GeoWebCache Takes the Ouch out of Tile Caching
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GeoWebCache Takes the Ouch out of Tile Caching

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Industry News
GeoWebCache Takes the Ouch out of Tile Caching
By Susan Smith

The need for a caching solution that could be easily integrated with GeoServer drove the development of GeoWebCache, a product that seeks to break down the limitations of tile caching. For those unfamiliar with GeoServer, GeoServer is an open source software server written in Java that allows users to share and edit geospatial data. Designed for interoperability, it publishes data from any major spatial data source using open standards.

Arne Kepp, core developer for GeoServer and the lead developer for GeoWebCache, talked with GISWeekly about the motivation behind GeoWebCache and plans for the product in the future.

GISWeekly: What was the impetus behind the creation of GeoWebCache? The history?

Arne Kepp: The motivation behind GeoWebCache was the need for a caching solution that could easily be integrated with GeoServer. OpenGeo has been focusing on an enterprise quality, fully supported open source web application stack. GeoWebCache plays a key role in the OpenGeo Stack, sitting between OpenLayers, the JavaScript front end, and GeoServer, which serves the data from a variety of data sources like PostGIS, Oracle, ArcSDE and more. A tile cache ensures scalability and improves the user experience. Since GeoServer was written in Java it made sense to use the same language, both to provide tight integration and to make it easy to install on all major platforms.

Through Google Summer of Code Chris Whitney was able to spend a summer creating what became known as jTileCache. It had very basic functionality, but also original ideas like using the Java Caching System to store image objects and compress them on the fly. Over the next nine months that code was then reworked by OpenGeo into what is today known as GeoWebCache. Through external funding we were able to add native interfaces for Virtual Earth and Google Maps, making it easy to use those clients against data served by WMS servers.

Last summer the project benefited from another generous Summer of Code grant, allowing Marius Suta to contribute code that enabled XML configuration using XStream and a RESTful configuration interface.

Google's Open Source Office has also funded OpenGeo to add streaming Google Earth support to GeoServer, and GeoWebCache benefited from this, gaining the ability to tile and cache KML placemarks and vectors.

Looking forward, we are continuing to break down some of limitations commonly associated with tile caches.

GISWeekly: What is GeoWebCache’s relationship to the GeoServer?

GeoServer is sort of like an older sibling. GeoWebCache has benefited tremendously from the collective experience of the GeoServer developer community and the feedback from GeoServer users. They have had a strong influence on the design and helped identify bugs. Originally GeoWebCache was intended to be a library for GeoServer, but since the WMS standard provides a very stable interface it turned out to be just as easy to develop a separate servlet.

GeoWebCache was first included as a plugin in GeoServer 1.7.1. In the 1.7.x series it basically has the same functionality as a standalone version of GeoWebCache, but the plugin is automatically configured and has a reduced footprint since it shares many libraries with GeoServer.

In the 2.x series of GeoServer, which is currently at the alpha-stage, we have started going beyond what can be achieved using the standard HTTP requests. If a layer is added or reconfigured, the tile cache will be informed immediately through a callback interface and reevaluate any existing tiles. However, GeoWebCache also has a RESTful configuration interface that allows other servers to achieve the same effect.

GISWeekly: What is new in the 1.1.0 release?

The main improvement in version 1.1.0 is the support for "modifiable parameters.” Other tile caches have associated one layer name with one set of tiles, meaning they only consider the bounding box and the layer name of the request, the rest is defined by the configuration of the cache. GeoWebCache has for a long time supported a separate set for each combination of spatial reference system and output format.

The new release takes this one step further, allowing you to configure filters and specify what other parameters constitute a set of tiles. For example, you can now serve the same layer with multiple styles, you can apply CQL filters, or you can use the time and elevation parameters introduced in WMS 1.3.0. One of the filter types uses regular expressions, which are extremely flexible, and the other is written for matching floating point numbers.

One existing feature that many users appreciate is the automatic configuration of GeoWebCache from a WMS getcapabilities document. The drawback with using this method has been that you could not specify additional projections or output formats. In 1.1.0 this problem has been reduced, if the configuration file and the getcapabilities document have overlapping layer names the two configurations will simply be merged. In the long run we still hope to provide an AJAX interface to make this easy.

Very basic WFS caching is included in 1.1.0. The motivation behind this is that GeoServer's WFS supports zipped shapefiles as an output format.
These can be several hundred megabytes and very expensive to compute, so any public server should cache them. Again, you can limit what queries are allowed by using a regular expression, but this is definitely a feature that will be improved over time.

But most importantly, the 1.1.0 release lays a lot of the groundwork for future development. Key to this is the pluggable H2 database which stores meta information about tiles, so that it will now be possible to remove tiles that have not been accessed in a certain time period, or find tiles that have been outdated by a recent change.

GISWeekly: Does GeoWebCache work with other open source software? Is it mostly used by developers?

GeoWebCache works great with any WMS compliant server, including MapServer and deegree. But there are also a number of people who use it in front of ESRI products, Ionic and even custom WMS servers. On the client side it currently works with any software that can use the OSGeo WMS-C recommendations, including OpenLayers and uDig. There are also custom clients that use the Google Maps API.

The user base is anything from professional developers to home users.
Based on the activity on the mailinglist, my impression is that developers are actually the minority. Most questions appear to come from end users who own an existing WMS solution and wish to improve its performance or reduce costs.

While some understanding of WMS makes life easier, there are also those that do not want to deal with OGC services and use GeoWebCache so that they can access their data in Google Earth or use the APIs that Google Maps and Virtual Earth provide.

GISWeekly: How does GeoWebCache speed up delivery of geographic data from OGC Web Services?

GeoWebCache acts like a proxy between clients and one or more WMS servers. When the client makes a request, GeoWebCache first checks to see whether it already has the corresponding tile. If not, the request is forwarded to the appropriate WMS server. When the response comes back, GeoWebCache first saves a copy (caches) and then forwards it to the client. The entire process adds only a few milliseconds to the time it takes to do the WMS request. Subsequent requests for the same tile are then answered in milliseconds using the copy, with the added benefit that this requires no resources on the WMS backend.

This improves the user experience and also opens up a number of new possibilities. For example, the response time becomes less important, so the WMS server can use more complex rules and render tiles that look better. You can also seed the cache in advance, using the built-in web interface, so that some or all tiles are cached before the instance is used in production.

GeoWebCache has been designed for speed and scalability. Even a laptop can serve tiles at several hundred megabits per second. I have come across blogs and emails where people assume that their instances would be limited to the throughput or seek times of their hard drives, since this is where the tiles are persisted. But this is generally not the case, most modern operating systems have something called disk block caches. This effectively moves the most requested tiles into memory, so they can be accessed at much higher speeds. OpenGeo hopes that this increase in capacity will also allow data providers to make their data available to a wider audience.

GISWeekly: What kind of relationship do you have with Google and Microsoft (Virtual Earth) and how do users benefit from using GeoWebCache with these geographic search engines?

In addition to Summer of Code, Google has contributed to both GeoServer and GeoWebCache by funding the development of three special output formats. Two of them are more closely related to Google Earth, namely raster super-overlays and regionated vectors. The first one works like the regular Google Earth background, improving the resolution of images as you zoom in. GeoWebCache can be used with any WMS server to achieve this effect.

The vector format uses OGC KML, and the key is that we gradually show more features as you zoom in. Developing code that automatically selects what items to show at what zoomlevel was a major undertaking. Both of these types of hierarchies can be cached using GeoWebCache. Google Earth requests a large number of tiles while you are zooming in or spinning the globe, so caching is crucial if you want to serve more than a few simultaneous clients.

The third format is what we call "geosearch" and most of the work is actually done in GeoServer. It is basically an XML sitemap, similar to those used for normal websites, and KML files representing each feature or row in the underlying database. The KML is automatically generated from any backend that provides vector data. Googlebot reads the sitemaps and then fetches all the KML placemarks. It analyzes the description of each feature and its location. After a period of about two weeks your data then becomes visible as a user-contributed placemark om GeoWebCache's role here is to provide fast access in case the person searching wants to view the entire dataset or download the data as a shapefile.

We have registered that Microsoft is also entering the domain of searching geospatial information, but so far we have not found documentation on how to contribute to the index. So in this sense our relationship is limited to providing an easy to user interface for Virtual Earth JavaScript developers. People who use the SilverLight edition of Virtual Earth have also used GeoWebCache to publish data from WMS servers, it turns out the SilverLight code uses the same tile indexes as Google Maps.

GISWeekly: What are your goals for the product?

The goal is to make tile caching as unobtrusive and easy to use as possible. I hope that the WMTS standard that OGC is working on will make it easier to develop clients and share tiles across applications. On the server side I want to make the cache more dynamic, to automatically expire tiles that are no longer accurate. This is particularly important to OpenGeo, one of our primary goals is to create software that lets end users contribute and edit geospatial information through their web browsers. The term we use for this is "wikiable maps", it is based on WFS with transactions, but maintains multiple versions of the same data.

On the enterprise side of things we are actively looking for clients to fund features that are particularly important for large users. These include clustering, with lateral cache synchronization, for increased scalability and reliability. We would also like to develop tools that make it easier to maintain a cache and gather detailed statistics about usage. To get there I have made a list of menu items that we hope clients will fund. That said, GeoWebCache is an exciting platform with a lot of possibilities. Things we have listed only represent a small subset of what can be done.

Top News of the Week

PCI Geomatics has joined the ESRI Business Partner Program. Together with ESRI, they will provide users with optimized desktop and server based workflows for correcting commercial satellite imagery along with tools for processing and analyzing radar imagery.

Safe Software announced that they have received Oracle's Spatial Excellence "Partnership Award" at the 2009 Oracle Spatial User Conference in Tampa, Florida. The Oracle Spatial Excellence Awards are given to those leading organizations that have contributed to the advancement of mainstream enterprise solutions using geospatial technology.

Intergraph and Stellar Grants Inc. teamed to offer an informative webinar at 1:00 p.m. Eastern on Tuesday, April 28 to assist utilities in applying for Smart Grid grants under the federal economic stimulus and recovery act.
The no-cost, one-hour webinar provided grant application strategy and process guidelines for utilities interested in the approximately $15.5 billion available in grants to modernize their grid infrastructure and operations. The grants are part of the nearly $800 billion included in the American Recovery and Reinvestment Act (ARRA) of 2009.

Acquisitions, Agreements, Alliances

Getmapping has teamed up with New Zealand Aerial Mapping (NZAM) in an arrangement which enables both companies to share resources and equipment to increase their flying and aerial survey capabilities. Getmapping has ambitious plans for the UK flying season in 2009 including the completion of its aerial survey of Scotland and a new survey of Wales. Thanks to this tie up with NZAM Getmapping has up to four aircraft at its disposal for UK surveys during the 2009 flying season.

ESRI announced that Interactive Visualization Systems (IVS) 3D has joined its business partner program. IVS 3D is a leading vendor of interactive 3D visualization and analysis software for marine information. This partnership will benefit organizations with workflows that visualize and analyze bathymetric data for use in the maritime community including the defense, petroleum, environment, and hydrographic sectors.

ImageTree Corporation has signed a strategic investment and technology development agreement with independent strategic investment firm In-Q-Tel. Under this agreement, ImageTree will leverage its patented technology and processes to help In-Q-Tel support the interests of the United States Intelligence Community, which includes the Central Intelligence Agency and 15 other organizations.


GeoTec Media, organizers of the 2009 GeoTec Event, June 1-4, 2009, Vancouver, BC, announced that the new online registration system is now live. This innovative new system allows attendees to manage their own registrations online, without the need for paper trails and faxing.

Team discounts saving 30 percent are available for organizations registering three or more people for the Three-Day Conference. All team registrations must be submitted together along with payment to receive the discount. This special offer expires May 8.

Click here for early registration and to save on conference fees. Early pricing ends 8 May and standard rates apply starting 9 May 2009.

The Open Geospatial Consortium, Inc. (OGC) announces the release of two Discussion Papers: Uncertainty Markup Language (UncertML) and the OpenGIS Web Coverage Service Standard (WCS) Extension for CF-netCDF Encoding ( OpenGIS Web Coverage Service Standard (WCS) Extension for CF-netCDF Encoding ).
UncertML is a conceptual model and XML encoding designed for encapsulating probabilistic uncertainties and may be used to quantify and exchange complex uncertainties in data. Most data contains uncertainty arising from sources such as measurement error, observation operator error, processing/modeling errors, or corruption. Processing uncertain data propagates and often increases uncertainty. Thus there is a need for a standard way of characterizing uncertainty that is readily interpreted by software systems. UncertML is based on a number of ISO and OGC standards, such as ISO 19138 Data Quality Measures, and addresses the ISO/IEC guide to the expression of uncertainty in measurement (GUM). UncertML utilizes the OGC Geography Markup Language (GML) Standard and the OGC Sensor Web Enablement Common (SWE) Standard.

ESRI announces the Business GIS Summit will coincide with the ESRI International User Conference (ESRI UC) at the San Diego Convention Center in San Diego, California, in July. This will allow ESRI to open its resources to the wider business geographic information system (GIS) community and help the entire ESRI user base learn from and apply the business benefits and process improvement strategies common to commercial-sector GIS users. Attendees of the ESRI UC and Business GIS Summit will be able to share experiences and best practices while taking advantage of the wealth of information and technical knowledge that has made both events so popular.

For more information on the summit and to register, visit Business GIS Summit .


Trimble announced revenue of $289.0 million for its first quarter ended April 3, 2009, down approximately 19 percent from revenue of $355.3 million in the first quarter of 2008. See press release

New Products

ArcGIS 9.3.1, which began shipping , helps you create and share modern Web maps that are relevant to your entire organization. This release of ESRI's integrated collection of geographic information system (GIS) software products focuses on improving the performance of dynamic map publishing and increasing the visibility of geographic information.

Edgetech America, Inc. has released the second major version of MapSpeller for ArcGIS. This ArcMap extension spell checks and corrects errors in map and layout annotations, grouped graphics, legends and scale objects conventionally and spatially (patent pending).

The latest aerial photography and detailed earth surface models from Bluesky are being used for demonstration in a state of the art software package developed to assess the risk and impact of flooding. The ISIS by Halcrow suite is one of the leading software packages for river modeling, used extensively across the world for flood forecasting, flood risk mapping and flood alleviation scheme design by government organizations, environmental regulators and engineering consultants. To support the launch of ISIS 2D Halcrow has included some GeoPerspectives aerial photography and Digital Terrain Models (DTMs) from Bluesky, to enable users to evaluate the improved modeling functionality.

Juniper Systems, Inc., a provider of intuitive field computer solutions for rugged applications, announces LandMark Mobile - A GPS Utility. LandMark Mobile incorporates real-time GPS data into any custom and third party application software. This innovative GPS utility manages the GPS receiver connectivity functions and provides services such as navigation, checking satellite status, and recording the position of specific occupied points. Point averaging and offset capabilities are included. LandMark Mobile, a Windows Mobile application, runs exclusively on the Allegro MX or Archer Field PC. The Allegro MX is a rugged handheld computer featuring a full keyboard. The Archer Field PC is a ultra-rugged PDA built to perform in extreme environments.

Juniper Systems, Inc. announces the new Allegro MX Field PC. The ultra-rugged Allegro features Windows Mobile 6.1, IP67 rating, robust full keyboard, integrated Bluetooth® Wireless Technology and Wi-Fi 802.11b/g option, long-term battery life, and highly outdoor-visible display. The Allegro MX runs Microsoft Windows Mobile version 6.1 and is powered by an XScale core 624MHz processor. The Allegro MX is an ideal solution for mobile GIS when running ESRI ArcPad or ArcGIS Mobile. Durable in extreme environments, the Allegro is the premier choice for those in need of a rugged field computer with a full keyboard. Use the Allegro to collect, document, navigate, communicate, search, and share information. The Allegro MX is your long-term field companion.

G-Tek Solutions, a start up GIS software provider specializing in stand alone GIS software, is pleased to announce two new GIS based products:
4MAT2KML Professional
G-Tek Solutions is optimistic in the use of KML file format and believes it will become more popular as a means of reducing production costs related to GIS. The objective of the software is to provide an alternative means at viewing data to organizations that may not have a huge budget and to help non-GIS users view data without expensive GIS software.

The upcoming release of IVS 3D’s Fledermaus software includes FM Geocoder, available both as a standalone module and as part of the FM Habitat and FM Pro bundles. Existing Fledermaus Professional license holders under a support and maintenance agreement will receive a no-cost upgrade to the new Version 7 FM Pro bundle that will include FM Geocoder.

Demonstrating continued commitment to delivering a digital map database with the broadest and deepest global coverage, Tele Atlas, a leading global provider of digital maps and dynamic content for navigation and location based solutions, announced the availability of new digital maps and related content covering Chile and Uruguay and updated maps of Argentina and Brazil. The announcement strengthens Tele Atlas’ regional lead by building on the company’s Latin American database, which now includes coverage of five countries, more than 1.7 million kilometers and more than 750,000 points of interest (POIs). Tele Atlas customers such as Digibase, Google and TomTom have already launched solutions using Tele Atlas Latin American maps.

Version 10.0 of InfoWorks, FloodWorks and InfoNet just released further underlines Wallingford Software’s acknowledged position as the pre-eminent modeling software developers for the water industry. A major addition to InfoWorks RS, CS and SD is the new collapsing wall functionality of the 2D engine. Initially developed to model cascades of falling dams V10.0 enables any type of barrier to collapse based on either; depth, water level, velocity or unit force criteria. A whole ‘wall’ or just segments can be collapsed. This new release incorporates considerable new enhancements and features that bring benefits by way of greater productivity, efficiency and performance.

ERDAS Inc. announces ERDAS TITAN 2009, Version 9.3.3, providing more flexibility in the industry’s most unique and powerful online network for sharing data. ERDAS TITAN can now be run both online and offline.

ERDAS TITAN is a secure solution for rapid permission-based data publishing from the desktop. ERDAS TITAN provides access to unlimited data resources across the organization and enables consumption in a variety of desktop, Internet and 3D virtual globe applications. Empowered by a 3D virtual globe, users create data and content mash ups that can be quickly published and viewed by others.

Around the Web

Free GIS and Shapefile Editor ForestPal

Nahyan visits Middle East Map 2009, WAM, April 27, 2009

New York City adds new features to GIS application April 27 2009, TransitWire



33rd International Symposium on Remote Sensing of Environment (ISRSE)
Date: May 4 - 8, 2009
Place: Palazzo dei Congressi
Stresa, Lago Maggiori, Italy

You are cordially invited to the 33rd International Symposium on Remote Sensing of Environment (ISRSE) which will take place on May 4-8.2009 in Stresa, Italy. This 33rd Symposium will represent a major event in the long series of internationally recognized ISRSE meetings. The overall theme of the symposium is the use of Earth Observation systems and airborne techniques for understanding and managing the Earth environment and natural resources.

4th National GIS Symposium in Saudi Arabia
Date: May 4 - 6, 2009
Place: Chamber of Commerce & Industry
Dammam Eastern, Saudi Arabia

“The Fourth National GIS Symposium in Saudi Arabia”. Featuring a state-of-the-art exhibit, plenary, keynote, and technical sessions, it would bring all stakeholders in the geospatial domain - academia, researchers, students, and the industry - onto one platform for interaction, sharing and discussion on various topics such as collaboration on technologies and experiences gained.

BE Conference 2009
Date: May 11 - 14, 2009
Place: Charlotte, NC USA

Save the Date! Be Conference 2009 will provide infrastructure professionals with an inclusive and engaging environment to learn about Bentley solutions from the leading provider of infrastructure software. The agenda will include technical workshops, best practices, and community and networking events designed to empower today’s globally connected infrastructure professionals.

Geodiffusion 2009
Date: May 13 - 14, 2009
Place: Le Capitole de Québec
Quebec, Canada

The 7th edition of Géodiffusion will take place on May 13th and 14th at the Théâtre le Capitole, in Quebec City. This year’s conference theme is : Business Intelligence and Geospatial Technologies : Must-Have Allies in Tough Economic Times. The 2009 edition boasts 2 full days of sessions on this important topic which affects your organization on a daily basis.

Where 2.0 Conference
Date: May 19 - 21, 2009
Place: Burlingame
San Jose, CA USA

Where 2.0 2009 delves into the emerging technologies surrounding the geospatial industry, particularly the way our lives are organized, from finding a restaurant to finding the source of a new millennium plague. Maps are everywhere now, from your desktop to your iPhone to your car to your oil rig, and presented as realistically or as representationally as suits your needs. Thanks to the launch of Geo-Eye and other projects, location information makes devices more useful, and is therefore becoming a given

Seventeenth Annual Pennsylvania GIS Conference 2009
Date: May 19 - 20, 2009
Place: Holiday Inn Hotel and Conference Center
Grantville, PA USA

This year’s Pennsylvania GIS Conference will explore the essential connection between geospatial technology and the development and sustainability of our critical infrastructure. Presenters from industry, academia, and government will showcase applications that support critical infrastructures in water resources, energy and the environment, public safety and health, and economic development. In addition, the latest hardware, software, and database trends will be demonstrated by the geospatial industry. This year it’s all technology and applications – no policy, no politics! Just pure GIS.

ESRI Regional User Conference
Date: May 20 - 21, 2009
Place: Victoria Conference Centre
720 Douglas Street Victoria , Victoria, BC, V8W 3M7 Canada

ESRI Canada is pleased to invite you to join other GIS professionals for this exclusive opportunity to learn about the latest advances in GIS technology and hear first hand how others in your community are using a geographic approach in their work.

GO! Sync Mobile GIS in Action at Truckee Donner PUD
Date: May 28, 2009
Place: USA

Presented by Ian Fitzgerald, Truckee Donner PUD
9:15am Pacific/11:15am Central/12:15pm Eastern

GeoTec 2009
Date: June 1 - 4, 2009
Place: Vancouver Convention Centre
Vancouver, British Columbia, Canada

GeoTec 2009 is proud to be back in Vancouver, the founding home of the conference in 1985. The GeoTec Event offers its attendees high caliber and timely presentations from knowledgeable industry leaders, geospatial technologists and users from Canada and the world.

Sponsored by GeoTec Media, publisher of GeoWorld magazine and developer of the Web portal, the 23rd annual event GeoTec Event is a world-leading technical event, and the largest geospatial technology event n Canada.

GIS: Real Business Value
Date: June 1 - 2, 2009
Place: Houston, TX USA

Today's competitive business environment has required organizations to become more diligent about their Information Technology (IT) investments. Geospatial Information Systems (GIS) are no different.

This has meant that business units advocating or using GIS must now compete for their share of a limited, and often shrinking, capital IT budget

Midwest Infrastructure & GIS Technical Conference
Date: June 1 - 4, 2009
Place: 725 Blue Harbor Drive
Sheboygan, WI 53081 USA

Focus of event will be Civil 3D and the WisDOT workflows of Civil 3D, GIS, GPS, LiDar, Map, Mapguide, Virtualizations, BIM, Navisworks, Utilities. See Invitation and Class List attachments.

ESRI Regional User Conference
Date: June 2 - 3, 2009
Place: University of Northern British Columbia, Conference Centre
3333 University Way , Prince George, BC, V2N 4Z9 Canada

ESRI Canada is pleased to invite you to join other GIS professionals for this exclusive opportunity to learn about the latest advances in GIS technology and hear first hand how others in your community are using a geographic approach in their work.

URISA's Second GIS in Public Health Conference
Date: June 5 - 8, 2009
Place: Westin Providence
Providence, RI USA

To provide an open and participatory forum for advancing the effective use of spatial information and geographic information system technologies across the domains of public health, healthcare and community health preparedness.