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Exploring Continental's AR-HUD

Posted: 07 Aug 2014     Print Version  Bookmark and Share

Keywords:Augmented Reality Head-up Display  AR-HUD  Continental AG  human machine interface  Adaptive Cruise Control 

Seen from the front side of the focusing screen, the subsequent optical path corresponds to that of a conventional HUD with the image reflected from the focusing screen onto the second, larger mirror (AR-HUD mirror) using a first mirror (folding mirror). From there, it is reflected onto the front screen. The emitting area of the optical system for the augmentation is nearly DIN A4 size. This results in a field of vision of size 10 x 4.8 in the augmentation level, which corresponds geometrically to an approximate width of the augmentable viewing area of 130 cm and a height of 63 cm in the direct field of vision. Information at this distance level can be read with the driver only having to slightly lower his eyes by 2.4. The picture generating units of both the status and augmentation levels produce a display with a luminance adapted to the ambient lighting of over 10,000 candela per square metre. Thus, the display is easy to read in nearly all ambient lighting conditions.

This system approach for an AR-HUD in Continental's test vehicle, with two picture levels over different projection distances, has a major advantage. In most traffic conditions, content can be implemented at the remote level and the near level concurrently. This allows all pertinent driving and status information to be shown within the direct view of the driver.

Data fusion and graphics generation in the AR-Creator
Numerous simulations and Continental subject tests demonstrated that drivers feel most comfortable when the augmentation begins approximately 18 m to 20 m in front of the vehicle and continues up to a distance of around 100 m, depending on the route. The AR-Creator control unit has to evaluate a number of sensor data streams in order to place the graphical elements in the exact position on the focusing screen from where they can be reflected precisely into the driver's AR-HUD field of vision. This requires considerable arithmetic.

The AR-Creator undertakes a data fusion from three sources. The mono-camera provides the geometry of the road layout. "Euler spirals," or mathematical descriptions of how the curvature changes in the lane in front of the vehicle, are also taken into consideration. The size, position, and distance of detectable objects in front of the vehicle are obtained from a combination of radar sensor data and interpretation of the camera data. Lastly, Continental's eHorizon provides the map frame, in which the data sensed on the spot is read. This eHorizon in the demo vehicle is static and only uses navigational data material. Continental is already working on the series production of networked and highly dynamic eHorizon products, enabling data from a wide variety of sources (i.e. Vehicle-2-Vehicle, traffic control centres, etc.) prepared for display in the AR-HUD. The vehicle's position on a digital map is shown using a fusion of vehicle dynamics, camera and GPS data.

The AR-Creator also uses the merged data to calculate how the geometric road layout in front of the driver looks from the driver's position. This is possible because the driver's eye position is known. The driver sets the correct position of the "eye box" once in the demo vehicle before starting to drive. This process can be automated with an interior camera in series production. It detects the driver's eye position and can track the positioning of the eye box. The term "eye box" denotes a rectangular area where the height and width correspond to a theoretical "viewing window." The driver only gets the complete AR-HUD picture while looking at the road through this window. The vehicle passengers do not see the content shown by HUD and AR-HUD.

Based on the adjustable position of the eye box, the AR-Creator "knows" where the driver's eyes are, and from which perspective they are seeing the road and their surroundings. If an assistance system reports a relevant observation, corresponding virtual information can be created at the right point in the AR-HUD.

Less is more
A lot of development work went into designing the virtual information. After numerous design studies and subject tests, Continental's motto for the AR-HUD was 'Less is more.' The developers wanted to confront the driver with only the minimum graphical information necessary to avoid covering the real traffic view.

Angular arrowheads as navigation aids can optionally "lie" flat on the road, for example. In the case of a change of direction, they can move to be upright and turn towards the new direction of travel, so that they work like a direction sign. This design enables virtual information to be given in narrow curves, although a real augmentation in this situation is not possible due to the lack of perspective visual range.

The warning for crossing a traffic lane boundary is implemented discreetly. The traffic lane boundaries are only highlighted by the demo vehicle AR-HUD if the driver is most likely crossing them unintentionally.

If a future eHorizon receives information about an accident in advance, a danger symbol with a correspondingly high attention value can be placed in the driver's field of view well in advance. Once this new form of interaction with the driver has been installed, there are many options in the HMI to provide the driver with situational and proactive information. The vehicle and driver are then speaking to each other, even if this dialogue takes place without words.

About the author
This article is contributed by Continental AG.

To download the PDF version of this article, click here.


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