Файл: rt-light-sim-ilft-e.pdf

6

A.F.S bending light (or curve-lighting) discussion.

This function may be optically provided by the mean of :
-

Increasing the flux of static additional lights.

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Changing the angle of the main low-beams.

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Changing dynamically the angle of additional lights.

Although all 3 solutions are different, the last one consists partially in a mixing of the two others. It
has been therefore decided to focus on it.

Curve-lighting strategy based upon car information

The minimum information required to perform curve-lighting is the steering angle.
When the vehicle speed is low, the usual steering angle is important, and generally not critic under a
reasonable value.

When the car speed is high, the usual steering angle is low and meaningless for small values.
Moreover, any quick small change of the light distribution could perturb the driver.
Therefore, the rotation angle of the additional lights is function of the steering angle, the vehicle speed,
and the set up of different parameters like :

•

The steering angle threshold versus vehicle speed.

•

Possibly a minimum angle versus vehicle speed.

Curve-lighting strategy based upon availability of navigation information

It has been shown that the driver tries to anticipate his or her trajectory by looking roughly at the
location where the vehicle would be on the road if he or she had to operate a braking down to the stop
position.

It may happen that this location is not synchronous with the steering angle :
-

The observed point is too far from the car.

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A long curve is followed by a short one.

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The road direction ahead is changing very quickly, as mountain curves…

For such cases, an anticipated orientation of the additional lights is possible if a navigation system
(GPS, cartography and final destination) provides enough details about the road 100 to 200 meters
ahead. Some of these parameters are :
-

If a series of turns has been detected, the distance between the end of the current turn and the
beginning of the next one.

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The angle, direction, spatial position and curvature of the current or next turns.

-

…

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In traditional process, the development of a new vehicle headlight system requires the manufacturing
of several prototypes. Night tests are essential to assess a new system and modify it accordingly.
Several iterations are thus necessary before obtaining a headlight system that suits car company
specifications. In order to reduce both development costs and delays, but also to maximise the quality
of the headlamp control strategies, the 

Renault

 driving simulator dedicated to headlamp studies was

used. The following paragraphs give an overview of Renault’s driving simulation activities with a
brief description of the dedicated software, developed by Renault.

Several simulators have been developed by the Renault Research Department since 1989. A dynamic
simulator that enhances driving realism thanks to coherent visual and kinaesthetic stimuli was recently
built in answer to the emergence of new research and development needs. Dynamic control systems
(Adaptive Cruise Control), assessment of man-machine interfaces can be quoted as examples. The

Driving Simulation and Virtual Reality Group

 also developed several static simulator to deal with

lighting simulations, as presented in the followings.

The SCANeR

©

 II

comprehensive driving simulation software system

Renault

’s simulators are based on commercial hardware and use SCANeR

©

 II driving simulation

software package. SCANeR

©

 II is a set of distributed, multi-platform application software allowing the

user to build a vehicle simulation. SCANeR

©

 II brings tools, from database creation to real-time

interactive simulation, to replay and post-processing. Traffic generation is at the heart of SCANeR

©

 II

with a comprehensive traffic generation engine handling all types of infrastructures. An intuitive
graphical interface allows to set-up traffic conditions to fit the application. The dynamics model is
based on  multi-body analysis and real-word measurements. It is interfaced with an advanced road
surface definition based on Bézier patches and including variable adherence, noise and road-type
factors. Beyond the accurate driving simulation environment SCANeR

©

 II provides supervision and

analysis tools. The experimenter has a view of  the vehicle and simulation through real-time update of
dials and maps. The modules described above correspond to distinct functional units that use a
common communication protocol in the SCANeR

©

 II software architecture.

8

A driving simulator for headlamp studies

Renault, Research Department has developed a real-time lighting simulation software able to render
high precision visual aspects of a light beam on the road in real-time, thanks to computer generated
images. This software, integrated in SCANeR

©

 II, accepts photometrical and colour data

characterising the projector. This data is issued from measures taken on an existing projector or from
computations based on CAD projector models. Thus, a projector can be assessed even before having a
physical prototype.

The driver is seated in the simulator
drive station. He or she drives
through a virtual environment.
The virtual environment is the
reproduction of the Aubevoye
Renault’s test track. This test track is
usually used for night tests. It
includes short turns like the “hairpin”
and “pow” ones, but also long turns
like the “shaped like a hook” bend. A
precise definition of the road in terms
of polygon was necessary to obtain a
realistic lighting rendering.

Using the vehicle commands, the
user can switch from low to high
beam or fog lights. He or she can also
modify in real-time the projector type
or version.

A graphical user interface allows to modify in real-time various projector parameters such as position,
pitch or colour. Photometrical measures can be taken on each point on the road. A grid is displayed on
the road for this purpose. Finally, a top view of the track can be displayed, for a better assessment
comparison of projector characteristics.

The « hairpin » turn

The « pow » turn

The « shaped like

a hook » turn

Renault test track

Renault lighting simulator screenshot

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Two different curve-lighting systems were proposed by 

Valeo

. Different types of parameters are

necessary to their modules so that they can determine the direction of the vehicle on the road. Two
strategies were studies : the first one uses

information on the vehicle speed and the steering wheel

angle ; the second one on the vehicle speed and the characteristics of the road.

Simulation of a navigation system in the driving simulator

Vehicle parameters are handled by standard SCANeR

©

 II software package and are provided to the

lighting module through SCANeR

©

 II network protocols . However a specific development became

necessary to deal with the geometrical characteristics of the road for the navigation system. It was
simulated in order to supply the control strategy with the required features.

A first study consisted in finding out one accurate criteria to decide whether a road is a bend or not.
The curve radius of the road had to be analysed along the road way. It was decided that the user would
define a ‘curve radius threshold’. This approach allows the experimenter to decide bends to detect for
a specific database. For the curve-lighting application applied on the Renault tests track of Aubevoye,
the curve radius threshold was adjusted to recognise different bends such as the “hairpin” bend or the
“shaped like a hook” turns. This application took also into account the possible inaccuracy of such an
approach due to inexact sporadic curve radii along a real-life road.

The software was also modified so that
not only the turn in which the vehicle is
currently driving could be detected, but
also the next turn the vehicle is getting
closer to. In this way, situations that are
taken into account in the second Valeo
strategy such as series of consecutive
turns could be handled in the simulator
environment. However the system is
still left unsure of which route to light
when faced with intersections.

Finally, different functions were
created to get the data concerning both
the current and next turns to be able to
feed the curve-lighting modules. Those
functions were used to generate a
scenario dedicated to curve-lighting in
the SCANeR

©

 II traffic interface. Thus

the required information concerning
road turns could be sent to the visual
module in which the Valeo strategies
had to be included.

Detection of current and next turns

10

Integration of the Valeo strategies in the lighting simulator environment

Software modules that deal specifically with the 

Valeo

 strategies were added to the visual module.

Information related to the vehicle parameters and the navigation data were captured on the network
and provided to the curve-lighting units. The rotation angles of the additional headlights were
consequently calculated by the software and then supplied to the visual model to get the corresponding
image generation.

SCANeR

©

 II software architecture

In order to compare both approaches during an experiment without having to restart it, a specific
software architecture was implemented to be able to switch from one strategy to the other using the
vehicle ‘warning’ switch by the driver.

The tests and the tuning of both strategies were handled rapidly and efficiently thanks to the simulator
environment and the facility to modify the mathematical formula in the software dedicated to the
curve-lighting. Both strategies were then compared in real-time. Advantages and drawbacks were
highlighted for each one of the two curve-lighting approaches during the experiments on the driving
simulator in the Aubevoye test track.

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A validation of the curve-bending strategies was carried out by lighting experts from 

Renault

 and

Valeo

. Both solutions introduced by 

Valeo

 showed specific advantages that are distinct from one

strategy to the other. An improved curve-lighting strategy could hence take the advantage of the fact
that the gains of both current approaches do not occur in the same road configuration. In this context, a
new strategy combining the two separate adaptive systems is to be developed and studied thanks to the

Renault

 lighting simulator.

The lighting simulator allowed to save cost on and headlight-systems prototypes, and on time that
would have been necessary for the headlight tuning process. Besides, a better quality of the 

Valeo

adaptive front-lighting systems was made possible thanks to a total control of the test environment.

Acquisition

interface

Interactively

driven vehicle

Dynamics model

Communication protocol

Vehicle

parameters

Visual module

Curve-lighting

strategies &

Image generation

Traffic display

 and control

Scenario control

Navigation

information

Autonomous traffic