Car Mirrors – Looking Back on Developments

Camera monitor systems enable digital mirrors based on ISO standard 16505

Under current law, vehicles must have equipment to provide “indirect vision”. This is achieved by simply using conventional mirrors attached to the vehicle. Under the new ISO standard 16505, the technical requirements are outlined for the replacement of mirrors of camera monitor systems. The Steinbeis Transfer Center “DSI – Digital Systems and Innovations” was involved in the drafting of the new standard and now offers advice on the topic, as well as courses, physical prototypes and measurement technology.

The new international ISO standard 16505, which defines “Ergonomic and Performance Aspects of Camera Monitor Systems,” describes the minimum technical requirements that must be fulfilled by a digital mirror or camera monitor system (CMS). These have a bearing on safety aspects, ergonomic factors, performance criteria and the testing of such camera monitor systems. The new standard forms the basis of new standard- conforming systems design and standard-conforming systems testing carried out by technical service providers.

Against the backdrop of recent technical developments in modern driver assistance systems, a variety of camera systems have now been introduced in series production vehicles. The offered functions range from simple rearview cameras to advanced 360°, all-round viewing systems and even night vision assistance with object recognition and sensor fusion. As a rule, under current legislation, such systems offered in series production are a driver convenience or assistance system and can not be considered as mandatory. ISO standard 16505, however, focuses on camera monitor systems which are intended to replace systems that are compulsory by law. These are means that are prescribed by law and make it possible to view objects indirectly, as is already the case with current vehicles which simply use conventional mirrors.

The automotive industry is currently busily trying to meet requirements relating to the reduction of carbon emissions in new vehicles. A key part of this is an emphasis on reducing vehicle weight and reducing air drag. Looking at vehicles as a whole makes it possible to pull together a variety of measures for optimizing vehicle design. One of these is the improvement of aerodynamic qualities by doing away with rearview mirrors. This is nothing new, but until now there was no international legislation framework for such solutions in vehicles in mass production. A Mercedes- Benz concept vehicle, the F200, did include a camera monitor system instead of a sideview mirror as early as 1996 – quite a futuristic concept at the time. In more recent years, a number of automotive companies have developed concepts vehicle which included camera monitor systems. The Volkswagen XL1 is already in small-scale production and is capable of minimal fuel consumption thanks to a variety of measures that help optimize the overall vehicle design. This concept includes a CMS to replace the sideview mirrors. Especially with driving cycles that are typical for larger commercial vehicles, this method of replacing mirrors can be particularly beneficial. Another Mercedes-Benz concept vehicle, Future Truck 2025 shows how this can be translated into practice with larger commercial vehicles. With commercial vehicles, too, mirror replacement systems are just one of a number of measures that can be combined to optimize carbon emissions.

On its own, ISO standard 16505 does not provide sufficient binding regulation for such mirror replacement systems. In Germany, the current version of UN-ECE Regulation No. 46 is applied for systems that enable indirect vision. Vehicles can be given an operating license if they fulfill the minimum technical requirements. The rules laid down under UNECE regulation No. 46 came from the commission of the United Nations for Europe (UN-ECE, whereby ECE stands for Economic Commission for Europe). As part of the UN-ECE, there is a World Forum for the Harmonization of Vehicle Regulations or UN-ECE WP.29. A committee was set up in 2009 to start an initiative to redraft UN-ECE Regulation No. 46 in order to take camera monitor systems into account as a replacement for mirrors. To define the technical parameters, an Informal Group on Camera Monitor Systems (IGCMS) was set up within the committee. One of the results of the work carried out by the IGCMS was a standards initiative for such systems, within the expert framework of the International Organization for Standardization (ISO). This standardization initiative was based on the realization that this technology is a highly complex issue. Detailed work was carried out on ISO standard 16505 between 2010 and 2014. The IGCMS II used ISO standard 16505 as a basis for the content of a new version of UN-ECE Regulation No. 46, which is aimed at permitting the use of prescribed indirect vision systems by using camera monitor systems. Once the standardization and regulatory process is complete, the use of CMS’s will be possible in vehicles in mass production and this is currently expected to happen after 2016. This will establish an international regulatory framework out of a combination of normative and regulatory guidelines. Since UN-ECE Regulation No. 46 is not applied by some countries outside the EU, the likelihood of approval will still have to be assessed on a country-bycountry basis. The Steinbeis Transfer Center DSI - Digital Systems and Innovations was also involved in technical aspects relating to these developments.

There are a variety of ways to improve vehicles by replacing conventional sideview mirrors with digital mirrors. As already mentioned, optimizing aerodynamics provides one way to reduce carbon emissions. This reduction depends on the driving cycle and the overall vehicle concept. According to a publication issued by the automotive supplier FICOSA, the carbon emissions of commercial vehicles can be reduced by around 1 to 2 percent. With e-vehicles it is possible to extend the driving distance and with sports cars the maximum speed can be raised. Especially in the premium segment, such a measure can even audibly improve the aero-acoustics for passengers. One key safety aspect that is improved with a CMS is visibility. For example, the field of vision laid down under UN-ECE Regulation No. 46 for a car (Group III, main sideview mirror) starts on the left and the right at 4 meters behind the eyes of the driver. This can result in invisible zones (“blind spots”) which can be captured and displayed by a CMS by widening the viewing angle using a wide angle camera. The technology also exists to adapt and optimize views depending on the situation. For example, image processing algorithms can be used to recognize dangerous objects such as a quickly approaching vehicle and give the driver an early warning. This could make the CMS a fundamental technology for the development of other driver assistance systems. With conventional mirrors, indirect vision can be adapted as required simply by moving the head, but this means the driver is constantly moving around. The need for drivers to move around can be reduced by showing the optimized viewing area and combining this with ergonomically positioned displays. Conventional mirrors also sometimes distract drivers with glare from the sun or vehicles behind the car. Glare can be significantly reduced with a CMS.

ISO standard 16505 defined the minimum technical requirements of a CMS. The minimum field of view that has to be displayed corresponds with guidelines under UN-ECE Regulation No. 46. One of the advantages of systems with mirrors compared to a CMS is that everything is in genuine real time. Processes involving a camera, data transfer, signal processing and a display can result in slight delays. Under ISO 16505, the system’s complete latency period must be under 200ms with an image refresh rate of at least 30Hz (or at least 15Hz under darkness). In terms of image resolution, ISO standard 16505 outlines a process which includes for the camera and display position as well as the compulsory visual acuity of the driver. As a quality criteria for image resolution, a modulation transfer function (MTF) is used. For each requirement, standard conform testing procedures are described. Since a camera monitor system involves electronic functions with a bearing on car safety, ISO standard 16505 has to be used for the systems designed in accordance with processes outlined under ISO standard 26262.

The German Federal Highway Research Institute (BASt) carried out a study on behalf of the Federal Ministry for Transport and Digital Infrastructure. This involved a comparative assessment of camera monitor systems and conventional mirrors and one key area looked at in the study was human-machine interaction. The results of the study show that, at a fundamental level, it is indeed possible to use a CMS for provinding indirect vision in cars and trucks (final report, dated Jan 22, 2015).


Professor Dr.-Ing. Anestis Terzis is director of the Steinbeis Transfer Center DSI – Digital Systems and Innovation and co-author of ISO standard 16505. Terzis is a professor in the design of digital systems at Ulm University of Applied Sciences and director of the vehicle electronics degree program. Terzis previously worked for 10 years at the carmaker Daimler AG in research and predevelopment, with a focus on driver assistance systems.

Professor Dr.-Ing. Anestis Terzis
Steinbeis Transfer Center DSI – Digital Systems and Innovations (Ulm)

Share this page