Method of automatically determining speed limits on a road and associated system

0001The present invention relates to a method for determining the speed limits on a road taken by a motor vehicle, and a system for implementing this method. The main object of the invention is to propose a solution for automatically determining, in all circumstances, information relating to a speed limit which applies to a road taken, or about to be taken, by a motor vehicle. The information thus determined can then be used in different applications fitted to the vehicle in question. In particular, but not limited to, the information relating to a speed limit is used in the context of a driving assistance system by indicating to the driver explicitly what is the maximum authorized speed, for example when this the latter is exceeding this maximum speed.

0002The field of the invention is, in general, that of driving assistance, which provides a set of assistance systems for the driver, essentially intended to improve traffic safety conditions. We have recently developed, for example:<ul id="ul0001" list-style="dash" compact="compact"><li>so-called night vision systems to help the driver to detect obstacles that are difficult to perceive in night traffic conditions in advance;</li><li>early turn detection systems, to warn the driver as soon as possible of the upcoming presence of a turn;</li></ul>

0003In the context of driving assistance systems, we are also now seeking to offer the driver a speed limit warning system: such a system must make it possible to automatically detect a speed limit in force on a route taken, or on a road that is about to be taken, by a vehicle. Indeed, actions concerning excessive speeds are necessary to reduce the number of accidents and the severity of their consequences. Many drivers do not respect the statutory speeds: 40% of the drivers do not respect them on motorways, 60% on national and departmental roads and 25% exceed the regulatory speed in town by more than 10 km / h.

0004Two different types of solutions have been proposed to date to automatically determine a speed limit in effect on a road.

0005The first type of solution lies in the use of information from a navigation system. These navigation systems are increasingly fitted to vehicles for guiding the driver from a starting point (corresponding to the current position of his vehicle) to a point of arrival (selected by the driver). They combine cartographic information with vehicle position information, given by a GPS system, and often allow to know in advance the characteristics of the road. In addition, information associated with the characteristics of the road resides in the speed limit associated with this road. Other information, such as indication of the presence of intersections, highway exits, etc. is also available through such a system. Furthermore, if the driver selects a so-called guidance option to go from point A to point B, the path that the vehicle is likely to take is known in advance, and knowledge of the speed limits that will be in force on this route can be widely anticipated, up to ten kilometers in advance.

0006However, a number of inherent flaws in this system limit its effectiveness:<ul id="ul0002" list-style="dash" compact="compact"><li>the current cartography is still very imprecise. It very often happens that at a given place, information is missing. Indeed, there are whole areas of the world that are not covered by the mapping databases;</li><li>it also happens that the information provided by the navigation system is aberrant. For example, if the driver has planned to go to a place B which he has memorized in his navigation system and if, finally, during the journey, he is led to go to a place C without following the indications given by the navigation system, then the information given by the navigation system is incoherent, even contradictory, in relation to the characteristics of the trajectory actually followed by the vehicle;</li><li>changes in the configuration of the road due to occasional events, for example the carrying out of works, entail a modification of the speed limits in force on the portion of road considered; these modifications are then not known to the navigation system;</li><li>loss of GPS coverage is also possible, for example when going through a long tunnel.</li></ul>

0007A second type of solution for automatically determining a speed limit in force is the use of information from an image processing system. Such a system involves at least one camera and image processing software applications. The camera takes an image of the road scene, and image processing makes it possible to detect the speed limit signs and to recognize the characters written in these signs. This system displays the speed limit of the detected sign, with a certain confidence index. A system known as "Speed ​​Limit Support" is such a driving assistance system which informs the driver of the speed limit of the road taken to help him not to exceed said speed; it is intended to complement the manual speed limiter, already sold on certain vehicles.

0008However, this type of system presents a certain number of malfunctions in certain traffic conditions, in particular in the presence of motorway exits, at night or when the vehicle is traveling at high speed, as well as in cases where there are limitations of specific speeds for different vehicle categories. In such cases, the proper functioning of the character recognition algorithms on speed limit signs is not guaranteed. In addition, in situations of intersections, bifurcations or the presence of several traffic lanes, such systems are unable to detect the speed limit signs actually in force, different signs intended for the different lanes present being identified, without being able to effectively carry out the association between each panel and the corresponding route. Added to this is the fact that the range of such systems is only a few tens of meters; consequently, in the presence of obstacles in front of the vehicle or in the presence of several consecutive turns, speed limit signs are not detected by such systems.

0009The document <patcit id="pcit0001" dnum="DE19938266"><text>DE19938266</text></patcit> describes a speed limit detection method and system aimed at supplementing the results from optical vision with cartographic data.

0010None of the existing systems is therefore entirely satisfactory for the automatic determination of the speed limits in force on a road taken by a motor vehicle.

0011The object of the invention proposes a solution to the problems which have just been exposed. In general, to determine a desired speed limit in force on a given road, the invention proposes the combination of the two previously mentioned systems, namely the navigation system and the system associating camera and image processing applications, in proposing to carry out a fusion of these two sources of information. A system for determining the current speed limit is thus obtained which is much more reliable than with the systems of the prior art. This in particular avoids the risk of confusion due to incorrect information or misinterpretation of this information. A particular example of implementation of the invention thus proposes in particular the advantage of being able to propose a degraded mode of operation, useful in the event of failure of one of the two systems, based on the other system, without failure; such a degraded mode is not available in the state of the art.

0012The invention therefore makes it possible to obtain information relating to a speed limit in force on a road taken, or about to be taken, by a motor vehicle, said information resulting from the fusion of the information provided by the two systems. separate. Advantageously, a confidence index is assigned at least to the navigation system, the confidence index then intervening in the fusion of the information. Advantageously, the information relating to the speed limits provided by at least one of the two systems is extrapolated in order to envisage other speed limits as being likely to be in force on the route considered; each of these other speed limits is then associated with a weighting coefficient, known as the belief mass, involved in the fusion of all the information then available relating to the speed likely to be effectively in force, fusion of information ensuring the final determination of the speed limit sought.

0013The invention therefore essentially relates to a method for automatically determining a speed limit in force on a road taken, or about to be taken, by a motor vehicle, comprising the following different steps:<ul id="ul0003" list-style="dash" compact="compact"><li>establish, by means of a first system, said navigation system involving in particular a data receiver of a geographic positioning system and cartographic data, a probable speed limit associated with a first confidence index;</li><li>constitute a first set of information comprising at least the probable speed limit, and the first confidence index;</li><li>establish, by means of a second system, called an image processing system, involving in particular a camera and image processing applications capable of identifying and interpreting speed limit signs placed in the vicinity of the road, a probable speed limit associated with a second confidence index;</li><li>constitute a second set of information comprising at least the probable speed limit, and the second confidence index;</li><li>determine the speed limit in force on the route considered, from the first set of information and the second set of information and taking into account the first confidence index and the second confidence index.</li></ul>

0014In addition to the main characteristics which have just been mentioned in the preceding paragraph, the method according to the invention may have one or more additional characteristics among the following:<ul id="ul0004" list-style="dash" compact="compact"><li>the first set of information is supplemented by a set of likely additional speed limits;</li><li>the probable speed limit and each additional probable speed limit are associated with a weighting coefficient, called belief mass, determined on the basis of at least one of the following parameters:</li><li>the first confidence index, and</li><li>an index of consistency between the likely speed limit and the characteristics of the route provided by the navigation system;</li><li>the additional likely speed limits are the two regulatory speed limits directly framing the likely speed limit,</li><li>the second set of information is supplemented by a set of additional probable speed limits;</li><li>the probable speed limit and each additional probable speed limit are associated with a weighting coefficient, called belief mass, determined on the basis of at least one of the following parameters:<ul id="ul0005" list-style="dash" compact="compact"><li>the second confidence index;</li><li>an indication of possible confusion between the figures constituting the probable speed limit established and other figures;</li></ul></li><li>the additional probable speed limits are the statutory speed limits for which an index of possible confusion between the figures constituting the established probable speed limit and the figures of the additional probable speed limit is greater than a threshold value called the critical threshold value;</li><li>the speed limit in force determined is associated with a third confidence index, developed at least from the first confidence index and the second confidence index;</li><li>the method comprises the additional step of exploiting the speed limit in force determined only if the third confidence index is greater than a third threshold value;</li><li>the first confidence index is developed from one or more parameters from a first set of parameters consisting of the following parameters:<ul id="ul0006" list-style="dash" compact="compact"><li>accuracy of the geographic positioning system,</li><li>level of information on the road,</li><li>road functional class,</li><li>type of road,</li><li>vehicle environment,</li><li>selection of a guidance mode by the driver and level of compliance between a planned route and information provided by on-board sensors of the vehicle,</li><li>accuracy of mapping digitization,</li><li>date of update of the cartography, and</li><li>road traffic conditions (density of vehicles on the road taken and fluidity); this status can be obtained for example by means of real-time traffic information.</li></ul></li><li>the first confidence index is produced by carrying out a weighted average of values ​​assigned to the following parameters, said parameters being associated with weighting coefficients resulting from a learning phase:<ul id="ul0007" list-style="dash" compact="compact"><li>accuracy of the geographic positioning system,</li><li>level of information on the road,</li><li>road functional class,</li><li>type of road,</li><li>vehicle environment, and</li><li>selection of a guidance mode by the driver and level of compliance between a planned route and information provided by on-board sensors of the vehicle;</li></ul></li><li>the second confidence index is developed from one or more parameters, from a second set of parameters relating to one or more images obtained by the camera, among the following:<ul id="ul0008" list-style="dash" compact="compact"><li>consistency index for identifying speed limit signs from one image to another,</li><li>texture measurement of the image considered,</li><li>shadow factor on the image considered,</li><li>vertical gradient of light decay, and</li><li>index of symmetry of the image considered;</li></ul></li><li>the second confidence index is produced by carrying out a weighted average of values ​​assigned to the set of parameters of the second set of parameters, these parameters being associated with weighting coefficients resulting from a learning phase;</li><li>the method includes the additional steps of:<ul id="ul0009" list-style="dash" compact="compact"><li>compare the first confidence index to a first threshold value and the second confidence index to a second threshold value,</li><li>in determining the speed limit in force, consider only the set (s) of information, among the first set of information and the second set of information, whose confidence index is higher than the threshold value to which it is compared;</li></ul></li><li>the step for determining the speed limit in force involves a Dempster - Shafer equation.</li></ul>

0015The present invention also relates to a system for automatically determining a speed limit in force on a road taken, or about to be taken, by a motor vehicle, implementing the method according to the invention with its main characteristics and possibly one or more additional characteristics mentioned, <b>characterized in that</b>'it comprises :<ul id="ul0010" list-style="dash" compact="compact"><li>a first system, called the navigation system, involving in particular a geographic positioning system and cartographic data to establish a probable speed limit associated with a first confidence index and to constitute a first set of information comprising at least the limitation of likely speed, and the first confidence index;</li><li>a second system, called an image processing system, notably involving a camera and image processing applications, capable of identifying and interpreting speed limit signs placed in the vicinity of the road, to establish a speed limit likely associated with a second confidence index and to constitute a second set of information comprising at least the probable speed limit and the second confidence index;</li><li>information processing means for determining, from the first set of information and from the second set of information, the speed limit in force on the route in question.</li></ul>

0016In addition to the main characteristics which have just been mentioned in the preceding paragraph, the system according to the invention may have the following additional characteristic:<ul id="ul0011" list-style="dash" compact="compact"><li>the system includes means for restoring the speed limit in force determined.</li></ul>

0017Finally, the present invention relates to any motor vehicle equipped with the system for automatically determining a speed limit in force on a road taken, or about to be taken, by the motor vehicle in question, with its main characteristics and possibly its additional characteristic.

0018The geographic positioning system can for example be a system comprising a network of satellites allowing the geodetic positioning of receivers with which they communicate, such as for example the GPS network. The data receiver is in this case a GPS receiver or antenna.

0019The invention and its various applications will be better understood on reading the description which follows and on examining the figures which accompany it.

0020These are presented for information only and in no way limit the invention. The figures show:<ul id="ul0012" list-style="dash" compact="compact"><li>to the <figref idref="f0001">figure 1</figref>, a representation of the principle of the invention, illustrating the combination of the systems on board the vehicle;</li><li>to the <figref idref="f0001">figure 2</figref>, a schematic representation of a first example of implementation of the method according to the invention;</li><li>to the <figref idref="f0002">figure 3</figref>, a schematic representation of a second example of implementation of the method according to the invention.</li></ul>

0021The various elements appearing in several figures will have kept, unless otherwise specified, the same reference.

0022On the <figref idref="f0001">figure 1</figref>, there is shown, schematically, the various elements involved in an example of implementation of the method according to the invention within a motor vehicle, making it possible to obtain a speed limit 153 in force on a route taken, or about to be borrowed, by a motor vehicle. The vehicle under consideration has a first system 101, called the navigation system, allowing in particular an estimate of the authorized speed at a given location, and in particular involving mapping data 111 and a GPS antenna 112 placed on the vehicle and able to receive precise location information. In the example considered, the first system 101 also involves on-board sensors 113 of the vehicle in question, of the speed sensor, gyroscope type, etc. These different sensors are capable of delivering different information making it possible in particular to check the consistency between the route actually followed by the vehicle, and the route provided by the navigation system.

0023The navigation system 101 makes it possible to obtain a first set of information 151 on the speed limit sought at a given location, in particular near the instantaneous position of the vehicle. The first set of information 151 includes at least one probable speed limit corresponding to the speed limit established by the navigation system 101, associated with a first confidence index IC1.

0024The first confidence index can be calculated for example by adopting the following equation: <maths id="math0001"><math display="block"><mi>IC</mi><mo>⁢</mo><mn>1</mn><mo>=</mo><mfenced><msub><mi mathvariant="normal">α</mi><mn>1</mn></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mn>1</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>2</mn></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mn>2</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>3</mn></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mn>3</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>4</mn></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mn>4</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>5</mn></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mn>5</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>6</mn></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mn>6</mn></msub></mfenced><mo>/</mo><mfenced><msub><mi mathvariant="normal">α</mi><mn>1</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>2</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>3</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>4</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>5</mn></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mn>6</mn></msub></mfenced><mo>,</mo></math><img file="EP2017807B1_D0001.tif" /></maths>with:<ul id="ul0013" list-style="none" compact="compact"><li>VS₁ : GPS positioning confidence index;</li><li>VS₂: Level of information on the route (given by the ADAS classification);</li><li>VS₃ : Road functional class: FC1 or FC2;</li><li>VS₄ : Type of road;</li><li>VS₅ : Environment (City, Highway exit, Intersection, ...);</li><li>VS₆ : Guidance mode selected or not by the driver;</li><li>and where α₁, α₂, α₃, α₄, α₅ and α₆ are weighting coefficients, called intermediate confidence indices, assigned to the different criteria according to the reliability of their information.</li></ul>

0025Thus different weights can be attributed to these criteria. For example, the road type can be a discriminating criterion on speed limits since the basic speed limits are already defined by road type. Consequently, this criterion can have a greater weight than for guidance mode, and therefore have a coefficient of 3 for the road type and a coefficient 1 for guidance mode.

0026Table 1 below gives an example of assigning values ​​to the different criteria involved. The acronym "SL" in Table 1 below indicates the speed limit considered.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1.</title><tgroup cols="16"><colspec colnum="1" colname="col1" colwidth="68mm" /><colspec colnum="2" colname="col2" colwidth="11mm" colsep="0" /><colspec colnum="3" colname="col3" colwidth="11mm" /><colspec colnum="4" colname="col4" colwidth="11mm" colsep="0" /><colspec colnum="5" colname="col5" colwidth="11mm" /><colspec colnum="6" colname="col6" colwidth="11mm" /><colspec colnum="7" colname="col7" colwidth="11mm" /><colspec colnum="8" colname="col8" colwidth="11mm" /><colspec colnum="9" colname="col9" colwidth="11mm" colsep="0" /><colspec colnum="10" colname="col10" colwidth="11mm" /><colspec colnum="11" colname="col11" colwidth="13mm" colsep="0" /><colspec colnum="12" colname="col12" colwidth="13mm" /><colspec colnum="13" colname="col13" colwidth="13mm" /><colspec colnum="14" colname="col14" colwidth="13mm" /><colspec colnum="15" colname="col15" colwidth="13mm" /><colspec colnum="16" colname="col16" colwidth="13mm" /><thead><row rowsep="0"><entry rowsep="1" align="center" valign="middle" /><entry namest="col2" nameend="col16" rowsep="1" align="center" valign="middle"><b>Speed ​​limits</b></entry></row><row rowsep="0"><entry morerows="1" rowsep="1" align="center" valign="middle"><b>Criteria</b></entry><entry align="center" valign="middle"><b>SL1</b></entry><entry align="center" valign="middle"><b>SL2</b></entry><entry align="center" valign="middle"><b>SL3</b></entry><entry align="center" valign="middle"><b>SL4</b></entry><entry align="center" valign="middle"><b>SL5</b></entry><entry align="center" valign="middle"><b>SL6</b></entry><entry align="center" valign="middle"><b>SL7</b></entry><entry align="center" valign="middle"><b>SL8</b></entry><entry align="center" valign="middle"><b>SL9</b></entry><entry align="center" valign="middle"><b>SL10</b></entry><entry align="center" valign="middle"><b>SL11</b></entry><entry align="center" valign="middle"><b>SL12</b></entry><entry align="center" valign="middle"><b>SL13</b></entry><entry align="center" valign="middle"><b>SL14</b></entry><entry align="center" valign="middle"><b>SL15</b></entry></row><row><entry align="center" valign="middle"><b>5</b></entry><entry align="center" valign="middle"><b>10</b></entry><entry align="center" valign="middle"><b>20</b></entry><entry align="center" valign="middle"><b>30</b></entry><entry align="center" valign="middle"><b>45</b></entry><entry align="center" valign="middle"><b>50</b></entry><entry align="center" valign="middle"><b>60</b></entry><entry align="center" valign="middle"><b>70</b></entry><entry align="center" valign="middle"><b>80</b></entry><entry align="center" valign="middle"><b>90</b></entry><entry align="center" valign="middle"><b>100</b></entry><entry align="center" valign="middle"><b>110</b></entry><entry align="center" valign="middle"><b>120</b></entry><entry align="center" valign="middle"><b>130</b></entry><entry align="center" valign="middle"><b>999</b></entry></row></thead><tbody><row rowsep="0"><entry align="center" valign="middle"><b>C1:</b> GPS MLCP Validated (> = 0.6)</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry></row><row rowsep="0"><entry align="center" valign="middle"><b>C1:</b> GPS MLCP between (0.3 <= MLCP <0.6)</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry></row><row><entry align="center" valign="middle"><b>C1:</b> GPS MLCP Not validated (<0.3)</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry></row><row rowsep="0"><entry align="center" valign="middle"><b>C2</b> : ADAS attribute Validated</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry></row><row><entry align="center" valign="middle"><b>C2</b> : ADAS attribute not validated</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry></row><row rowsep="0"><entry align="center" valign="middle"><b>C3</b> : Functional class of the route (FC1, FC2) Validated</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry></row><row><entry align="center" valign="middle"><b>C3</b> : Functional class of the route (FC1, FC2) Not Validated Not Validated</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry></row><row rowsep="0"><entry align="center" valign="middle"><b>C4:</b> Road type: European</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry></row><row rowsep="0"><entry align="center" valign="middle"><b>C4:</b> Type of road: Highway</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry></row><row rowsep="0"><entry align="center" valign="middle"><b>C4</b> : Route type: National</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry></row><row rowsep="0"><entry align="center" valign="middle"><b>C4:</b> Route type: Departmental</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.3</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry></row><row><entry align="center" valign="middle"><b>C4:</b> Type of road: Municipal</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry></row><row><entry align="center" valign="middle"><b>C5:</b> Driving situation: City</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry></row><row><entry align="center" valign="middle"><b>C5:</b> Driving situation: Out of town</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry></row><row><entry align="center" valign="middle"><b>C5:</b> Driving situation: Intersection</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0.4</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry></row><row><entry align="center" valign="middle"><b>C5:</b> Driving situation: No Intersection</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.7</entry></row><row><entry align="center" valign="middle"><b>C5:</b> Driving situation: Motorway exit</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.5</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.2</entry></row><row><entry align="center" valign="middle"><b>C5:</b> Driving situation: No motorway exit</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0</entry><entry align="center" valign="middle">0.1</entry><entry align="center" valign="middle">0.2</entry><entry align="center" valign="middle">0.7</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.9</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry></row><row rowsep="0"><entry align="center" valign="middle"><b>C6:</b> Guidance mode enabled</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry><entry align="center" valign="middle">0.8</entry></row><row><entry align="center" valign="middle"><b>C6</b> : Guidance Mode Not Validated</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry><entry align="center" valign="middle">0.6</entry></row></tbody></tgroup></table></tables>

0027In other examples of determining the first confidence index, other parameters can be taken into account, in particular the accuracy of the digitization of the cartography, the date of updating of this cartography, the state of road traffic. ..

0028The state of road traffic (vehicle density on the road taken and fluidity) can be obtained for example through traffic information in real time. Traffic information in real time, also called "RDS / TMC" (for "Radio System Data / Traffic Message Channel" in English), allows the navigation system to calculate routes taking into account information delivered in real time by service operators, who transmit information relating to the state of road traffic. This transmission to the user is carried out by radio waves. Information related to road traffic can also be transmitted by mobile telephone networks and thus be received on a reception terminal associated with the navigation system. It is also possible to obtain information via a device for accessing a global or global computer network (such as the Internet), connected or integrated into the navigation system.

0029The vehicle also has a second system 102, called an image processing system, which is also capable of estimating the speed limit on a road taken, or about to be taken, by the vehicle. The system 102 notably involves a camera 121 capturing images of the road about to be taken by the vehicle, and a set of image processing applications 122 whose algorithms in particular make it possible to identify limitation signs speed signs arranged in the vicinity of the road, that is to say visible from the vehicle, and to interpret the figures represented on these panels to deduce the speed in force on the road in question. The algorithms used can, for example, involve shape recognition applications to recognize the round shapes of speed limit signs, associated with color discrimination making it possible to retain only the signs having a red outline, and recognition algorithms. character to identify the figures represented, individually or as a whole.

0030The image processing system 102 makes it possible to obtain a second set of information 152 comprising at least one probable speed limitation at the location considered. In certain embodiments of the invention, the probable speed limitation is associated with a second confidence index IC2.

0031An example of calculation of the second confidence index can correspond, for a captured image, to the following equation: <maths id="math0002"><math display="block"><mi>IC</mi><mo>⁢</mo><mn>2</mn><mo>=</mo><mfenced><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">e</mi></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mi mathvariant="normal">e</mi></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">o</mi></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mi mathvariant="normal">o</mi></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">g</mi></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mi mathvariant="normal">g</mi></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">s</mi></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mi mathvariant="normal">s</mi></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">vs</mi></msub><mo>×</mo><msub><mi mathvariant="normal">VS</mi><mi mathvariant="normal">vs</mi></msub></mfenced><mo>/</mo><mfenced><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">e</mi></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">o</mi></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">g</mi></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">s</mi></msub><mo>+</mo><msub><mi mathvariant="normal">α</mi><mi mathvariant="normal">vs</mi></msub></mfenced><mo>,</mo></math><img file="EP2017807B1_D0002.tif" /></maths>where the different criteria C_i speaker have the following attributions:<ul id="ul0014" list-style="none" compact="compact"><li>VS_e : Entropy (texture measurement of the image considered);</li><li>VS_o : Shadow factor on the image considered;</li><li>VS_g : Vertical gradient of light decay on the image considered;</li><li>VS_s : Symmetry index of the image considered;</li><li>VS_vs: Consistency index for identifying speed limit signs from one image to another: the greater the number of consecutive images leading to the establishment of the same speed limit value, the higher the value of this index is important;</li><li>and where α_e, α_o, α_g, α_s and α_vs are weighting coefficients assigned to the different criteria Ci according to the reliability of the information and the relevance of the associated criterion.</li></ul>

0032The information sets 151 and 152 are then merged into a data fusion system 154 to determine the desired speed limit 153. For this purpose, information processing means intervene, in particular with a microprocessor and specific software applications. , implemented in the data fusion system 154. The speed limit sought necessarily corresponds to a regulatory speed limit, that is to say a speed limit that can be encountered on the roads. The regulatory speed limits therefore constitute a closed set, known as the discernment framework D, which also represents all the speed limits which may be obtained as a result of output from one of the two systems. This framework is defined, for example, as follows:<ul id="ul0015" list-style="none" compact="compact"><li>D = {5,10,20,30,45,50,60,70,80,90,100,110,120,130,999}. The value 999 represents the case where there is no or no more speed limit.</li></ul>

0033A third confidence index IC3 is advantageously associated with the desired speed limit 153. It makes it possible to present a level of reliability of the information obtained at the output of the fusion system 154. It is then used freely according to the examples of implementation: for example, if the third confidence index is less than a threshold value, provision is made to choose the use of a degraded operating mode in which no information relating to a the current speed limit is not provided to the driver. The speed limitation results provided by the system according to the invention are therefore not exploited. In an exemplary implementation, the third confidence index is equal to the average of the first confidence index and the second confidence index.

0034In a particular example of implementation of the invention, if at least one of the two confidence indices is too low, for example less than a previously determined threshold, then only the system providing the best confidence index is considered and we considers the speed limit provided by this system as the desired speed limit.

0035A first detailed implementation of the method according to the invention is illustrated with reference to the <figref idref="f0001">figure 2</figref> : <ul id="ul0016" list-style="none" compact="compact"><li>In this first embodiment, the fusion system 154 only involves the probable speed limitation, here 80 km / h, and the probable speed limitation, here 90 km / h, established respectively by the first system 101 and by the second system 102, associated with their respective confidence index, 50% for IC1 and 64% for IC2.</li></ul>

0036Different decision calculations are possible: one can either directly determine the speed limit associated with the best confidence index as the desired speed limit, or carry out a weighted average of the two likely and probable speed limits, the weighting coefficients corresponding to respective confidence indices. An intermediate speed limit value is then obtained; the speed limit sought is then the regulatory speed limit closest to the intermediate speed limit, 90 km / h in the example illustrated.

0037In a second embodiment of the method according to the invention, illustrated in <figref idref="f0002">figure 3</figref>, a step 300, relative to the first embodiment, is added in the course of the process.

0038The added step 300 consists, for each of the two systems, in enriching the information sets 151 and 152 with other speed limits, respectively likely or probable, complementary, from the speed limit obtained at the output of each of the two on-board systems.

0039Thus, for example, for the navigation system 101, the probable speed limit initially determined is supplemented by the two regulatory speed limits which directly frame the speed limit initially determined. In the example illustrated, if the speed limit 80 km / h has been determined to be probable, the first set of information 151 is then supplemented by the speed limits 70 km / h and 90 km / h. Other examples of implementation take into account the presence of particular characteristics of the route taken, by considering for example the presence or absence of a motorway exit (in order to avoid for example, that the method of determination does not confuse the speed limitation of the deceleration band, detected by the image processing system, with that of the taxiway, on which the vehicle is moving), the possible presence of intersections, particular geographic characteristics (steep drop, etc.). Table 2 below gives an example indicating by which additional probable speed limits, also called focal elements, the first set of information 151 is completed for each probable speed limit which has been determined by the first system 101.<tables id="tabl0002" num="0002"><table frame="all"><title>Table 2.</title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="55mm" /><colspec colnum="2" colname="col2" colwidth="55mm" /><colspec colnum="3" colname="col3" colwidth="56mm" /><thead><row><entry valign="top"><b>Likely speed limits</b></entry><entry valign="top"><b>Number of likely additional speed limits</b></entry><entry valign="top"><b>Additional likely speed limits (focal elements)</b></entry></row></thead><tbody><row><entry>5</entry><entry>2</entry><entry>10, 999</entry></row><row><entry>10</entry><entry>3</entry><entry>5, 20, 999</entry></row><row><entry>20</entry><entry>3</entry><entry>10, 30, 999</entry></row><row><entry>30</entry><entry>3</entry><entry>20, 45, 999</entry></row><row><entry>45</entry><entry>3</entry><entry>30, 50, 999</entry></row><row><entry>50</entry><entry>6</entry><entry>45, 60, 90, 110, 130, 999</entry></row><row><entry>60</entry><entry>3</entry><entry>50, 70, 999</entry></row><row><entry>70</entry><entry>3</entry><entry>60, 80, 999</entry></row><row><entry>80</entry><entry>3</entry><entry>70, 90, 999</entry></row><row><entry>90</entry><entry>4</entry><entry>50, 80, 100, 999</entry></row><row><entry>100</entry><entry>3</entry><entry>90, 110, 999</entry></row><row><entry>110</entry><entry>6</entry><entry>50, 90, 100, 120, 130, 999</entry></row><row><entry>120</entry><entry>3</entry><entry>110, 130, 999</entry></row><row><entry>130</entry><entry>5</entry><entry>50, 90, 110, 120, 999</entry></row><row><entry>999</entry><entry>0</entry><entry>x</entry></row></tbody></tgroup></table></tables>

0040We then assign to each of the speed limits present in the information set 151 an index, designated as belief mass M, which corresponds, for each of the speed limits considered, to a probability that said speed limit considered is the speed limit sought. The most important belief mass is thus attributed to the probable speed limit given by the navigation system 101, the additional probable speed limits adopting lower belief masses, determined in particular according to the characteristics of the route available by the system. navigation (for example, if the road is identified as a highway, the belief masses of the focal elements will be greater for high speed limit values); the sum of the masses of belief allocated for the first set of information is then 100%.

0041Likewise, for the image-processing system 102, the probable speed limit initially determined is supplemented by regulatory speed limits with which the shape recognition algorithm could have confused at least one of the figures present. on the panel. In the example illustrated, if the speed limit 90 km / h has been determined as probable, the second set of information 152 is then supplemented by the speed limits 60 km / h and 80 km / h, the risk of confusion between 9 and 6 on the one hand, and between 9 and 8 on the other hand, being important. Other examples of implementation take into account the continuity over several successive images of the presence of the information relating to the presence of a given speed limitation to determine the focal elements: if between several images detecting the speed limitation 90 km / h appear one or more isolated images on which appears another speed limit, then this other speed limit will belong to the focal elements.

0042Again, each of the speed limits present in the information set 152 is then assigned an index, designated as belief mass M, which corresponds, for each of the speed limits considered, to a probability that said speed limit considered to be the speed limit sought. The most important belief mass is thus attributed to the probable speed limit given by the image processing system 102, the additional probable speed limits adopting lower belief masses, determined in particular as a function of a confusion index. possible between the figures of the established speed limit and other figures. This possible confusion index is specific to each shape recognition algorithm likely to intervene in the system 102.

0043In general, the determination of the indices of confidence, and / or masses of belief, and their intervention in the fusion of knowledge from the two systems depend on the fusion strategy adopted. Advantageously, in the invention, different methods extracted from the so-called belief theory can be used in the data fusion system 154. In particular, one of the methods known as the "conjunctive combination" of Dempster-Shafer, associated with a so-called Dempster-Shafer equation, gives particularly convincing results. Other methods, based on Bayesian theories, or set theory by fuzzy logic can also be used in the data fusion system 154. These methods appear in a step 301 represented in the<figref idref="f0002">figure 3</figref>.

0044Once the speed limit in force has been established, this can for example be displayed on a screen.

0045It is also possible to provide embodiments in which the speed limit in force established is compared to the speed of the vehicle. According to certain variant embodiments, if the vehicle speed is higher than the speed limit in force established, the system alerts the driver, either by a display on a screen, either acoustically or haptically (vibrator under the seat for example) or by hardening the accelerator pedal. According to an alternative embodiment, the system can automatically reduce the speed of the vehicle (by intervening at the level of cruise control for example), when the speed of the vehicle is greater than the speed in force determined by the method according to the present invention.