Post on 21-Dec-2015
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