Abstract: An electronic vehicle accessory includes a non-volatile memory, and a controller coupled to the non-volatile memory and to a speed sensor of the vehicle for receiving speed data representing the vehicle's current speed. The controller determines when the vehicle's current speed falls below a predetermined threshold and stores variable data in the non-volatile memory when the vehicle's speed is below the predetermined threshold. The electronic vehicle accessory may be an instrument panel, an electronic compass, and/or a mini-trip computer, which may be housed in an overhead housing. By storing variable data in the non-volatile memory as a function of the vehicle's speed, the present invention ensures that the most up-to-date data is stored in the non-volatile memory before the vehicle's ignition is turned off while eliminating excessive stores that shorten the lifetime of the non-volatile memory.

Abstract: A rearview mirror assembly is provided for a vehicle which incorporates a self-contained magnetic field sensor in the mirror housing. When mounted to a fixed pivot point in a single ball mounting bracket, the mirror housing pivots around the magnetic field sensor. When the magnetic field sensor is mounted within the mirror housing either to the housing or to the mirror, compensation for the rotation position of the mirror about a vertical axis is provided by an empirically predetermined compensation value whereby direct reading of the angle is adjusted by a processor or by mechanically mounting the field sensor at an angle representative of the compensation value. Other ways of rotation compensation are also disclosed. Compensation for tilt about a horizontal axis is provided by an elliptical compensation algorithm in a microprocessor.

Abstract: An electronic compass system and method in which an automatic calibration process is available while the vehicle is in use. The procedure uses a binning process to collect and count data points which automatically triggers the automatic calibration process, and which is also used for manual calibration. Also, there is a procedure for detecting and rejecting anomalous magnetic events outside the vehicle through a jitter phenomenon.

Abstract: A method for determining the direction of the Earth's magnetic field, which may be interfered with by magnetic materials built into equipment and by electric currents, using an electronic magnetic compass which contains three magnetic field sensors and two devices for measuring inclination is provided. The electronic magnetic compass is arranged in N different spatial positions, in each of these N positions, the inclination sensor signals and the magnetic field sensor signals being measured and inclination values and magnetic field values being determined from these signals. On the basis of these inclination values and magnetic field values, the magnitude of the Earth's magnetic field vector is determined using the vector equationconst=b.sub.g =b.sub.E sin(i)=g.sup.T L(b.sub.E)=g.sup.T m(b.sub.mes -b.sub.o)with ##EQU1## N having to be at least equal to the number of parameters to be determined in the vector equation.

Abstract: Inventive electrical-computational method and system for aligning a magnetic gradiometer, and for determining magnetic gradients using a magnetic gradiometer which is inventively aligned. For each correlation of a correction magnetometer's vector with a reference magnetometer's vector, three correction coefficients and an offset coefficient are evaluated, using a mathematical approximation technique (such as least-squares) upon voltage outputs for various relative orientations of magnetic fields in relation to a magnetic gradiometer. An inventive matrix formula is used for determining magnetic gradients. A correction magnetometer matrix (matrix of voltages generated by each correction vector of the correction magnetometer) is multiplied by a coefficient matrix (matrix of correction and offset coefficients).

Abstract: An electronic compass (10) for use in a boring tool (12) which will provide an orientation of the boring tool relative to the earth's magnetic field. In addition, a more straightforward left or right deviation from an initial bearing can be determined. The invention can correct for pitch angle and roll angle variation as well. The magnetic field is sensed by an axial magnetic field (12), a radial magnetic field sensor (18) and a plane-normal magnetic sensor (24) which are preferably magnetoresistive sensors.

Abstract: A method for converting distorted compass data values into corrected data values which employs linear transforms. A linear transform is formulated and programmed into the read only memory of the microcomputer of the electronic compass system. The microcomputer uses the linear transform to transform compass data readings distorted by ferrous metals in the environment of the vehicle into corrected data readings and then uses the corrected data readings to compute headings.

Abstract: An electronic compass is described for use in vehicles. The compass employs a magnetoresistive sensor for sensing the earth magnetic field and the sensor is operated in alternate set/reset bias modes. In a first embodiment, the compass is provided with deviation compensation by a closed loop system including measurement of the sensor output signals and an offset current strap for nullifying the vehicle deviation field. In a second embodiment, deviation compensation is provided by operation in an initial calibration mode and by operation in a normal calibration mode to adjust compensation, as needed, on a long term basis during normal operation of the compass. In the initial calibration mode, while the vehicle is being driven, the signal peak values are adjusted to a nominal earth field level by changing the offset current. Then, compensating signal reference values for each axis are determined as each peak for that axis is determined.

Abstract: A vehicle compass system having a magnetic field sensor coupled to a processing circuit which samples the sensor data and implements a calibration routine that generates compensation signals to compensate the sensor for the effects of vehicular magnetism so that accurate heading information can be displayed on a display coupled to the processing circuit. If the signal levels detected are outside of a variable threshold, then the calibration routine is run. Also provided is a circuit for receiving vehicle position information in response to which the processing circuit adjusts the signals supplied to the display in order to account for magnetic variations between the true north and magnetic north.

Abstract: An apparatus for measuring a weak magnetic field in a background D.C. magnetic field such as the earth's magnetic field or the like includes a magnetic pickup portion that is supported by a support mechanism which does not impede minute movement in the x- and y-axis direction. A pair of A.C. linear gradient magnetic fields whose directions of gradients are parallel to the x-axis and y-axis, respectively, are used for obtaining reference signals for sensing the position of the pickup portion. The frequencies of the A.C. linear gradient magnetic fields are set to be sufficiently higher than the frequency of the weak magnetic field that is to be measured. The A.C. linear gradient magnetic fields are provided by A.C. current flowing in two pairs of linear conductors which are perpendicular to each other.

Abstract: The present invention relates to a method and a device for correcting measurement errors of a magnetometer mounted on a vehicle. According to the method, a theoretical corrective model is defined in accordance with the following equation: ##EQU1## where ?A!, ?C!i and Hp are elements to be determined, Hm is the measured field, H the effective field, and ?M! is a transformation matrix, and in which a vector error is defined in accordance with the following equation: ##EQU2## where the square of the error thus defined is determined and the coefficients of the model which minimize the sum of the squares of the error moduli for all the measurements taken are identified.

Abstract: A compass circuit has a magnetic field sensor adapted to be positioned in a vehicle near a source of varying magnetic fields. A detector is coupled to the compass circuit for providing a signal applied to the compass circuit which responds for displaying the compass heading prior to the magnetic field disturbance to provide accurate heading information. In a preferred embodiment, the detector senses when a door is opened and the compass heading prior to the opening of the door is displayed.

Abstract: An electronic compass is described for use in vehicles. The compass employs a magnetoresistive sensor for sensing the earth magnetic field and the sensor is operated in alternate set/reset bias modes. In a first embodiment, the compass is provided with deviation compensation by a closed loop system including measurement of the sensor output signals and an offset current strap for nullifying the vehicle deviation field. In a second embodiment, deviation compensation is provided by operation in an initial calibration mode and by operation in a normal calibration mode to adjust compensation, as needed, on a long term basis during normal operation of the compass. In the initial calibration mode, while the vehicle is being driven, the signal peak values are adjusted to a nominal earth field level by changing the offset current. Then, compensating signal reference values for each axis are determined as each peak for that axis is determined.

Abstract: An electronic compass is described for use in vehicles. The compass employs a magnetoresistive sensor for sensing the earth magnetic field and the sensor is operated in alternate set/reset bias modes. In a first embodiment, the compass is provided with deviation compensation by a closed loop system including measurement of the sensor output signals and an offset current strap for nullifying the vehicle deviation field. In a second embodiment, deviation compensation is provided by operation in an initial calibration mode and by operation in a normal calibration mode to adjust compensation, as needed, on a long term basis during normal operation of the compass. In the initial calibration mode, while the vehicle is being driven, the signal peak values are adjusted to a nominal earth field level by changing the offset current. Then, compensating signal reference values for each axis are determined as each peak for that axis is determined.

Abstract: Process for compensating a magnetic interference field in a vehicle having a navigation installation. During a calibration run for initial compensation, a first set of interference field parameters is determined from the measurements of the magnetic field probe (interference field vector V1, axes a, b of the elliptical locus curve E1, oblique position) and transformed onto points of a circular locus curve with the radius a about the origin (0); the distance from the origin (0) and the angle are calculated for each pair of measurements. The calculated radius values and the circularly transformed pairs of measurements (MP) are averaged and entered in their appropriate memory cell in a segmented memory for 360.degree. with a plurality of memory ceils (predetermined angular region). Variant 1: for each segment, the radius difference (.DELTA.

Abstract: A magnetic compass comprising an arrangement to displace a correcting marker to create a compass correcting coefficient equal to the sum of the variation and the deviation errors effecting the compass so as to counteract the compass error, and to indicate the true course. The correcting marker becomes the steering reference and a vessel is steered so that the correcting marker is aligned with the true course to be steered by the vessel. Repeaters fed from this compass, which repeaters are fed by the hunting between the compass card and the displaceable correcting marker, indicate the true course as well as true bearings. The displacement of the correcting marker can be controlled from a computer programme which displaces the correcting marker in dependence upon the effecting variation and deviation. Thus the magnetic compass shows true course and the repeaters show true course and true bearings automatically.

Abstract: An arrangement for correcting declination in an optically readable bearing compass having a body enclosing a hermetically sealed capsule containing a compass card and a main reading line calibrated indicate bearing to the earth's magnetic pole without correction of declination. The compass body further includes an opening or passage having an optical system therein suited to facilitate taking the bearing indicated by the wind rose. The compass has a movable auxiliary reading line which is adjustable with respect to the compass body and the main reading line to both sides from its center position corresponding to the zero value of declination thus permitting the correction of bearing error caused by the geographic displacement between the true North Pole and the magnetic north pole.

Abstract: An apparatus for mounting a magnetometer including a frame and a platform mounted for rotation within the frame. The magnetometer and one or more counterweights are mounted within the platform such that gravity acting on the counterweights maintains the magnetometer in a horizontal orientation. A first coil is coupled in parallel with the magnetometer and is wound around the perimeter of the platform. A second coil is wound around the perimeter of the frame such that the first and second coils form an air core transformer. The second coil terminates in two terminals which provide a communication port. A sensing circuit coupled to the port electrically communicates with the magnetometer via the inductive coupling provided by the transformer. In alternative embodiments, each of the first and second coils is implemented as two coils with associated diodes.

Abstract: An adjustable magnetic compass for adjustably compensating for the magnetic variation between magnetic north and map north. The adjustable compass includes a compass dial having directional indicia applied thereto, and a lubber line for operative alignment relative to the directional indicia. The lubber line can be rotatably adjusted relative to the directional indicia so as to visually compensate for the magnetic variation between magnetic north and map north with respect to the geographic location in which the adjustable magnetic compass is to be located.

Abstract: A compass circuit has a magnetic field sensor adapted to be positioned in a vehicle near a source of varying magnetic fields. A source of correction signals is coupled to the compass circuit for providing correction signals applied to the compass circuit for correcting the heading display of the compass circuit when differing levels of magnetic field disturbance occurs to provide accurate heading information. In a preferred embodiment the source of correction signals includes a detector circuit coupled to the vehicle accessory for providing signals directly corresponding to the source of magnetic field interference.

Abstract: In a direction detecting apparatus for a vehicle, when signals input from an earth magnetic sensor into calculating means are judged to be outside a predetermined judging area, an alarm for prompting magnetization correction is given, thereby the direction detecting apparatus can surely display the alarm at any case without the necessity to rotate the vehicle.

Abstract: The invention provides a direction sensor and a method of calibrating a direction sensor having a relative heading sensor and an absolute heading sensor. The method allows calibration of both the relative heading sensor and the absolute heading sensor at the same time, by taking advantage of the known angular relationship between maxima and minima on the measurement curve of the absolute heading sensor. Such maxima and minima are found by rotating the sensors through an angle of at least 360.degree., reading the absolute and relative heading sensor outputs at numerous points and comparing each successive output. The relative heading sensor output at the minimum is subtracted from that at the maximum, and the difference divided by the known angle to arrive at a conversion constant for the relative heading sensor. The center and radii of the measurement curve of the absolute heading sensor may be found by determining the maxima and minima of the curve in two perpendicular directions.

Abstract: An apparatus and method for compensating for the measured variation in bearing between magnetic north as read on a compass and true north as may be determined by juxtaposition with the sun at a given time. Such apparatus and method is particularly useful in vessels or other environments in which there are either or both disturbances in the natural magnetic flux pattern of the earth and natural variations between natural magnetic and true north.

Abstract: A vehicle compass system that is adapted to be calibrated in the assembly plant during final assembly of the vehicle. In particular, two factory calibration modes are disclosed: an automatic factory calibration mode wherein the calibration sequence is automatically initiated upon the occurrence of a uniquely definable event on the assembly line, and a manual factor calibration mode wherein a calibration button sequence is actuated at a specified location on the assembly line. In addition, an automatic adaptive calibration process is disclosed which continuously updates the calibration constants each time valid new heading data is obtained. In particular, heading vectors for the four main N, S, E, and W heading directions are calculated and stored in memory when the system is initially calibrated. Thereafter, whenever new heading direction data is obtained, the value of the new heading vector is used to update the value of the closest of the four main heading vectors.

Abstract: A scaling system and technique which employs an analog-to-digital converter having at least 10-bit accuracy and a ranging circuit to compensate for abnormally large vehicle magnetic fields. The ranging circuit employs variable resistance negative feedback, which enables an electronic compass system to reduce the output voltage of an integrator to within the fixed output voltage range of the integrator. An analog-to-digital converter of at least 10-bit accuracy makes resolution of heading information possible and enhances the accuracy of subsequently performed calibrations.

Abstract: The invention provides a direction sensor and a method of calibrating a direction sensor having a relative heading sensor and an absolute heading sensor. The method allows calibration of both the relative heading sensor and the absolute heading sensor at the same time, by taking advantage of the known angular relationship between maxima and minima on the measurement curve of the absolute heading sensor. Such maxima and minima are found by rotating the sensors through an angle of at least 360.degree., reading the absolute and relative heading sensor outputs at numerous points and comparing each successive output. The relative heading sensor output at the minimum is subtracted from that at the maximum, and the difference divided by the known angle to arrive at a conversion constant for the relative heading sensor. The center and radii of the measurement curve of the absolute heading sensor may be found by determining the maxima and minima of the curve in two perpendicular directions.

Abstract: A vehicle-direction detecting apparatus compensates for the direction detected by each sensor to provide a correct direction. A difference signal between the first direction signal based on the XY output signal of a geomagnetic sensor and the second direction signal acquired by integrating the output signal of an angular velocity sensor is computed, it is discriminated whether or not an absolute value signal of the difference signal is greater than a first predetermined value, it is discriminated whether or not the output signal of differentiating means which has differentiated the absolute value signal is greater than a second predetermined value, it is discriminated whether or not the XY output signal of the geomagnetic sensor has a value within a predetermined range, and the first or second direction signal is compensated for in accordance with the results of the above discriminations.

Abstract: A method for harmonizing an equipment relative to a vehicle, such as a helicopter, based upon sensing of gravitational and magnetic fields in a number of reference systems. The equipment is installed fixedly on board the vehicle which, relative to a first absolute reference system (RM), has an orientation defined by a second reference system (R2) tied to the vehicle. The equipment is subjected to the earth's gravitational field represented by a gravity vector g oriented along its gradient, as well as to the earth's magnetic field represented by a vector H oriented along its gradient. The orientation of the equipment is defined, relative to the first absolute reference system (RM), by a third reference system (R3).

Abstract: A method for harmonizing an equipment relative to a vehicle, such as a helicopter, based upon sensing of the gravitational field in a number of reference systems. The equipment is installed fixedly on board the vehicle which, relative to a first absolute reference system (RM), has an orientation defined by a second reference system (R2) tied to the vehicle. The equipment is subjected to the earth's gravitational field represented by a gravity vector g oriented along its gradient. The orientation of the equipment is defined, relative to the first absolute reference system (RM), by a third reference system (R3). The equipment includes a device for measuring the components of the gravity vector g, and the vehicle carries a computer, a memory associated with the computer; and a link connecting the equipment to the computer and to the memory. The gravitational field is measured when the vehicle is in a number of different orientations, and the equipment is harmonized to the vehicle based thereon.

Abstract: A magnetic transient detection technique which alerts a microcomputer of an auto-calibrating compass when electrical transients which produce magnetic transients have occurred. The technique employs an electronic compass control circuit having a sampling rate high enough to isolate electrical transients from transients produced by normal motion of the vehicle. Accelerations in data values defined as the difference between two changes in the coordinates for the center of the earth's magnetic field circle, are calculated and compared to predetermined threshold accelerations. Previous acceleration values and their associated vehicle magnetic field vectors can be stored in the microcomputer. After a magnetic transient is detected, its associated vehicle magnetic field vector is subtracted from the resultant magnetic field to yield vehicle heading. Once detected, magnetic transients are also used to initiate auto-calibration.

Abstract: A method for selecting calibration data which uses mean square error to minimize variations in the calculated origins of the earth's magnetic field vector. A microcomputer having a memory calculates and stores the origin of the earth's magnetic field vector from the last three headings or data points. The x and y coordinates of the origins are summed with all the previous x and y coordinates and the mean square errors of the x and y coordinates are calculated. A figure of merit for the mean square errors is calculated. An adjusted origin is determined and stored by weighing the newly calculated origin by a figure of merit and adding it to the previous origin. Provision is made for reinitializing all quantities to zero when the sum of the mean square errors exceeds a predetermined maximum.

Abstract: An electronic compass (10) having at least two sense windings (11, 12) is mounted in a vehicle. The outputs (x(h), y(h)) of the windings are measured for a number of compass directions (headings). From this data an error difference angle (.phi.), from a nominal angle, which actually exists between the output windings is calculated. Preferably a look-up table (21, 39) is created relating actual compass heading (h) to measured sense winding outputs by utilizing the calculated error difference angle (.phi.). This table is then utilized for calculating actual compass heading based on actual measured sense winding outputs. The calculated error angle (.phi.) can also be used to calibrate the compass without creating a look-up table. The calibrated compass compensates for misalignment of the sense windings and provides a more accurate electronic compass without requiring creating a calibration table by orienting the compass in a very large number of exactly known directions.

Abstract: The direction of a terrestrial magnetism is detected by a terrestrial magnetism sensor mounted on a vehicle, and an output circle is generated on an X-Y coordinate by turning the vehicle on the ground, when the vehicle passes through a foreign magnetic fields the direction of the foreign magnetic field is detected by the terrestrial magnetism sensor, and the course thereof is determined on the basis of former output circle before passing through the foreign magnetic field and the output of an angular velocity sensor of the vehicle after passing it, then a new center of the output circle is determined by evaluating an intersection of the line representing the foreign magnetic field and the line representing the course of the vehicle on the X-Y coordinate.

Abstract: An electronic compass is described for use in vehicles. The compass employs a magnetoresistive sensor for sensing the earth magnetic field and the sensor is operated in alternate set/reset bias modes. The compass is provided with deviation compensation by a closed loop system including measurement of the sensor output signals and an offset current strap for nullifying the vehicle deviation field.

Abstract: A flux-gate sensor orientation method which minimizes display jitter in electronic compasses which employ an n-point display or which calculate headings using the arctangent method. The method entails orienting the flux-gate sensor in a direction of plus or minus .+-.360.degree./2n relative to actual magnetic direction, so that instability points occur at display point boundaries. The method of the present invention finds application in microprocessor-based electronic compass systems but also makes possible the construction of a simple electronic compass employing small scale integration logic instead of a microprocessor.

Abstract: An output signal processing unit of a fluxgate sensor including a fluxgate for detecting the magnetic north of a vehicle and a low pass filter for removing a high frequency component from an output of the fluxgate sensor, characterized in that it comprises, a rate sensor detecting an angular velocity of rotation based on the turning of the vehicle, the low pass filter making the cutoff frequency thereof high or low depending on the increase or decrease of the angular velocity of rotation of the rate sensor.

Abstract: A system for measuring a traveling direction of a vehicle includes a geomagnetic sensor and a gyro sensor. The system utilizes first and second indicies for deriving the vehicle traveling direction. The first index is indicative of disturbance of a geomagnetic field on a short interval basis, and the second index is indicative of disturbance of the geomagnetic field on a long interval basis. The system further utilizes a correction value indicative of a drift error caused by the gyro sensor for deriving the vehicle traveling direction. The system varies a rate of dependence upon an output of the geomagnetic sensor and an output of the gyro sensor based on the first and second indicies and the correction value when calculating the vehicle traveling direction.

Abstract: In a compass, the direction of the geomagnetism is detected by magnetic sensors and an azimuth detector, and data on the direction of the geomagnetism is supplied to a controller. A ROM stores declination data representing the angle formed between the direction of the geomagnetism and the direction of the geographic meridian. The data on the direction of the geomagnetism is corrected in accordance with the declination data stored in the ROM, to thereby obtain geographical direction data. This geographical direction data is displayed on a display device. In this manner, the compass enables the user to easily know a true direction.

Abstract: In a magnetic compass of the kind in which a sensor derives coordinates of a sensed magnetic field, automatic correction of hard-iron and soft-iron distortions is achieved by storing a set of measured values of the magnitude of the sensed magnetic field for different discrete directions of the alignment axis of the compass relative to an estimated origin. If measured values have been accumulated for more than a predetermined number, but not all, possible directions, values are interpolated for the remaining directions to provide a set of measured and interpolated values defining a substantially elliptical locus of the sensed magnetic field vector (E.sub.T.) New coordinates for the estimated origin are derived and the measured values adjusted to take account of changes in the estimated origin. The heading is corrected for displacement of the origin due to hard-iron effect and for ellipticity of the locus due to soft-iron effects.

Abstract: A system measures a traveling direction of a vehicle based on a direction toward a coordinate position defined by output data from a geomagnetic direction sensor from a first center coordinate position of a corresponding output circle. The system derives a second center coordinate position based on the output data from the geomagnetic direction sensor. The system utilizes a first group of the second center coordinate positions and a second group of the second center coordinate positions. When it is decided that the first center coordinate position is shifted, then a new or corrected center coordinate position is derived based on the first group of the second center coordinate positions, on the other hand, when it is decided that no shift of the first center coordinate position is generated, then the corrected center coordinate positiion is derived based on the second group of the second center coordinate positions.

Abstract: An improved fluxgate instrument for measuring heading as well and pitch and roll angles is disclosed. A plurality of fluxgate sensors are continuously energized with a DC feedback signal derived from the reading of each sensor so as to minimize magnetic cross-coupling between the sensors. In addition while two sensors are gimbally mounted to sense the horizontal components of the earth's magnetic field, the vertical field is sensed by two sensors strapped down relative to the instrument casing for sensing the earth's vertical magnetic field in order to compensate for latitude. Finally, sine and cosine coils surround the gimbally mounted sensors and generate AC fields which are sensed by the gimbally mounted sensors and are used to calculate the pitch and roll angles.

Abstract: A ststem measures a traveling direction of a vehicle based on a direction toward a coordinate position defined by output data from a geomagnetic direction sensor from a first coordinate position of a center of a corresponding output circle. The system utilizes a preliminary coordinate position as a preliminary corrected value of the first center coordinate position and a correction value indicative of reliability of the preliminary center coordinate position for deriving a finally corrected value of the first center coordinate position. The reliability of the preliminary center coordinate position is derived from previously stored data in terms of a derived variation in a vehicular traveling direction. The system derives the finally corrected value of the first center coordinate position based on the preliminary center coordinate position and the correction value such that the finally corrected value is derived closer to the preliminary center coordinate position when the correction value is derived larger.

Abstract: An electronic flux gate compass calibration method and apparatus. An electronic flux gate compass mounted on a terrestrial vehicle is first rotated 360 degrees by driving the vehicle in a circle to determine four reference points where the locus of points representing the orthogonal outputs of the compass crosses over the X and Y axes of a reference Cartesian coordinate system. These four reference points are employed to calibrate the orthogonal outputs of the compass and compute a calibrated compass heading. Thereafter, as the vehicle moves from place to place, the output of the compass is monitored. If the output is within a predetermined region around one of the reference points, the reference point is modified to be closer to that output point. When the vehicle has moved through a closed loop, i.e., rotated a net 360 degrees, the compass is recalibrated.

Abstract: An electronic compass for use in a vehicle includes compensation for attaining a high degree of accuracy without operator intervention or the need to drive the vehicle in a deliberate circular path. An automatic method for accurately determining maximum and minimum voltage values from a flux gate sensor having orthogonal sensing windings is provided that operates continuously to adjust for required changes in both the offset and gain compensation factors. The flux gate sensor is further mounted within the vehicle such that the axis of one of the sensing windings is positioned approximately 45.degree. with respect to the vehicle's longitudinal direction. The angled mounting of the sense winding axis results in strong sensing signals when travelling on most roads. The electronic compass further provides visual representation on the outer peripheral segments of an alphanumeric display to prompt the operator to drive in a circle during a manual compensation mode.

Abstract: Method and apparatus for correcting the output of an onboard vehicle terrestrial magnetism sensor. An azimuth computation reference circle is obtained from the terrestrial magnetism sensor output, the circle in turn being used to correct the sensor output. When the reference circle is dislodged, the least square method is used to fine a true azimuth computation reference circle.

Abstract: A system for measuring a traveling direction of a vehicle includes a geomagnetic sensor and a gyro sensor. The system utilizes first and second indices for deriving the vehicle traveling direction. The first index is indicative of a disturbance of the geomagnetic field on a short distance basis, and the second index is indicative of a disturbance of the geomagnetic field on a long distance basis. The system varies a rate of dependence upon the geomagnetic sensor and the gyro sensor based on values of the first and second indices when calculating the vehicle traveling direction.

Abstract: Method and apparatus are disclosed for compensating a magnetic compass in a vehicle for magnetic deviation. With the compass installed, the angle indicated by the magnetic compass relative to a direction axis of the vehicle is measured. A test magnetic field is added at a known angle relative to the direction axis of the vehicle. The strength of the test magnetic field required to displace the direction indicated by the compass through a predetermined angle is memorized. Then, the strength of the resultant magnetic field is calculated using the measured angle, the predetermined angle and the memorized strength of the magnetic field. After determining the strength of the resultant magnetic field with the vehicle oriented in any selected direction, the vehicle is then reoriented in a direction one hundred eighty degrees away from the selected direction and the strength of the resultant magnetic field in that orientation is determined in the same way.

Abstract: An apparatus and method for measuring a forward direction of a vehicle in which to derive a coordinate position of a center (O.sub.x, O.sub.y) of a directional circle derived from an output of a geomagnetic direction sensor after a magnetization on a vehicle body occurs, the magnetization on the vehicle body is determined from the output of the geomagnetic direction sensor installed in the vehicle and each parameter of a peak quantity (X.sub.max, Y.sub.max), peak direction (D.sub.x, D.sub.y), and a center value of an output circle before the present disturbance occurs is calculated, optimum coefficients are selected and set according to each parameter from among the previously derived coefficients, a magnetization quantity is calculated from each parameter and each optimum coefficient using a linear combination technique, and the coordinate position of the center of the output circle after the magnetization on the vehicle body occurs from the derived magnetization quantity.

Abstract: In a locator for location and direction detections of moving bodies which employs, in the direction detection, a magnetic direction sensor for outputting direction data and a gyro for outputting angular speed data, the locator for location and direction detections of moving bodies comprising a normal judgement function for the magnetic direction sensor which compares a direction variation quantity within an assigned time which is obtained from the difference of the direction data of the magnetic direction sensor, and an angle variation quantity within the assigned time which is obtained from an integral value of the angular speed data of the gyro, and in the case that the difference between the compared quantities is over a first predetermined value, judges that an error has occurred in the direction data of the magnetic direction sensor.

Abstract: Magnetic compasses may be affected by local disturbances in the magnetic field in their vicinity. These disturbances may be caused by the addition or removal of a metal article concerned with a vehicle in which the compass is mounted, and may also be due to local variations in the Earth's magnetic field. The system described herein compensates for such disturbances in the magnetic field to maintain the accuracy of the magnetic compass by transforming an ellipsoidal locus to a spherical locus at a different orientation in space. For example, a one-shot algorithm is employed in which data collected during a setting maneuver of the vehicle is processed to fit a generalized reduced quadric equation having six or less coefficients rather than the nine calibration points required in the prior art for fitting a generalized quadric equation for an ellipsoid. The present invention thus significantly reduces the processing power required.