measurement of road scenes visibility : distance of detection , of recognition , of identification

(version Française ICI)

Measuring the road scenes visibility is a topic studied since the 60s and several approaches have been developed. Most measurements using a laser and a receiver, measure the attenuation of the light power transmission to study the influence of atmospheric disturbance , or of the light power reflection to study the power of raising the visibility of road markings .

This measure is easy to implement on a roadside , but it has some major drawbacks:

 - It is assumed that the atmospheric disturbance of visibility is isotropic (which is not necessarily the case )

 - It depends on the distance between the transmitter and the receiver ( it then requires a model of the atmospheric disturbance to deduce the attenuation on a few hundred meters - generally because the measurement is made over a short distance ) ... and if the disturbance of visibility is localized  (like a fog ), it is not certain that the sensors are present precisely at the location of the disturbance ... or you should deploy sensors throughout the infrastructure.

 - It does not look the markings under the same angle as the driver

 - It ignores the characteristics of human vision that does not need the same image quality for " good view " , depending on the size of the objects that compose the scene, according to the ambient brightness, etc.

 - It is not take int account systems used to restore the visibility while driving ( wipers , lighting, ... ) and the interaction with the road infrastructure.

For all these reasons , it is interesting to have a "true " measurement of visibility, ie a measure that react exactly like the human visual perception system .

The most advanced works in this area come from the military sector where stealth considerations are very important. Early on , the military wanted to have theoretical models for predicting the probability of detecting a stationary soldier or a tank in its wooded surroundings , for example, depending on camouflage used.

The selected models describe the human vision on several fronts:

 - Sensitivity of the eye to the wavelength ( color )
 - Sensitivity of the eye to the contrast
 - Sensitivity of the eye to the object size
 - Influence of light level on visual performance
 - Etc ...

The company NEXYAD aggregated all of this work and has integrated them into a single tool for measuring visibility : VisiNex .

VisiNex (http://www.visinex.net/) is de facto a standard because it is the only product in the world that provides a visibility measurement system used by several industries -with 100% correlation with human eye :

 - Automotive : vehicle has organs to restore visibility ( lighting, wiping the windshieldn washing, demisting , defrosting , ... ) . By measuring changes in visibility during the use of these organs under controlled perturbation (eg a machine calibrated artificial rain as RainNex ) , the effectiveness of these bodies is measured, the level of visibility they can restore and how quickly they restore . VisiNex is used by automotive manufacturers and suppliers .

 - Road infrastructure : road infrastructure implement labeling techniques and road lighting to enhance the visibility of the road. It is advantageous to have a visibility measurement to characterize the effectiveness of these techniques, any time and for all levels of wear ... VisiNex is in this context used , among other things, by road markings manufacturing companies.

VisiNex The tool also uses the results of military work called " Johnson's criteria " that predict , for a given level of disturbance (eg rain on the windshield, regularly swept by the wipers ) and at every moment , the driver's ability to detect objects , to recognize , to identify them.

For more information : http://nexyad.net/Automotive-Transportation/?page_id=159