPIRE, GeoPortal Network: Liberty United, 
mash ups 
1 APPROACHES TO FINDING SPATIAL DATA 
As part of the national innovation co-funding scheme “Space for Geo-information” 
the project “GeoPortal Network: Liberty United” ran from late 2005 till the end of 
2008. Purpose of the project was to promote access to geo-spatial information via 
web services. To achieve this goal, a network of geo-portals that is governed by a 
minimum set of rules was developed (Zevenbergen, Bulens et al. 2009).  
 
There are several approaches for finding spatial web services (Hoogerwerf, 
Kuyper et al. 2008). One approach for opening up metadata is a top down approach 
as depicted in Figure 1. Such an approach was for instance followed for the Dutch 
National Clearinghouse Geo-Information (NCGI). The NCGI as a clearinghouse was 
started in the mid nineties already (Crompvoets 2006). A clearinghouse was initially 
meant to disclose spatial data through the internet. Key element was to provide 
metadata on spatial datasets.  
 
 
Figure 1 Top down approach for disclosing metadata 
In the Netherlands the NCGI appeared to be far ahead of time. Major drawback 
was the complete absence of the ability to obtain the data themselves. Finding data 
was not the only function of clearinghouses, another major function was to serve as 
an internet shop to get access to the data. Because owner organizations were not yet 
able to deliver data through the internet clearinghouses struggled to survive. So, 
experiences of organizations participating in both the GeoPortal Network project and 
the NCGI show that this approach does not work very well for a geo-information 
infrastructure.  
 
Instead, it was decided to use a thematic approach for opening up metadata (see 
Figure 2). In line with the INSPIRE principle the data are located and maintained at 
their source and the application of open standards allows everyone to contribute to 
the network. Within the frame of the GeoPortal Network project, several thematic 
portals were created. The “Red Portal” for instance contains information regarding 
the built environment, the “Brown Portal” deals with subsurface data and the “Green 
Portal” focuses on environmental data.  
 
 
Figure 2 Thematic disclosure of metadata 
This thematic approach is still supply driven. However, a more demand driven 
approach seems more appropriate. Users who are looking for spatial information to 
answer a certain question will get in touch with an organization close to them (for 
instance a municipality) instead of searching for an answer using a thematic portal. 
Therefore, attention in the project shifted from the creation of thematic portals to the 
underlying web services and the creation of web applications developed with a 
specific purpose in mind (see Figure 3).  
 
A lot of these web applications are so called mash ups. A mash up is a web 
application which has been created by combining data and functionality of existing 
web applications. Organizations have two options for publishing spatial information 
on their web site: they can either develop their own application or they can re-use 
existing components and embed those in their web site.  
 
Figure 3 Disclosure using user oriented web applications 
The web services layer of the architecture outlined in the previous paragraph 
consists of services to publish spatial data. Examples of web services found in this 
layer are Web Map Services (WMS), Web Feature Services (WFS) and Web 
Coverage Services (WCS). A Web Map Service (WMS) produces maps of spatially 
referenced data dynamically from geographic information (Open Geospatial 
Consortium Inc. 2004). A Web Feature Service (WFS) provides a client with access 
to the actual features encoded in Geography Markup Language (GML) (Open 
Geospatial Consortium Inc. 2005). A Web Coverage Service (WCS) describes and 
delivers multi-dimensional coverage data over the internet (Open Geospatial 
Consortium Inc. 2008).  
 
Catalogue services are used to discover spatial data. A Catalogue Service for the 
Web (CSW) supports the ability to publish and search collections of descriptive 
information (metadata) for data, services, and related information objects (Open 
Geospatial Consortium Inc. 2007).  
 
Initially, we did not set out to develop new tools within the frame of the GeoPortal 
Network project. It was our intention to implement the network using existing 
software. However, as it turned out, not all the tools needed to implement the 
network outlined in this paper were available. Existing tools work really well for 
specific applications or in predefined environments, but a lot of the tools available do 
not strictly adhere to the open standards or do not use all possibilities offered by the 
standards (Vanmeulebrouk, Bulens et al. 2009). This prevents an adequate 
adaptation of interoperability standards. Innovations in the application domain are still 
a prerequisite to force these developments to take place.  
2 TOOLS DEVELOPED  
Spatial data can be published using a number of applications. The tools needed 
to publish spatial data were catered for. However, there are little standards compliant 
CSW implementations available and therefore a true OGC/ISO compliant CSW 
dubbed eXcat was developed. A platform independent, extensible framework for the 
development of standards compliant internet GIS applications was also lacking, 
which led to the development of such a framework. This framework was dubbed 
Luigi.  
2.1 eXcat 
eXcat offers an OGC compliant CSW server and client written in Java and based 
on the eXist XML database management system (eXist 2009) and the Geotools open 
source library (GeoTools 2009). The catalogue server can be used to publish 
ISO19115/19139 compliant metadata in accordance with the CSW 2.0.2 standard. 
Metadata queries are very efficiently processed by the server using the web 
technology standards XQuery and XPath which are incorporated in eXist. The server 
can be easily configured to support XML representations of other metadata formats. 
Metadata can be stored using the standard eXist administration client or by using the 
WebDAV interface.  
 
Two CSW clients are offered. The integrated client, entirely written in XQL (XML 
Query Language), is very useful for developers and experts, offering access to the 
eXcat server and other remote CSW servers and supporting flexible setting of 
request parameters, Queries can be expressed using the Common Query Language 
(CQL) and are optionally translated to ogc:Filter expressions. XSL style sheet 
transformations are used to present the responses in XML or human readable 
format. In addition, a stand-alone CSW client based on JavaScript and AJAX was 
developed. This client can be easily integrated in existing web pages and offers a 
simple search tool for querying local or remote CSW servers.  
 
Harvesting of metadata is also supported by eXcat, allowing retrieval of (selected) 
metadata records from remote servers for local storage. Selection criteria can be 
configured for each remote server individually. eXcat is a web application and is 
available as a war file which can be downloaded from 
http://gdsc.nlr.nl/gdsc/tools/excat. Basic installation is as simple as dropping the war 
file in the webapps directory of the servlet engine.  
2.2 Luigi 
Luigi is a user-friendly internet GIS application framework which seamlessly 
integrates web services from different sources (Vanmeulebrouk, Lokers et al. 2008). 
End-users navigate to a web-site from where the internet GIS application created by 
using the framework is downloaded. This application subsequently connects to the 
various web services. Luigi was developed using the Adobe Flex development 
framework.  
 
Adobe Flex is a platform independent platform for developing rich internet 
applications (Adobe 2008). The client platform for applications developed using the 
Flex SDK is either the Flash Player plug-in (for browser based applications), or the 
Adobe AIR runtime (for desktop applications).  
 
The Flex platform is quite suitable to develop highly interactive internet GIS 
applications like the one described here as: 
• Flex is platform independent. Flex applications have to be developed for one 
platform only, the Flash platform. 
• Flex applications can both run in a web browser, using the Adobe Flash 
Player or on the desktop, using the Adobe AIR runtime. Flash Player is 
available on 98.8% of the PC’s in some countries (Frei, Dübendorfer et al. 
2008).  
• Flex offers a rich set of user interface components 
• Flex offers a rich set of user interface effects 
• Flex server calls are asynchronous. This allows users to continue to work with 
the application while the server is processing their requests. 
 
Because of the modular design of the framework, adding new functionality is easy 
for Flex developers having access to the source code or a pre-compiled library of the 
framework. Developers can for example add new visual controls, support for 
additional data formats and new tools operating on the map control, thus adapting or 
extending the “out-of-the-box” functionality of the framework according to the specific 
requirements of the application. 
3 EXAMPLE APPLICATIONS 
In this paragraph, some of the application which have been developed within the 
frame of the GeoPortal Network project will be discussed. All the examples are set up 
according to the architecture described in Figure 3 and use eXcat and Luigi if 
needed.  
3.1 TopoXplorer 
The TopoXplorer internet GIS application was developed for the Wageningen UR 
library. This library possesses numerous analogous topographical maps from the 
Netherlands, the oldest dating back as far as 1850. These maps are used by 
students and researchers. To simplify the use of these maps, the analogous maps 
were scanned and geo-referenced. The TopoXplorer internet GIS application was 
developed to make the digital maps available to users. It allows users to choose 
between different topographical maps and to choose a year for which they want to 
call up a map. The so called swipe tool allows users to compare two topographical 
maps at a certain location (see Figure 4). TopoXplorer was based on the first 
incarnation of the Luigi framework.  
 
 
Figure 4 TopoXplorer internet GIS application 
3.2 Cross border Water Management Initiative (CWMI) 
Purpose of the Cross border Water Management Initiative (CWMI) was to 
integrate subsurface data from Germany and the Netherlands. A portal was 
developed in which data regarding soil and groundwater from both sides of the 
border are presented. Users can not only call up maps, but also graphs. Users can 
choose between the Dutch and the German representation of the data. The portal 
contains an internet GIS client which was based on Luigi.  
3.3 Atlas Demonstrator 
There is a strong need for information on external conditions or surroundings in 
which people live or work. Environment, health and safety are important factors for 
our social well being. The Ministry of VROM in the Netherlands started a project 
called “Atlas Leefomgeving” to provide professionals and citizens with this 
information. Therefore the Atlas project started to build an Atlas Demonstrator (see 
Figure 5) based on the INSPIRE principles. It is meant to demonstrate the use of 
distributed web services from national, regional and local governmental organisations 
to bring together all data sources in order to provide adequate information on the 
living environment for the users. The Atlas Demonstrator end-user application was 
based on the Luigi framework. Metadata (both from spatial data and documents) 
plays an important role in the application. This metadata was opened up using eXcat.  
 
Figure 5 Atlas demonstrator 
3.4 Designer 
The above mentioned examples of internet GIS applications are compiled by GIS 
specialists for a certain target audience. The GIS specialist decides what 
components and spatial data should be present in the application. A web-tool dubbed 
designer was developed which allows end-users to compile their own application. 
Users can select components and services from a panel and link those together to 
create their own internet GIS application. It is a service chaining environment for 
spatial web services.  
 
Users can choose from a number of components: a map control, a navigation 
map control and a legend control. A locator client can be used to provide geocoding 
functionality. The following spatial web services are supported by Designer: CSW, 
WMS and WFS. Users can either select a service from a predefined list or enter the 
URL of their own web service. The CSW client facilitates searching of remote CSW’s. 
A coordinate transformation service can be used to obtain bounding boxes in the 
WGS84 coordinate reference system. This bounding box can also be used to filter 
CSW records.  
 
 
Figure 6 Designer 
4 CONCLUSION 
Together with of the shelf tools, the newly developed tools provide the technical 
foundation of our network. It can therefore be concluded that software is not a barrier 
for the adoption of the principles laid down in the INPSIRE directive. It is now up to 
the owners of geo-spatial data to take the next step and make their data available 
using standards compliant web services.  
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Why new tools were developed for the “GeoPortal Network: Liberty United” project

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NARCIS

Wageningen Yield