Web based GIS Nurul Hawani Idris Geoinformation Department Universiti Teknologi Malaysia 2013/Sem 2

Transcription

1 Web based GIS 4583 Nurul Hawani Idris Geoinformation Department Universiti Teknologi Malaysia 2013/Sem 2

2 Contents Web GIS origin and evolution Web GIS concept Web fundamental Web GIS basic architecture and components Thin versus thick client architecture

3 The history of Web The US Department of Defence ARPA network of geographically separated computers to exchange information stopped functioning or destroyed 1969 connect 4 Western universities ARPAnet

4 The history of Web node government agencies, universities, research institutes 1989 more than computers connected Before 1990s services only for , Usenet News, file transfer, Telnet - complex to use mostly professional use 1990 Tim Berners-Lee researcher at European Organisation for Nuclear Research (CERN) invented HTTP, HTML, URL

5 Father of GIS Roger Tomlinson first computerised GIS in 1962

6 The history of Web He developed web server and web browser World Wide Web Father of Web Internet a massive network of networks that connect millions of computer world wide WWW - A system of interlinked hypertext documents and programs that can be accessed via the Internet by using HTTP Web the face of the Internet

7 The history of Web GIS 1993 Xerox Corporation Palo Alto Research Center (PARC) developed Xerox PARC Map Viewer Simple map zoom capabilities, layer selection, map projection conversion functions

8 The history of Web GIS Web browser HTTP request Web server Web server perform mapping operation, generate new map return to web browser Web browser receive and display map image Advantages: could use GIS without locally installed as in desktop GIS

9 The history of Web GIS 1994 the Canadian Atlas Information Service National Atlas of Canada Interactive mapping allow select data layers (ecological regions, road, administrative boundaries) submit the map request 1995 Alexandaria Digital Library (by University of California) and National Geospatial Data Clearinghouse (by USGS) specify keywords, area, search maps and satellite images facilitate data sharing early example of geoportal US Census Bureau released TIGER mapping service public query and map demographic information of states, counties, cities deliver information available in the national census database in online format

10 The history of Web GIS 1995 GRASSLinks developed by Susan Huse as PhD dissertation University of California Developed interface between the web server and GRASS allowed users to select data layers, submit request to web server, server forwarded the request to GRASS (buffer, overlay, reclassification, mapping operations) 1996 MapQuest released web mapping application. Allow to view maps, look for local business, find optimum route, plan trips represent early precedent for the consumer mapping website 1996 GIS companies release their commercial Web GIS software

11 Web GIS in Web 2.0 Web 2.0 first coined by Darcy DiNucci Tim O Reilly at O Reilly Media Web 2.0 Conference Suggest new version of Web but does not signify any update of any technical specification Cumulative changes to the way software developers and users use the Web The new features # Harnessing collective intelligence Web 1.0 read only content and top down flow information Web 2.0 read-write and bottom up flow information

12 Web GIS in Web 2.0 Advantages derived from Web 2.0 companies/applications Ebay, Amazon, blog, Wikipedia # The Web as a platform platform for computing and software development Software as a Service (SaaS) software capabilities delivered as Web services Web applications and Cloud computing dynamically scalable, virtualized resources as web services remixed in the cloud to build new applications

13 Web GIS in Web 2.0 # Lightweight programming models - web systems support lightweight and easy programming models (e.g. AJAX)and create new functionality with mashups # Software that reaches beyond single device # Rich usability easy to use, easy on the eye, user experiences on dekstop alike. Web 2.0 = User generated content + Web as a platform + a rich use experience

14 Web GIS in Web 2.0 Google Maps, Google Earth, Bing Map, Nokia Maps detailed maps, high resolution ground imagery Street View by Google The Bird s Eye aerial photo by Microsoft Oblique Imagery

15 Accessibility

16

17

18 Web GIS Concept A type of distributed information system Minimal architecture server (web application server) and client (Web browser, desktop app, mobile app) Server has URL to find on Web Client relies on HTTP specification to send request Server perform requested operation Send a responses to the client via HTTP Format of responses HTML, binary image, XML, JSON Web GIS- any GIS that uses Web technology to communicate between components

19 Web GIS Concept Web GIS server Internet HTTP HTTP Web browser client Desktop Client HTTP Mobile client

20 Web GIS Concept HTTP main protocol used by different components of Web GIS to communicate If the Internet is down, some thick clients can function caches and preloaded data/functions Two tier system - simplest architecture Three tier system data tier More than three tier mashup approach Desktop GIS expand its functionality to make use of web resources use basemap from Bing Map or USGS

21 Web GIS Concept GeoWeb geospatial Web the merging of geospatial information with abstract (non geospatial) information (i.e. web pages, photos, videos, news) that dominates the Web (Haklay, Singleton and Parker 2008) Related to geotagging and geoparsing research area. GeoWeb - refer to the emerging distributed global GIS widespread distributed collaboration of knowledge and discovery that promotes and sustain worldwide sharing and interoperability (Scharl and Tochtermann 2007) Highlight the potential for Web GIS to grow

22 Functions Mapping (visualisation) and query Geospatial analysis analytical functions related to daily life measuring distance and area, finding optimum driving path, finding the location of an address or place, proximity analysis to find the business nearby In chemical spill, dispersion modeling used to calculate the affected area, overlay analysis to calculate the population to be evacuated In retail, site selection is used to determine the most profitable location to open a new business outlet Solar radiation modeling to find best location to place solar panel Earthquake models to predict a tsunami Web GIS Concept Crime analysis find danger zones that need more police patrols Optimal routing analysis distance, speed limits, time windows, traffic conditions, bridge height barriers, legal constraints

23 Web Fundamentals A basic Web application client/server architecture Basic web application 3 tier architecture Database server Web server Client Internet Presentation tier Data tier Logical tier (middle tier)

24 Web Fundamentals The basic workflow 1. A user uses a web client and initiate a request to the web server by typing URL address 2. The web server receives the request, parses the URL, locate the corresponding document/scripts, and returns the document/execute scripts to the client as a responses. Common responses in HTML format 3. Web client receives responses, render it, and present to users

25 Web Fundamentals HTTP WWW involves multiple parties need a protocol to define rules and procedures for all parties to follow HTTP a set of rules and procedures that both web client and web servers use to communicate with each other 8 method requests GET, POST, HEAD, PUT, DELETE, TRACE, OPTIONS, CONNECT HTTP request and responses message have headers and bodies HTTP response header 1. cache control, 2. content type (MIME type to indicate the type of message body either HTML, JPEG, Audio file and etc) 3. Status code 500 (server error) 403 (forbidden)

26 Web Fundamentals HTTPS Secure Hypertext Transfer Protocol the use of HTTP over an encrypted secure sockets layer (SSL) connection Plain HTTP data transferred easy to intercepted. Encrypting data can avoid eavesdropping Sensitive data user profile, password, credit card information URL Uniform Resource Locator A subset of URI (Uniform Resource Identifier) Specifies where an identified resource is available on the Internet and mechanism to retrieving it Web address Globally unique URL

27 Web Fundamentals Basic syntax Protocol: //hostname [:port]/filename?query_string#anchor Protocol specify the transport protocol HTTP, HTTPS, FTP Hostname IP address specifies the web server to be reached Port number optional default port :80 File path filename for the resource on web server Query string to pass the parameter to a script on web server Anchor to specifies location or section on a web page

28 Web Fundamentals

29 Web Fundamentals Web server Web application server Apache, Tomcat Internet Information services Programming languages Java EE, JSP, Servlet.. ASP.NET, C#, VB.NET PHP Python Internet Data exchange format XML JSON AMF Web browsers IE, Firefox, Safari, Chrome Browser based languages HTML/CSS Javascript/AJAX Flex Silverlight JavaFX Web Client Desktop/mobile languages.net and.net for mobile Java and Java.ME Python

30 Web Fundamentals Javascript not Java family platform independent AJAX popular since 1995 use asynchronous communication between web server and browser web page can retrieve data from the server in the background without interfering with the display and behavior of existing pages Adobe Flex open source framework flash player plugin (web browser) or Adobe AIR Silverlight cross browser platform need silverlight plug in

31 Web Fundamentals XML Extensible mark up language Define own tag and attributes Platform independent Plain text file Self- descriptive Can be validated against schema The most common data exchange format Bulky use tags to delimit data Parsing XML (ie extracting values from certain nodes in XML) is not efficient, esp in Javascript)

32 Web Fundamentals JSON (Javascript Object Notation) Lightweight Smaller in size than XML Easy to parse in Javascript

33 XML vs. JSON An XML example <?xml version= 1.0 encoding= UTF=8?> <students> <student> <name>john</name> <hobby> soccer</hobby> </student> <student> A JSON example { student : [ } { name : John, hobby : Soccer }, { name : Lisa, hobby : Movie } ] movie</hobby> <name>lisa</name> </student> <hobby>

34 Web GIS basic architecture and components GIS database server GIS server Client (browser, desktop, mobile)

35 Web GIS basic work flow 1. A user use a Web GIS application through a client 2. The client sends a request to the Web Server via HTTP 3. The web server forward GIS related requests to the GIS Server 4. The GIS Server retrieve the needed data from GIS database, process the request (generate map, conduct query, perform analysis) 5. Web server send the data, map or other result to the client via HTTP 6. The client then display the results to the user

36 Components GIS database data storage and management framework Strong GIS database capabilities: Stores a rich collection centralised or distributed system Applies sophicticated ruleds and relationships to the data Define geospatial relational models (i.e. topologies, road network) Maintain integrity of spatial data with a consistent and accurate database Works within a multiuser access, editing environment, versioning support Support custom features and behavior Provides a means for robust data security, backup, recovery, rollback Maintain high performance when volume increases and number of simultaneous user increases

37 Components Web GIS Clients two roles End user interface Thick client some geospatial processing tasks e.g. dynamic classification for thematic mapping, cluster, heat-map analysis Web browser client static HTML and simple Javascript RIA (rich internet application) browser technologies AJAX, Flex, Silverlight, JavaFX e.g. ArcGIS Explorer Online - Desktop Application client - act as a Web GIS client - Java,.NET Do not run inside a web browser E.g. Google Earth, ArcGIS Explorer Desktop Mobile client ArcGIS Mobile, ArcGIS for iphone, Bing Maps Mobile, Google Earth Mobile Virtual Globe geobrowser NASA World Wind, Google Earth, Bing Maps

38 Thin Client Architecture Relies on the server to perform most of work The client simply sends the user s request to the server The server does the processing The results, HTML format embedded with GIF, PNG, JPEG images Eg. PARC Map Viewer Advantages Do not need to install no plugin Do not need powerful client Disdvantages Pressure on the server Limited user interaction

39 Thick Client Architecture Relies on the client to perform most functions The thick client requests the source data (e.g. coordinate) from the server, and then renders maps and performs analysis on the client side Advantages Fast interaction with the users as the logic, program, runs locally and data resides locally Less pressure on the server since there are fewer trips to the server Disadvantages Inconvenience installation plug ins or native application Limitation posed by the Internet bandwidth and client computing power Not feasible - transfer gigabytes of data, and client perform sophisticated GIS operations

40 Very thin client Best practice Best practice Very thick client GIS database GIS database GIS database Analysis Map, Query Internet Client Basemaps Query Analysis Internet Client Operational layers Internet Analysis Map, Query Data Client