IMPROVED VEHICLE NAVIGATION SYSTEM AND METHOD

Abstract: The improved vehicle navigation system and method uses information from a Global Positioning System (GPS) to obtain velocity vectors, which include speed and heading components, for "dead reckoning" the vehicle position from a previous position. If information from the GPS is not available, then the improved vehicle navigation system uses information from an orthogonal axes accelerometer, such as two or three orthogonally positioned accelerometers, to propagate vehicle position. Because the GPS information should almost always be available, the improved vehicle navigation system relies less on its accelerometers, thereby allowing the use of less expensive accelerometers. The improved vehicle navigation system retains the accuracy of the accelerometers by repeatedly calibrating them with the velocity data obtained from the GPS information. The improved vehicle navigation system calibrates the sensors whenever GPS data is available (for example, once a second at relatively high speeds). Furthermore, the improved vehicle navigation system does not need to rely on map matching to calibrate sensors. System flexibility is improved because map matching is oblivious to the hardware, and the system hardware can be updated without affecting map matching or a change in the map database.

Description: IMPROVED VEHICLE NAVIGATION SYSTEM AND METHOD FIELD OF THE I NVENTION The present nncntion relates gcneralK to vehicle navigation stems More particularly, , the present invention relates to an improved vehicle navigation system and method using infoπnation from a Global Positioning System (GPS) to obtain velocity vectors for \ chicle position ^ propagation, and if information from the GPS is not available, then using infoπnation from a multiple axis accelcrometcr to propagate vehicle position BACKGROUND OF TH E I NVENTION Current vehicle navigation systems use GPS, such as an electromagnetic wave positioning s\stcm to determine a vehicle's position Such a GPS system is the Navigation Satellite Timing 10 and Ranging (NAVSTAR) Global Positioning which is a space-based satellite radio navigation stem eloped by the U S Department of Defense (DoD) GPS includes NAVSTAR GPS and its successors. Differential GPS (DGPS), or am other electromagnetic wave positioning sy stems NAVSTAR GPS receivers provide users with continuous three-dimensional position . and time data I ^ NAVSTAR GPS consists of three ma|or segments Space. Control, and User as illustrated in Figure 1 The space segment 2 consists of a nominal constellation of 24 operational satellites which c been placed in 6 orbital planes above the Earth's surface The satellites arc in circular orbits in an orientation which normally provides a GPS user with a minimum of five satellites in view from any point on Earth at any one time The satellites broadcast an RF signal which is 20 modulated a precise ranging signal and a coarse acquisition code ranging signal to provide navigation data This navigation data, which is computed and controlled by the GPS control segment 4. includes the satellite's time, its clock correction and cphcmeiis parameters, almanacs, and health status for all GPS satellites From this information, the user computes the satellite's precise 25 position and clock offset The control segment consists of a Master Control Station and a number of monitor stations at vanous locations around the world Each monitor station tracks all the GPS satellites in view and passes the signal measurement data back to the master control station There, computations arc performed to determine precise satellite cphcmeris and satellite clock errors The master control station generates the upload of user igation data from each satellite This data is subsequently rcbroadcast the satellite as part of its na igation data message The user segment 6 is the collection of all GPS receivers and their application support equipment such as antennas and processors This equipment allows users to receive, decode, and process the information necessary to obtain accurate position vclocitv and timing measurements Tins data is used by the receiver's support equipment for specific application requiicments GPS supports a wide vaπetv of applications including navigation surveying, and time transfer GPS receivers may be used in a standalone mode or integrated ith other systems Currently, land-based navigation systems use vehicle speed sensor, rate g\ ro and a reverse gear hookup to "dead reckon" the vehicle position from a previousK known position Tins metiiod of dead reckoning, however, is susceptible to sensor error, and therefore requires more expensive sensors for accuracy and dependability The systems that use odometers. ros and rev erse gear hookups also lack portability due to the required connections to odometers and the frailtv of gv ros Moreover, these systems are hard to install m different cars due to differing odometer configurations which can have different connections and pulse counts in the transmission Odometer data also vanes with temp, load weight, tire pressure, speed Alternative connections to cnπse control or ABS sensors bring up safety concerns Prior systems use a road network stored in a map database to calculate current vehicle positions These systems send distance and heading information to perform map matching, and map matching calculates the current position based on the road network and the inputted data These stems also use map matching to calibrate sensors Map matching, however, has inherent inaccuracies because map matching must look back in time and match data to a location As such, map matching can only calibrate the sensors when an absolute position is identified on die map. but on a long, straight stretch of highway, sensor calibration using map matching may not occur for a significant period of time Accordingly, there is a need for a potentially portable, vehicle navigation system which is flexible, accurate, efficient and cost-effective in determining a current position from a previous position SUMMARY OF THE INVENTION Tlie improved vehicle navigation system and method uses information from a Global Positioning System (GPS) to obtain velocity vectors, which include speed and heading components, for propagating or "dead reckoning" the vehicle position from a previous position. If information from tlie GPS is not available, then the improved vehicle navigation system uses information from an orthogonal axes accelcromcter. such as two or three orthogonally positioned accelerometers. to propagate vehicle position. Because the GPS information should almost always be available, die improved vehicle navigation system relies less on its accelerometers, thereby allowing tlie use of less expensive accelerometers. Tlie improved vehicle navigation system retains the accuracy of tlie accelerometers by repeatedly calibrating them with tlie velocity data obtained from the GPS information. The improved vehicle navigation system calibrates tlie sensors whenever GPS data is available (for example, once a second at relatively high speeds). Furthemiorc. the improved vehicle navigation system does not need to rely on map matching to calibrate sensors. System flexibility is improved because map matching is oblivious to tlie hardware, and the system hardware can be updated without affecting map matching or a change in the map database. The use of accelerometers in the improved vehicle navigation system eliminates die need for connections to a heading sensor, speed sensors or a reverse gear, making the improved vehicle navigation system cheaper to install and potentially portable. Tlie improved vehicle navigation system has sensors which arc effectively calibrated because tlie scale factors for tlie accelerometers vary in a known manner dependent on temperature but fairly independent of other vehicle characteristics. In contrast, for example, an odometer loses accuracy if tire diameter changes due to falling tire pressure. If a third axis acceleration measurement sensor is added, the improved vehicle navigation system can operate completely independent of vehicle sensors, further increasing flexibility in mounting. The third acccleromcter provides pitch to assist in calibrating tlie other accelerometers and in providing more accurate information by, for example, detecting a banked turn. In accordance with another aspect of the present invention, tlie improved vehicle navigation system interrogates a map database to obtain heading information for the mapped path segment which the vehicle is moving on. The improved vehicle navigation system updates the heading component for the vclocitv w ith the heading infoπnation from the map database Tlie updated v clocitv is used to propagate the vehicle position BRIEF DFSCRIPTION OF THE DRAWI NGS Other aspects and advantages of the present invention may become apparent upon reading ^ the following detailed description and upon reference to the drawings in which FIG 1 is a general illustration of the various segments in the NAVSTAR GPS s stem, FIG 2a shows an improved vehicle navigation system using the improved position determination svstem according to the principles of the present invention, and FIGS 2b show various hardware configurations for systems using aspects of die improved vehicle navigation 0 system according to the principles of the present invention, FIG 3a shows a block/data flow diagram of the improved vehicle navigation svstem of FIG 2a and FIG 3b shows a block data flow diagram of alternative improved vehicle navigation systems according to aspects of the present invention, FIGS 4a and 4b show flow charts for gathering acceleration information and orienting the ^ multiple axis acccleromcter, FIG 5a shows a block diagram of a zero motion detect system according to die principles of tlie present invention, and FIG 5b shows a flow chart for die operation of the zero motion detect svstem of FIG 5a, FIGS 6a and 6b show a general flow chart of the operation of the improved vehicle 0 navigation sv stem of FIG 2a. and FIGS 7a-7e show general diagrams illustrating how the improved vehicle navigation system updates the heading information ith the map heading for position propagations While the invention is susceptible to various modifications and alterative foπns, specifics thereof have been shown way of example in the drawings and will be described in detail It 5 should be understood, however, that the intention is not to limit the invention to the particular embodiment described On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims DETAILED DESCRIPTION OF THE RAWINGS An illustrative embodiment of the unproved vehicle nav igation sv stem according to die principles of die present invention and mcthodoiogv is described below as it might be implemented to determine a current position from a previous position In die interest of clarity, not all features of an actual implementation arc described in this specification It will of course be appreciated that in the development of any such actual implementation (as in anv dev elopment project), numerous implementation-specific decisions must be made to achieve the developers' specific goals and subgoals, such as compliance with system- and business-related constraints, which will vary from one implementation to another Moreover, it will be appreciated that such a development effort might be complex and timc-consuniing, but would nevertheless be a routine undertaking of device engineering for those of ordinary skill having the benefit of this disclosure Aspects of the improved vehicle navigation system can be used in connection vvidi a vaπetv of svstem configurations in which GPS signals arc used for position propagation FIG 2a illustrates, in block diagram form, an cxcmplarv arrangement and use of an improved vehicle navigation s stem 10 for an automobile 12 In this embodiment, the improved vehicle navigation system 10 uses a GPS antenna 14 to receive the GPS signals Tl e antenna 14 is preferably of πght-hand circular polarization, has a ga minimum of -3dBιC above 5 degree elevation, and has a gain maximum of +6 dBiC Patch or Helix antennas matching Uicsc specifications can be used The GPS antenna 14 can be connected to a preamplifier 16 to amplify the GPS signals received by die antenna 14 Tlie prc-amplificr 16 is optional, and the GPS antenna can be directly connected to a GPS receiver 18, which is powered by a power source 20 for the vehicle navigation system 10 The GPS receiver 18 continuously determines geographic position by measuring die ranges (the distance between a satellite with known coordinates m space and die receiver's antenna) of several satellites and computing the geometric intersection of these ranges To determine a range, the receiver 18 measures the time required for the GPS signal to travel from tlie satellite to die receiver antenna. Tlie timing code generated by each satellite is compared to an identical code generated by the receiver 18 The receiver's code is shifted until it matches die satellite's code The resulting time shift is multiplied bv the speed of light to arrive at die apparent range measurement Sincc the resulting range measurement contains propagation dclav s due to auiiospheπc effects, and satellite and receiver clock errors, it is referred to as a "pseudorangc " Changes in each of these pseudoranges over a short period of time are also measured and processed bv tlie receiver 18 These measurements, referred to as "dclta-pscudorangcs," are used to compute velocitv Delta ranges arc in meters per second which arc calculated by the receiver from pseudoranges, and die GPS receiver 1 can track the carrier phase of the GPS signals to smooth out die psuedoranges The velocity and time data is generally computed once a second If one of the position components is known, such as altitude, only three satellite pseudorange measurements are needed for the receiver 16 to determine its velocity and time In tins case, only Uiree satellites need to be tracked GPS accuracy has a statistical distribution which is dependent on two important factors The accuracv which can be expected will vary vvidi the error in the range measurements as well as die geometrv or relative positions of the satellites and the user The Geometric Dilution of Precision (GDOP) indicates how much the geometric relationship of the tracked satellites affects the estimate of the receiver's position, vclocitv . and time There are four other DOP components which indicate how the geometry specifically affects errors in horizontal position (HDOP), vertical position (VDOP), position (PDOP), and time (TDOP) DOPs arc computed based on the spatial relationships of the lines of sight between die satellites and the user Tlie motion of the satellites relative to each other and die user causes the DOPs to vary constantlv For the same range measurement errors, lower DOPs relate to more accurate estimates The errors in the range measurements hich arc used to solve for position mav be magnified by poor gcomctrv The least amount of error results when die lines of sight have the greatest angular separation between them For example, if two lines of sight arc necessary to establish a user position, tlie least amount of error is present when the lines cross at right angles The error m die range measurement is dependent on one of two levels of GPS accuracy to which the user has access PPS is the most accurate, but is reserved for use by the DoD and certain authorized users SPS is less accurate and intended for general public use The SPS signal is intentionally degraded to a certain extent by a process known as Selective Availability (SA) SA is used to limit access to tlie full accuracv of SPS in the interest of U S national security Differential GPS (DGPS) may be used to correct certain bias-like errors in the GPS signals A Reference Station receiver measures - 1 - ranges from all visible satellites to its surveyed position Differences between the measured and estimated ranges arc computed and transmitted via radio or other signals to differential equipped receivers 'hosts in a local area Incorporation of dicse corrections into die range measurements can improve dicir position accuracy λs shown in FIG 2a, the GPS receiver 18 provides GPS measurements to an application unit 22 The application unit 22 consists of application processing circuitrv 24, such as a processor, emorv busses, the application software and related circuitry, and interface hardware 26 In one embodiment of the present invention, the application unit 22 can be incorporated into die GPS receiver 1 The interface hardware 26 integrates die various components of die vehicle navigation svstem 10 ith the application unit 22 In this embodiment, a 2 or 3 axis accelerometer 28 prov ides acceleration signals to the application unit 22 The accelerometer 28 can include recentlv available and low cost, micro-machined accelerometers An odometer 29 provides information which can be used in place of the infoπnatioii derived from the accelerometers, but tlie odometer 29 is optional because it reduces the portability of the system A map database 30 stores map information, such as a road network, and provides map infoπnation to die application unit 22 The map database should have some level of known accuracy, confidence, or defined error In this embodiment, evcrv change in street segment heading is designated as a shape point which has a heading with a fixed measurement error A user interface 32, which includes a display and keyboard, allows interaction between the user and the improved vehicle navigation system 10. FIGS 2b shows alternative configurations which can incorporate aspects of die improved vehicle navigation as would be understood by one of skill in the art FIG 2b contains reference numerals which correspond to the reference numerals of FIG 2a FIG. 2b shows that a system 10 can include a combination of the features, such as those shown in dashed lines For example, tlie impro ed vehicle navigation system could rely upon infomiation provided by the GPS receiver 18, the orthogonal axes accelerometer 28 and the map database 30 to propagate vehicle position In additional embodiments, the improved vehicle navigation system 10 uses the orthogonal axes accelerometer 28, odometer 29 and the map database 30 according to odicr aspects of die present invention. Odier embodiments can include a speed sensor 34, a heading sensor 36, such as a gyro, compass or differential odometer, and a one or two way communication link 38 Other configurations and combinations are possible which incorporate aspects of the present invention as would be understood by one of ordinary skill in the art Moreover, the improved vehicle navigation system can be incorporated in an advanced dπver information s stem which controls and provides information on a vaπety of automobile functions FIG. 3a shows a block and data flow diagram for the improved vehicle navigation system 10 of FIG. 2a The GPS receiver 18 provides position information, velocity information, psuedoranges and delta pseudoranges to tlie sensor integrator 40 The sensor integrator 40 uses the velocity information to determine a current position for the vehicle In this embodiment, if GPS velocity information is not available, the sensor integrator 40 can calculate GPS velocity using the available delta range measurements to determine a current position. GPS velocity information is derived from a set of delta range measurements, and if only a subset of delta range measurements is available, the vehicle navigation system can derive GPS velocity information from the subset of delta range measurements. The vehicle navigation system uses the GPS position information at start-up as a current position and as a check against the current position. If the current position fails the check, then the GPS position can replace the current position In accordance with another aspect of the present invention, FIG. 3b shows the flexibility and accuracy of certain embodiments of the improved vehicle navigation system. The vehicle positioning block 22 receives longitudinal acceleration information, ai mg , a lateral acceleration information, aι,ι, a gyro heading, θ fo an odometer distance, S, map heading, θ m -., and GPS information, including a velocity vector v σ , a position vector χ G and delta range measurements dRi. When GPS velocity information is available and reliable, the vehicle positioning 22 propagates the position vector x(t) with the GPS velocity vector v c as follows- x(t) = x(t - 1) + v G Δ . If the difference between the GPS heading and the map heading is within a threshold, the map heading is used as the heading If the GPS velocity information is not available or unreliable (at low velocities below 1 5 m/s), the vehicle positioning will propagate the position vector x(t) using the available velocity vector with the most meπt as follows x(t) - x(t - J) + vΔ /. In this particular embodiment, the improved vehicle navigation system can obtain the information used to propagate the vehicle position from several sources such as the available GPS delta range measurement(s), the orthogonal axes accelerometer using lateral and longitudinal acceleration information, the odometer distance and GPS heading, a distance calculation and map heading, the GPS speed information and map heading, gyro heading and longitudinal speed and other variations In this embodiment, if the difference between the current heading and map heading is less than a threshold value, then the map heading is used as the heading Vehicle positioning 22 calibrates v a from , when possible The GPS position information is used as an overall check on die current position For example, if | if (t) - χ G 0)\ ^ (18 5 * PDOP) dien x(l) = x (l) Otherwise x(l) - χ ( , (l) In certain embodiments all raw inputs could go into a Kalmann filter arrangement which outputs the velocity vector Tlie sensor 28 for the embodiments of FIGs 3a and 3b, which is a multiple axis accelerometer. provides acceleration mfomiation for at least two orthogonal axes (lateral, longitudinal and/or vertical) Tlie accelerometers 28 produce a voltage measure As shown in FIG 4a for the longitudinal accelerometer, the acccleromcter data is read at step 48, and d e zero offset (set at the factory and constantlv re-checked and reset bv the Zero Motion Detector mentioned below) is subtracted from this measure at step 49 to produce a number of volts displacement from zero Tins number of volts displaced from zero is dien multiplied bv a scale factor (set at die factorv and continuousK rc-ca bratcd bv the GPS) to produce a number of G's of acceleration at step 50 Tins number of G's of acceleration is then multiplied by die number of meters per second squared per G to produce meters per second squared of acceleration at step 5 1 The meters per second squared of acceleration is then multiplied b> the delta time (integrated once) to produce a velocity at step 52 Tins velocity is saved for die next second Tins acceleration information can be used to dctcπninc change in distance information. Δ DIST. and change in turn rate information, Δ θ Initially, the i proved vehicle navigation system requires initial conditions for various items such as accelerometer orientation acccleromcter zero offset, accelerometer scale factor, odometer pulses per mile, and initial vehicle orientation Factory defaults will be used for each of diese items so that no initialization will be necessary Those items ill also need to be maintained, but not necessarily in the absence of all power (i e battery loss, or removal from vehicle) An option will be available to manuallv initialize these items This would allow immediate use of the system, without having to wait for GPS to be acquired for calibrating these items Once GPS has been acquired and is determined to be useable based on its Figure of Merit, GDOP. and Number of Satellite Measurements Used. GPS can be used to calibrate all of die configurable items It will first dctcπninc the accelerometer orientation as described in FIG 4b At power on the assignment of accelerometers to each of the lateral, longitudinal and down axes (if three axis accelerometer is used) arc in the same orientation as the last power down, ich ill be sa ed in some non-volatile storage If three accelerometers are used, one will be measuring die Earth's gravity The acccleromcter measuring one G (Earth's Gravity) w ill be assigned to the Down Axis For the other two axes, as shown in FIG 4b. the following procedure will take place At step 53. the acceleration data is obtained as described in FIG 4b The acceleration measurements from each of the two accelerometers will be compared until dieir difference reaches a pre-defined threshold at step 54 The reason for this is to ensure diat the accelerations are uneven enough that a valid compare against current vehicle conditions can be made idiout ambiguilv As shown in steps 55-61 for this particular embodiment, once this situation occurs and there is acceleration data computed from the GPS data, the acceleration from each of tlie accelerometers will be compared to the lateral and longitudinal accelerations computed from die GPS and the accelerometers with the closest acceleration values for each of Uiose axes will be assigned to those axes Additionally, the initial vehicle orientation is detcmiined because the vehicle heading relative to Tnic North can be computed from the GPS velocities With reference to FIG 3a, the sensor integrator 40 can use die longitudinal and lateral acceleration information as described below to determine a current position for the vehicle if GPS velocity information is not available In any event, if GPS is available or not. the sensor integrator 40 provides the current position and a velocity (speed and heading) to a map matching block 42. The map matching block 42 provides road segment information for die road segment diat d e vehicle is determined to be travelling on, such as heading, and a suggested position The sensor integrator 40 can update the heading component of the velocity information vvidi die heading provided by the map matching block 42 to update the current position If the map matching block 42 indicates a good match, then the map matched position can replace die current position If not, the sensor integrator propagates the previous position to the current position using die velocity information As such, the sensor integrator 40 dctcπiunes the current position and provides die current position to a user interface and/or route guidance block 46 Tlie map matching block 42 also provides correction data, such as a distance scale factor and/or offset and a turn rate scale factor and or offset, to a sensor calibration block 44 The sensor integrator 40 also provides correction data to the sensor calibration block 44 The correction data from the sensor integrator 40. however is based on die GPS information Thus, accurate correction data based on the GPS lnfoπnation is continuousK available to calibrate the sensors 28 (2 or 3 axis acccleromcter) as well as for other sensors 29. 34 and 36 depending on the particular embodiment The correction data from the map matching block may be ignored by die sensor calibration block 44 until a good match is found between die map information and the current position If a inghlv accurate match is found by map matching 42. most likelv after a significant maneuver such as a change in direction, the map matched position is used as a reference point or starting position for position propagation according to the principles of the present invention Tlie sensor calibration block 44 contains the sensor calibration parameters, such as scale factors and zero factors for the sensors 28. 29 and provides the calibration parameters to the sensor integrator 40 to calibrate the sensors 28, 29 In one embodiment, die system can combine die sensor integrator 40 and sensor calibration 44 into GPS engine 18 using its processor In certain embodiments, the route guidance and user interface, the sensor integrator 40 and die sensor calibration 44 is perfoπned on an application specific integrated circuit (ASIC) If the accuracy of a current position is dcteππined to be high (for example, a map matched position at a isolated turn), the improved vehicle navigation svstem 10 can update die current position with the known position After the vehicle has moved a distance from the known position which is now a previous position, the improved vehicle navigation system must accurately propagate the vehicle position from the previous position to the current position Tlie calculations that will be pcrfoπncd to compute the vehicle position will take place in diree coordinate frames The vehicle position will be reported in geodetic coordinates (latitude, longitude, altitude) The non-GPS data will be provided in body or platfoπ coordinates Tlie GPS velocities and the equations used for velocity propagation of position will take place in die North. East. Down frame The geodetic frame is a representation of the Earth Centered Earth Fixed (ECEF) coordinates that is based on spherical trigonometry This is the coordinate frame that die mapping database uses Us units are degrees and meters displacement in height above die geoid These coordinates will be with respect to the WGS-84 Earth model, which is the Earth model used by the Global Positioning System (GPS) This is mathematically equivalent to the North American Datum 1983 (NAD 83) s stem which the mapping database is referenced to Tlie North East Down frame is a right-handed orthonormal coordinate s stem fixed to die vehicle vvidi its axes pointing to the True North. Tπic East, and Tπie Down (perpendicular to the Earth) directions The body coordinates form a right-handed orthonormal coordinate sv stem with dieir origin at die navigation unit, the x axis pointing toward the nose of the vehicle, the right axis pointing out die right door of die vehicle and the z axis pointing down perpendicular to the Earth During normal operation of the system, and with GPS available, die following arc die equations that will be used for computing the vehicle position and the calibration of die accelerometers and odometer Definitions x = position vector [latitude longitude altitude] x = velocity vector [north east down] .v = acceleration vector [nordi east down] C v = Transformation matrix which rotates a vector from die Body coordinate frame to the North East Down coordinate frame. The following superscripts will be used to denote the origin of the data: G = GPS A = Accelerometer 0 = Odometer The following subscripts will denote time - cither tune of validity or time period of integration. t = current time t- 1 = time of last data set before the current data set t-2 = time of data set before t- 1 Note that t-1 and t-2 do not necessarily iniplv a one second difference, but only data collection and/or data validity times. The following subscripts will denote coordinate reference frames' N = North East Down B = Body (Nose Right Door Down) G = Geodetic (latitude longitude height) To use the information from the non-GPS sensors, their data needs to be rotated from the body frame to the North East Down frame. This is a rotation about the yaw axis measured in degrees from True North to the Nose Axis of the vehicle. The equations for diis is: - N _ ✓-._< / -fl I X ~ ( Λ' ( X Thc steady state position propagation equation is based on the phvsical definition of velocitv and acceleration The current position is equal to the previous position plus the integral of vclocitv plus tlie double integral of acceleration x, = v, . - I xdt + \ ( \ ϊdt)dι ι l i 1 t - 1 Tlie following infoπnation is collected at time t f / Tlie velocitv' from GPS which was valid at die previous second This consists of χ e ~ Velocity in die True East direction (meters/second), x" = Velocity in the True North direction (meters/second), x" = Velocity in die Up direction (meters/ second). jr;^ ; The acceleration computed from GPS velocities diat was valid from tune t-2 to time t-1 , x The raw GPS position. x t The speed computed from die number of odometer counts that occurred from lime t-1 to time t, and x ' Tlie acceleration computed from die accelerometers which occurred from time t-1 to tune t The following other information is available for use at time t, but was collected at a previous time x t 3 Tlie velocity from GPS which was valid two time units ago, X I . J Tlie position computed at die previous time, jjj., Tlie acceleration, computed from die accelerometers, from time t-2 to time t-1 , and jr;,. ; Tlie vclocitv' computed from die odometer counts from time t-2 to time t- 1 When GPS is available and has produced a valid position and velocity solution, the following equation will be used for die propagation of die vehicle position x, = χ,. > ■ >- \ dl + j ( \ ϊdljdt t- 1 t- 1 i - l or x, = x.-t - d, , * ^ - / * (M ) - ((- 1 χ : ';y (M ) : ) -(- 7 χ y (M ) 2 )) This equation is die current position is equal to the previous position plus die GPS velocity (vector) times the delta time plus the GPS acceleration from two time periods ago minus die Acccleromcter acceleration from two time periods ago (a correction factor) plus tlie Accelerometer acceleration from the current second In certain embodiments, other sensor information, such as the odometer information, can be used in the above equations if it is determined to be more appropriate than the accelerometer information Also computed at this second arc (1) die GPS heading 1 computed as the inverse tangent of die East and North velocities. . c θ = a tan/— ■ ); X (2) die distance from time t-1 to tune t. computed from the GPS velocity valid at time t-1 and die double integration of the longitudinal Accelerometer acceleration from time t-1 to = i( Xι-1 My + (. Xι- I to/ * (to/ (3) the distance from time t-2 to tune t- 1. computed from die GPS velocity and acceleration from tune t-2 to time t-1 This will be used as a calibration factor for bodi the Vehicle Speed Sensor and the Longitudinal acccleromcter = (ii 2 * to / + (χi. 2 * to/ - - 7 * (to/, (4) the change in heading from time t-2 to time t- 1 from die GPS heading computed at those times. This is used as a correction factor for the lateral accelerometer. θ = θ?. 2 - θ?-, The use of GPS velocity information for vehicle position propagation in a vehicle navigation system is described in more detail in copending U S patent application no 08/579 ,902 , entitled "Improved Vehicle Navigation System And Mediod Using GPS Velocities" and filed concurrently with this application Each sensor needs to have calibrations pcrfoπncd on it. The calibrations will be performed using known good data from the GPS receiver 18. The GPS receiver 18 has velocity accuracy to within one meter per second. The GPS velocity information becomes less accurate in low velocitv- states of less than 1.5 /s. The GPS velocity infomiation is time tagged so diat it matches a particular set of odometer and acccleromcter data on a per second basis. Map matching provides correction factors, but they arc based on long teπn trends and not directly associated vvidi any specify time interval. Sensor calibration using the GPS velocities will typically involve die following sensors. Odometer (Vehicle Speed Sensor) Calibration. The odometer output is the number of ticks of a counter, with a specified number of ticks to be equal to one unit of linear distance traversed. An example is diat the GM Vehicle Speed Sensor has 4000 pulses per mile. This will have a default value from the factory and a calibrated value stored in FLASH diereafter. The odometer will be calibrated once per second from the GPS velocity and acceleration diat occurred over that same time period, when valid GPS data is available. Lateral Accelerometer. Tlie lateral acccleromcter measures centripetal acceleration. It is used to compute turn angle from the equation: Turn angle in radians is equal to the quotient of centripetal acceleration and tangential velocity. The lateral acccleromcter has two values which need to be calibrated: The zero offset and the scale factor. Tlie zero offset is the measurement that die acccleromcter outputs when a no acceleration state exists. The scale factor is the number that is multiplied by the difference between the acccleromcter read value and die accelerometer zero offset to compute the number of G's of acceleration. The zero motion detect system discussed in FIGs. 5a and 5b will be used to compute the acccleromcter zero offset value. The first derivative of the GPS velocities will be used to compute the scale factor calibration. Longitudinal Acccleromcter. The longitudinal accelerometer measures the acceleration along the nose/tail axis of the vehicle, with a positive acceleration being out the nose (forward) and a negative acceleration being out the rear of the vehicle. The longitudinal accelerometer has two values which need to be calibrated: The zero offset and the scale factor. Tlie zero offset is die measurement that the accelerometer outputs when an no acceleration state exists. The scale factor is die number that is multiplied by the difference between the accelerometer read value and the accelerometer zero offset to compute the number of G's of acceleration. The first derivative of die GPS velocities will be used to compute the scale factor calibration. The zero motion detect system shown in FIGs. 5a and 5b will be used to compute the accelerometer zero offset value. FIG. 5a shows the zero motion detect system with a motion sensor 64 (an orthogonal axes accelerometer in this embodiment) providing motion signals. An amplifier 65 amplifies the motion signals, and in this particular embodiment, the motion signals are digitized in an analog to digital converter 67. The motion signals are provided to a zero motion detection and offset calculation block 69 which is in the application unit 22 (FIG. 2a). The vehicle navigation determines a zero motion state by comparing samples of the motion signals from the motion sensor 64, such as an accelerometer, a gyro, or piezoelectric sensors with a threshold (the threshold is determined by vehicle vibration characteristics for the type of vehicle that the unit is mounted in, or the threshold for motion sensor could be set using other sensors which suggest zero motion, such as odometer, GPS or DGPS). The vehicle navigation system uses at least one of the samples to determine die zero offsets if the zero motion state is detected. At least two samples are preferred to compare over a time interval and averaging diose samples to obtain a zero offset for the motion sensor 64. If a zero motion state exists, the vehicle navigation system sets a zero motion flag 71 and uses at least one of the samples to determine the zero offset for the sensor providing die processed motion signals. The system also provides offset data signals 73 which reflect the zero offset for the sensor providing die motion signals or the raw data used to calculate die zero offset. Upon detecting a zero motion state, the vehicle navigation system can resolve ambiguity of low velocity GPS measurements because the velocity is zero. GPS velocities do not go to zero, so ambiguities exist when in a low velocity state of less than 1.5 m/s. If a zero motion flag is on, then the ambiguities are resolved because die system is not moving. As such, the system freezes the heading and can also set the speed component of velocity to zero. The following high level language program shows the operation of htis particular embodiment of the zero motion detect system. NUMSAMPLES = 16 (in filter array) WORD DATA[NUMSAMPLES-1] WORD NOISE FOR (1=0; I < NUMSAMPLES; I++) NOISE = NOISE +|DATA[I] - DATA[I+1]| If (NOISE > THRESHOLD) ZERO_MOTION_FLAG = 0 ELSE ZER0_M0T10N FLAG = I . FIG. 5b shows a flowchart of a variation of the zero motion detect system. At step 75, the system intializcs the variables I and NOISE to zero, and at step 77. the first value of die array is read. The counter 1 is incremented at step 79, and the system reads the next sample at step 81. At step 83. the system begins to accumulate the differences between consecutive samples of the motion signals. The system loops through steps 1-87 until all the samples have been read and die difference between consecutive samples accumulated in the variable NOISE. Once all die samples have been read, the system compares the variable NOISE with the threshold value at step 89. If the NOISE variable is greater than the threshold, dien the svstem determines that motion has been detected in step 91. If the NOISE variable is less than the threshold, the system sets the zero motion flag and deteπnines diat the velocity is zero at step 93. Tlie setting of die zero motion flag can set distance changes to zero, lock the heading and current position. Additionally, at step 95, the sv stem calculates the zero offset for the sensor being sampled. With regard to FIG. 5b and the high level program above, the sv stem is described as sampling die motion signals from one sensor 64. such as one axis of the orthogonal axes accelerometer. In this particular embodiment, the otion signals for each of die orthogonal axes of die acccleromcter is sampled and zero offsets for each is detcmiined. Furthermore, zero offsets, sensor calibration or resolving of ambiguities can be accomplished for other sensors using the zero motion detection system according to the principles of the present invention. Tlie use of a zero motion detection system in a vehicle navigation system is described in more detail in copending U.S. patent application no. 08/579 ,903 , entitled "Zero Motion Detection System For Improved Vehicle Navigation System" and filed concurrently with this application. FIGS. 6a and 6b show a general flowchart illustrating how the improved vehicle navigation system 10 propagates a previous position to a current position. At step 150. the improved vehicle navigation system dctcπiiincs if the vehicle is in a zero motion state as described above. If so, the system, at step 1 2. sets the change in distance to zero, locks the heading and current position, and calibrates the zero offsets. If the system dcteπnincs that the vehicle is moving, the system proceeds to step 154 to determine if a GPS solution is available. If GPS is available, the system uses the GPS velocity infoπnation to detemiine the current position. The GPS velocity information is very accurate above velocities of 1.5 ni/s because GPS delta ranges arc used to calculate die velocities. Using the GPS velocities for position propagation has other advantages. For example, the GPS receiver does not require calibration because of no inherent drift, and die GPS measurements can be used to calibrate other sensors. Moreover, cheaper sensors can be used because diere is no need to use the sensors very often, and the sensors can be calibrated very often using die GPS measurements The GPS receiver supports portability because it is independent of the vehicle and does not require a link to the vehicle odometer and reverse gear. As shown in step 156, the system calculates east and north accelerations as follows e-acc = e-vel - last.e-vel (1) n-acc = n-vel - last.n-vel (2). The accelerations are used to calculate east and north displacements as follows: e-dist = (e-vel*Δ t) + l/2(e-acc* (Δ t) 2 ) (3) n-dist = (n-vel » Δ t) + 1 /2(n-acc » (Δ t) 2 ) (4) The current position is calculated as follows lat = lat + (n-dist * degrees/meter) (5) long = long + (e-dist * degrees/meter) (6), where degrees/meter represents a conversion factor of meters to degrees, taking into consideration die shrinking number of meters in a degree of longitude as the distance from die Equator increases Finally, at step 156, the system calibrates the sensor items, such as the accelerometer scale factors and the odometer distance using information from the equations described above The system can keep the sensors well calibrated because calibrating can occur once per second (scale factors) if the vehicle speed is above 1.5 m/s. If a full GPS solution is not available at step 154, die system checks at step 58 whether any GPS measurements are available. If so, the system computes the velocity information from the available subset of delta range measurements at step 160 If, at step 162, the velocity information is good, the system calculates current position using the equations 1-6 at step 164 but without calibrating the acceleration scale factors and die odometer distance in this embodiment. If die GPS velocity is determined not to be good at step 162, the system checks the heading component of die GPS velocity at step 166 If the GPS heading component is determined to be valid, then at step 168, the change in distance is set with die odometer distance, and the heading is set with the GPS heading calculated from the GPS delta range measurements Alternatively, an odometer is not used, and die distance is derived from die longitudinal acceleration information Widi this heading and distance, the system calculates a position (lat, long) at step 170 using the equations as follows e-dist = Δ Dist * s (headιng) (7) n-dist = Δ Dist * cos(headιng) (8) After calculating the east and north distances, the system determines die vehicle position using equations 5 and 6, but calibration is not performed at dns point in this embodiment If die s stem determines at step 166 that the GPS heading is not valid (GPS blockage or low velocitv') or at step 158 that the GPS measurements are insufficient, the system falls back on the orthogonal axes accelerometer(s) and die odometer in dus particular embodiment GPS velocitv' information is subject to errors at speeds of less than 1 5m/s, unless using a more accurate GPS system For example, in a vehicle navigation system using DGPS, the threshold velocity is lower because of the higher accuracy of the system As such, the vehicle navigation system proceeds to step 172 to determine die change in distance using lateral and longitudinal acceleration information from die orthogonal axes accelerometer(s) At step 174, the system compares the longitudinal distance from die accelerometer with the odometer distance, and if die difference between them exceeds a direshold value, the odometer distance is used at step 176 If the difference is less dian the threshold, then the accelerometer distance or die odometer distance can be used for the distance at step 178 According to some aspects of the present invention, the system could fall back on only the orthogonal axes accelerometer(s) As shown in dashed step 173, if an odometer is not used, the distance is deπved from the longitudinal acceleration information Once the change in distance is determined, die system calculates the position at step 180 using the following equations to determine heading as follows speed = Δ Dist / Δ t (9) Δθ= aι„ ( lateral acceleration) / longitudinal speed (10) heading = heading + Δθ(modulo 360°) (11) After determining heading, die system uses equations 7 and 8 to determine die east and north distances and equations 5 and 6 to determine position The use of multiple, orthogonal axes acceleration information to propagate a vehicle position from a previous position to a current position is descπbed in more detail in copending U S patent application no 08/580 ,177 , entitled "Improved Vehicle Navigation System And Mediod Using A Multiple Axes Accelerometer" and filed concurrently with this application Aftcr determining the initial current position at step 1 6 164 170 or 180 die s stem proceeds to step 182 where the current position is compared idi die GPS position If die current position is within an acceptable distance (within 100m for example) from die GPS position, die system detcmiincs that the current position is v alid at step 184 If not. die s stem replaces the current position with the GPS position at step 186 At this point, die svstem sends to a map matching step 188 a position and velocitv . which has speed and heading components Depending on the configuration of the map database 30. other information can be sent to die map matching block 188, such as heading and distance based on the current and previous positions, a current position and figures of merit (FOM) for each The map matching block 188 sends back a map matched current position, distance, heading, FOMs for each and calibration data In tins embodiment, the map matching block 188 interrogates the map database 30 (FIG 2a) to obtain a heading of die mapped padi segment which die vehicle is determined to be traversing The map matching block 188 updates die heading associated with die current position, which was based on GPS and or sensor calculations, to obtain an updated current position As such, the map matching block 188 uses die map heading to update the heading based on the GPS vclocitv information, the heading based on die GPS position information of step 186. the heading from the sensors, or the heading based on a current position determined dirough a combination of GPS and sensor information, such as an embodiment widi all raw inputs going into a Kalman filter As shown in FIG 7a. the vehicle navigation svstem 10 (FIG 2a) uses GPS velocity liifomiation to propagate a previous position 191 to a current position 192 (by adding displacements 194 and 196 obtained from the vclocitv information (integrated) to the previous position) In FIG 7b if GPS information is not available, the vehicle navigation s stem uses sensor nifomiation to propagate the previous position 191 to current position 192 using heading and distance 198 If the difference between the GPS heading (or current heading from the sensors if GPS is not used) and the map heading is within a threshold, dien the map heading is used as the heading for position propagation The vehicle navigation svstem 10 can accomplish this in alternative ways For example, as shown in FIG 7c using GPS velocities, die vehicle navigation system 10 rotates the GPS velocity vector 200 to align with the map heading 202 if die GPS and map headings are within the threshold and integrates the rotated GPS velocity vector 204 to obtaui the displacements 208 and 210 As sho n, the updated current position 206 is obtained bv applvmg orthogonal displacements 208 and 210 to the previous position 191 Errors usually involve heading determinations due to drift errors in gyro or compass Displacement is easy to test and one of the most accurate components m the GPS measurements and also in the sensors, so the system uses the entire displacements from die GPS velocitv information or the dead reckoning sensors, such as die accelerometers Thus, die unproved vehicle navigation sv stem can use low cost sensors hich are less sensitive because heading can be corrected with map heading As shown in FIG 7d, if the vehicle navigation system uses sensor information to propagate the previous position 191 to current position 192 using heading and distance 198, die map heading 202 can be used as the heading for position propagation to die updated current position 206 FIG 7e shows an alternative way of updating die GPS heading and dius die current position by projecting die velocity vector 200 to align with the map heading 202 and integrating the projected velocity 212 to obtain displacements 214 and 216 Tlie system 10 obtains the updated current position 192 by applying the displacements 214 and 216 to the previous position 191 Tlie use of map heading to update the information obtained from the non-GPS sensors or a combination of GPS and other sensors can be accomplished in a similar manner as would be understood by one of skill in the art Depending on the lnfoπnation available and die particular embodiment, the improved vehicle navigation system can react differently to die information provided by the map matching block 188 The improved vehicle navigation system will rely heavily on the GPS foπnation for positioning and a high frequency of sensor calibration because GPS information is available a great deal of the time When GPS is available, the improved vehicle navigation system can use die map matching block 188 to provide an overall check on the current position and to provide position and heading correction data which is used if map matching 188 determines it is highly reliable In this particular embodiment, the current position (vv/o map matching) is determined once per second If the vehicle has travelled more than 1 meters since the last call to map matching 188, then the current position is passed to map matching 188 If the vehicle is travelling at high speed, the system will go to map matching 88 at each current position determination at die maximum rate of once per second When GPS is not available or unreliable, the improved vehicle navigation system has well calibrated sensors to rely on. and the improved vehicle navigation system can rely more on the information from the map matching block 188 for positioning and sensor calibration Thus, the improved vehicle navigation s stem provides several significant advantages, such as flexibility modularity . and accuracy at a cheaper cost because GPS information can be used to calibrate sensors more often and updating can be performed at a complete stop These advantages occur because the system relies heavily on GPS velocity information to propagate vehicle position Tlie GPS velocity information is more reliable (within about 1 m/s) dian the GPS position data (widnn about 100 m) Position data from GPS velocity information propagated positions is smoother than GPS position data which is not accurate enough by itself for turn-by- turn vehicle position propagation Tlie principles of the present invention, which have been disclosed by way of die above examples and discussion, can be implemented using various navigation system configurations and sensors Tlie improved vehicle navigation system, for instance, can be implemented widiout using an odometer connection and obtaining distance information from die accelerometer inputs when GPS is not available to improve portability and installation costs Moreover, die improved vehicle navigation system can obtain dead reckoning information from GPS signals when a full set of GPS measurements is available, and use its sensors when anything less dian a fiill set of GPS signals is available Those skilled in the art will readily recognize diat these and various odier modifications and changes may be made to the present invention widiout strictly follo ing die exemplary application illustrated and described herein and without departing from the true spirit and scope of die present invention, which is set forth in the following claims

Claims: CLAIMS 1 An improved v ehicle navigation sv stem composing a map database with map information said ehicle navigation sv stem derives a map heading from said map information and a GPS receiver which provides GPS vclocitv information said vehicle navigation svstem uses said GPS velocity information to propagate a previous position to a current position and interrogates said map database to obtain said map heading infoπnation, said vehicle navigation system updates said velocity information with said map heading for propagating said previous position to said current position if the difference between the heading of said velocity information and said map heading are within a threshold 2 Tlie system of claim 1 wherein said svstem uses said velocity to propagate a previous position to a current position 3 The s stem of claim 2 wherein said system rotates said velocity to align with said map heading and integrates the rotated velocity to obtain displacements, said system obtains said current position by appl ing said displacements to said previous position 4 The mcdiod of claim 2 wherein said svstem projects said velocity onto said map heading and integrating said projected vclocitv to obtain a displacement and obtaining said current position by applying said displacement to said previous position 5 A method of estimating the velocity of a vehicle known to be on a mapped path comprising interrogating a map database to obtain a map heading of said mapped path, and updating said velocity with said map heading if the difference between the heading of said velocity and said map heading arc ithin a threshold 6 Tlie method of claim 5 further including the step of using said velocity to propagate a previous position to a current position 7 Tlie method of claim 6 wherein said step of using includes rotating velocity to align with said map heading and integrating rotated velocity to obtain a displacement and obtaining said current position by applying said displacement to said previous position 8 The method of claim 6 wherein said step of using includes proiecting said velocity to align with said map heading and integrating said projected velocity to obtain a displacement and obtaining said current position by applying said displacement to said previous position 9 An unproved vehicle navigation s stem, comprising an orthogonal axes acccleromcter which provides longitudinal and lateral acceleration information, said vehicle navigation s stem uses said lateral acceleration infoπiiation to derive heading change, said vehicle navigation system uses said heading change to propagate a previous position to a current position 10 The system of claim 9 wherein said system uses heading change and said longitudinal acceleration liifoπnation to propagate a previous position to a current position 1 1 The system of claim 9 including a GPS receiver which provides GPS velocity information, said vehicle navigation sy stem uses said GPS velocity information to propagate a previous position to a current position if GPS velocity information is used 12 The system of claim 1 1 wherein said vehicle navigation system determines lateral and longitudinal calibration information from said GPS velocity information to calibrate said orthogonal axes accelerometer 13 An improved vehicle navigation svstem, comprising a GPS receiver which provides GPS velocity information, said vehicle navigation system uses said GPS velocity information to propagate a previous position to a current position, an orthogonal axes accelerometer provides longitudinal and lateral acceleration infoπnation. said vehicle navigation system determines lateral and longitudinal calibration information from said GPS velocity information to calibrate said orthogonal axes accelerometer, said vehicle navigation system dctcπnincs heading change using said lateral acceleration information, said vehicle navigation system uses said heading change to propagate a previous position to a current position if said GPS velocity infoπiiation is not used 14 The system of claim 13 wherein said sy stem uses said longitudinal acceleration information and said heading change to propagate a previous position to a current position if said GPS velocity information is not used 15 A method of propagating a previous position to a current position in a position determination system, said method including the steps of providing longitudinal acceleration infoπnation from a multiple axes accelerometer, providing lateral acceleration infoπiiation from said multiple axes accelerometer. deriving heading change using said lateral acceleration information, and using said heading change to propagate a previous position to a current position 1 The method of claim 15 wherein said step of using includes using said longitudinal acceleration and said heading change to propagate a previous position to a current position 17 A method of propagating a previous position to a current position in a position determination system, said method including the steps of: providing longitudinal acceleration information from a orthogonal axes accelerometer; providing lateral acceleration information from said orthogonal axes accelerometer; determining longitudinal speed from said longitudinal acceleration infomiation: deriving heading change from said lateral acceleration infomiation and said longitudinal speed, and using said heading change and said longitudinal acceleration to propagate a previous position to a current position. 18 The method of claim 17 further including the steps of. providing GPS velocities: dctcmiiiiing lateral and longitudinal calibration information from GPS velocities; and calibrating said orthogonal axes acccleromcter with said lateral and longitudinal calibration infomiation 19. The method of claim 18 further including die steps of: updating scale factors for said orthogonal axes accelerometer using said lateral and longitudinal calibration infomiation. 20. A vehicle navigation system having a GPS receiver which provides GPS velocity infomiation. said vehicle navigation system uses GPS velocity infomiation to propagate a previous position to a current position. 21. A method of determining a current position from previous position including the steps of: providing GPS velocity infomiation; and using said GPS velocity infomiation to propagate a previous position to said current position. 22. The method of claim 21 wherein said step of using further includes die steps of. detemiining cast and north displacements from said GPS velocity infomiation: and applying said cast and north displacements to said prev ious position to obtain said current position 23 An improved vehicle av igation sv stem hav mg a GPS rtcciv cr which provides GPS delta range information and GPS velocitv infoπiiation calculated from a set of said GPS delta range information, said vehicle navigation sv stem calculates GPS v clocitv information from a subset of said GPS delta range infomiation when said set of GPS delta range infomiation is not available and uses said GPS vclocitv infomiation to propagate a previous positton to a current position 24 A method of detcπnining a current position including die steps of providing a subset of GPS delta range infomiation, calculating GPS velocity infomiation from said subset of GPS delta range mfoπnation, and using said GPS velocity information to propagate a previous position to said current position 25 An improved vehicle navigation system has a motion detection sensor which provides motion signals having zero offsets, said vehicle navigation system comparing said motion signals with a threshold to determine a zero motion state, and if in said zero motion state, said vehicle navigation system determines said zero offsets 26 Tlie system of claim 25 wherein said sy stem determines said zero offsets by averaging said motion signals 27 The improved vehicle navigation system of claim 25 wherein said vehicle navigation svstem locks heading changes and calibrates velocity measurements if said vehicle navigation system is in said zero motion state 28 An improved vehicle navigation system, comprising a GPS receiver which provides GPS velocity infomiation, said vehicle navigation system uses said GPS velocity infoπnation to propagate a previous position to a current position, and an orthogonal axes acccleromcter provides motion signals having longitudinal and lateral acceleration infomiation and zero offsets, said vehicle navigation system deteπnines heading change using said lateral acceleration information, said vehicle navigation system uses said heading change to propagate a previous position to a current position if said GPS velocity infomiation is not used, said vehicle navigation s stem compares said motion signals with a thrcshold to detemiine a zero motion state, and if said vehicle navigation svstem is in said zero motion state, said vehicle navigation s stem determines said zero offsets 29 An improved vehicle navigation sv stem. comprising a GPS receiver which provides GPS vclocitv information, said vehicle navigation svstem uses said GPS velocity infoπnation to propagate a previous position to a current position and an orthogonal axes acccleromcter provides motion signals having longitudinal and lateral acceleration infomiation and zero offsets, said vehicle navigation system determines heading change using said lateral acceleration information, said vehicle navigation system uses said heading change to propagate a previous position to a current position if said GPS velocity infomiation is not used, said vehicle navigation system comparing said motion signals with a direshold to detemiine a zero motion state, and said vehicle navigation sy stem locks heading changes and calibrates said zero offsets if said vehicle navigation system is in said zero motion state 30 A method of detecting a zero motion state, said mediod comprising the steps of providing a motion sensor signal. determining a zero motion state by comparing at least two samples of said motion sensor signal with a threshold, and using at least one of said samples to determine said zero offsets if said zero motion state is detected 31 The method of claim 30 further including the step of providing a zero motion signal upon detecting a zero motion state to resolve ambiguity of low velocity measurements 32 An improved vehicle navigation system, comprising a GPS receiver which provides GPS velocity infomiation, said vehicle navigation system uses said GPS velocity infomiation to propagate a previous position to a current position, an orthogonal axes accelerometer provides motion signals having longitudinal and lateral acceleration infomiation and zero offsets, including longitudinal and lateral acceleration infomiation, said vehicle navigation system determines heading change using said lateral acceleration information and longitudinal speed, said vehicle navigation system uses said heading change to propagate a previous position to a current position if said GPS velocity infoπnation is not used, said vehicle navigation system comparing said motion signals with a direshold to determine a zero motion state, and said vehicle navigation svstem locks heading changes and cahbrates said zero offsets of said orthogonal axes acccleromcter if said vehicle na igation svstem is in said zero motion state an odometer provides displacement information, said vehicle navigation svstem determines displacement using at least one of said longitudinal acceleration infomiation and said displacement information said vehicle navigation system dctcmiincs heading change from said lateral acceleration infomiation. said vehicle navigation system determines odometer calibration infoπnation from said GPS velocity infomiation if said GPS velocity information is used, said vehicle navigation system uses said heading change and said displacement to propagate a previous position to a current position if said GPS velocity information is not used, and a map database w Inch stores map infoπiiation, said vehicle navigation system determines a heading from said map infoπnation, said vehicle navigation system updates said GPS velocity infomiation with said heading before propagating said previous position to a current position 33 An improved vehicle navigation system comprising a GPS receiver which provides GPS velocity infoπiiation, said vehicle navigation system uses said GPS vclocitv infomiation to propagate a previous position to a current position, an orthogonal axes accelerometer provides longitudinal and lateral acceleration infomiation said vehicle navigation system determines lateral and longitudinal calibration infoπnation from said GPS velocity information to calibrate said orthogonal axes accelerometer if said GPS velocity infomiation is used, and an odometer provides displacement infoπnation, said vehicle navigation system determines displacement using at least one of said longitudinal acceleration information and said displacement infomiation. said vehicle navigation system dctcmiincs heading change using said lateral acceleration infomiation, said vehicle navigation system uses said heading change and said displacement to propagate a previous position to a current position if said GPS velocity infomiation is not used, and a map database which stores map infomiation, said vehicle navigation system deteπnmes a map heading from said map infomiation, said vehicle navigation system updates said GPS velocity information with said map heading before propagating said previous position to a current position if the difference between said map heading and die heading of said GPS velocity infomiation is within a threshold 34 Tlie sy stem of claim 33 wherein said svstem determines heading change using said longitudinal acceleration information 35 An improved vehicle navigation system comprising a GPS receiver which provides w hich provides GPS delta range infomiation and GPS velocity infomiation calculated from a set of said GPS delta range infomiation, said vehicle navigation system uses said GPS velocity infomiation when said set of GPS delta range information is available and calculates GPS velocity information from a subset of said GPS delta range infomiation when said set of GPS delta range infomiation is not available and uses said GPS velocity information to propagate a previous position to a current position, an orthogonal axes accelerometer provides motion signals having longitudinal and lateral acceleration infomiation and zero offsets, said vehicle navigation system determines heading change using said lateral acceleration information, said vehicle navigation system uses said heading change to propagate a previous position to a current position if said GPS velocity infomiation is not used, said vehicle navigation s stem comparing said motion signals idi a direshold to detemiine a zero motion state, and said vehicle navigation system locks heading changes and calibrates said zero offsets if said vehicle navigation system is in said zero motion state, and a map database hich stores map information, said vehicle navigation system determines a map heading from said map infomiation, said vehicle navigation system updates said GPS velocity infoπnation with said map heading before propagating said previous position to a current position if the difference between the heading of said GPS velocity information and said map heading is within a threshold 36 An improved vehicle navigation system, comprising a GPS receiver which provides GPS velocity infomiation, said vehicle navigation system uses said GPS velocity infomiation to propagate a previous position to a current position, an ordiogonal axes acccleromcter provides longitudinal and lateral acceleration information, said vehicle navigation system detcπmnes heading change using said lateral acceleration infomiation. said vehicle navigation system uses said heading change to propagate a previous position to a current position if said GPS velocity information is not used, said vehicle navigation system determines latitudinal and longitudinal calibration information from said GPS velocity infoπnation to calibrate said orthogonal axes accelerometer. an odometer provides displacement infomiation. said vehicle navigation sy stem determines displacement using at least one of said longitudinal acceleration infomiation and said displacement infomiation. said vehicle navigation system dctcmiincs heading change using said lateral acceleration infomiation. said vehicle navigation system uses said heading change and said displacement to propagate a previous position to a current position if said GPS velocitv infomiation is not used, said vehicle navigation system deteπnines odometer calibration infomiation from said GPS velocity infomiation if said GPS velocity information is used to calibrate said odometer, and a map database which stores map infomiation, said vehicle navigation system determines a map heading from said map infomiation, said vehicle navigation system updates said GPS velocity infomiation widi said map heading if the difference between die GPS heading and said map heading are within a direshold before propagating said previous position to a current position 37 An improved vehicle navigation system, comprising a GPS receiver which provides GPS velocity infomiation, said vehicle navigation system uses said GPS velocity infomiation to propagate a previous position to a current position. an orthogonal axes acccleromcter provides motion signals having longitudinal and lateral acceleration infomiation and zero offsets, said vehicle navigation system determines heading change using said lateral acceleration infomiation. said vehicle navigation system uses said heading change to propagate a previous position to a current position if said GPS velocity infomiation is not used, said vehicle navigation system comparing said motion signals with a direshold to detemiine a zero motion state, and said vehicle navigation system locks heading changes and calibrates said zero offsets if said vehicle navigation system is in said zero motion state, said vehicle navigation system dctcmiincs lateral and longitudinal calibration information from said GPS velocity infomiation to calibrate said orthogonal axes accelerometer if said GPS velocity information is used if said vehicle navigation is not in said zero motion state, and a map database which stores map infomiation. said vehicle navigation system determines a map heading from said map infomiation, said vehicle navigation system updates said GPS velocity infomiation with said map heading if the difference between the heading of said GPS velocity infomiation and said map heading is within a threshold before propagating said previous position to a current position

Inventors: CROYLE STEVEN R, SITTARO ERNIE R, SPENCER LARRY E II, CROYLE, STEVEN, R., SITTARO, ERNIE, R., SPENCER, LARRY, E., II
Applicants: CROYLE STEVEN R, ROCKWELL INTERNATIONAL CORP, SITTARO ERNIE R, SPENCER LARRY E II, CROYLE, STEVEN, R., ROCKWELL INTERNATIONAL CORPORATION, SITTARO, ERNIE, R., SPENCER, LARRY, E., II
Application year: 1996
Main classification: G01C
IPC codes: G01C21, G01P21, G01S5, G01S11, G08G1