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1April 2007

Linköpings universitet / IDA / Div. for Human-Centered Systems

Imad Abugessaisag-imaab@ida.liu.se

20071030

Web GIS Web GIS & &

GeoWebGeoWeb ServicesServices

2April 2007

References

Internet GIS: Distributed Geographic Information Services for the Internet and Wireless Networks. By Zhong-Ren Peng , Ming-HsiangTsou.

Connecting Our World: GIS Web Services by, Winnie Tang, Jan Selwood.

Spatial Portals Gateways to Geographic Information, by Winnie Tang, Jan Selwood.

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3April 2007

Internet GIS: a research field

A research and application area that utilize Internet and other Internetworking systems to facilitate:

• Access

• Processing

• Dissemination

of geographic information and spatial analysis knowledge.( Peng and M. Tsou, 2003).

4April 2007

Internet Atchitecture for GIS

Two reasons make geographical information providers explore Internet to disseminate geospatial data ( Gillavry, 2000):

1. Internet architecture and protocols allows the user to interact visually with the spatial data.

2. The near ubiquitous nature of the Internet allows the Internet to be widely accessible.

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5April 2007

Web mappingWeb mapping as development in GIS makes it possible to sharegeospatial information using available web browsers. Maps can be presented as a general purpose maps that can only display locations and other geographical features (cartographic elements).

6April 2007

Components of Internet GIS

Web GIS has the uniqueness of its components and architecture comparing with the rest of web applications, as publishing maps over the Internet requires special architecture. Four components comprises web GIS

Client

Client

Client

Data ServerMap ServerWeb Server

With

Application Server

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7April 2007

Components of Internet GIS: Clients

Internet GIS users use clients to interact and perform different operations and tasks. Users of GIS use Graphical User Interface (GUI) to interact with different applications, (clients) relies on HTML.

HTML are not sufficient for user interaction, DHTML make interaction with spatial object more efficient.

A client side application can used such as plug-ins, Java applets, Java beams and ActiveX controls.

8April 2007

Components of Internet GIS:Web server and application server -1-

Web server is HTTP server; its function is to respond to the request made by the browser (client). Three ways are used by theweb server to respond to client request:

– Sending existing HTML document to the client.– Sending Java applets or Activex control to the client.– Passing requests to other program and invokes other program that capable to process

the quires. ‘

Application server is a glue program that receive client requestwhen it was passed by the web server the application server actsas middle ware that connect both web server and any other server-side applications such as map server.

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9April 2007

Basic functions of application server is to :– Establish maintain, and terminating the connection between the

web server and the map server.– Acts as translator between the web server and map server.

– Interpreting client requests and passing them to the map server.

– Managing concurrent processing and requests.

– Balancing the load among the map servers and data servers.

– Acting as manager for state, security and transaction.

Application server could include model such as CGI or ASP.

Components of Internet GIS:Web server and application server -2-

10April 2007

Map server components also known as a spatial server in some commercial product. Map server perform traditional desktop GIS functions.

The role played by the map server is to reply to the spatial query by performing spatial analysis and generates maps to the client.

Components of Internet GIS:Map server -3-

Filtered features dataTo client for manipulations

Map image in graphic formats.( GIF) / (JPEG)

Map server output

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11April 2007

Spatial and non spatial databases are modeled in either relational or non relational models, will be stored in data server. Other components such as web server and map server can access the database using SQL.

Components of Internet GIS:Data server - 4-

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Map publishing methods over the webStatic maps are published over the Internet web sever, in the case of static map the server handle the maps without need to any GIS programs, the server can be any HTTP server.The server response to the client’s request by sending JPEG or GIF file.

Image file

Client computerwww browser

URL Request

HTTP Server

Graphic Image

The maps should be in a format that can be understood by the

browser.

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13April 2007

Dynamic maps

Dynamic maps need GIS software that connected with web server the software will be able to generate maps up on client request.

The information sent by the client to the web server should include information such as the requested layer and map extension.

This architecture is known as Internet Map server (Toon, 1997).

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Client computerwww browser

URL Request

HTTP Server

GIS Server

GIS Interface Program

Image file

Graphic Image

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15April 2007

GIS web services

A software components that can be accessed through the WWW, and used by other applications.

GIS web services provide spatial data or functionality on the WWW.

It help the users to access GIS data and functionality through the web and to integrate them with their own systems and applications without the need for users to develop or host specific GIS tools and data sets themselves.

GIS web services can range from single functions such as distance calculation and simple spatial search routines to complex map generation, spatial editing and modelling.

16April 2007

ArcWeb services

• GIS content and capabilities delivered via the Internet.

• Requests for inforamtion sent to ESRI.

• Responses sent back to user.

• Built using ArcIMS and ArcSDE

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17April 2007

Portrayal model for interactive map

Open Geospatial Consortium, Special Interest Group (SIG) on WWW mapping produces a portrayal model for interactive map

18April 2007

OGC four tiers -1-

1st tier: Select, it represent selection process by the user to be able to retrieve data from geospatial data source, this can be accomplished by using map query constraints. Also this layer allows the user to perform thematic search and selection.

2nd tier: Display element generator, this tier turn the selected geospatial data, performed by displaying a sequence of elements. During this process styles are attached to the maps.

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19April 2007

OGC four tiers -2-

• 3rd tier: Render, in this tier the displayed element (s) will be rendered.

• 4th tier: Display, this process responsible to make the rendered map in the previous process visible to the user on the web browser.

20April 2007

The data flow between OGC tiers

• The data flow between these four tiers shows the conversion process from data type to another one according to specific tier requirements.

• Feature data type returned as result for user query at selection tier, display elements generated from the second tier, and image that are produced from rendering process.

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21April 2007

Information flow over OGC portrayal

Features data and coverage

Display elements

Rendered image

Produced by user selection in 1st tier

Produced by display element generator 2nd tier

Produced by rendering process 3rd tier

22April 2007

Types of connection between OGC tires

Browser GIS

Browser + Plug-in

GIS, Geo-DB

Local GIS Geo-DB, File system

FAT

Thin

Thin

Client Server

FAT

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23April 2007

Types of connection between OGC tires

• Thin client – FAT server: Server takes the responsibility to perform all process except the display of resulting maps that will take place at the client site. Possibly the web server can select the required map, render and generate the display elements, and display the rendered map to the client.

• FAT client – thin server: In this model the user have full access to the Geodatabase as well s/he will request GIS functionality at the client site, all processes done at the client site except the selection process took place at the server.

• Balanced client – server: In this model of balanced performance, the selection process and display element generation is done on the server side. The client side requires either Plug-in or Java Applet these are needed to increase the efficiency ofthe client site graphical manipulation.

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Quality of Services ( QoS )

“A new research direction for the next generation of the Internet and focuses on the new technologies and standards to provide resource assurance and servicesdifferentiation for various Internet applications”. There are two major technologies under the QoS framework, integrated services and differentiated services”

Wang, 2001

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25April 2007

QoS for InternetGIS

• Performance qualities.

• User interactivity with available services.

• Portability of the services

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The standards behind Web services

Web services are made possible by the acceptance of the standards; the most important are the eXtendable Markup Language XML.

HTML remains as the primary way to of formatting Web page but it was rigid.

HTML can not be used for meaningful interaction between the user and remote web server.

XML was proposed as a solution. XML was designed to complement rather than replace HTML.

XML was extendable unlike HTML, which was rigidly defined to describe a single generic type of document, Where XML permits their user to define their own definitions….. Then any type of data can be described.

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27April 2007

Sample XML code

It is important to understand that XML was designed to store, carry, and exchange data. XML was not designed to display data.

<?xml version="1.0" encoding="ISO-8859-1"?> <note><to>Tove</to> <from>Jani</from> <heading>Reminder</heading><body>Don't forget me this weekend!</body></note>

28April 2007

Geography Markup Language

GML or Geography Markup Language is an XML based encoding standard for geographic information developed by the OpenGISConsortium (OGC). The objective is to allow internet browsers to view web based mapping without additional components or viewers.

http://www.opengeospatial.org/

GML is a powerful new way to look at spatial information using XML encoding. It promises. however, much more than a mere encoding standard. The inherent transformability and accessibility of GML will open a whole new domain in geo-spatial information management.

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29April 2007

Mapping test bed

• (A platform upon which assortments of experimental tools and products may be deployed and allowed to interact in real-time. Successful tools and products may be identified and/or amended in an iterative evolutionary, interdependent process).

Michigan University School of Information

• Three basic interfaces agreed upon by WMS, these interfaces are regarded as server requests to the client (WMS 1.0 specifications).

30April 2007

WMS requests

• The GetMap which help to portrait the map and produce it in one of the standard picture formats,

• GetFeatureInfo, as can be understood from the name this request is responsible for giving answers to the query about the map features from the Geodatabase.

• GetCapabilities inform other programs about the server capabilities and the level of disaggregation of the maps that could be produced this request are known as

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31April 2007

Spatial portals (1)

Web sites that make it easier to find, & use GI available on the WWW, the portals also considered as gateway to GI.

They revolutionize the way we store, manage, find, share and use knowledge about the world.

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Spatial portals (2)

Portals link information providers with information users.

Spatial portal allow organizations to open their archives to the public.

Act as brokers between user and service providers:– A regional data hub publish their services at the portals that allow the

users to search and browse published services. – If the user find the interesting service the portal then passes the user

directly to the appropriate service provider.

Advantage is that the user can access up-to-date, authorized information through a single location, and service providers only need to update one location to reach many users

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33April 2007

Spatial portal: functions

Service search

Spatial data, Metadata search, Structured interface, Tools to view, explore, and download information services.

Service discovery

Metadata viewer, Map viewer, Link to content provider, Connect to service, Download service

Inform

News / discussion form, Standards and cookbooks, Thesauri and gazetteers

Administration

Catalog maintenance, Harvesting, Security, User management, and Hardware/ network

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Spatial portals: its typesCatalog portals

For creating and maintaining indexes that describes available information services.

Application portals

Combine information services into a Web-based mapping package that generally focuses on a particular task or applications.

Enterprise portals

Third type of spatial portal, involves the integration of spatial data and functionality with business enterprise solutions. It help the organization to manage distributed information resources.

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35April 2007

Map Servers

Autodesk MapGuide Open Source.

Internet Map Server Technology (ESRI).

Geomatica Web Server (PCI Geomatics).

GeoMedia WebMap.

Internet Application Server (GE Power Systems - MapExplorer(Triscape).

XMap Web (DeLorme)

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ArcIMS:Offers a Highly Scalable Server Architecture

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37April 2007

Imagery Servers & Geoprocessing Web Services

ImageConnect

Image Web Server

ArcWeb Services (ESRI)

MapPoint Web Service (Microsoft)

38April 2007

3D View Servers

Google Earth (Download and install client application).

Map 24 (3D option available after selecting map).

TerraGate (TerraExplorer)

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39April 2007

Q & AThanks