Monitoring Roads Traffic with Image Web Server

Monitoring Roads Traffic with Image Web Server


Clive Poole
Regional Manager, Earth Resource Mapping, Asia Pacific.
Email: [email protected]

During Sydney Olympic 2000, authorties ensured smooth running of transport systems using Image Web Server

Managing road traffic in a city of millions is always a demanding job. But what happens when Sydney decides to host the 2000 Olympic Games? How does the city ensure smooth running of transport systems when they are suddenly flooded not only with daily commuters, but also with hun-dreds of thousands of visitors?

Although Sydney employs several state-of-the- art real-time monitoring systems, how does the city guarantee a clear, overall picture of its many highways and side streets? Tradi-tional transport management methods simply don’t work in an environment where a finite road network is pushed to capacity. Sydney’s Roads and Traffic Authority (RTA) in al-liance with Earth Resource Mapping (ERM) and Digital Earth Pty. Ltd., have created a solution that finally solves this small but vital problem – not only for the Sydney Olympics, but for transportation authorities worldwide. Consider the case of Chris Ruwoldt, Transport Operations Planning Manager for RTA, who went to work and encountered a pressing problem at the worst possible time. The week before Sydney’s opening ceremony, two Senior Traffic Operations Controllers were hotly disputing an application for Road Occupancy. In Chris’ words: “ A factory was upgrading its driveway and needed to block off the kerbside lane. Bear in mind the RTA receives over 1000 applications every month for road occupancies and preparations for the Olympics Games are in full swing. The lane was a State Road; therefore approval was required from the RTA prior to the work being done. Before they can give approval, Controllers must assess the traffic impact of the closure. The impact of closing one lane of two is much more significant than closing one lane of three. The applicant didn’t put on their application what lane configuration was at that location. The Controllers got into a debate because one thought it was a two-lane road and the other thought three. I walked over to my computer and called up ERM’s software Image Web Server. I panned and zoomed into the particular area. We found it was three lanes. End of discussion. Application approved.”

Fig. 1: 200 metre view, 20cm airphoto
 mosaic geolinked with a raster map 
of Sydney

Before the Games, surveyors in the RTA Spatial Information Section were asked to provide a mapping interface to help plan and manage ‘Road Occupancies’. (Road Occupancy is an event, that purposely interrupts the free and normal flow of traffic. For example, a Road Occupancy may be required to repair a kerb, trim trees, supply concrete to a building site, or for an event such as a march, NewYear’s Eve celebrations, etc. Such ‘Road Occupancies’ are planned events, as opposed to unplanned events such as motor vehicle accidents and breakdowns).

Despite having extensive vector databases and real-time camera networks, RTA’s system lacked the ability to fill in the gaps between this data. RTA conceived that high resolution digital aerial photography and raster street maps, integrated with the system, would solve this problem. Further, the system had to display the imagery in a web browser, ArcView and Microsoft Word; and be simultaneously accessed by users across a network. Digital Earth and ERM approached RTA with a solution that meets all of these requirements–Image Web Server.

Digital Earth knew that coverage of such a wide area would take hundreds of files and add up to over 600 gigabytes of data. Their approach was to mosaic the data using ER Mapper and then compress it to a manageable size using ERM’s Enhanced Compressed Wavelet (ECW) technology. The compressed data was then to be built into an Image Web Server so that RTA could access it across a network. RTA requested a trial system using sample imagery. Andrew Hallam, Technical Manager for Digital Earth, created several sample pages, one of which displayed aerial photography and raster street maps in the browser using “geolink” mode. (That is, if you roamed or zoomed in one image the other would display the same area). Another web page stimulated a suburb search function. RTA decided to integrate Image Web Server technology with their system based on Digital Earth’s trial. Andrew Hallam, Digital Earth and Robert Leake, Development Photogrammetrist for RTA collaborated to process all imagery and develop the website. The project was broken into two stages. In the first stage, three different types of imagery were purchased:

  • 20cm, color aerial photography of the Sydney metropolitan area
  • 1m aerial photography covering all major roads in the Greater Sydney Area, including Newcastle in the north, Katoomba (Blue Mountains) in the west, and Wollongong in the South
  • 2m raster street maps of the Greater Sydney Area.

Andrew and Robert mosaiced the imagery using ER Mapper 6.1. In order to use the Image Web Server as the delivery mechanism they needed to then compress the imagery into ECW format. As a further challenge, RTA required the imagery to be displayed in two different projections based on the GDA94 datum: Map Grid of Australia (Zone 56) and RTA’s custom Lambert projection of New South Wales. In Andrew’s words: “All the imagery was provided in TIFF format with TIFF World files providing georeferencing information. These files had to be converted into mosaics no larger than 100 gigabytes each, in order to be served on the RTA’s Corporate Edition of Image Web Server (the Corporate Edition has a limit of 100-gigabytes per image served). That meant we had to create a total of ten mosaics (five mosaics for each projection), four of which contained 96 gigabytes of raw data. We processed approximately 600 gigabytes of data using two computers equipped with 160 gigabytes of usable hard disk space and a DLT tape drive. We were also able to save several mosaic algorithms in one directory and compress them using a batch process. The 96 gigabyte mosaics took about 17 hours each to compress so we took advantage of weekends to create several ECW files.”

Fig. 2: Inspecting road occupancy request with Image Web Server

Due to ER Mapper’s algorithm functionality,which allows for real-time image processing with very low hardware requirements, the project was successfully completed on available equipment.

Another benefit ER Mapper brought to this project is the ability to mosaic imagery of varying resolution (or cell size). The Sydney mosaics contain both 20cm and 1m resolution data, but can be viewed as one complete image. Using ER Mapper’s Image Display and Mosaic Wizard, RTA could easily fuse the two data sets with a few mouse clicks, and then watch the software process the real-time results. By overlaying wide-area coverage 1m data with the 20cm small-area coverage, RTA could easily fill in any gaps in the higher resolution dataset.

The second stage of the project was the development of the website that is used as first point of access to the imagery. During the Olympics, the main requirement was to be able to search for a suburb and display both the aerial photography and raster street map of the area in a web browser. The user then roams and zooms to their area of interest.

The user enters part or all of a suburb name, selects the projection they wish to view, and clicks on the “Search” button. A database on the server is queried and a list of matching suburbs and images is returned. Clicking on the image “Quality” hyperlink displays the selected suburb using the selected image, and also displays the associated raster street map.

“The fact that Image Web Server makes all this possible is transparent to most people. They now have fast and efficient access to the imagery from their desktop, and they don’t have to understand the technology that makes it happen. Although Image Web Server is relatively new, the RTA already gets significant benefit from it. It provides access for many people to a large quantity of valuable imagery. As the access to Image Web Server is rolled out to other groups within the RTA the benefit will increase as more people think up new ways to use the imagery”, continues Andrew Hallam.