EXAMENSARBETE
MASTER OF SCIENCE PROGRAMME
Department of Environmental Engineering Division of Geographical Information Technology
2004:234 CIV • ISSN: 1402 - 1617 • ISRN: LTU - EX - - 04/234 - - SE
Implementation of
OpenGIS-specifi cations
Web Map Service and Web Feature Service in the Solen-environment
Göran Strand and Niklas Wikman
Preface
This report is the result of Niklas Wikman and Göran Strands master thesis in Environmental Engineering at Luleå University of Technology. After five toughening years, which has given us character, it was time for a new challenge. The last 5 months has been spent in the small town of Lycksele, writing our master thesis performed to serve Cartesia GIS. Examiner for our master thesis is Professor Anders Östman. We want to give our thanks to our supervisor, Roger Engefelt, and to our own geodesy expert Carina Borg. We also want to give thanks to Magnus Heldestad and Ulf Karlsson, for their effort to sort out the conceptions, and all the other employees at Cartesia GIS in Lycksele for their support during this master thesis.
Lycksele 2003-09-23
Göran Strand Niklas Wikman
Abstract
Many companies and organizations such as municipalities, transport companies, forestry companies and hydroelectric power suppliers, use geo-referenced data in their daily work. Often they buy and import data that they consider necessary for their activities. It might be, for instance, topographic data, road network data and real estate data. Geo-referenced data are expensive and an organization does almost never buy data just to use it for only one small project. Thereby, there is a risk that existing geographic data will be underutilized.
Cartesia offers solutions (software and services) that handle geo-referenced information. Cartesia’s Solen- concept includes a series of products that organize, analyze and present data. Today the Solen products handle data stored in the customer’s databases. No functionality in the products allows the user to use external data “on the fly”, which have not been imported at earlier stage.
OGC (Open GIS Consortium) is an USA based organization, which develops specifications for open system solutions. OGC consists of large companies and organizations working together to create open spatial interfaces for anyone to use, independent of network, application or platform. In that way, geo referenced data will be easier to handle and exchange. OGC have produced a number of specifications, specifying different types of web services. Two of those specifications, WMS (Web Map Service) and WFS (Web Feature Service), describe how map images and geospatial data shall be requested by the client and supplied by the server. The basic idea is that an increasing number of organizations will offer their geo-referenced data according to these specifications.
When the specifications become established and commonly used, an application with WMS and WFS support will be able to request data from all those organizations. The advantage when using standards is that it will be easier to combine data from different suppliers. The user will be able to request specific data and customize his data to perform a certain analysis. The need for specific import routines will be drastically reduced or perhaps even removed.
By implementing WMS and WFS support in future products, Cartesia can allow their customers to request external geo-referenced data in a smooth and straightforward way. The products will be more attractive to existing users and maybe also attract for some new.
The master thesis is divided in two parts. The first is an evaluation part where server and client software supporting WMS and WFS are examined. The evaluation is based on a number of criteria important to Cartesia, such as, support for data formats, reference systems and development environments. Prices will also be considered. By comparing software according to these criterions, the evaluation results in a recommendation. It concludes that client software ArcObjects 8.3 and server software Cadcorp SIS Active Server Component are suitable products on which WMS and WFS functionality can be developed.
An application is developed in the second part of the thesis, to show how a Windows application can access data over the Internet according to the specifications above. Cartesia are planning to release the next generation of products in .NET environment and they also have the ambition to release the products on the ESRI platform. For that reason, the developing work in this thesis is carried out in VB.NET with ArcObjects as the map engine. The development work shows that it is possible, however time demanding, to develop a “thick” client with WMS/WFS functionality without a development component that is supporting those specifications. To have a VB.NET Windows application to request and receive external data, the WebRequest namespace can be used.
Most of the WMS services work in line with the HTTP GET method. The major part of the WFS services,
however, is based on the HTTP POST method.
Sammanfattning
Många företag och organisationer använder dagligen geografiskt data i sin verksamhet. Det kan vara kommuner försäkringsbolag, åkerier, skogsbolag eller vattenkraftbolag. Ofta köper de det geografiska data de anser sig behöva i sin verksamhet. Det kan vara höjddata, data över vägnät, fastighetsdata eller dylikt. Geografiska data är dyrt och en organisation köper sällan data som endast behövs vid ett enstaka tillfälle. Dessutom krävs en viss arbetsinsats för import av data. Härmed finns en risk att existerande data underutnyttjas.
Cartesia GIS AB levererar lösningar, produkter och tjänster, som hanterar geografisk information. Cartesias Solen-koncept omfattar en serie programvaror som organiserar, bearbetar och presenterar data. För närvarande hanterar Solen-produkterna endast data som finns lagrade hos kunden, antingen genom egen datainsamling eller import. Ingen tjänst finns idag för att vid behov direkt nyttja externa geografiska data via Internet.
OGC (Open GIS Consortium) är en amerikansk organisation som verkar för standardisering av öppna system.
OGC består av stora företag och organisationer som tillsammans utvecklar gränssnitt till geodatatjänster som skall kunna användas av alla oavsett nätverk, applikation eller plattform. Därmed ska geografiskt data lättare kunna hanteras och utbytas. OGC har tagit fram ett antal webservice-specifikationer. Två av dessa är WMS (Web Map Service) och WFS (Web Feature Service), som beskriver hur kartbilder respektive geodata anropas av klienten och tillhandahålls av servern. Idén är att allt fler organisationer ska erbjuda sina geografiska data enligt dessa specifikationer. När specifikationerna blir allmänt etablerade kommer en programvara som stöder specifikationer ha möjlighet att hämta data från alla dessa organisationer. Eftersom det rör sig om specifikationer så finns möjlighet att kombinera geografiskt data från olika leverantörer. Användaren kan hämta precis de data som behövs för en speciell analys. Behovet av specifika importrutiner kommer att reduceras drastiskt eller kanske försvinna helt.
Genom att implementera WMS och WFS lösningar i framtida produkter kan Cartesia erbjuda sina kunder möjlighet att hämta tillfälligt geografiskt data på ett snabbt och smidigt sätt. Produkterna skulle bli attraktivare för dagens användare och möjligen locka nya.
Examensarbetet består av två delar. Den första delen utvärderar server- och klientprogramvaror som stöder WMS- och WFS-specifikationerna. Utvärderingen har sin utgångspunkt i en rad kriterier som är viktiga för Cartesia. Kriterierna är stöd för dataformat, referenssystem och utvecklingsmiljö. Hänsyn tas även till prissättningen av produkterna. Genom att jämföra varje produkts egenskaper mot uppdragsgivarens krav resulterar utvärderingen i en rekommendation. Här föreslås klientmjukvaran ArcObjects 8.3 samt servermjukvaran CadcorpSIS Active Server Component som lämpliga produkter att bygga WMS och WFS tjänster på.
En applikationsutveckling utgör den andra delen av examensarbetet vars syfte är att visa hur en Windows- applikation, som Solen, kan nå data över Internet i enlighet med ovan nämnda specifikationer. Då vår uppdragsgivare har som mål att utveckla nästa Solen version i .NET miljö och ambitionen att successivt även leverera lösningar på ESRI-plattform så sker examensarbetets utveckling i VB.NET med ArcObjects som kartmotor.
Utvecklingsarbetet visar att det är möjligt, om än tidskrävande, att utveckla en tjock klient med WMS/WFS
funktionalitet även om kartmotorn inte stöder specifikationerna. För att en VB.NET Windowsapplikation ska
kunna anropa och ta emot externt data, kan WebRequest namespace användas. De WMS services som finns
använder HTTP GET metoden, medan de flesta WFS services använder HTTP POST.
Contents
1 Introduction... 1
1.1 Background... 1
1.1.1 Cartesia GIS AB ... 1
1.1.2 GIS (Geographic Information System)... 2
1.1.3 Concept of the Solen environment... 2
1.1.4 OGC and their web services for data distribution... 3
1.2 Purpose ... 3
1.2.1 Solution approach... 3
1.3 Goal ... 4
1.4 Area of research... 4
1.5 Method... 4
2 Theory... 5
2.1 The Solen Concept... 5
2.2 OGC... 5
2.2.1 The Concept of OGC... 5
2.2.2 Historic overview ... 5
2.2.3 Advantages when using OGC-supported software ... 6
2.2.4 INSPIRE, an OGC promoting initiative ... 6
2.3 Client/Server... 6
2.3.1 Client ... 6
2.3.2 Thin Client... 7
2.3.3 Thick Clients... 7
2.4 Web Services ... 7
2.4.1 Standards for Web Services... 7
2.4.1.1 XML (Extended Markup Language) ... 7
2.4.1.2 HTML (Hyper Text Markup Language)... 7
2.4.1.3 HTTP (Hyper Text Transfer Protocol) ... 7
2.4.1.4 SOAP (Simple Object Access Protocol)... 8
2.4.1.5 WSDL (Web Service Description Language) ... 8
2.4.1.6 UDDI (Universal Description Directory and Integration) ... 8
2.4.1.7 URL (Uniform Resource Locator)... 8
2.4.2 HTTP Request rules... 8
2.4.2.1 HTTP GET ... 8
2.4.2.2 HTTP POST ... 9
2.4.3 OWS (OpenGIS Consortiums Web Services) ... 9
2.4.4 WMS (Web Map Service) ... 9
2.4.4.1 Operations of WMS... 9
2.4.4.2 Classes of WMS ...10
2.4.4.3 Raster formats for WMS...10
2.4.5 WFS (Web Feature Service)...11
2.4.5.1 Requirements for Web Feature Service...11
2.4.5.2 Communication between the WFS and the Client-application...11
2.4.5.3 Operations of WFS ...12
2.4.5.4 Classes of WFS...13
2.4.5.5 Vector data for WFS...13
2.4.6 GML ...14
2.4.7 SVG ...14
2.4.8 SLD...14
3 Evaluation of WMS and WFS software products ...15
3.1 Evaluation criteria - Client software ...15
3.1.1 OGC specifications...15
3.1.2 Data format...15
3.1.3 Development platform ...16
3.1.4 Type of component...16
3.1.5 Price...16
3.2 Evaluation Criteria – Server software...17
3.2.1 OGC – specifications...17
3.2.2 Reference system...17
3.2.3 Data format...19
3.2.4 Price...20
3.3 Evaluation and analysis ...20
3.3.1 Description of client software...20
3.3.2 Description of server software...23
3.4 Results of the evaluation...25
3.4.1 Client evaluation result...25
3.4.1.1 Criterion 1 – WMS/WFS support...25
3.4.1.2 Criterion 2 – Development product ...25
3.4.1.3 Criterion 3 – Development platform...25
3.4.2 Server evaluation result ...26
3.4.2.1 Criterion 1 – WMS/WFS support...26
3.4.2.2 Criterion 2 – Coordinate systems ...26
3.4.2.3 Criterion 3 – Data formats ...26
3.4.2.4 Criterion 4 – Price ...26
3.5 Discussion, regarding evaluation ...26
4 Development of CWS client ...29
4.1 Development with ArcObjects 8.3 using VB.NET...29
4.1.1 COM-technology...29
4.1.2 VB.NET - History...30
4.1.2.1 Programming History ...30
4.1.2.2 Visual Basic History...30
4.1.3 Changes in VB.NET compared to VB6...30
4.1.3.1 Data ...31
4.1.3.2 Component Authoring ...31
4.1.3.3 UserControl ...31
4.1.3.4 Web Changes...31
4.1.3.5 Windows API (Application Programming Interface)...32
4.1.3.6 Namespace...32
4.1.3.7 Run-Time...32
4.1.3.8 VB.6 and VB.NET together ...32
4.1.4 Wrappers...33
4.1.5 ArcObjects performance in .NET ...33
4.2 Usage of XML in the development of an OWS-client...33
4.3 Establish client-server connection ...33
4.4 WMS Request parameter ...34
4.4.1 GetCapabilities ...34
4.4.2 GetMap ...35
4.4.3 GetFeatureInfo...37
4.5 WFS request parameters ...37
4.5.1 GetCapabilities ...38
4.5.2 GetFeature ...40
4.5.3 DescribeFeatureType...40
4.6 Result of development ...41
4.6.1 CWS (Cartesia Web Service) client...41
4.6.2 How to implement WMS/WFS in a client...43
4.6.3 Functionality for WMS client...44
4.6.4 Functionality for WFS client ...44
4.6.5 To consider when developing CWS-functionality...45
4.7 WMS/WFS servers ...45
4.8 Discussion - The Future Solen concept...46
5 Conclusions...47
5.1 Conclusion related to the goal of the evaluation...47
5.2 Conclusions related to the goal of the development ...47
6 References...48
7 Acronym ...53
Appendix A, evaluation tables ...54
1. Client components ...54
OGC specifications support ...55
Data formats ...56
Development environment ...57
2. Server software ...58
OGC Specifications support...59
Geographical data formats...60
Database formats ...61
Reference system support...62
3. Questionnaire...63
Server questions ...63
Client questions ...64
Appendix B, development...65
1. WMS...66
GetCapabilities response ...66
GetMap response...71
GetFeatureInfo response...72
2. WFS ...74
GetCapabilities response ...74
WFS DescribeFeatureType response...76
1 Introduction
1.1 Background
First of all, there are many different things in the world that would be nice to have on a map. The desired information may therefore differ from one day to another and the need for a certain feature type may appear suddenly and unexpected.
A forestry company may require vegetation indices over a potential logging area. A company that sells hydroelectric power wants water level data for all their water reservoirs. A rescue team in the Swedish mountains is eager to know if there are any cabins in the area they are going to. The missing skier may be in one of those, seeking shelter from the storm.
It’s reasonable to believe that people concerned in the examples above, perhaps except for the lost skier, have access to some sort of geo-referenced data. Most likely purchased externally, imported and locally stored. Some of them might even get their type of data through a specific service on the Internet.
What happens if the forestry company needs data about protected nesting eagles in the logging area?
What if the power supplying company has to consider data about marinas and ferry traffic downstream the river?
What if the rescue team suddenly needs data about cabins and wind shelters on the Norwegian side of the boarder?
Who supplies the requested information?
How can this information be accessed trough a method that is both fast and efficient?
This is the point where the companies today have to acquire and import geo-referenced data or terminate further investigation. If they are lucky, they will find an on-line-supplier for the desired data type. But that online service does presumably not work together with another Internet data source or the locally stored data. There are different ways of how to request data, different data formats, and different projections and so on.
Companies operating in many regions, or in some way having interests in a number of areas, are facing the problem of geo-referenced data and its availability. To handle this problem, there are new ways to request data that covers exactly the desired attributes in a specific area at a specific time, without facing the limitations of today’s services…
1.1.1 Cartesia GIS AB
Cartesia was founded 1995 in Lycksele, Sweden and has today about 60 employees in 5 different cities. Cartesia have grown through expansion into new market segmentations and by purchasing other information technology companies. Headquarter is still located in Lycksele. Cartesia develops and supplies products and solutions for the infrastructure market and other companies and organizations, using geographical information. A major part of Cartesia’s software development is based on MapInfo’s products. Cartesia’s GIS-programs are adjusted to different environments such as client-, Internet- and PDA (Personal Digital Assistant)-systems.
(Cartesia, 2003)
Figure 1: GIS example (www.gis.com, 2003)
1.1.2 GIS (Geographic Information System)
“GIS is a System of computer software, hardware and data, and personnel to help manipulate, analyze and present information that is tied to a spatial location“ (www.gis.com, 2003)
GIT (Geographical Information Technology) in a more technical contexts is a technology that makes it possible to implement and take advantage of geographical information in a wide area of contexts. It is believed that eighty percentage of all information is connected to a spatial position. Non-spatial information about a geographical object is often the key information for the end user of the GIS system, for an example: wells on a map that are presented as a point objects. It is possible to connect attribute data to the point.
The attribute data for a well could be information about water level or information about the ownership of the well. The more different types of attribute data available, connected to the geographical data the more advanced analysis are possible to make for the GIS-user.
An example of GIS-usage:
Imagine a market analysis planner. He provides data of where most customers have the possibility of attending their services, for example restaurants. The planner has probably a lot of
different conditions to fulfill. One condition may be the number of clients that has the possibility to get to the service within a calculated time. The amount of time that is critical will differ depending of what type of service being offered; it may be five minutes for a Pizza-place and two hours for the Porsche dealership.
To be able to calculate the time the transportation will take for the client, calculations must be made considering what speed the clients can be transported in. This depends on how they may transport them selves to the service, by cars, train or maybe by foot. The choice of transportation will probably differ depending on the service being provided, for instance a supermarket or a newsstand. These calculations are usually made for urban areas where it is impossible to go the shortest way as the crow flies because of the houses. That’s why one of the layers will contain street data. To be able to compare the different premises that are possible to rent, one of the layers will have to contain data over available buildings for rent. And to complete the analysis the planner will need statistic data over the citizens in the requested area. To raise the quality of the analysis it is an advantage if the statistics is differentiated on, for example, age or education depending of what kind of service the service provider provides. The service provider will only be interested in the number of families with children if the service is to sell toys, and only interested in people with an age between 18 and perhaps 30 if it is a nightclub.
With a GIS adapted for this example it would be easy to execute an analysis of where the service could be located to have most costumers possible to serve. Of course the planner could try to do this with statistics on paper and paper maps and so on, but if there are, let’s say 100 different locations to choose from, it may take a year for the planner to do it without a GIS system instead of only an hour with a GIS system containing the essential data.
1.1.3 Concept of the Solen environment
Solen is a GIS desktop application for analysis and management of geographic data. Solen is Cartesias “core”-
product and therefore important for Cartesias future. Since the development started, the Solen Application has
been refined and updated to its fifth generation and used by almost 100 different municipalities. The Solen
concept consists of the Solen Administration, Solen Pro, Solen X, Solen Mobile, and Solen Portal. Solen is
developed for GIS analysis in desktop, Intranet, PDA and Internet environments. Solen Pro and Solen X are two
desktop software for the everyday GIS-tasks. The software can be used for creating presentations, making
analysis using connection to registries, refining the GIS-data and to print reports. Most of the Solen customers
are municipalities, governmental institutions and a couple of the costumers are companies. (Cartesia, 2003)
1.1.4 OGC and their web services for data distribution
OGC (Open GIS Consortium) is a non-profit organization composed of important actors in geospatial industry.
That includes companies, universities and public organizations from all over the world. OGC delivers software interface specifications to make geospatial information and services easier to handle independent of network, application or platform. These specifications explain how functions, formats, requests etc. shall be used to make a GIS-solution openly available for global use. A web service is a summarizing term of the operations and functions for integration of data networks and computers for production of functions and services. The web service that is used in this report handles the distribution of raster and vector data from a server and provides the data through the Internet to the user. WMS (Web Map Service) is an OGC developed specification for how to distribute map images thought web services. WFS (Web Feature Service) is an OGC developed specification for how to distribute geospatial features thought web services. The specifications has the same purpose as a standard, namely to build up a framework on how to use a certain technique so that as many users as possible will have the possibility to integrate and use the techniques, functions and operations. The only difference between a specification and standard is that the specification is developed by a commercial organization. (OGC 1, 2003)
1.2 Purpose
In order to increase the awareness and usage of standardized web services in the GIS business, this master’s thesis will examine the WMS- and WFS specifications from OGC. To achieve a greater understanding for these services this master’s thesis will explore the market of WMS- and WFS-supporting GIS software products and evaluate them. It will also show how to implement the specifications in a GIS-software that is not already supporting these specifications.
1.2.1 Solution approach
Many GIS-users are working with map data, purchased by their organization. The data are sometimes insufficient. A municipality may, in a certain occasion, need to view geographic data covering the neighbor municipality or a larger region. It is hard to purchase data for a specific area, in an easy and dynamic way.
Because of this difficulty, it is reasonable to assume that GIS-projects across region boundaries tend to be complicated and that they sometimes never take place.
Companies and organizations in areas such as forestry- or insurance businesses are daily meeting this problem.
Today Cartesia are, in their products, not able to present a solution for it, which limits the products usefulness for current customers as well as it limits Cartesias possibility to reach new market segments and market shares.
Web Service for GIS technology is a useful tool to provide any public geo-referenced information, for a wide audience. Web service is an efficient way of distributing geo-referenced data in a wide range of services for example real-estate information, weather reports or watchtower locations for tourists.
Open GIS Consortium develops, among other specifications, specifications in the web service area. Two of those are WMS and WFS, which describes web services for map images and geospatial data. The basic idea is that more and more organizations will offer their geo-referenced data according to these specifications. When the standards become established and commonly used, an application with WMS and WFS support will be able to request data from all those organizations. The advantage when using standards is that it will be easier to combine data from different suppliers. The user will be able to request specific data and customize his data to perform a certain analysis.
During the last years, networks and hardware have improved in power and performance, which has created possibilities to handle more advanced data traffic over the Internet.
Based on an evaluation of different software for use on server side and client side, this report will suggest
Cartesia a server/client solution. The evaluation of the products will consider parameters such as OGC-support,
projection support, data formats and more technical aspects. To that, the report will also consider the prices to be
able to suggest a suitable solution to Cartesias needs and demands on functionality.
1.3 Goal
Our goal is that this Master Thesis should be a valuable start for developing client software for Web Map- and Web Feature Services and for setting up Web Map- and Web Feature Services.
• The goal for the evaluation is to find the optimal development component for development of a thick WMS client and the optimal server software product for publishing WMS services for Cartesia. WFS support is an advantage but not as essential as WMS.
• The goal for the development is to develop a client application that handles “information enhanced”
maps according to the OGC specification WMS and to be able to load features according to OGC specification WFS. The application shall allow the user to combine a WMS raster image with local map data. The development work will also try to identify problems and shortcomings noticeable in the products and specifications.
1.4 Area of research
This project will be divided in two parts – evaluation and development. The theme through both parts will be the OGC specifications WMS and WFS. Other OGC specifications may be briefly mentioned but not investigated in this thesis.
The evaluation part will result in a suggestion of a suitable client and a likewise suitable server product for Cartesia to base their OWS (OGC Web Services) development upon. The evaluation will take notice to a number of criteria, important to Cartesia. Another GIS company with different priorities and criteria, may come to other solutions. Regarding WFS, this report will focus on Basic WFS, which means “read only” functionality and leave out transactional WFS. Transactional WFS means a WFS service where the client may insert, update or delete features within the services.
The Solen will be the starting point and the raw model for the programming work. The application will be desktop software just as the existing Solen. The development will otherwise have no connection to today’s Solen product. The project will demonstrate how to feed a powerful GIS analyze software with map data through the OGC web services WMS and WFS. The development will focus on and have the goal to present map images from WMS and geospatial data from WFS. The thesis will not consider commercial issues as how to make the product available for the market, how it should be paid for and how to handle copyrights for map data. Nor will the application be designed with a well-considered GUI (Graphic User Interface).
1.5 Method
The first half of the report, the evaluation, is based on a literature study, mail contacts, interviews and telephone interviews. A literature study is performed in the beginning of this master thesis and that is why some new development components or server software may enter the market during the development period of the thesis.
They are not included in this report.
CWS (Cartesia Web Services) is defined as the OWS that are interesting for Cartesia as a start when implementing OGC web services into their products. For this Master thesis, CWS consists of WMS and WFS.
The collecting of data about interesting WMS- and WFS-products or some other geomatical topic is made through interviews with interesting producers and people in the branch through mail, telephone or in person. The collection of data about different development components for CWS-client functionality and server software are compiled by letting the suppliers answer the questions in a questionnaire. The goal is to get consistent data from all the producers to make the evaluation as fair as possible.
To reach the goals of the development, a requirement specification is developed, adapted to Cartesias goals for
functionality of their future WMS- and WFS-client application. The demand specification is produced in
cooperation with Roger Engefelt, project coordinator at Cartesia. Requirement specification also consists of
information about preferable development environment, and the best-suited development component, for the
WMS and WFS client, who will be appointed in the evaluations result. The method of solving programming
problems through the development part of this master thesis is to use Internet forums, help-pages on the Internet
and technical support from Cartesias partners.
2 Theory
2.1 The Solen Concept
“Solen is an application that can be used for the administration and distribution of digital maps as an integral part of the customers IT strategy”
The Solen concept started with a consult project for Sollentuna municipality in the middle of the nineties, by developing a GIS application with an interface that was easy to use so that the implementation would be wider in the organization. Since this project started, the Solen application has been refined and developed to Cartesias
“core-product” and has been updated to a fifth generation and used by almost 100 different municipalities. The Solen concept is built of the Solen Administration, Solen Pro, Solen X, Solen Mobile and Solen Portal. Solen Administration is developed to create and maintain maps for desktop, Intranet, PDA and Internet environments.
It’s also used for setting up unique user id´s, to create views, links and additional geo spatial functionality. The Solen Pro and Solen X are the two classic desktop client software products for the everyday GIS-tasks. These products can be used for creating presentations, perform analysis, refine GIS-data and print reports. The Solen Portal and Solen Mobile are applications for GIS through Internet and field work using only PDA’s. A big advantage of the Solen concept is the possibility to connect all registry and file-based information through the map via a metadata base where all the core information is stored.
Most of the Solen customers are municipalities or governmental institutions, while a few of them are companies.
The different programs of Solen have a simplified interface compared to its own core product, MapInfo Professional. It is possible to configure the user level through the Solen Administration software which makes it suitable for a wide range of user groups to be able to work in a GIS-environment at their own level. While introducing Solen in a new organization, the environment is adjusted to the specific costumer. The Solen environment is an interoperable solution that supports the most important database- and data formats. There is a number of different Plug Ins to Solen for integrating different registries or domain specific functionality, for example Fast (Real Estate), Folk (People) and Park.
(Cartesia, 2003)
2.2 OGC
2.2.1 The Concept of OGC
OpenGIS Consortiums mission is”a world in which everyone benefits from geographic information and services made available across any network, application, or platform.”
The OGC is not a standardization organization but a consortium that has commercial purposes composed of all the important actors in the geospatial industry. That includes companies, universities and other organizations from all over the world. OGC delivers spatial interface specifications to make geospatial information and services easier to handle independent of network, application or platform. (OGC 1, 2003)
The relationship between OGC and the standardization organization ISO is strong and OGC, are working to get all their specifications adopted as ISO standards. (Kottman, 2003)
2.2.2 Historic overview
The OGC story began in the U.S. army in the early 1980:s. At that time a group was formed to develop spatial analysis software. They were working for the army’s CERL (Construction Engineering Research Laboratory) in Champaign, Illinois under direction of Bill Goran and their goal was to help DOD (Department of Defense) to implement GIS for military- and civil purposes. After not having been able to find any commercial software of interest they soon developed the open source, UNIX-based software called GRASS. (Geographic Resource and Analysis Support System). Its popularity amongst US federal agencies and universities increased fast and in the early 90:s the user mailing list contained of more than 6000 names and the number of enterprise applications was growing rapidly.
At this time, three organizations were formed because of the increasing divergent in usage of the GRASS
applications. One of them was GIASC, an organization formed by federal agencies to support and coordinate the
GRASS development in US Government. Another of the organizations was GRASS TURF, an association of
individual GRASS users, public and private organizations and universities. TURF was the user forum. These organizations came together 1992 and became OGF (Open GRASS foundation). At this stage OGF decided to expand their area of interest to comprise private sector development as well as support capability for GRASS. A couple of years later, OGF was for the first time sponsored by a commercial company. The development tended to be more and more based on networks, and interoperability became their key word. In this period of time OGF worked out a strategy for how to make spatial resources available for private and public users and to share information in the branch. The demand for open interfaces was obvious and so was the need of a new type of organization. An industry consortium would be a more suitable form than a foundation to handle these kinds of issues and that’s why the OGC (Open GIS Consortium) was founded in 1994 with eight character members. The OpenGIS Consortium has grown ever since and consists of 254 members in October 2003. (OGC 2, 2003)
2.2.3 Advantages when using OGC-supported software
The major advantage of building geospatial software utilizing OGC specifications is the fact that the attendance from key companies in the business is strong. The interoperability is an important factor for the GIS-application distributors when enticing customers to choose their products. The more interoperable the product gets, the better the possibility will be to integrate the application into the customer’s present and future products.
(OGC 1, 2003)
These are specifications that OGC has developed until 14 may, 2003
Simple Features Specification for OLE/COM 1.1
Simple Features Specification for CORBA 1.0
Simple Features Specification for SQL 1.1
Catalog Services Implementation Specification 1.1.1
Grid Coverages Implementation Specification 1.0
Coordinate Transformation Services Implementation Specification 1.0
Web Map Services Implementation Specification 1.1.1
Geography Markup Language Implementation Specification 3.0 Web Feature Service Implementation Specification 1.0
Filter Encoding Implementation Specification 1.0
Styled Layer Descriptor Implementation Specification 1.0 Web Map Context Documents Implementation Specification 1.0
Figure 2: Standards from OGC (OGC 1, 2003)
2.2.4 INSPIRE, an OGC promoting initiative
INSPIRE (INfrastructual for SPatial Information in euRopE) is an European Commission initiative about access to geo referenced information to support understanding of the complexity and interactions. European Union is currently investigating a suggestion about GIS legislation to force governments and public authorities to make their data available according to industry standards such as the OGC specifications. (INSPIRE, 2003)
2.3 Client/Server
A client/server architecture can be described as follows: The architecture consists of a central process, a server, which accepts requests from multiple user processes, so called clients. There are both advantages and disadvantages with the client/server model compared to desktop software. An advantage of Client/Server solutions is that data are stored and shared commonly by the users. A desktop solution most certainly will cause data corruption because of the multiple data storage. A disadvantage of the client/server model has been, at least until now, that it is harder and sometimes not possible to produce client/server solutions when producing advanced systems like GIS-applications. The connection between server and client may be overloaded. The server processing may be overloaded because of to many simultaneously connected clients. One problem is due to the speed of Internet that is getting better but still cannot be compared to the speed of the communication between a computer’s CPU and its hard drive. (ESRI 1, 2003)
2.3.1 Client
A client is a type of software that asks the servers to do things for them. Examples of services that clients
requests from servers could be sending data from a database or providing information about Internet addresses
for a certain task. (OGC 3, 2003)
2.3.2 Thin Client
A thin client is clients with a limited processing capacity, having the server do all the work. The server has sufficient software and computer power. (Pagina 10, 2003)
2.3.3 Thick Clients
A thick client is a client that only partly uses server for processing or providing information and integrates this functionality to a desktop application. A thick client offers the advantages of both client/server and the desktop model. Data distribution through the Internet provides the “thick client” with data that is up to date and the same time being able to provide advanced functionality through the desktop-part of the application. A thick client might need to be upgraded when updating the application.
2.4 Web Services
There is a common confusion about what web services means. A web service is here defined as a technology for integrating functions and operations through communications between different systems. This should not be mixed up with “services on the net” that are commercial services distributed through a web interface.
A web service is a summarizing term of the operations and functions for integration of data networks and computers for production of functions and services in an existing system and available for other systems. There are a number of different standards developed with connection to web services for example UDDI, SOAP, WSDL and XML. (Pagina, 2003) These standards are described later in this chapter.
Functionality is available through a web service, which is distributed from someone’s computer/server. Web Services may appear as programmable classes by both methods and functions distributed. These classes can be reached and used another application.
For example: A programmer wants to produce a stock trade information application. She/He can benefit from web services distributing present value of stocks or news about different companies’ financial status. It is easy to integrate all necessary information about how the companies’ situations are, through web services.
Web services are a standardized technique for software to communicate with, and distribute functions to, each other instead of communications with users. (Mackenzie&Sharkey, 2002)
2.4.1 Standards for Web Services
2.4.1.1 XML (Extended Markup Language)
XML is a universal format for data on the web. XML provides the ability for developers to describe and deliver rich, structured data from any application in a standard and consistent way. XML is a complementary language to HTML. (MSDN, 2003)
XML is a simplified version of the language SGML (Standard Generalized Markup Language) that is used as a format for structured text and supports the ISO 8879. XML is used in a similar way for production of Web pages and advanced distributed platform independent database systems. SGML is just more complex then XML.
(Pagina 1, 2003)
2.4.1.2 HTML (Hyper Text Markup Language)
HTML is a language used for producing web pages and handling Hyper Text Documents. HTML derives from SGML (Se under 2.3.1.1). HTML-documents are a type of a document that is produced and handled by HTML- editors through the HTML-code. The HTML-standard is produced and developed by the standardization organization W3C (World Wide Web Consortium) and has been redeveloped for its fourth generation. (Pagina 3, 2003)
2.4.1.3 HTTP (Hyper Text Transfer Protocol)
Http is a protocol for the communication between the web server and the web browser. This protocol is specially
designed for searches in information systems. Http is the original transfer protocol for the web. (Pagina 4,
2003) More technical information is given in chapter 2.4.2.
2.4.1.4 SOAP (Simple Object Access Protocol)
SOAP is a method for applications to communicate with each other through an Internet connection independent of platforms. SOAP is using XML to define the format of information and adds the necessary HTTP-headers to be able to send them. SOAP consists of three parts:
1. An envelope that defines a framework for describing the content of a message and how to process it.
2. A set of encoding rules for expressing instances of application-defined data types.
3. A convention for representing remote procedure calls and responses.
SOAP can potentially be used in combination with a variety of other protocols. SOAP was developed by Microsoft, DevelopMentor and Userland Software and has been recommended to the IETF (Internet Engineering Task Force) as a standard. It is an important component in the concept of Web Services. (Pagina 2, 2003) 2.4.1.5 WSDL (Web Service Description Language)
WSDL is an XML-format for the description of web services. WDSL differentiate the description of the abstract functionality of the web service from the specific details of how the service is performed. (Pagina 6, 2003) 2.4.1.6 UDDI (Universal Description Directory and Integration)
UDDI is a web based distributed catalog that can be used to make lists of web service providers which makes it possible for them to find each other. It is used in a similar way as the yellow pages in a traditional phonebook.
(Pagina 5, 2003)
UDDI defines a SOAP-based web service for locating WSDL-formatted protocol descriptions of web services.
UDDI provides a foundation for developers and administrators to share information about web services across the Internet. (MSDN 2, 2003)
2.4.1.7 URL (Uniform Resource Locator)
URL is a system for address codes on the Internet. For example www.luth.se is the URL-address of the Luleå University of Technology on the Internet. (Pagina 7, 2003)
Unlike web data formats, such as HTML and XML, and web protocols, such as HTTP and HTTPS, there is only one web naming/addressing technology, namely: URLs. (W3C 1, 2003)
2.4.2 HTTP Request rules
Hypertext Transfer Protocol is the protocol used in communication between servers and web browsers. The protocol is especially suited for searches in information systems based on hypermedia. (Pagina 4, 2003).
Hyper medias are systems handling sound-, image- or film data. Basically there are three request methods supported by HTTP. They are HTTP GET, HTTP POST and HTTP PUT. At least one of these methods is defined for each service specified by OGC (OGC WMS, 2002).
POST and PUT are not yet defined for WMS. The HTTP POST method is under development by OGC and there is an early version “WMS Part2 XML for Requests Using http POST 0.0.3”. WFS support the POST method and the GET method. The GET method for WFS is in most cases only supported for the GetCapabilities requests though.
2.4.2.1 HTTP GET
This method has a number of reserved characters for different usage. When the characters, are found in their roles, listed in Figure 3, they are to be taken literally in the URL. Else, if the characters appear in other roles, for example as values of a parameter, they are to be encoded following the rules of IETF RFC 2396. The URL formed to be a GET request is on the whole nothing but a prefix to which further parameters may be attached.
The prefix string contains parameters as protocol, hostname, optional port number, path, question mark and in certain occasions server specific parameters. The client attaches the request parameters as name/value pairs. The URL formed has to be valid according to the CGI (HTTP Common Gateway Interface Standard). The question mark ‘?’, before the chain of parameters and the ‘&’ between the individual parameters are separators in line with the CGI standard. (OGC WMS, 2002)
General OGC web service request looks like this:
http://host[:port]/path?{name[=value]&}
The URL shall end in a ‘?’ or a ‘&’ depending of the presence of additional server-specific parameters or not.
The [] indicates 0 or 1 occurrence of an optional part and {} indicates 0 or more occurrences. The part
‘name=value&’, indicates one or more name/value pairs defined by an OGC Web Service.
Character Reserved Usage
? Separator indicating start of query string
& Separator between parameters in query string
= Separator between name and value of parameter
/ Separator between MIME type and subtype in format parameter value : Separator between Namespace and Identifier in SRS parameter value , Separator between individual values in list-orientated parameters
Figure 3: Operators for HTTP GET requests (OGC WMS, 2002).
2.4.2.2 HTTP POST
The POST method is not based on name-value pairs as the GET method. The URL is coded to optional format before the request is send. When requesting WFS data the URL is coded to XML format.
2.4.3 OWS (OpenGIS Consortiums Web Services)
OWS consists of WMS (Web Map Service), WFS (Web Feature Service), WCS (Web Coverage Server), Web Map Context Document and WRS (Web Registry Service) so far. WMS and WFS are described in sections 2.4.4 and 2.4.5 of this report. (OGC WMS, 2002)
WCS extends the WMS specification to handle geospatial coverage. A WCS delivers raw data, values and properties, of geographic locations instead of generated maps.
When handling several maps from one or more servers as a group, the WMC specification specifies how this group of maps can be described in a platform independent format for storage or transmission between clients. A Web Map Context document contains information about for example the bounding box and map projection shared by all the maps.
The WRS defines a mechanism to classify, register, describe, search, maintain and access information about OGC web recourses.
2.4.4 WMS (Web Map Service)
This specification specifies the behavior of a service providing geo-referenced raster maps. It describes operations to get information about a map supplied by a server working in line with the WMS specification. To that, it also describes operations to get the actual map and how to formulate requests to the server in order to get feature info i.e. the contents of the map. Maps are often stored and used in formats such as PNG, GIF or JPEG.
The specification explains how to request these maps in a standardized way and how the server describes its data content. (OGC WMS, 2002)
2.4.4.1 Operations of WMS
The WMS-specification describes three operations, explained below. A web browser can ask for these operations by sending the request as an URL (Uniform Resource Locators). The content of such an URL depends on what type of information being asked for. All URL:s independent of operation contains version number and parameters for the request.
GetCapabilities (demanded): Receive metadata. The data is machine- as well as human readable information of the contents of the service and of accepted request parameters. Since each WMS is independent, it has to supply machine-readable explanation of its content (capabilities). The explanation, i.e. the meta data, gives the user the possibility to formulate a proper request and renders the possibility to create searchable catalogs, which guide the user to a specific WMS.
GetMap (demanded): Receive a map image that has well defined geospatial and dimensional parameters. The
client specifies the map information with parameters referred to number of layers and their styles, part of the
world to be shown (BoundingBox), projection and coordinate system (Spatial Reference System or SRS).
Finally, wanted display format, display size (height and width) and transparency and color of background can be requested. Several maps with same BoundingBox, SRS and display size can together represent a combined map.
The combined map is only conceivable when the display format is supporting transparent pictures, which makes underlying layers visible. Furthermore, these layers may be picked up from different servers. That’s why the users are able to compose their maps based on individual needs and wishes. WMS GetMap operation thereby uses a network of map servers. This may be compared with the more commonly used vertical integrated map web sites on the internet, where all map data are stored in one place and where the map data are accessible through that internet page’s own interface only.
GetFeatureInfo (optional): Receive information about features shown on the map. This operation makes the maps “information charged” and the users get the opportunity to ask about information referred to different areas on the map. In the GetFeatureInfo operation the client states map of concern and area of interest on that map.
The request is formulated in the URL as a deviation in X- and Y direction from the top left corner and the number of areas around that given position, the user is interested in.
2.4.4.2 Classes of WMS Standard
A WMS handling the two required operations GetCapabilities and GetMap is a standard WMS.
Queryable
Optionally a WMS can allow the GetFeatureInfo operation. When it does, its maps are said to be "queryable,"
and a client is able to request information about features on a map. This is performed by adding to the map URL further parameters to specify a location (an X, Y offset from the top left corner) and the number of nearby features about which to return information. (OGC WMS, 2002)
2.4.4.3 Raster formats for WMS
Raster graphics, the opposite of vector graphics, are built up by pixels. Raster images cannot be enhanced through rescaling. They will keep the same information content no matter of zooming and enlargement of the images. When enlarging a raster image the pixel pattern appears clearly (pagina.se).
The WMS specification does not specify what raster format to use. It is optional and the map supplier is free to offer his raster images in any raster format. There is an uncountable number of raster formats to use. They differ from each other in many ways and they all have their pros and cons. Common raster formats of interest when displaying map images are described in this part.
Bitmap is the standard Windows image format. (WorldStart, 2003). It is a non-compressed memory-demanding format supporting unlimited number of colors. Its file suffix is .bmp. (Mackenzie&Sharkey, 2002)
GIF, shortening for Graphics Interchange Format, is a compressed image format often used on the Internet.
CompuServe, one of the largest data communication systems in the US, has developed GIF. Lossless compression of the GIF images is reached by using the LZW algorithm (pagina.se). GIF images are small but limited to 256 colors. Uncolored pixels can be set as transparent. Suffix is .gif. (MacKenzie,&Sharkey) JPEG stands for Joint Photographic Experts Group. This format is also used on the Internet for storing photographs and other graphics where a large number of colors and grayscales are demanded. JPEG format is supported by standardization organizations as ISO and ITU The JPEG format can be greatly compressed.
Compressed files do loose information and quality because of the compression type, which discards information.
Transparency is not possible. JPEG file suffix is .jpg. (Pagina 11, 2003)
TIFF means Tagged Image File Format. This format was very common earlier but is rarer nowadays. It is still a common format for scanned images (Pagina 12, 2003). TIFF files can be small or large depending of which type of TIFF being used to store the file. LZW is a loss less type of compression. Compression won't result in a file as small as a JPEG file and because of that TIFF is not used on the Internet. Suffix is .tif.
(MacKenzi&Sharkey)
PNG or Portable Network Graphics is a relatively rare file format. Originally created as a substitute to GIF and
TIFF. W3C has approved the standard. Files in PNG format are pretty small but not as small as GIF or TIFF files
(MacKenzie&Sharkey). This file format is seldom supported even though Internet Explorer and other programs
are able to visualize its pictures. PNG type of images loads faster and allows higher quality then GIF. All pixels, even the colored ones can be transparent. Suffix is .png. (Pagina 13, 2003)
2.4.5 WFS (Web Feature Service)
When using WFS, features are modeled as geographic objects, which might be stored in an object-based data format like vector data. Examples of features could be anything that can be placed in time and space, including desks, buildings, cities, trees, forest stands, ecosystems, delivery vehicles, snow removal routes, oil wells, oil pipelines, oil spill, and so on.
The WFS is a way of distributing geographical features through a web service to a client application or a browser. The client will be able to request the selected data for the needed extent. WFS are a standardized way of distributing vector data to large audience. WFS offer the possibility to the users to be able to load vector data for a requested extent whenever the user requires the information.
WFS is accessible trough the Internet or an Intranet. The vector standard is working with the http (Hypertext Transform Protocol) and supports the insert, update, delete, query and discovery operations for geographical objects. The features are usually transported in GML (Geographic Markup Language, see 2.4.6)-format to the client application. (OGC-WFS, 2002)
2.4.5.1 Requirements for Web Feature Service A WFS has to fulfill six requirements:
1. The interfaces must be defined in XML.
2. Features must be expressed with GML within the interface.
3. WFS must be able to present features using GML.
4. The predicate or filter language will be defined in XML and be derived from CQL as defined in the OpenGIS Catalogue Interface Implementation Specification.
5. The data store used to store geographic features should be opaque, and impossible to get in touch with from the client applications and their only view of the data should be through the WFS interface.
6. Usage of a subset of XPath expressions for referencing properties.
(OGC-WFS, 2002)
Figure 4: The functioning of the communication between a WFS and a client. (OGC-WFS, 2002)
2.4.5.2 Communication between the WFS and the Client-application Requests aiming to create a transaction between the WFS and the WFS-client should proceed as follows:
1. A client application sends a GetCapability-request to receive a capability document from the WFS. The document contains a description about the operations supported and a list of all feature types the WFS can serve.
2. The client application creates a GetFeature-request to the WFS for one or more feature types that the WFS can serve.
3. The request is specified using the WFS Specification 1.0.0 definitions of Feature types.
4. The request is posted to a web server.
5. The WFS is invoked to read and serve the request.
6. When the WFS have completed processing the request, it will generate a status report and hand it back to the client application. In the event that an error has occurred, the status report will indicate that fact. (OGC-WFS, 2002)
2.4.5.3 Operations of WFS
The WFS supports the common OGC operations; insert, update, query and discovery, on geographic features using http as the distributed platform. To support transaction and query processing, the following requests are defined for WFS:
The GetCapabilities request consists of information about what data and operations the WFS supply. The GetCapabilities response will be distributed in XML-format.
The DescribeFeaturetype describes the structure of any feature type it can service. It is used to connect attribute data to the features and make them queryable. Also the DescribeFeatureType responses will be distributed in XML-format.
A web feature service must be able to serve a request to retrieve feature instances. In addition, the client should be capable to specify which feature properties to fetch and should be able to limit the query spatially and non- spatially. The GetFeature response will consist of the actual feature data and will be distributed in GML 2.1.1 by default but if the WFS supports ESRI: s Shape, GMLZIP or XML_SVG data could be distributed in wanted format.
A web feature service may be able to serve transaction requests. A transaction request is composed of operations that modify features; that are creating, update, and delete operations on geographic features.
A web feature service may be able to process a lock request on one or more instances of a feature type for the
time of a transaction and will not be editable for any other user during transaction. (OGC-WFS, 2002)
2.4.5.4 Classes of WFS
There are two different classes of WFS defined in the WFS specification:
Basic WFS consists of GetCapabilities, DescribeFeatureType and GetFeature operations. This would be considered a read only web feature service.
A transaction web feature service would support all the operations of a basic web feature service and in addition it would implement the transaction operation. Implementation of the LockFeature operation is optional choice when establishing a transaction operation. (OGC-WFS, 2002)
Figure 5: Illustrates the communication between a client and transactional WFS. (OGC-WFS, 2002)
