Abstract: A personal mobile device housing contains a display screen, a wireless telephony communications transceiver, and a battery charger interface. A temperature sensor and a gyro sensor whose zero turn rate output contains an offset are also included. A lookup table has gyro zero turn rate offset correction values associated with different temperature values. A programmed processor accesses the lookup table to correct the output of the gyro sensor for zero turn rate offset. It is automatically determined, during in-the-field use, when the device is in a motionless state, and the output of the temperature and gyro sensors are read. The read gyro output is written to the lookup table as part of a pair of associated temperature and zero turn rate offset correction values. Other embodiments are also described and claimed.

Abstract: A multi-turn angle sensor includes rotors 60, 62, 64, each of which rotates in a different manner with respect to an input shaft 19, and a common stator portion 66. The rotors and pole teeth disposed around the rotors form each of resolvers 600, 620, 640. At least two of the resolvers are arranged on a single plane vertical to the rotation central axis of each of the rotors. The common stator portion 66 surrounding each of the rotors is formed by laminating electromagnetic steel sheets 106, each of which has an identical shape including a plurality of sets of pole teeth corresponding to each of the rotors. A single length of unspliced electrical wire is wound around each of the pole tooth sets. This facilitates automation of assembly.

Abstract: An azimuth calculation program is a computer-executable program that performs an azimuth calculation using output of a magnetic sensor. The azimuth calculation program includes a first step of generating one triangle in three-dimensional space using three output values of a magnetic sensor unit, a second step of determining a circumcircle of the triangle, and a third step of performing an azimuth calculation using center coordinates of the circumcircle and output values of the magnetic sensor.

Abstract: A computing device connects with a measurement machine. The measurement machine includes a raster ruler and a measurement unit. The computing device reads environmental temperatures from a temperature sensor. Compensation coefficients of the standard workpiece and compensation coefficients of the raster ruler are calculated. The computing device calculates total compensation coefficients of the standard workpiece and the raster ruler. When the measurement machine measures an object workpiece, the computing device calculates a total error of the object workpiece according to the total compensation coefficients of the standard workpiece and the total compensation coefficients of the raster ruler. Coordinates of the object workpiece are calculated according to the total error and mechanism coordinates of each axis of the measurement machine.

Abstract: Described is an apparatus for calibrating a position finding device, having a comparer for comparing a received radio signal pattern to a multitude of reference radio signal patterns, a determiner for determining a signal strength difference, and a determiner for determining a calibration value. The comparer for comparing is configured to select a selection subset from the multitude of reference radio signal patterns by means of a measure of matching between the received radio signal pattern and one reference radio signal pattern, respectively. Determination of the calibration value is based on the signal strength difference, and the determiner for determining the calibration value is further configured to provide the calibration value to the position finding device.

Abstract: A method for correction of the measured values of optical alignment systems with at least two measurement planes which are located in succession in the beam path. From each measurement plane, the beam path to the light source is transformed back in order to compute new incidence points using a beam which has been corrected by taking into consideration imaging errors.

Abstract: A system for controlling a computer is provided. The system includes a position sensing apparatus configured to be disposed in operative proximity to a sensed object and thereby obtain positional data pertaining to the sensed object, and engine software configured to receive the positional data and process the positional data to determine an assessed actual position of the sensed object relative to a neutral reference position and output control commands based on the assessed actual position of the sensed object, the control commands configured to control presentation of a rendered scene, the control commands being scaled relative to changes in the assessed actual position of the sensed object, the scaling of the changes in assessed actual position of the sensed object causing presentation of the rendered scene to be skewed; wherein the engine software is further configured to automatically correct the skewing of the rendered scene by modifying the control commands.

Abstract: Disclosed is a technique of correcting a resolver offset by measuring and correcting an offset of a resolver assembled to a motor of an eco-friendly vehicle in an accurate and simple way. The offset measurement process includes, after completing the assembly of a resolver a resolver to a motor, rotating the motor by using a rotation device able to transfer a rotation force to the motor, setting a voltage instruction and current-controlling the motor according to the voltage instruction, and obtaining a d-axis current and a q-axis current, which are feedback currents, during the current-control of the motor. Then when the system is in a steady state, a resolver offset ({tilde over (?)}) is calculated from the d-axis current and the q-axis current by using {tilde over (?)}=tan?1(d-axis current/q-axis current).

Abstract: A dynamically self-adjusting magnetometer is disclosed. In one embodiment, a first sample module periodically generates an electronic signal related to at least one magnetic field characteristic of a monitored environment. A second sample module periodically generates an electronic signal related to at least one magnetic field characteristic of a monitored environment. A summing module sums the absolute value of the electronic signal from the first sample module and the electronic signal from the second sample module. A delta comparator module receives the electronic signals from each of the first sample module, the second sample module and the summing module and compares each of the electronic signals with a previously received set of electronic signals to establish a change, wherein an output is generated if the change is greater than or equal to a threshold.

Abstract: In a rotation angle positioning device 6 including: a rotation angle detection device 7 which has a detection target ring 8 and an angle detection sensor 9; and a rotating-shaft driving device 10 rotating a rotating shaft so as to cause a rotation angle to become a given command value ? for rotation angle, there are provided: an error pattern storage unit 11a storing a tooth-to-tooth period error pattern F made up of errors between detected rotation angles by the angle detection sensor 9 and actual rotation angles, corresponding to respective correction dividing points of an arbitrary tooth-to-tooth period in the detection target ring 8; and a command value correction unit 11b correcting the command value ? for rotation angle based on the tooth-to-tooth period error pattern F to find a corrected command value ?2 for rotation angle.

Abstract: A method of determining a positioning error of a CNC machine is provided and an system thereof. A calibration element is placed within the CNC machine. A first sensor reading is taken of the calibration element. A second sensor reading is taken and the sensor is moved in a manner that the difference between the first and second sensor data decreases until the difference becomes less or equal to a pre-determined threshold value. A positioning error of the tool head is determined based on the movement of the sensor.

Abstract: A measurement apparatus, which measures a surface position of an object by detecting interfering light between measurement light reflected by the object and reference light reflected by a reference surface, includes: a detector configured to detect the interfering light to output an interference signal; and a processor configured to obtain the surface position based on a sine signal and a cosine signal which are obtained from the interference signal output from the detector and have a phase corresponding to an optical path length difference between the measurement light and the reference light. The processor includes a correction processing unit configured to correct the sine signal and the cosine signal to reduce frequency noise components contained in the sine signal and the cosine signal.

Abstract: In an electronic device and a method of correcting time-domain reflectometers, two channels of a time-domain reflectometer are connected to a corrector using cables, and the two channels are enabled to transmit pulses. Parameters Step Deskew and Channel Deskew of the two channels are zeroed. Resistance values of the two channels are measured simultaneously, and the value of the parameter Step Deskew of one of the two channels is adjusted according to the Resistance values of the two channels. Times of achieving the same resistance value of the two channels are measured after the cables and the connector have been disconnected, and the value of the parameter Channel Deskew of one of the two channels is adjusted according to the times of achieving the same resistance value. The adjusted values of the parameters Step Deskew and Channel Deskew are displayed through a display unit.

Abstract: An apparatus for determining the position of a movable separation element which is arranged within an accumulator as a separator between a gas space and a fluid space, wherein the determination apparatus comprises at least one pressure sensor for the detection of pressure data, at least one ultrasonic sensor for the detection of ultrasonic data and at least one calculation unit for the evaluation of the data with the aid of which determination apparatus the position of the separation element can be determined

Abstract: In a position detection device, an amplitude modulation is executed for AC excitation signals Sc using modulation wave signals. Differential amplifiers execute a voltage conversion of the modulated wave signal Sin, Cos to digital data SIN, COS and transmit them to a microcomputer. The microcomputer multiplies the modulated wave signals SIN, COS with parameters cos ?, sin ?, and executes a subtraction of the multiplied value to obtain an error-correlation value ?. An angle calculations section in the microcomputer receives a detected value ?c obtained by multiplying the error-correlation value ? with a binary detection signal Rd. The binary detection signal Rd corresponds to a positive sign or a negative sign of the signal Sc. The sampling time of the AC excitation signal Sc is set to a time at which an absolute value of the AC excitation signal Sc exceeds a regulated value.

Abstract: Provided is a calibration apparatus and method of a three-dimensional (3D) position and direction estimation system. The calibration apparatus may receive inertia information and intensity information during a predetermined period of time, may calculate distances between a transmitter and the respective receivers, and may calibrate a signal attenuation characteristic of each receiver using the distances between the transmitter and the respective receivers.

Abstract: Certain embodiments provide an angle detector comprising: an AD converter configured to analog-to-digital convert plural-phase signal waves having respective different phases; a corrector configured to delay a phase of an excitation signal by an amount corresponding to a phase difference between the excitation signal and the signal wave; a wave detector configured to perform synchronous detection to an output signal from the AD converter in synchronization with the excitation signal whose phase is corrected; and an angle calculator configured to calculate an estimated rotation angle using an output signal of the wave detector and output the estimated rotation angle to the AD converter.

Abstract: A rotary encoder includes a single read-head and a circular scale. The encoder is self-calibrated by acquiring calibration samples with the read-head for rotational angles of the circular scale, and estimating spatial frequency and spatial distortion parameters of the encoder from the calibration samples.

Abstract: Methods, systems, and computer-readable media are described herein for using a modified Kalman filter to generate attitude error corrections. Attitude measurements are received from primary and secondary attitude sensors of a satellite or other spacecraft. Attitude error correction values for the attitude measurements from the primary attitude sensors are calculated based on the attitude measurements from the secondary attitude sensors using expanded equations derived for a subset of a plurality of block sub-matrices partitioned from the matrices of a Kalman filter, with the remaining of the plurality of block sub-matrices being pre-calculated and programmed into a flight computer of the spacecraft. The propagation of covariance is accomplished via a single step execution of the method irrespective of the secondary attitude sensor measurement period.

Abstract: Apparatuses and methods calibrate attitude dependent magnetometer alignment parameters of a magnetometer mounted together with other angular position sensors on a device without prior knowledge of the local magnetic field and allowing a constant but unknown offset of the yaw angle in the reference attitudes with respect to an earth-fixed coordinate system. The method includes acquiring magnetic field measurements from the magnetometer and corresponding estimated angular positions subject to an unknown yaw offset relative to a gravitational reference system. The method further includes iteratively computing a scale and vector components of a quaternion representing a misalignment matrix, an inclination angle of local magnetic field, and a yaw angle offset, using an extended Kalman filter (EKF) infrastructure with a specific designed model and constraints, based on the magnetic field measurements and the corresponding estimated angular positions.

Abstract: Methods and devices for determining a gyroscope bias are described. In one aspect, the present disclosure provides a processor-implemented method of determining a bias for an axis of a gyroscope. The method includes: representing a plurality of gyroscope readings for the axis in a histogram, the histogram including a plurality of bins associated with respective ranges; and determining the bias for the axis of the gyroscope by identifying a concentration of the gyroscope readings within the histogram.

Abstract: The position and orientation of a target object is obtained based on first measurement data obtained by a first sensor (first calculation). The position and orientation of the target object is obtained based on second measurement data obtained by a movable second sensor set in a position and orientation different from that of the first sensor (second calculation). When the position and orientation obtained by the first calculation and that obtained by the second calculation match each other, the position and orientation obtained by the first or second calculation or a position and orientation calculated from the position and orientation obtained by the first calculation and that obtained by the second calculation is output as the position and orientation of the target object.

Abstract: A robotic controller for autonomous calibration and inspection of two or more solar surfaces wherein the robotic controller includes a drive system to position itself near a solar surface such that onboard sensors may be utilized to gather information about the solar surface. An onboard communication unit relays information to a central processing network, this processor combines new information with stored historical data to calibrate a solar surface and/or to determine its instantaneous health.

Abstract: An alternating current (AC) electromagnetic tracker system with increased operational range and an ability to compensate for electromagnetic distortion in the local operating environment. The system uses multiple “N” sources/transmitters located at known positions in a common reference frame. A sensor receives the generated signal of each of the sources and a processor computes a position and orientation of the sensor from each. The processor further uses the known relative position and orientation between the N sources to compensate for distortion in the operating environment.

Abstract: Techniques are described for determining particle displacement or particle velocity data from particle acceleration measurements. In an embodiment, an apparatus comprises an interface configured to received particle acceleration data, one or more processors, and one or more storage media. The one or more storage media store instructions for determining one or more of particle velocity data or particle displacement data, based upon the particle acceleration data, by processing the particle acceleration data using a filter that at least approximates a Wiener filter and that uses one or more damping factors selected to provide stability in the presence of noise in the particle acceleration data.

Abstract: An optical encoder may include an encoder disk, an illumination system, and a detector to detect light diffracted from the encoder disk. The encoder disk may include a signal track comprising a diffraction grating, and an index track comprising a reflective index mark, wherein a width of the index mark is larger than a pitch of the diffraction grating. An indexing method may include providing an encoder disk, providing an illumination system to direct light to the encoder disk, providing a detector structured to detect light diffracted from the encoder disk, calculating an estimated count of quadrature states from a rising edge of an index pulse to a middle of the index interval, and calculating the quadrature state at an approximate center of the index pulse. A dynamic parameter correction method may include calculating a target gain and offset and correcting values based on the target gain and offset.

Abstract: A method for checking situation and position data of an instrument with at least a first section having at least a first sensor and at least a second sensor. The method encompasses the metrological determination of the situation or position, or its change, of the first sensor and the second sensor, determining a variable feature of the spatial reference between the situation or position of the first sensor and the situation or position of the second sensor at least at a first point in time, at a second point in time and at a third point in time. The method further encompasses determining, by means of a criterion, whether a difference of the variable feature between a first expression at a first point in time and a second expression at a second point in time still exists at a third point in time.

Abstract: A feedback system for controlling a servo motor comprising at least one rotary angle sensor and at least one rotary speed sensor, wherein the rotary angle sensor supplies a measured rotary angle value to a computer, wherein the rotary speed sensor supplies a measured rotary speed value to the computer, the actual rotary speed values are the measured rotary angle values interpolated according to the integrated measured rotary speed values, and wherein at high rotary speeds, the actual rotary speed values are the calibrated measured rotary angle values, differentiated with respect to time, and at low rotary speeds, the actual rotary speed values are the measured rotary speed values.

Abstract: A method and system for calculating pipeline integrity business risk score for a pipeline network is provided. The method includes a step of first calculating a structural risk score, an operational risk score and a commercial risk score for each pipeline segment in a pipeline network. The method further includes calculating pipeline integrity business risk score for each pipeline segment. The structural risk score, operational risk score, commercial risk score and pipeline integrity business risk score for each pipeline segment is rolled-up to calculate the respective risk scores of a pipeline network. The rolled-up risk scores are calculated by computing weight factors for each pipeline segment, relative risk scores weight of each pipeline segment and relative risk scores contribution of each pipeline segment. The system of the invention comprises executable files, dynamic linked libraries and risk score computing modules configured to display the risk scores using a dashboard.

Abstract: A manual positioning device includes at least one receiver, a reference network, a first switch, and at least one second switch. The at least one second switch, together with the first switch, is configured to switch at least two different reference signal paths for determining reference signals on the reference network.

Abstract: The invention relates to a portable electronic device and method for determining altitude. The device can comprise a satellite-positioning sensor for determining the elevation of the device on the basis of satellite data, a barometric sensor for measuring atmospheric-pressure information and/or an acceleration sensor for measuring acceleration information, and means for determining the altitude reading on the basis of the satellite-based elevation and the atmospheric-pressure and/or acceleration information. According to the invention, the means for determining the altitude reading are arranged to calculate a corrected altitude reading with the aid of the rate of change in elevation determined at least partly on the basis of the elevation determined on a satellite basis and atmospheric-pressure and/or acceleration information. With the aid of the invention, the altitude profile of exercise can be measured precisely.

Abstract: A person is detected by an observer device. A person detection history is recorded in a person detection history database. A position where the person is detected for the first time is estimated by a first-time detection position estimating unit, to be stored in a first-time detection position history database. The position of the door of the room in terms of local coordinates is estimated by a doorway position estimating unit. The calibration information as to the position of the observer device is calculated by a position calibration information calculating unit based on the door position in terms of local coordinates and that in terms of global coordinates.

Abstract: Provided is method of calibrating Y-axis direction position of contact tip of form measuring instrument including: table rotatable about Z-axis; contact tip capable of contacting workpiece; and contact tip driving means to drive contact tip in at least X- and Z-axis directions among X-, Y- and Z-axis directions perpendicular to one another. Method performs tracing measurement of inclined surface or inclined cylinder side surface which is part of workpiece obtained by inclining workpiece placed on table about Y-axis, or side surface of off-centered cylinder having center axis off-centered in X-axis direction by rotating surface to obtain measurement value at each angular position of rotation of table, obtains angular position of rotation at which smallest value among measurement values of tracing measurement is detected as angular position of rotation with smallest detected value, and adjusts Y-axis direction position of contact tip based on angular position of rotation with smallest detected value.

Abstract: A measurement apparatus includes a mount configured to mount an object, a probe configured to move with respect to the object so as to measure a shape of the object, an interferometer configured to measure a position of the probe with respect to a reference mirror, and a calculator configured to calculate the shape of the object using a measured value relating to the shape of the object that is obtained based on the position of the probe measured by the interferometer and a relative displacement between the object and the reference mirror that is obtained based on a signal from a sensor for the object and the reference mirror while the probe is moved.

Abstract: A method for calibrating a vision system of a vehicle includes the steps of projecting a pattern in proximity to the vehicle and calibrating the vision system using an image of the pattern generated by the vision system.

Abstract: A method for determining long-term offset drifts of acceleration sensors in a motor vehicle is provided. In one step, the longitudinal vehicle speed is determined in the vehicle's center of gravity. In another step, the share of the driving dynamics in the longitudinal reference acceleration formula and in the transversal reference acceleration formula is calculated from the longitudinal vehicle speed and the yaw rate. In yet another step, the share of the driving dynamics in the reference acceleration on the vehicle level formula is calculated by converting the driving dynamic reference accelerations formula calculated for the center of gravity to the position formula and the orientation of the sensor formula. In a further step, the long-term offset drift of the sensor is determined from the measured values of the sensor and the share of the measured value in the driving dynamics by means of a situation-dependent averaging process.

Abstract: According to one embodiment, a moving state estimation apparatus includes a sensor, a storage, a first estimation unit, a second estimation unit, a calculation unit and a correction unit. The sensor detects acceleration data. The first estimation unit estimates certainty degrees of the moving states. The second estimation unit calculates orientations of the terminal based on the acceleration data, and to estimate terminal states. The calculation unit calculates reliability degrees of the moving states. The correction unit corrects the certainty degrees in accordance with the reliability degrees, to obtain corrected moving states with the certainty degrees corrected.

Abstract: There is provided an apparatus caused to acquire information indicating a measured magnetic field vector and information relating to an uncertainty measure of the measured magnetic field vector in at least one known location inside the building, wherein the indicated magnetic field vector represents magnitude and direction of the earth's magnetic field affected by the local structures of the building, and to generate the indoor magnetic field map for at least part of the building on the basis of at least the acquired information and the floor plan.

Abstract: In a dial indicator correcting method, a first command is sent to a single drive shaft for controlling a push rod to move toward dial indicators. The method records a first indicated value of each dial indicator when the push rod contacts with one of the dial indicators, and records a second indicated value of each dial indicator when the push rod has contacted all the dial indicators. The method further sends a second command to the single drive shaft for controlling the push rod to move when a distance of the push rod equals a measuring range, and records a third indicated value of each dial indicator when the push rod moves with each moving step. By subtracting the third indicated value from the second indicated value, a forth indicated value of each dial indicator is obtained and is corrected by a running deviation of the single drive shaft.

Abstract: The invention relates to a circuit arrangement of a sensor-triggered control and/or display system in the context of a safety-critical application with a DSP and a method for monitoring the DSP, characterized-in-that the position and/or attitude signals transferred to the DSP are reduced in terms of their information content, the reduced information content is delivered to a position and attitude computation instance and checked as to whether the unambiguous position and/or attitude determined by the DSP agrees with the inaccurate and/or ambiguous position and/or attitude determined by the position and attitude computation circuit within the scope of the accuracy and/or ambiguity, and a sensor fault signal is output if the check is negative.

Abstract: A measuring instrument includes a main body, a stylus configured to be movable in relation to the main body, an encoder for detecting the amount of displacement of the stylus relative to the main body, a calculating section for calculating a measurement value from the amount of displacement detected by the encoder, a display section for displaying the measurement value calculated by the calculating section, an operation section for issuing a command to the calculating section, and a storage section that stores an effective measurement range larger than a lower limit and smaller than an upper limit of the movement stroke of the stylus. The calculating section makes a determination as to whether or not the amount of displacement detected by the encoder falls within the effective measurement range stored in the storage section and displays the result of such a determination on the display section.

Abstract: A method for calibrating a specimen stage of a metrology system is provided, in which a specimen that has multiple marks is positioned successively in different calibration positions, each mark is positioned in the photography range of an optical system by means of the specimen stage in each calibration position of the specimen, and the mark position is measured using the optical system. A model is set up that describes positioning errors of the specimen stage using a system of functions having calibration parameters to be determined. The model takes into consideration at least one systematic measurement error that occurs during the measurement of the mark positions. The values of the calibration parameters are determined based on the model with consideration of the measured mark positions.

Abstract: Based on a left tooth surface (28) having a maximum accumulated pitch error ALmax (when clockwise direction is a positive direction) and a right tooth surface (29) having a minimum accumulated pitch error ARmin (when clockwise direction is a positive direction), which are conceived to most likely have insufficiently ground portions, a correction value ?? which cancels these accumulated pitch errors for suppressing the accumulated pitch error after grinding is obtained. A reference tooth groove angle ?0 is corrected by the correction value ??, thereby obtaining the meshing angle ? of the work gear. All teeth detection and signal processing in a short period of time is realized by using a displacement sensor and a high-speed meshing-dedicated circuit board.

Abstract: A device, a method and a guiding device for setting out contours, points or works, including a computer-controlled measuring device provided with a movable measuring probe and a portable base unit provided with a rotatably supported elongate arm. The measuring probe is connected to the measuring device by means of a cord or a wire via the elongate arm, and the measuring device is provided with sensors for measuring a length or a change in the length of the cord or the wire and rotation of the arm in at least one degree of freedom for providing position data of the measuring probe.

Abstract: A system for evaluating data points against cadastral regulations to include a plurality of software modules programmed into a computer system with software and hardware configured to store and update a cadastral rule database containing a plurality of rules for determining the validity of the cadastral data (10). The cadastral database obtained from a data source reference data that is indicative of a plurality of established reference data points wherein the received input data corresponds to a plurality of measured data points with steps to co-process the input data and the referenced data according to the plurality of cadastral rules to determine an indication for the plurality of data points (20).

Abstract: Method for compensating the drift of a gyro mounted on a vessel subjected to at least rotational motions, about horizontal axes centered around an equilibrium position, and vertical translational motions, which vessel includes a three-axial accelerometer for measuring the acceleration of the vessel along three directions, includes low pass filtering the output signal from the gyro, calculating an inclination signal based upon the measurement values of the accelerometer and low pass filtering it, compensating the output signal from the gyro based upon the difference between the two low pass filtered signals, selecting the cut-off frequency of the low pass filtration of the inclination signal so that it is larger than a typical oscillation frequency for the translational motions but smaller than a typical oscillation frequency for the rotational motions, calculating a total force vector from the three measurement values, and calculating the inclination signal based upon the total force vector.

Abstract: Provided is an error measurement and correction device of a stage of a wafer prober. The error measurement and correction device includes a jig member, a vision module, a central processing unit, and an interface unit. The jig member is disposed on a chuck on the stage, and the vision module is disposed on an upper plate of the wafer prober disposed at a position facing the jig member to enable the camera of the vision module to acquire images of the patterns of the jig member and transmits the acquired images to the central processing unit. The central processing unit acquires images of the patterns of the jig member disposed on the chuck by using the vision module to extract reference position information, moves the stage at a unit interval of the pattern, acquires images of the patterns of the jig member again to extract measured position information, and generates and stores mapping data by calculating difference between the measured position information and the reference position information.

Abstract: A method for calibrating vehicle cameras is simplified by providing painted patterns on a road surface and by capturing those patterns by the cameras to be calibrated. According to a predefined positional relationship of the cameras with the painted patterns, captured images of the painted patterns are bird's-eye converted and matched with reference to calculate camera positions in a vehicle, thereby enabling an automatic calibration of camera directions and the like.

Abstract: An information processing apparatus that acquires estimated altitude data corresponding to a position based on detection information detected by a sensor at or near the position, and corrects altitude data associated with the position based on the estimated altitude data.

Abstract: There is provided a system for carrying out a height calibration process in a wireless indoor location tracking network, comprising: a plurality of fixed location tracking nodes disposed indoors to cover an indoor area, wherein the plurality of fixed location tracking nodes is configured to carry out location tracking in the indoor area; a mobile tag configured to communicate with at least one location tracking node at a given time at least for the purposes of determining the location of the mobile tag, wherein that the mobile tag comprises a height sensor configured estimate the height of the mobile tag; and at least one location tracking node of the plurality of fixed location tracking nodes is a calibration node configured to co-operate in carrying out a height calibration process during operation of the location tracking network, wherein the height of each calibration node is known.