Web GIS – About and Need Arup Dasgupta Honorary Advisor GIS 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 search and retrieval Catalog Catalogs Middleware Clients Servers Geoprocessing Services Access to transformed data Service Chaining Direct data access Features Content Repositories Coverages Other data

Telecommunications Technology Client-Server Technology Distributed Computing Platforms CORBA 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/RSRDBMS

Granularity and Coupling Tightly Coupled Loosely Coupled Coarse Grained Fine Grained CORBA COM SQL HTTP & XML SQL High-Level Interface (HLI) Low-Level Interface (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 Platform A Platform B 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 OGC Interfaces OGC Interfaces

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 metadata Metadata 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 Catalogues Spatial services servers with metadata and OpenGIS interfaces Collection of service metadata Metadata for an online service, and a URL Metadata for an online service, and a Collection of service metadata Metadata for an online service, and a URL Collection of service metadata Metadata for an online service, and a URL Need a Processing Function! 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 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 flow Web Server ArcGIS ArcIMS ArcView Minnesota mapserver WMS services Native services Web Browser AutoCAD GeoMedia Oracle MapExtreme “getMap” WMS Request Request (HTTP CGI form) Response (JPEG file)

Multiple overlaid maps One GetMap request: Web Map Service (WMS) can get multiple maps Borders Elevation 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 Feature Server GetFeature request: Feature & attribute data Web Feature Service (WFS) returns data. I-95 I-295 I-87

Multiple thematic data layers GetFeature request: Web Feature Service (WFS) gets operable feature data from multiple servers Cities Borders Elevation 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 Map Server Web Feature Server Web Coverage Server

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-graphic portrayals!

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 Fax: +91-(79) Phone: