june 9-11, 2004 carleton university ottawa canada ogc in open source products tom kralidis jeff...

June 9-11, 2004 • Carleton University • Ottawa • Canada

OGC in Open Source Products

Tom Kralidis

Jeff McKenna

Peter Pulsifer

Bart van den Eijnden



• Interoperability Overview

• Benefits of OGC in the Organization

• Examples / Demos

• OGC / Open Source Issues

• Comments/Questions/Discussion

Infrastructure

• Many pieces working independent of make, model

• Open interface– Can communicate with other things

• Transparent / Invisible

• Cooperative

• Distributed

The Distributed Approach

• Distributed Spatial Data infrastructure• Cost / Feasibility• One Source• Up-to-date Data• Data Management Issues• Less:

– Local storage space– redundant data

• How?– Web Services

Web Services

• Independent of– operating systems– programming languages– Organizations

• How?– non-proprietary data / messaging

standards• eXtensible Markup Language (XML)

Web Services

• Until recently everyone is developing in their own little world (metadata => data => applications)

• From functionality to interoperability• Internet is driving these changes: no net,

then little reason to interoperate• Being “open” is a strong selling point

– E.g. VCR cassettes: VHS vs. BETA– E.g. mix and match your home stereo

system components

Web Services- Benefits

• Lower software integration costs

• Maintaining legacy systems

• Using standards lowers IT costs of

collaboration with external partners,

vendors, clients

Web Services Architecture Approach

Applicationse.g., Transportation Planning, Climate Change Monitoring,

Site Assessment

Servicese.g., Metadata Service,

gazetteer service,Web Map Service

Datae.g., topographic, thematic, imagery,

toponymy, metadata

Users

OtherApplications

For Example…

A trip planning web site that calculates the best route between two cities

usesGazetteer service,Road network server,Web mapping service

based onGeographical Names,Road network featuresBase maps

OpenGIS Consortium

• Standards body for geospatial processing over the Internet– Free, public specification– Rapid specification development using

• Technology integration experimentation• Develop and spec in parallel• Testbeds

– Sponsor requirements– Industry participation

OGC Specifications

• WMS• WFS• WCS• Web Map Context• GML• SLD• Filter• Catalog

• WCTS• Grid Coverages• Location Services• Simple Features

– CORBA– SQL– OLE/COM

Web Map Service (WMS)

• Provides images of map data defined by a geographic / spatial component

• Provides point based query functionality

• Interoperable means of map compositing


• Interoperable, ‘just-in-time’ approach to map delivery

• Map compositing from multi-servers

GeoGratis – http://geogratis.gc.ca/

Web Mapping: Phase I

Toporama: http://toporama.cits.rncan.gc.ca/

Web Mapping: Phase I

•Interoperability•Common Standards•Services

•Interoperability•Common Standards•Services

Web Browser

Viewer Client

MapServer

MapServer

MapServer

MapServer

inte

rnet

Web Map Servers

Web Mapping with WMS


• Provides images of map data defined by a geographic / spatial component

• Provides point based query functionality• OGC adopted specification

– 1999: Version 1.0.0– 2001: Version 1.1.0– 2002: Version 1.1.1

• CGDI endorsed specification


• HTTP-based communication– HTTP GET or POST mechanism

• Operations• GetCapabilities• GetMap• GetFeatureInfo (optional)

– Operation keywords are case-insensitive– Operation values are case-sensitive

Web Feature Service (WFS)

• Feature level access to spatial data– Finer grained access and query

• Spatial and non-spatial query capability– Attribute and / or geometry

• Returns GML– Can further transform with XSLT to SVG, style with

SLD, etc.

• Transactional capability– INSERT, UPDATE, DELETE, LOCK, …

• Security considerations


• GetCapabilities– Provides XML ‘Capabilities’ or service functionality

metadata, and feature metadata– Parameters

• Version (version of specification)• Service (multiple services may exist from this service, e.g.

WMS, WFS, WCS)• Request (GetCapabilities)

http://ceoware2.ccrs.nrcan.gc.ca/cubewerx/cwwfs/cubeserv.cgi?datastore=CEOWARE2&version=1.0.0&service=WFS&request=GetCapabilities


• DescribeFeatureType– Provides schema information about a feature type

(fieldnames, data types)– Parameters


WMS, WFS, WCS)• Request (DescribeFeatureType)• Typename (name of feature type)http://ceoware2.ccrs.nrcan.gc.ca/cubewerx/cwwfs/

cubeserv.cgi?datastore=CEOWARE2&version=1.0.0&service=WFS&request=DescribeFeatureType&typename=EOS_DATA_GATEWAYS


• GetFeature– Provides query interface of data– Parameters


WMS, WFS, WCS)• Request (GetFeature)• Typename (name of feature type)• Filter (more on this later)http://ceoware2.ccrs.nrcan.gc.ca/cubewerx/cwwfs/

cubeserv.cgi?datastore=CEOWARE2&version=1.0.0&service=WFS&request=GetFeature&typename=EOS_DATA_GATEWAYS

Geography Markup Language (GML)

• XML encoding of geospatial information– XML dialect

• Basic application framework for handling geospatial information

• Enables complex features & feature associations between data

• Human-readable• Can be processed by many XML tools in various

development environments


GMLSchemas

GeometryDefinitions

ApplicationSchema

InformationCommunityDefinition

InstanceDocument

Data InstanceAs static data or

throughService Instance


• New features in version 3.0.0– Topology– Temporal– Enhanced Geometry– Coverages– Units of Measure

Styled Layer Descriptors (SLD)

• Symbolization to map data• Styling• Addresses lack of symbolization within

current and past OGC services• Cartographic design of GeoData• Augments OpenGIS specifications

– Can custom style WMS content– Can custom style WFS content


• Example of an SLD document:

• http://cgdi-dev.geoconnections.org/prototypes/sld/gcdb.xml

Filter Encoding

• XML Definition of data query language for online services– GML used for geometry querying semantics– Used as filter grammar for OpenGIS WFS– Stand alone specification

• Can be applied to any service as a query approach

Filter Encoding

• Example:<Filter>

<PropertyIsEqualTo><PropertyName>ORGID></PropertyName><Literal>CCRS</Literal>

</PropertyIsEqualTo></Filter>

• Used in OGC WFS– http://ceoware2.ccrs.nrcan.gc.ca/cubewerx/cwwfs/cubeserv.cgi?

datastore=CEOWARE2&version=1.0.0&service=WFS&request=GetFeature&typename=EOS_DATA_GATEWAYS&filter=<Filter><PropertyIsEqualTo><PropertyName>ORGID></PropertyName><Literal>CCRS</Literal></PropertyIsEqualTo></Filter>

OpenGIS Web Map Context Documents - Overview

• ‘bookmarkable’ XML encoding of state of a web mapping application

• Analogous to ‘project’ files in most popular GIS software packages

• Enables sharing of application scenarios, demonstrative presentations, etc.

Web Mapping – Same data; multiple applications (OpenGIS Web Map Context Documents)


Semantic Interoperability• Ability to share meaning rather than simply

exchange data• Semantic heterogeneity:

– Same ‘symbol’/term different meaning– Different terms similar meaning

• OGC currently proposes consensus approach to dealing with semantic heterogeneity

• Moving towards the use of formal Ontologies


Tools– Glossaries and data dictionaries– Thesauri and Taxonomies– Metadata, XML Schemas & Data Models (i.e.

ISO 19115, GML, UML)– Formal ontologies and inference: Description

logics (DAML+OIL) <-open standard


• No reinventing the wheel

• Plug-and-Play with other standards-based systems

• Multi Vendor Interoperability

• Underlying system could change – interface remains standards-based– Less impact on end clients– Not tied to specific solutions


Product URL OGC Specification(s)

UMN MapServer http://mapserver.gis.umn.edu/ WMS,WFS,Context,SLDFilter,GML

PostGIS http://postgis.refractions.net/ Simple Features for SQL

MapBuilder http://mapbuilder.sourceforge.net/ WMS,Context

deegree http://deegree.sourceforge.net/ WMS,WFS,WCS,WCASWFS-G,WTS,WCTS

GeoServer http://geoserver.sourceforge.net/ WFS-T

maplab http://www.maptools.org/maplab/index.phtml WMS

Chameleon http://www.maptools.org/chameleon/index.phtml WMS,Context,WFS

inlineWMS http://sourceforge.net/projects/inlinewms WMS

JUMP http://www.vividsolutions.com/jump/ GML

GEOS http://geos.refractions.net/ Simple Features for SQL

gml4j http://gml4j.sourceforge.net/ GML

MySQL Spatial http://www.mysql.com/ OGC Geometry Model

MapSurfer http://mapsurfer.sourceforge.net/ WMS

PyOGCLib http://pyogclib.sourceforge.net/ WMS

QuickWMS http://www.inovagis.org/quickwms/ WMS

Studio http://www.maptools.org/studio/ SLD,Context,WMS

OpenMap http://openmap.bbn.com/

GeoTools http://www.geotools.org/ GML,SLD,Grid Coverages,WCTS,Filter


Demo 1: application framework based on OGC standards and Open Source.

Open Source GIS products used:

• UMN Mapserver• Chameleon and PHP/Mapscript• OGR (as a PHP module)• Deegree WCaS (Web Catalog Server)


Application function: find services

Uses: • OGC Web Services Stateless Catalog Profile

0.0.6 (WCAS)• ISO19119 datamodel


Application function: find layers

Uses: • OGC Web Services Stateless Catalog Profile

0.0.6 (WCAS)• ISO19115 datamodel• Layers are coupled to services in the ISO19119

datamodel, so an extra request is necessary to find the service on which the layer is available


Application function: querybuilder

Flow:• Perform DescribeLayer request on SLD WMS• Perform DescribeFeatureType on associated

WFS to get list of columns• Use SLD + Filter to highlight features on map


Application function: download shapefile

Flow:• Perform DescribeLayer request on SLD WMS• Perform GetFeature with BBOX Filter on

associated WFS using AOI defined in application• Use OGR to convert GML to shapefile


• Demo 2 (Jeff McKenna)


OGC / Open Source Issues

• General– “OGC Compliant” – be careful!– Namespaces in OGC XML-based documents



• General– XML (GML) is very expressive yet very

verbose -> performance problems– Researchers working on ‘feature streaming’ to

deal with this issue (not yet in OGC process)– Applicability of specs in functional

applications: bridging the gap– slow emergence of specs



• Semantic– Current consensus approach may limit use

outside of simple domains (i.e. where concensus cannot be achieved)

– OGC is not the only standard -> ISO, FGDC, Domain specific, W3C -> requires a ‘reference ontology’ to mediate between standards


Comments/Questions/Discussion

Thanks!

Tom Kralidis (tom.kralidis at ec.gc.ca)

Jeff McKenna (mckenna at dmsolutions.ca)

Peter Pulsifer (pulsifer at magma.ca)

Bart van den Eijnden (bart at geodan.nl)


june 9-11, 2004 carleton university ottawa canada ogc in open source products tom kralidis jeff...

Documents

map deliverymap compositing

citiesusesgazetteer

caweb mapping

based query functionalityogc

multiserversweb mapping

road network server

phase igeogratis http

little reason