| With the development of automobile industry and advancement ofelectron technology , technology content of electron technology inautomobile becomes more and more high. But compare with internationalpredetermine level, the whole level of electron technology in our country isstill unenlightened. The capability of study, development production ofautomobile electron equipment is weak. The task that to raise automobiletechnology content ,raise security and easement of automobile ,raiseelectronic and informationized level of auto and to develop auto navigationsystem of our own country has no time to delay.The function of auto navigation system in elementary level is navigation,navigation is based on exact orientation. Vehicle navigation may usemultifarious vehicle orientation mode, including GPS, INS and DR and so on.Because orientation transducer has measure error, the vehicle situationachieved by auto navigation system also has certain error. So GIS that basedon vector map has become important component of automobilenavigation .Making use of vector map information ,to amalgamate variouskinds of sense organ orientation data and produce auto position estimate,namely map matching arithmetic.The theory of map matching orientation arithmetic :to compare the autoposition or run contrail that achieved by other ways with electronic maproadway data of vehicle carry and show Real-time location of vehicle. Mapmatching process can be separated to two dependent process:one is to lookfor present running roadway of vehicle, the other is to project present positionpoint to the running roadway of vehicle.Before beginning matching arithmetic, we should filtrate candidateroadway and achieve valid information about roadway(including geometricshape ,width of roadway ,and so on).Making use of GPS take-over machine,to provide orientation information for vehicle and select the roadway thatdistant from original position point within 100m as calculation roadway, it iscertain that the reliability that vehicle situate these roadways. This articleselects measure value of vehicle position as the center of a circle and theroadway that radius is within 100m as candidate roadway.To assure the real time of matching arithmetic , we should not directlycalculate the distance that the orientation point distant from each roadway toconfirm the roadway is candidate roadway or not ,but to adopt a kind ofapproximate calculation way, namely so-called floating windowtechnology .the basic theory is :select those roadway that within certain rangeas initial candidate roadway, and then make regular choice to these originalcandidate roadwayFor each candidate roadway , a matching measurement value is definedto reflect the probability that the candidate roadway can become matchingroadway. The first value is space distance between two roadways ,the moresmall, the two roads is more similar. The second value is separation angle oftwo roads ,the more small , the two roads is more similar.Matching degree is defined as a function that correlates with projectiondistance d and direction separation angle.f(d,θ)= wd d + wθθabove formula shows, matching degree of each roadway is determined byprojection distance d and direction separation angleθ,the more small thereflection distance and the direction separation angle is, the bigger thematching degree of candidate road is , and the bigger the possibility that theroad becomes candidate road is.vice versa.In the formula, f(d,θ) is matchingdegree measurement function of candidate roadway, wd and w θ isrespectively the proportion that projection distance d and direction separationangleθ in matching degree measurement function.. Besides, the functionmatches relation formula :wd + wθ = 1idiographic value changes with the location of measure point in the road netand automatically changes in the muster{[0.4,0.6], [0.5,0.5]}.if the programcan confirm that present orientation point situates around road cross, thenincreases confidence in angle information, proportion values will be such: wd= 0.4,wθ = 0.6. in other situations ,the two will be considered as comparablyimportant ,the proportion value will be : wd = wθ = 0.5.d andθ is designedas nether expression:d=1/ di θ=1/θiIn the formula: di and θi is respectively projection distance anddirection separation angle between measure point and the number icandidate roadway .commonly, di andθi is not equal to 0,if is equal to 0, wecan make them become a very small number;for fi ,using nether estimationprinciple to make farther match and finally get matching result. Tracing backto continuous six historical measure points from present measure point,respectively gets projection distance that corresponds to the number icandidate roadway, getting the average value as the projection distance ofpresent measure point di..Tracing back to continuous six historical measurepoints from present measure point, respectively gets direction separationangle that corresponds to the number i candidate roadway, getting theaverage value as the direction separation angle of present measure pointθi..If roadway only has matching measurement value ,it can not integrallyexpress match degree. Because of complexity of roadway net , multifariousprinciples have to be considered. If two roads is too similar, then matchingactivity will stop.Each candidate roadway has corresponding matching measurementvalue. the candidate road that matching value is maximal becomes matchingroad, using projection method, project from GPS point to match road, foot ofa perpendicular is match point .If foot of a perpendicular is out of matchingroad , other ways will be adopted.Finally, under the environment of VC with MAPX , reading factual map,simulating GPS orientation point. Matching effect picture and analysis resultare achieved through map matching arithmetic.According to practical data, matching rate max achieves about 80percent .in the future, every step will be perfected to increase matching rate . |
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