Web GIS – About and Need

Arup DasguptaHonorary AdvisorGIS Development

GIS is becoming Ubiquitous

User

Mediator GIS Expert

Mainframe GIS

Desktop User

Applications Software

Developer

Mobile user

Service Provider

GIS Databases are Distributed

User Applications

Metadata update

Metadata searchand retrieval

CatalogCatalogCatalogs

Middleware

Clients

Servers

Geoprocessing Services

Access totransformed data

ServiceChaining

Direct data access

FeaturesContentRepositories

Coverages Other data

Telecommunications Technology

Client-Server TechnologyDistributed Computing PlatformsCORBA OLE/COM DCE JAVA

OGIS Model

Applications

Programs

Products

Industry Integrators

Vendors

Interface

DSS

Open Geodata Interoperability Specification

• Open Geodata Model• OGIS Service Model• Information Communities Model

OGIS Consensus Process

GIS/RS

RDBMS

Granularity and Coupling

TightlyCoupled

LooselyCoupled

CoarseGrained

FineGrained

CORBA

COM

SQL

HTTP & XML

SQL

High-LevelInterface (HLI)

Low-LevelInterface (LLI)

Loosely Coupled Architecture

Based on asynchronous communications Provides a lightweight and resilient foundation for

applications that do not require tight coordination. Uses a well defined cross-component interface The technology at either end of the interface can be

modified without changing any of the other components

Allows totally independent teams to build compliant code that has zero impact for builds and source sharing across the teams.

This allows massive scaling which is something the industry has had a difficult time with.

Facilitates the isolation of architectural boundaries. This provides easier debugging abilities

Loosely Coupled Architecture

• “Datagrams” vs. interfaces•Tightly-coupled vs. loosely-coupled

•Fine-grain vs. coarse-grain• IT spec dependencies

PlatformA

PlatformB

Distributed Servers

Net “Service over the wire”

Disadvantages

Assumes anonymous participants and generally benign failure modes

Integrity and survivability in hostile environments generally requires different assumptions.

Can require more design time. There can be performance impacts

Hybrid Approach

OGCInterfaces

OGCInterfaces

Summary

Early programming was tightly coupled Web Services programming is loosely coupled Both have advantages and their place Hybrids are possible Different systems exist to ‘model’ these

architectures Simple systems can have an ad hoc design Complex systems need a proper architecture

Elements of a Web GIS

Services Catalogue and Registry Service Web Map Services Web Feature Service Web Coverage Service

Specifications Geographical Feature Encoding Feature Styling Specification Web Map Context Specification

Registered geodata metadataMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URLMetadata for a feature collection, and a URL …..

Data Catalogue

a URL

Where?When?How?What?Who?Why?

Spatial data servers with metadata and OpenGIS Catalogue Server interfaces

Extensions to Catalogue: Service Registries

Registry Services provide a common mechanism to classify, register, describe, search, maintain and access information about Web resources. Service Registries contain metadata about the

description of services, their location on the Web, and the means of accessing and using these services (i.e., interfaces and bindings). Service Registry Services provide access to these metadata and the means for clients and services to bind to the published resource.

Experiments using UDDI (Universal Description, Discovery and Integration), WSDL (Web Services Description Language), etc

a URL

Service CataloguesSpatial services servers with metadata and OpenGIS interfaces

Collection of service metadataMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a

Collection of service metadataMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URL

Collection of service metadataMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URLMetadata for an online service, and a URL

Need a ProcessingFunction!

Registry information

model

Service information

model

OpenGIS® Web Map Service Specification

Provides a uniform access interface for Web clients to ask for and receive map “pictures” rendered by map servers on the Internet.

Easy to implement http://clearinghouse1.fgdc.gov/scripts/ogc/ms.pl?version=1.1.1&

request=map&srs=EPSG:4326&bBox=-180,-90,180,90&width=400&height=200&format=JPEG&styles=BLACK&layers=boundary,coastline,elevation,lakes,rivers&

WMS request flowWeb

Server

ArcGIS

ArcIMS

ArcView

Minnesotamapserver

WMSservices

Nativeservices

Web Browser

AutoCAD

GeoMedia

Oracle

MapExtreme

“getMap” WMS Request

Request (HTTP CGI form)

Response (JPEG file)

Multipleoverlaid

maps

One GetMaprequest:

Web Map Service (WMS) can get multiple maps

BordersElevation

cloud cover

Cities

WMS GetMap returns a server’s “dumb” JPEG, GIF or PNG representation of the data on the server. It does NOT return the actual data, only a bitmap of the data.

WMS can’t “give data away.”

Roma

WMS GetFeatureInfo returns attribute data for a feature or coverage at a specified point.Lat/

Long

elev. = 237 m.

WMS can query by pointing.

OpenGIS® Web Feature Service 1.1

The WFS operations support INSERT, UPDATE, DELETE, QUERY and DISCOVERY operations on vector geographic features using HTTP as the distributed computing platform.

QUERY and DISCOVERY are mandatory. The basic interface, like WMS, allows user/client to

specify Bounding Box (AOI) and Coordinate Reference System

The WFS FILTER specification defines how to use OGC Query Language to perform query operations (same as Catalog)

Returns features as GML 3.0 encoding (default)

Web FeatureServer

GetFeaturerequest:

Feature &attributedata

Web Feature Service (WFS) returns data.

I-95

I-295

I-87

Multiplethematic

data layers

GetFeaturerequest:

Web Feature Service (WFS) gets operable feature data from multiple servers

Cities

BordersElevation

Each layer is data, not merely a view:

Country is:_ Name: Italy_ Population: 57,500,000_ Area: 301,325 sq km. . .

Web Feature Server enables distributed, vendor-neutral data maintenance.

X

Turn left ahead!

Web Coverage Service (WCS) 1.0

Scope: Retrieval of gridded, swath, TIN or other "coverage" data in binary or other formats(HDF, GeoTIFF, NITF, NetCDF, etc.) Elevation,

Orthoimagery Operations:

GetCapabilities GetCoverage

Web MapServer

Web FeatureServer

Web CoverageServer

OGC Specifications enable information fusion

OpenGIS® Geography Markup Language (GML)

GML supports encoding of digital feature data, for data communication Facilitates interoperability of separately developed

applications GML is an application of the eXtensible Markup

Language (XML) XML is a structured text format for encoding data XML specified by World Wide Web Consortium

(W3C) GML specifies XML Schemas for standardized XML

encoding of geographic features, their geometry, and their attributes

OpenGIS® Style Layer Descriptor Version 1.0

Controls the presentation (style) of a map portrayal

Allows fine grained control for symbolization on a layer by layer basis

Rule-based Uses XML Allows rules for portrayal of points, line

strings, polygons, text, and other commonly used geometries.

One data file… …many different maps!

OpenGIS Styled Layer Descriptor

… and non-graphicportrayals!

OpenGIS ® Web Map Context Specification

Describes a standardized approach to enable the capture and maintenance of the context - or state information - of a Web Map Server (WMS) request so that this information can be reused easily in the future user session.

New Additions

Geographic Objects The OpenGIS(r) Geographic Objects Implementation

Specification a set of core packages that support a small set of Geometries, a basic set of renderable Graphics that correspond to those

Geometries, 2D device abstractions (displays, mouse, keyboard, etc.),

supporting classes. GML for JPEG 2000

This specification defines how GML is to be used within JPEG 2000 based geographic imagery.

specification of the uses of GML within JPEG 2000 data files packaging mechanisms for including GML within JPEG 2000

data files.

OWS-4 Demonstration

My contact details:

A. R. Dasgupta

Honorary Advisor, GIS Development

and

Distinguished Professor,

Bhaskaracharya Institute for Space Applications and Geoinformatics,

Gandhinagar 382007

Email: arup.dasgupta@gisdevelopment.net

Fax: +91-(79)-23213091

Phone: +91 98253 29382