Cameras are an essential component of any ITS system. For example, in open road bridge tolling and congestion charging cameras are used to enforce transponders, whereas for speed enforcement, cameras are employed for legal evidence of an infraction. Although analog cameras remain widely used, an ongoing transition from analog to digital interface cameras is apparent. Increasing resolution and higher frame rate requirements have surpassed analog interface capabilities. Digital interface cameras can offer this level of performance without significant cost increases. A Camera Link or GigE Vision interface is commonly used for connecting a camera to a PC in demanding traffic applications such as tolling or enforcement. Both technologies provide high bandwidth to facilitate high resolution and fast frame rate transfer of uncompressed, low latency image data 24/7. GigE Vision offers additional benefits such as off-the-shelf Ethernet components for reduced integration costs and long cable lengths up to 100 metres on a single copper link or more using switches or fibre optics.<ins>
From Gigabit Ethernet to GigE Vision
The popular Ethernet networking solution was initially developed to implement a distributed network intended to improve communication efficiency and network reliability. By the early 1990s, internet service providers began to emerge. Since then we have seen the internet propel Ethernet hardware into every single computer built today, redefining the method and speed of communication. Gradually supplanting Fast Ethernet, Gigabit Ethernet was first introduced by 1999, becoming very common and economical within several years. Camera companies quickly recognized this technology as an appealing interface for cameras due to off the shelf components, high bandwidth and cable length. In 2006 the Automated Imaging Association (AIA) introduced the GigE Vision standard which ensures that third-party software, hardware and other off-the-shelf system components interoperate over an Ethernet network for an easy and low-cost solution. Today, many camera manufacturers including Allied Vision Technologies (AVT) are offering GigE Vision cameras with resolutions ranging from VGA to 29 Megapixel.
Seeing is believing
Regional demographic changes, the increasing number of vehicles on the road and the on-going development or modernization of infrastructures are a constant challenge for any ITS integrator. Manufacturers such as Sony and Kodak are racing to develop sensor technologies that help enable these applications through improved sensitivity and better imaging performance. ExView HAD technology from Sony for instance, became recognized for excellent low light sensitivity and IR response with the introduction of the ICX285 device. Open road tolling and congestion charging applications in particular became primary users of cameras that employ this sensor favouring the resolution, aspect ratio and frame rate of the device. Recently Sony has added two new devices to the ExView line-up; the ICX674 and ICX694, provide the same image quality and sensitivity benefits as the ICX285 while doubling resolution and frame rate. <del></del>
In parallel, camera vendors battle for market share through early adoption and implementation of the sensor while developing new camera capabilities most suitable for the desired target market. Allied Vision Technologies for example has recently released the Prosilica GT, a camera family specifically designed for the ITS and outdoor imaging customer.
Existing lens controls such as video auto iris, designed for continuous imaging are inadequate for asynchronous triggering often used in tolling and speed enforcement applications. This is because video auto iris lenses, originally designed for analog interface cameras, rely on a continuous video reference signal to change the iris opening. A digital interface camera operates in the digital domain allowing users to synchronize image capture with real world events such as a passing vehicle. To address this scenario, Kowa Optimed has developed the P-iris lens control. Termed for precise iris control, these lenses allow users to move and freeze the iris at a desired location using a stepper motor. This capability allows asynchronous image capture to be used with digital interface cameras and remote lens control. On bright, sunny days, this can be used to manage blooming and smearing inherent to CCD or shutter inefficiency experienced by CMOS. During cloudy conditions the iris can be opened to minimize exposure time and prevent motion smear images. This enables the camera to achieve a range of camera adjustments without any additional lens components reducing system cost, size and weight.
Prosilica GT – a GigE Vision ITS camera
The Prosilica GT camera family aims to answer many ITS integrators issues: how to capture consistent high quality images in varying climates and lighting conditions.
The Prosilica GT are GigE Vision compliant cameras that are able to operate in extreme temperatures from -20°C to 65°C with a ribbed heat sink style enclosure that ensures conduction cooling of key components and maximises heat dissipation. A DC auto-iris / P-iris port for motorized lens control supports cooperative management of gain, exposure and iris. The Prosilica GT camera family features Power over Ethernet (PoE), a technology that supplies image data and power across the same Ethernet interface. Models featuring a selection of highly sensitive sensors with resolutions from VGA to 6 Megapixel and frame rates up to 120 fps are currently available. All models boast a number of in-camera features including configurable I/O to synchronize the image capture process with traffic system peripherals, low-latency trigger for timely image capture, IEEE1588 Precision Time Protocol used to manage clock synchronization of multiple devices across an Ethernet network and much more.
What next for cameras in ITS?
While ongoing transition from analog to GigE Vision and other digital interfaces is sure to continue, demand for increased resolution and faster frame rates, along with new camera peripherals is on the rise as well. Camera installation and maintenance costs are motivating integrators to reduce the number of camera installations. In an open-road tolling concept, a single camera could replace multiple lower resolution devices to reduce system complexity, sources of failure and required infrastructure. The replacement camera must offer the same level of performance as the previous system which means higher resolution and faster frame rates. Growing acceptance of digital camera technology is motivating optical companies to improve existing motorized lens control schemes.