Transcript Slide 1
Web GIS Technologies
A R Dasgupta Honorary Advisor GIS Development
Reference Model for Open Distributed Processing
RM-ODP Viewpoints
Viewpoint Name Definition of RM-ODP Viewpoint
Enterprise Information Computational Engineering Technology Focuses on the purpose, scope and policies for that system.
Focuses on the semantics of information and information processing.
Captures component and interface details without regard to distribution Focuses on the mechanisms and functions required to support distributed interaction between objects in the system.
Focuses on the choice of technology.
OGC Services Framework OSF Services OGC Service Taxonomy
Application Services Geographic Human Interaction Registry Services Data Services Portrayal Services Geographic Information Management Geographic Information Management Geographic Human Interaction Processing Services Geographic Processing Interaction
OGC Services
Realising Services in Web
Services Interoperability Stack
OGC Simple Feature Specification
Interface for OpenGIS Simple Features.
Designed for tightly coupled applications Spatial and non-spatial properties Two dimensional The supported geometry types include points, lines, linestrings, curves, and polygons.
application programming interfaces (APIs) provide for publishing, storage, access, and simple operations on Simple Features.
Three profiles CORBA OLE/COM SQL
Geometry Class Hierarchy
Geometry Class Operations
SQL Schema for Feature Tables
Model the Data
Design the schema Use an abstract modeling technique such as UML ISO 19100 series ISO/TS 19103 – Conceptual Schema Language (units of measure, basic types), ISO 19107 – Spatial schema (geometry and topology objects), ISO 19109 – Rules for application schemas (features), etc.
Make sure partners agree to the model
Geography Markup Language (GML)
XML
Example of XML and XSD
A Sample Stylesheet
SVG Display in a Browser
GML: Representing Geographic Features
Another Information Community’s Schema
Highway is: _Pavement thickness _Right of way _Width
GML defines a data encoding in XML that allows geographic data and its attributes to be moved between disparate systems One Information Community’s Schema
Road is: _Width _Lanes ….
Cell tower is: _Owner _Height _Licensees …. Cell transm. Platform is: _Location _No. of antennas _Elevation ….
(an instance of in another IC’s schema) Mayberry Road Mayberry’s Cell Tower Cell Transm. Platform (an instance of Road in one IC’s schema)
Geographic Data
…and its GML Schema…
…and a GML snippet
Web Services
Broad interpretation of Web Services.
http (post/get) SOAP Rest (somewhat!) Provide: access to data data transactions access to metadata metadata transactions visualization (maps) data processing XML General Model Client Request (message) XML Response (optional attachment) W S
Web Registry Service
WRS Characteristics
Support for searching and retrieving inspired by Z39.50 services (search, present) Support for publishing many kinds of (meta)data — more than just data product or service descriptions Employs a general and flexible model (ebRIM) that can accommodate arbitrary information resources Common operations inspired by WFS requests (e.g. transaction) Schema-agnostic image/png) —the content of metadata may conform to any schema or Internet media type (e.g. application/xml, application/pdf, audio/mpeg,
Role of Registry Services
Purpose
: locate, access, and manage arbitrary metadata in an open, distributed system
service offer type definition service instance
Find Client (Browser) Registry Interfaces Bind Publish Service Provider A registry is intended to support the retrieval, management and storage of shared metadata information resources
Web Mapping Service (WMS)
OGC Web Mapping Service (WMS)
WMS Primary specification for requesting maps and visualization via the WWW. ISO’s WMS draft (Doc. 19128) is based on the OGC WMS specification.
Digital Earth Viewer example Calling client specifies the bounding box of the layers needed, the styles in which these layers are to be displayed, the spatial reference system to be used, the desired output format, the output size, And background transparency and color.
OGC Web Mapping Service (WMS)
3 requests
getCapabilities:
obtain service level metadata describing service content and acceptable request parameters .
getMap:
obtain a map image whose geospatial and dimensional parameters are well-defined.
getFeatureInfo (optional): ask for information about particular features shown on a map.
OGC WMS – Get Capabilities
OGC WMS GetMap
Spatial Context Spatial Reference System (EPSG) Corners of map (geographic extent) Image width & height List of “layers” Layer name Symbolization style Return Format GIF | JPEG | WebCGM | SVG, etc.
Background info (color, transparency) Exception Type = InImage | Encoded/Parseable
WMS overlay example
REQUEST1:
http://amapco.com/mapserver.cgi
?
VERSION=1.1.0&REQUEST=GetM ap& SRS=EPSG:4326& BBOX= 97.105,24.913,78.794,36.358& WIDTH=560&HEIGHT=350& LAYERS=AVHRR-09 27&STYLES=& FORMAT=image/png& EXCEPTIONS=application/vnd.ogc.
se_inimage
REQUEST2:
http://b-maps.com/map.cgi
?
VERSION=1.1.0&REQUEST=GetMap& SRS=EPSG:4326& BBOX=-97.105,24.913,78.794,36.358& WIDTH=560&HEIGHT=350& LAYERS=BUILTUPA_1M,COASTL_1M,P OLBNDL_1M& FORMAT=image/png&STYLES=style1,st yle2,style3& TRANSPARENT=TRUE& EXCEPTIONS=application/vnd.ogc.se_in
image
WMS Context
Approved specification for describing, in a portable and platform-independent format (XML) , a specific grouping of one or more maps from one or more map servers for storage in a repository or for transmission between clients.
Think of it as a map “bookmark”
WMS Context document
Web Feature Service (WFS)
Web Feature Service (WFS)
GetCapabilities Client
GetCapabilities WFS Request WFS Response Web Feature Server WFS
– Defines the list of feature types that this instance can operate upon and -->
– Defines the capabilities of the filter supported by this feature instance-->
Web Feature Service (WFS)
DescribeFeatureType Client
version="1.0.0“ service="WFS" xmlns="http://www.opengis.net/wfs" xmlns:ns01="http://www.server01.com/ns01" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
Opaque Feature Store
Web Feature Service (WFS)
getFeature Client
version="1.0.0“ service="WFS“ xmlns:myns=http://www.someserver.com
Filter Encoding Implementation Specification
XML encoding of the OGC Common Catalog Query Language (CQL) as a system neutral representation of a query predicate. Can be used by services to query objects from a web accessible repository.
Examples Spatial operators (equals, disjoint, touches, within, overlaps, crosses, intersects, contains, within, beyond, bbox) Comparison operators (propertyIsEqualTo, propertyIsNotEqualTo, propertyIsLessThan, propertyIsGreaterThan, etc) Logical operators (And, Or, Not) Arithmetic operators (Add, Sub, Mul, Div)
Copyright 2003 Global Science & Technology, Inc.
Approved OpenGIS
®
Specifications
Tightly coupled: Simple Feature Access 1.1 – OLE, SQL, CORBA Gridded Coverages 1.0
Focus on Web Services (loosely coupled).
Catalog 2.0.1 Coordinate Transformation 1.1
Web Map Service (WMS 1.3) Web Feature Service 1.1
Filter 1.1 Geography Markup Language 3.1.1 (GML) Style Layer Descriptors 1.0
Web Coverage Service 1.0
Web Map Context 1.0
Location Service Core Specification Set 1.0
Geographic Objects 1.0
GML in JPEG 2000 1.0
Web Map Context 1.1
OGC Common 1.0
My contact details: A. R. Dasgupta Honorary Advisor, GIS Development and Distinguished Professor, Bhaskaracharya Institute for Space Applications and Geoinformatics, Gandhinagar 382007 Email: [email protected]
Fax: +91-(79)-23213091 Phone: +91 98253 29382