Technology Assesment Report
On
Open GIS
Prepared For
Dr. Ronald Briggs
Course: GIS Management and Implementation (GISC 6383)
Prepared by
Rumana Reaz Arifin
Amna Alsarabi
Fall 2006
Table of Contents
What is Open GIS ……………………………………………………3
Open Geospatial Consortium…………………………………………5
OGC Specification………………………………………………...... 5
Web Map Service……………………………………………………..7
Web Feature Service………………………………………………….9
Web Coverage Service……………………………………………… 10
Beneficiary Group……………………………………………………11
ESRI’s support for OGC……………………………………………..12
Comparison of different Map Services………………………………13
Open GIS Applications………………………………………………16
Conclusion…………………………………………………………...18
References……………………………………………………………18
What is Open GIS
Open GIS is a concept of the full integration of geospatial data into mainstream information technology. It is defined as transparent access to heterogeneous geodata and geoprocessing resources in a networked environment.
What this means is that GIS users would be able to freely exchange data over a range of GIS software systems and networks without having to worry about format conversion or proprietary data types. The intent is to move away from the current status in which specific GIS applications and capabilities are tightly coupled to their internal data models and structures.
For example, utilizing an ESRI based software package also requires ESRI proprietary data structure such as ‘Shapefiles’ in order to utilize all analytical aspects of the software. Currently, a user who wishes to gain access to geodata developed by another agency is generally faced with a complex data conversion task. Here comes the solution of Open GIS---the interoperability established by OpenGIS standards will enable web users to combine data from many locations by eliminating obstacles created by platform differences.
The features of OpenGIS are:
· To make Geospatial information, easy to find, access or acquire (regardless to its physical location).
· To make Geospatial information from different sources, easy to integrate or use in spatial analyses, even when sources contain dissimilar types of data (raster, vector, coverage, etc.) or data with disparate feature-name schemas.
· To provide platform for Geospatial information from different sources to be easy to register, superimpose, and render for display.
· To provide support for Special displays and visualizations, to be easy to generate.
· It should be easy, to incorporate into enterprise information systems geoprocessing resources from many software and content providers.
Additionally, Open GIS seeks to facilitate the exchange of information not only between individual GIS systems but also to other systems, such as statistical analysis, image processing, document management, or visualization. Especially with the proliferation of geo-based websites, the networking component of GIS systems with other data processes is becoming more important.
In summary, the fundamental requirements of an Open GIS are:
· Interoperable application environment - a user environment that is configurable to solve a problem irrespective of the data structure origin or software.
· Shared data space - a generic data model supporting a variety of analytical and cartographic applications.
· Heterogeneous resource browser - a method for exploring and accessing the information and analytical resources available on a network - this is becoming an especially important goal with the rise of geo-based Internet sites.
Open Geospatial Consortium
About OGC
It is the platform for bringing in the concept of OpenGIS into reality. It is an international voluntary consensus standards organization. In the OGC, more than 330+ commercial, governmental, nonprofit and research organizations worldwide,(ESRI, Intergraph, MapInfo, MapServer, Oracle to name a few) collaborate in an open consensus process encouraging development and implementation of standards for geospatial content and services, GIS data processing and exchange. It was previously known as Open GIS Consortium when it was founded in 1994.
Goal of OGC
OGC manages consensus processes that result in interoperability among diverse geoprocessing systems. Much geospatial data is available on the web and in off-line archives, but it is complex heterogeneous, and incompatible. Users must possess considerable expertise and special geographic information system (GIS) software to overlay or otherwise combine different map layers of the same geographic region. So, common interfaces are the only way to enable overlays and combinations of complex and essentially different kinds of geographic information to happen automatically over the Internet. OGC brings together the key players and provides a formal structure for achieving consensus on the common interfaces.
The end goal of OGC is to adopt widespread technology standards and business processes in an effort to support georeferenced data throughout the global community.
OGC Specification
OpenGIS Specifications are technical documents that detail interfaces or encodings. These specifications are the main "products" of the Open Geospatial Consortium and have been developed by the membership to address specific interoperability challenges. The documents are available to everyone at no cost.
Abstract Specification
The Abstract Specification provides the conceptual foundation for most OGC specification development activities. The Abstract Specification provides a reference model for the development of OpenGIS Implementation Specifications.
Implementation Specifications
Implementation Specifications are written for a more technical audience and detail the interface structure between software components. An interface specification is considered to be at the implementation level of detail if, when implemented by two different software engineers in ignorance of each other, the resulting components plug and play with each other at that interface.
The most important OGC specifications:
· OGC Reference Model - a complete set of reference models.
· WMS - Web Map Service
· WFS - Web Feature Service
· WCS - Web Coverage Service
· CAT - Web Catalog Service
· SFS - Simple Features - SQL
· GML - Geography Markup Language
· WPS-Web Processing Service
OGC Reference Model
The OGC Reference Model describes a framework for the ongoing work of the Open Geospatial Consortium (OGC) and their specifications and implementing interoperable solutions and applications for geospatial services, data, and applications.
It has the following purposes:
· Provides a foundation for coordination and understanding (both internal and external to OGC) of ongoing OGC activities and the Technical Baseline.
· Update/Replacement of parts of the 1998 OpenGIS Guide.
· Describes the OGC requirements baseline for geospatial interoperability.
Web Map Service (WMS)
The OGC Web Map Service (WMS) Version 1.3 Interface Specification provides an excellent mechanism for quickly developing applications that allow a client to display CAD and GIS data without costly data conversion. The WMS utilizes an HTTP request structure that packages a request to one or more servers that understand a WMS request. The server processes the WMS request and sends back a geo-registered picture to the client. The picture may be a PNG, a GIF, or a JPEG image. Since the WMS allows the client to specify a coordinate reference system, all picture images are returned to the client in the same reference system, allowing the pictures to be "displayed" one on top of the other.
This specifiaction defines three operations:
· returns service-level metadata.
· returns a map whose geographic and dimensional parameters are well-defined.
Furthermore, individual maps can be requested from different servers. The Web Map Service thus enables the creation of a network of distributed map servers from which clients can build customized maps.
WMS Application – Intergraph’s Support
Intergraph's uses OpenGIS Web Map Service (WMS) implementation to deliver data to the MapServer platform. In essence MapServer acts as a WMS client to the Intergraph system. Intergraph's GeoMedia WebMap running on Windows 2000 and GeoMedia WebMap Publisher is the main system for map distribution which is compitable with WMS implementation.
That means there is no additional configuration required to use the GeoMedia WebMap Publisher created maps; the WMS implementation uses them directly. Because the implementation follows the OpenGIS Web Map Service specification, the server can understand and respond to requests from software clients. The MapServer system then uses that data, along with planning and zoning data, to serve maps for users.
Figure: Copenhagen maps delivered via GeoMedia Web Map and GeoMedia WebMap Publisher.
Figure: Copenhagen maps delivered via MapServer.
Here, the building colors are the same as those above. That's because most of the map layers are actually the same, published using the Web Map Service Specification from GeoMedia WebMap and GeoMedia WebMap Publisher, then read into MapServer using that same specification, and republished along with other data layers.
Web Feature Service (WFS)
The purpose of the OGC Web Feature Service Interface Specification is to provide a structure and mechanism for query and retrieval of geographic features. The WFS requests are generated on the client and are posted to a WFS server using HTTP. The default payload encoding for transferring exposed features from the server to the client is the Geography Markup Language (GML).
There are numerous commercial and open source implementations of the WFS interface standard, including a Open Source WFS reference implementation, called GeoServer.
WFS Data manipulation operations include the ability to:
· Create a new feature instance
· Delete a feature instance
· Update a feature instance
· Get or Query features based on spatial and non-spatial constraints
The basic Web Feature Service allows querying and retrieval of features.A transactional Web Feature Service (WFS-T) allows creation, deletion, and updating of features.
Figure: A transactional WFS application
Web Coverage Service (WCS)
A WCS provides access to potentially detailed and rich sets of geospatial information, in forms that are useful for client-side rendering. The WCS may be compared to the OGC Web Map Service (WMS) and the Web Feature Service (WFS); like them it allows clients to choose portions of a server's information holdings based on spatial constraints and other criteria.
Unlike WMS, the WCS provides available data together with their detailed descriptions; allows complex queries against these data; and returns data with its original semantics (instead of pictures) which can be interpreted, extrapolated, etc. -- and not just portrayed.
Unlike WFS which returns discrete geospatial features, the WCS returns representations of space-varying phenomena that relate a spatial-temporal domain.
The specification defines three operations:
· The GetCapabilities operation returns an XML document describing the service and brief descriptions of the data collections from which clients may request coverages.
· The DescribeCoverage operation lets clients request a full description of one or more coverages served by a particular WCS server.
· The GetCoverage operation returns a coverage bundled in a well-known coverage format.
Catalog Service (CAT)
The OGC Catalog Service defines common interfaces to discover, browse, and query metadata about data, services, and other potential resource.
Simple Features-SQL (SFS)
Simple Features-SQL are an OpenGIS standard which specifies digital storage of geographical data (point, line, polygon, multi-point, multi-line, etc) with both spatial and non-spatial attributes.
Simple Features are based on 2D geometry with linear interpolation between vertices. In general, a 2D geometry is simple if it contains no self-intersection. The OpenGIS Simple Features specifications define various spatial operators, which can be used to generate new geometries from existing geometries.
Geography Markup Language (GML)
The Geography Markup Language (GML) is the XML grammar, defined by the Open Geospatial Consortium (OGC) to express geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic transactions on the Internet.
GML model
The original GML model was based on the World Wide Web Consortium's Resource Description Framework (RDF). Subsequently, the OGC introduced XML schemas into GML's structure to help connect the various existing geographic databases, whose relational structure XML schemas are more easily defined.
Beneficiary Group
It is kind of a question often asked that who is going to be benefited by this kind of interoperability program. The answer is USER. A much larger population of users than currently use GIS and remote sensing softwares, producers, owners, stewards, and resellers of geodata will be benefited. Because…….
· The majority of GIS in operation today follow an Homogeneous or Proprietary approach, where the specific GIS applications and capabilities are tightly coupled to their internal data models and structures like in ESRI products.
· It limits the flexibility of users to deal with GIS data, software and perform analysis. Users need to depend on certain vendors and their proprietary data and software.
· Within this model, an organization would also typically, adopt an associated vendor file format as an internal standard.
Open GIS intents to move from current GIS practice and provides Distributed GIS where:
· The major benefit is the ability to distribute and then combine disparate data to produce new combinatorial datasets, regardless of the original format. Therefore promoting information exchange across organizations.
· Users are not restricted to specific vendor systems or formats.
· User can access raster and vector data, regardless of its original matter.
Software developers and integrators who either provide geoprocessing software or who seek to integrate these capabilities into general purpose information systems will also get benefit for the following reasons:
· The market will be much bigger;
· The web server, tools, and applet markets will be strong;
· The geo-processing software integration business will be booming;
· Current users will buy the new versions of software that have OpenGIS Conformant interfaces;
· Sophisticated and specialized applications will proliferate.
· There will be new jobs for metadata and data semantics experts, geographers who help build and integrate geographic "content" for web sites, data coordinators, etc.
As a whole increasingly the users will be affected.
ESRIs’ support for OGC
ESRI being the market leader in GIS, is a Principal member of Open Geospatial Consortium, Inc. (OGC). ESRI fully encompasses Open Geospatial Consortium, Inc. (OGC) specifications and standards as well as comprehensive IT standards such as those related to ISO, W3C, ANSI, CEN, and many other leading industry standards.
ESRI's goal is to support appropriate specifications as they become finalized and to participate in the development of GIS standards via active participation in ISO and OGC.
ESRI is able to contribute knowledge in interoperability and ensure the realization of standards compliance in ESRI software products.
· ArcGIS is founded upon key interoperability and Web computing concepts and is in use today by tens of thousands of organizations that rely on GIS and IT interoperability