Method for determining the direction of the spin axis of a rotating device

Abstract

A method for determining the direction of a spin axis of a rotating device, the rotating device including an XYZ magnetic field sensor. The method includes: determining the overall direction of a magnetic field; causing the rotating device to rotate around the spin axis; when the rotating device rotates around the spin axis, using the XYZ magnetic field sensor to measure at least one magnetic field value that changes with time; based on the measured at least one magnetic field value, calculating the magnetic field component of the magnetic field in the local body coordinate direction of the spin axis of the rotating device; and determining the direction of the spin axis using the calculated magnetic field component of the magnetic field and the determined overall direction of the magnetic field.

Description

Technical Field

[0001] Aspects of the disclosed embodiments generally relate to systems and methods for determining the direction of a spin axis of a rotating apparatus. Background Art

[0002] It is important to track the movement of one or more projectiles (also referred to herein as spinning equipment), such as, for example, one or more balls (e.g., rugby or basketball) used in playing a sporting game, to determine statistical information related to the sporting game. Such statistical information may include the number of shots or points, shots, passes, and the performance of one or more athletes in the sporting game. Such tracking is typically accomplished using a camera, manual verification of statistics by a person, and the use of sensors contained in the one or more projectiles. However, known methods for analyzing the movement of one or more projectiles are not well developed, making it currently impossible to adequately analyze a sporting game utilizing one or more projectiles.

[0003] One of the problems with tracking the motion of a projectile is that it is difficult to determine the direction in which the projectile is traveling along its trajectory. The direction of a projectile is crucial for analyzing, for example, how a shot is made. Direction measurement can theoretically be accomplished, for example, using a positioning beacon setup (i.e., triangulation or trilateration). The problem with this setup is that it requires beacons and is therefore expensive and complex. In addition to direction, the position of a projectile is also important in many applications. For example, when analyzing the position information of a projectile in a game, it is necessary to know before and after a shot or kick. Positioning systems based on beacons have been used to measure the position of a projectile. Such systems are expensive and complex.

[0004] Additionally, direction measurements can be made using an electronic compass. However, an electronic compass cannot be used to determine the direction of a trajectory, because it only indicates the direction of the magnetic field relative to the compass. There is no information about the direction in which the projectile is moving with an electronic compass. For example, an electronic compass may indicate that the left side of the projectile is facing north, but the projectile itself is moving east. Due to the arbitrary orientation of the projectile relative to the trajectory, an electronic compass cannot track the properties of the trajectory that we are interested in.

[0005] Another problem related to measuring the properties of a projectile that has been thrown / projected to a ballistic trajectory is determining how fast the projectile is spinning (i.e., the spin rate) and what the tilt angle between the spin axis and the ground is. The spin rate is an important parameter for analyzing how to manipulate a projectile. For example, when shooting a basketball, the ideal spin rate is about three revolutions per second. In another example, when trying to kick a soccer ball in a curve, a non-zero spin rate is required to form a projectile curve.

[0006] The measurement of the spin axis is very important, for example in the case of a basketball game. If the spin axis is not parallel to the playing field, the basketball may bounce in an unfavorable way when it hits the basket. Likewise, a horizontal spin axis ensures that the Magnus effect increases the angle of entry of the ball, making the basket appear larger.

[0007] Additionally, existing systems that track the motion, position, or spin rate of a projectile consume more power because they have multiple sensors and those multiple sensors are always on. As mentioned above, some systems also require external beacons.

[0008] Therefore, in view of the foregoing discussion, there is a need to address the aforementioned shortcomings in determining the direction of a projectile's travel. In particular, the problems addressed by various aspects of the disclosed embodiments relate to determining the direction of the spin axis of a spherical object, projectile, or ball. In addition, the present disclosure provides an improved method for determining the position of a projectile.

[0009] Embodiments of the present disclosure substantially eliminate or at least partially address the aforementioned shortcomings in determining the direction of the spin axis of a rotating device. Summary of the invention

[0010] According to a first aspect, aspects of the disclosed embodiments are directed to a method for determining the orientation of a spin axis of a rotating device, the rotating device comprising an XYZ magnetic field sensor, the method comprising:

[0011] -Determine the overall direction of the magnetic field;

[0012] - providing the rotating apparatus with rotation about a spin axis, wherein the spin axis is defined along a line including a point in three-dimensional space that remains stationary during the rotation of the rotating apparatus;

[0013] - When the rotating device rotates around the spin axis, the XYZ magnetic field sensor is used to measure multiple magnetic field values ​​that change over time;

[0014] - calculating the magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating device from the measured plurality of magnetic field values; and

[0015] - Determining the direction of the spin axis using the calculated magnetic field components of the magnetic field and the determined overall direction of the magnetic field.

[0016] According to a second aspect, the present disclosure provides a rotating device, the rotating device comprising:

[0017] -main body;

[0018] - an XYZ magnetic field sensor arranged inside the body and configured to measure at least one magnetic field value varying with time when the rotating device rotates around the spin axis; and

[0019] - a control module disposed within the body and communicatively connected to the XYZ magnetic field sensor, wherein the control module is configured to:

[0020] - receiving at least one measured magnetic field value;

[0021] - calculating a magnetic field component of at least one measured magnetic field value in the direction of the local body coordinates of the spin axis of the rotating device from the received at least one measured magnetic field value; and

[0022] - determining the direction of the spin axis using the calculated magnetic field components of the at least one measured magnetic field value and the determined overall direction of the at least one measured magnetic field value.

[0023] According to a third aspect, the present disclosure provides a system for determining a position of a rotating device, wherein the rotating device is configured to:

[0024] - Determine the direction of the spin axis of the rotating device;

[0025] - Estimating the horizontal displacement of the rotating device from the location where the rotating device was ejected to the specified target; and

[0026] - providing the determined direction of the spin axis and the estimated horizontal displacement to a portable computing device,

[0027] The portable computing device is configured to use the provided direction and displacement values ​​to determine the position of the spinning equipment relative to a specified target. The position of the equipment can be used to present an analysis of a game or practice performed with the spinning equipment to a user, for example.

[0028] According to a fourth aspect, the disclosed embodiments are directed to a method for determining the orientation of a spin axis of a rotating device, the rotating device comprising an XYZ magnetic field sensor and a gyroscope, the method comprising:

[0029] -Determine the overall direction of the magnetic field;

[0030] - providing the rotating apparatus with a rotation about a spin axis, wherein the spin axis is defined along a line including a point in three-dimensional space that remains stationary during the rotation of the rotating apparatus;

[0031] - when the rotating device rotates around the spin axis, measuring at least one magnetic field value using the XYZ magnetic field sensor;

[0032] - measuring at least one angular velocity value and orientation value using a gyroscope; and

[0033] - Determining the direction of the spin axis using the measured at least one magnetic field value, the at least one angular velocity value, the orientation value and the determined overall direction of the magnetic field.

[0034] Other aspects, advantages, features and objects of various aspects of the disclosed embodiments will become apparent from the accompanying drawings and the following detailed description of illustrative embodiments, which is interpreted in conjunction with the appended claims.

[0035] It will be appreciated that the features of the various aspects of the disclosed embodiments are susceptible to being combined in various combinations without departing from the scope of the disclosed embodiments as defined by the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] When read in conjunction with the accompanying drawings, the above summary of the invention and the following detailed description of illustrative embodiments will be better understood. In order to illustrate the present disclosure, exemplary configurations of the present disclosure are shown in the accompanying drawings. However, the present disclosure is not limited to the specific methods and means disclosed herein. In addition, it will be appreciated by those skilled in the art that the accompanying drawings are not drawn to scale. Whenever possible, identical elements are represented by identical numerals.

[0037] Embodiments of the present disclosure will now be described, by way of example only, with reference to the following drawings, in which:

[0038] Figure 1 is a schematic diagram of a rotating device according to an embodiment of the present disclosure;

[0039] Figure 2 is a schematic diagram of a system according to an embodiment of the present disclosure;

[0040] Figure 3 is a schematic diagram of a rotating device according to an embodiment of the present disclosure;

[0041] Figure 4 is a schematic diagram of a playing field according to an embodiment of the present disclosure;

[0042] Figure 5 is a graphical representation of the acceleration of a projectile as measured by an accelerometer attached to a rotating apparatus according to an embodiment of the present disclosure;

[0043] Figure 6 is a graphical representation of values ​​of magnetic field components according to an embodiment of the present disclosure; and

[0044] Figure 7 is a flow chart illustrating an exemplary process flow of a method for determining the direction of a spin axis of a rotating device according to an embodiment of the present disclosure.

[0045] In the accompanying drawings, underlined numbers are used to indicate the item in which the underlined number is located or the item adjacent to the underlined number. Ununderlined numbers are associated with the item identified by the line connecting the ununderlined number to the item. When a number is ununderlined and has an associated arrow, the ununderlined number is used to identify the general item to which the arrow points. DETAILED DESCRIPTION

[0046] The following detailed description illustrates embodiments of the present disclosure and ways in which these embodiments may be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art will recognize that other embodiments for carrying out or practicing the present disclosure are also possible.

[0047] The present disclosure provides a method for determining the direction of a spin axis of a rotating device, the rotating device comprising an XYZ magnetic field sensor, the method comprising:

[0048] -Determine the overall direction of the magnetic field;

[0049] - providing the rotating apparatus with a rotation about a spin axis, wherein the spin axis comprises a line including a point in three-dimensional space that remains stationary during the rotation of the rotating apparatus;

[0050] - Using an XYZ magnetic field sensor to measure multiple magnetic field values ​​that vary over time as the rotating device rotates around its spin axis;

[0051] - calculating the magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating device from the measured plurality of magnetic field values; and

[0052] - Determining the direction of the spin axis using the calculated magnetic field components of the magnetic field and the determined overall direction of the magnetic field.

[0053] Thus, the method determines the direction of the spin axis of a rotating equipment. The rotating equipment may be, for example, an object or projectile, such as a basketball, rugby, volleyball, baseball, bowling, lacrosse, handball, soccer, tennis, ice hockey, javelin, etc. In general, the term rotating equipment refers to an object that has a rotational motion or a tendency to a rotational motion during use.

[0054] According to the present disclosure, a rotation about a spin axis is provided for a rotating apparatus. As an example, when a basketball is thrown, the basketball usually rotates due to the spin caused by the hand of the athlete (i.e., the basketball is a rotating apparatus). In one method, a rotation about a spin axis is provided for a rotating apparatus. The spin axis is defined along a line including a point in three-dimensional space that remains fixed during the rotation of the rotating apparatus. Therefore, in essence, the term "spin axis" refers to a geometric line about which the rotating apparatus rotates. Compared to the rotating apparatus, the spin axis remains fixed in a local reference frame.

[0055] Another example of a rotating device is a javelin. When a javelin is thrown, it tends to rotate along its longest axis. Another example of a rotating device is a hockey puck. When the puck is shot or passed, it will tend to leave the ice and "fly" through the air. It is common for a moving puck to also rotate. Additionally, a puck can also rotate as it slides on the ice.

[0056] Another example of a rotating equipment is a football. When the football is rotated, it may roll on the football field (the football will rotate during the rolling).

[0057] The overall direction of the magnetic field is determined. The overall direction refers to, for example, the direction towards the magnetic north pole. The direction can be determined using, for example, an external device such as an electronic compass of a smart phone, or can be determined for each location using a rotating device. As an example, a map can be used to define the overall direction of the magnetic field relative to a basketball court.

[0058] In one embodiment, the rotating equipment includes one or more magnetic field sensors. In one embodiment, one or more magnetic field sensors are attached or arranged inside (i.e., inner surface) of the rotating equipment. One or more magnetic field sensors are configured to measure magnetic field values ​​in X, Y and Z directions. In one embodiment, one or more magnetic field sensors can be selected from a three-axis magnetometer, but are not limited to this. In one embodiment, the magnetic field sensor includes three separate sensor elements arranged orthogonally relative to each other to form an XYZ magnetic field sensor. In one embodiment, each magnetic field sensor is configured to measure a magnetic field value that varies over time, for example, each magnetic field sensor optionally provides a value related to magnetic field strength every 0.1 seconds. The magnetic field sensor optionally provides a value related to magnetic field strength every 1 second or 10 seconds. In one embodiment, each magnetic field sensor is individually calibrated to remove the most significant error sources.

[0059] When the rotating device rotates around the spin axis, the XYZ magnetic field sensor of the rotating device measures multiple magnetic field values ​​that change over time. The measured multiple magnetic field values ​​are used to calculate the magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating device.

[0060] The direction of the spin axis is determined using the calculated magnetic field components of the magnetic field and the determined overall direction of the magnetic field.

[0061] According to one embodiment, the control module is used to perform calculations and determinations. In addition, the control unit can be used to measure and / or collect measurement results from the XYZ magnetic field sensor. The control module can be a computing unit arranged inside the rotating equipment. Alternatively, the control module can be outside the rotating equipment (and communicate wirelessly) without limitation, and the control module can be selected from a mobile phone, a smart phone, a mobile Internet device (MID), a tablet computer, an ultra-mobile personal computer (UMPC), a tablet computer, a personal digital assistant (PDA), a web surfer, a handheld personal computer (PC) and a laptop computer. The control module optionally communicates with the server via a network. In one embodiment, the network is a wired network, a wireless network, or a combination of a wired network and a wireless network. In one embodiment, the network is the Internet. In another example, a portion of the functions of the control module can be arranged inside the rotating equipment (in the form of a microcontroller), and a portion can be arranged outside the rotating equipment (in the form of a smart phone connected to the microcontroller via a wireless connection such as Bluetooth).

[0062] The control module uses the calculated magnetic field components of the magnetic field and the determined overall direction of the magnetic field to determine the direction of the spin axis. The determined direction of the spin axis can be used to analyze in which direction the rotating equipment is moving along its trajectory (i.e., the forward direction). As an example, the direction of the spin axis can be used to determine that the ball (during a projectile) is traveling toward the east, or at a 45 degree angle relative to a basketball court or other sports field, for example.

[0063] In one example embodiment, in a basketball game, the ball is a rotating equipment, and the quantity may be the angle between the spin axis of the ball and the horizontal plane, wherein a non-zero angle indicates that the player has a problem with the shooting technique. In another example embodiment, in a rugby game where a rugby ball is a rotating equipment, the spin axis of the rugby ball is used to determine the change in the direction of the rugby ball's trajectory and the change in the direction of the rugby ball's spin axis in the surrounding environment, which is a key parameter for calculating the overall shape of the rugby ball's trajectory.

[0064] In one embodiment, the overall magnetic field is the homogeneous earth's magnetic field surrounding the rotating equipment.If the rotating equipment is located in at least one of (i) an indoor environment or (ii) an outdoor environment, the magnetic field will be substantially constant.

[0065] According to one embodiment, the magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating device is determined by the following mathematical formula:

[0066]

[0067] In one embodiment, the magnitude of the magnetic field is arbitrary, and the magnetic field of any single basket is characterized by parameters such as magAz, which is the horizontal direction of the surrounding magnetic field relative to the x-axis of the chosen global reference frame, and magEle, which is the vertical direction of the magnetic field or the tilt angle of the magnetic field relative to the local horizontal plane. For any single basket, the normalized magnetic field, i.e., the magnetic field with unit magnitude, is expressed as follows:

[0068]

[0069] As an example, in a basketball game using a right-handed coordinate system, x points toward the basket along the sideline of the court; y points to the right and is orthogonal to the sideline, and z points vertically downward. In one embodiment, the overall reference system specified in this manner is called the court reference system.

[0070] In one embodiment, the target structure, such as a basketball hoop, is typically metal. Sometimes, the ground plane may locally perturb the magnetic field, but the uniformity assumption is generally only valid when the basketball is tossed or otherwise flying through the air.

[0071] The spin axis expressed in the local reference frame is constant during any period of time including the unimpeded motion of the spinning equipment, such as the flight of the spinning equipment through the air or the sliding of a hockey puck on the ice. In one embodiment, a constant spin axis in the local reference frame does mean a constant spin axis in the global reference frame. Even if the spin axis is constant, the angular velocity about the spin axis is not necessarily constant.

[0072] In an example embodiment, the direction of the spin axis is determined by: finding a direction that minimizes the variance of the plurality of measured magnetic field values; resolving a sign ambiguity associated with the direction found that minimizes the variance of the plurality of measured magnetic field values ​​by comparing two consecutive measured magnetic field values ​​among the plurality of measured magnetic field values ​​with each other; and by using the found direction with the resolved sign as the direction of the spin axis.

[0073] Therefore, the direction found that minimizes the variance of the measured plurality of magnetic field values ​​(minimum variance solution) may have two possible solutions (negative and positive, i.e., a sign ambiguity associated with the solution). The solution is further analyzed by comparing two consecutive measured magnetic field values ​​of the measured plurality of magnetic field values ​​to each other to resolve the sign ambiguity associated with the found minimum variance solution.

[0074] In one embodiment, the found axis is used to perform a basis transformation into a basis in which one of the axes is aligned with the spin axis.The direction found that minimizes the variance of the measured plurality of magnetic field values ​​and the resolved sign are used as the direction of the spin axis.

[0075] Denote by M a real-valued Nx3 matrix comprising a plurality of magnetic field values ​​measured over a time period of interest. The spin axis is determined by adopting a new orthogonal and right-handed basis for the measured plurality of magnetic field values ​​such that the variance of the measured plurality of magnetic field values ​​in the direction of at least one basis vector is minimized. In one embodiment, the basis vector with the minimum variance including only noise and some variation of the magnetic field is determined as the spin axis. The spin axis expressed in a local reference frame is determined as the solution to the optimization problem:

[0076] Make w T w=1,

[0077] The solution is to determine a linear combination of three orthogonal axes that minimizes the variance of multiple magnetic field values ​​measured in the direction of the unit vector (w). In one embodiment, since the variance is always positive, sign ambiguity occurs. The optimization problem proposed above is equivalently expressed as:

[0078]

[0079] Therein, the unity constraint is a characteristic of the chosen parameterization. In one embodiment, the above minimization problem is formulated as a variance maximization problem, the goal of which is to determine an axis orthogonal to the spin axis.

[0080] The optimization problem is solved by any optimization routine starting from an arbitrary initial guess until the sign ambiguity, resulting in one of the two optima. Furthermore, the singular value decomposition is solved by using the following equation:

[0081] UΣV T =svd(M)

[0082] And select the one with the smallest variance (Mv i )'s right singular vector v i (columns of V) to get a specific initial guess for the optimization algorithm. This is equivalent to resolving V into the normal matrix M T The feature vector of M. In one embodiment, the selected v i It is possible to generate an estimate of the spin axis yourself, but the most accurate estimate of the spin axis is usually obtained as a solution to the proposed variance minimization problem.

[0083] In one embodiment, due to sign ambiguity, determining the spin axis of the rotating device results in two possible solutions for the spin axis, which correspond to alternative projection directions. The sign ambiguity is resolved by analyzing the collected data (i.e., multiple magnetic fields). In one embodiment, the observed magnetic fields are measured at known time intervals and / or at a constant sampling rate and stored in time sequence.

[0084] In one embodiment, the magnetic field components of the calculated magnetic field are not constant. For example, nutation and precession may cause the calculated magnetic field components to vary over time, and this variation information is used to obtain more information about the trajectory of the rotating equipment.

[0085] In one embodiment, the control module constructs a dynamic model representing the rotation of the spinning equipment. The dynamic model uses the following Rodrigues' rotation formula to determine the spin rate consistent with the dynamic model and time-dependent data:

[0086]

[0087] where θ represents the net rotation angle about the spin axis, and [s a ] × Yes a The skew-symmetric form of is further assumed to be constant spin rate, θ = ωt.

[0088] Rodrigues' rotation formula expands to:

[0089]

[0090] It is used to convert any sample triple into i 、m j The coupling is as follows:

[0091] m j =C(ω(t j -t i ))m i

[0092] From this, after algebraic manipulation, three equations of general form are obtained for each pair of sample triplets, whose values ​​are as follows:

[0093] acos(ωt)+bsin(ωt)+c=0

[0094]

[0095]

[0096]

[0097] Ignoring multiples of π, this equation may contain up to two unique results:

[0098]

[0099] However, only one result of this equation provides consistent values ​​of ω and sample triples m on different axes i 、m jIn one embodiment, a pair of observed magnetic fields may produce a negative discriminant (a 2 +b 2 -c 2 ), and thus produce fictitious results.

[0100] In one embodiment, if the average of the consistent spin rate estimates is positive, then the direction of the spin axis obtained above is correct. In another embodiment, if the average of the consistent spin rate estimates is negative, then the direction of the spin axis obtained may be reversed.

[0101] When the rotating device rotates around a constant axis in the homogeneous magnetic field, the control module can optionally estimate the surrounding homogeneous magnetic field about the spin axis s by using its average value. a The component in the direction of . Use the following equation to calculate the mean:

[0102]

[0103] In one embodiment, the rotation of the rotating equipment is modeled as a constant but arbitrary rotation occurring about a single spin axis of the rotating equipment. sa Independent of magnetic field direction.

[0104] In one embodiment, the control module estimates b by modeling the measured multiple magnetic field values ​​with a minimal three-parameter model. sa , this minimal three-parameter model ensures that the norm is constant over the entire time period of interest. Initially, a basis for the measured multiple magnetic field values ​​is generated, where one of the axes is the spin axis s a For the parameter α given by the solution of the optimization problem sa and β sa , the basis for the multiple magnetic field values ​​measured is defined by the following matrix:

[0105]

[0106] Where the spin axis is in the second row of the matrix, the basis vectors for the third row are generated so that the basis vectors for the third row are orthogonal to the spin axis; and the basis vectors for the first row are generated so that the basis vectors for the first row are the cross product of the second and third rows. When converted to such a basis, the measured multiple magnetic field values ​​can be modeled using a three-degree-of-freedom model of the following form:

[0107]

[0108] where ω is the spin rate estimated above and θ0 represents the phase shift, which is estimated by:

[0109]

[0110] The signal model is used to minimize the parameter b by minimizing the following or similar cost function: sa The uncoupled estimates of , ω, and θ0 are combined together:

[0111]

[0112] So that the minimum three-parameter model f(b sa ,ω,θ0) as close as possible to the observed data (e.g., magnetic field value) m(t). Once the cost function is chosen, its value is minimized from the initial guess. In addition, if the spin axis is horizontal, an alternative approach is the solution of a constrained minimization problem, which is solved by: |b sa |≤cos(magEle).

[0113] In one embodiment, b sa The estimate of can depend on magnetic field parameters, and the magnetic poles can include an additional trend to retrieve all neighboring solutions.

[0114] In one embodiment, the control module obtains the direction of the projectile traveling toward the basket by expressing the horizontally observed magnetic field as follows:

[0115]

[0116] Whenever 1-(b sa -sin(α)sin(magEle)) 2 -sin 2 When (magEle)>0, where α is the angle between the spin axis and the horizontal ground plane. The control module detects that the horizontal component of the spin axis is usually orthogonal to the projection direction. In the basketball example, this yields two candidate solutions:

[0117]

[0118] In another embodiment, the control module detects that the angle β between the projectile direction and the horizontal component of the spin axis may not be equal to And the angle α between the horizontal ground plane and the spin axis may not be equal to 0. In this article, the control module forms a magnetic field on the spin axis b. sa The analytical formula for the component in the direction of is as follows:

[0119]

[0120] The above formula can be simplified in the following steps to obtain the formula for determining the projectile direction s d The above equation can be simplified using matrix multiplication to obtain:

[0121] b sa =cosαcos(magEle)cos(magAz-s d -β)+sin(magAz)sin(magEle)

[0122] Furthermore, using trigonometric identities, b sa Simplified to:

[0123] b sa =cosαcos(magEle)cos(magAz-s d -β)+sin(magAz)sin(magEle)

[0124] s d The value of can be obtained by further simplifying the above equation into the following formula:

[0125]

[0126] According to one embodiment, the control module obtains the direction of the projectile traveling toward the basket by expressing the magnetic field observed at an elevated level as follows:

[0127]

[0128] in,

[0129] 1-([b sa -sin(α)sin(magEle)] / cos(α)) 2 -sin 2 (magEle)>0

[0130] Thus, for example, in games such as rugby, cricket, and javelin throwing, where the angle α between the horizontal ground plane and the spin axis is not equal to 0, this leads to the following two candidate solutions:

[0131]

[0132] In one embodiment, the control module resolves the spin axis by adopting a model of the form

[0133]

[0134] where R is the rotation matrix, C(·,·) represents the Rodrigues rotation formula above, ω is the spin rate, and θ is the projection direction.

[0135] In one embodiment, the control module uses a first branch selection method to select a branch. In one embodiment, when releasing the rotating equipment, the control module uses an auxiliary method to resolve the orientation of the rotating equipment. In one embodiment, the orientation converts the acceleration measured during the release of the rotating equipment into a coordinate system related to, for example, a basketball court.

[0136] In one embodiment, the control module uses a user device communicating with the rotating equipment through a network to select a branch. In one embodiment, the user device can be selected from a mobile phone, a personal digital assistant (PDA), a tablet computer, a desktop computer or a laptop computer, but is not limited thereto.

[0137] In one embodiment, the control module processes the received signal strength indicator (RSSI) information to estimate the distance between the athlete and the user device. In one embodiment, if the location of the user device is known and the projectile distance has been estimated, the control module selects a branch.

[0138] The control module automatically selects branches by collecting many indicators and adopts machine learning techniques. In an example embodiment, a neural network (NN)-based classification network or a NN-based function fitting network that indicates the index of the correct branch directly estimates the projection direction. The control module can automatically weight different estimated projection directions to generate a combined solution, and may reject inconsistent projection direction estimates, and automatically limit the solution to the correct interval to achieve maximum robustness.

[0139] According to one embodiment, determining the direction of the spin axis further comprises determining the angle between the spin axis (of the projectile or ball) and the horizontal ground plane. The determined angle can be used to refine the determined direction of the spin axis.

[0140] In addition, determining the direction of the spin axis may further include: determining an angle of the spin axis relative to a horizontal ground plane; and determining an angle of the projection direction relative to a horizontal component of the spin axis.

[0141] Furthermore, according to one embodiment, the control module is configured to determine the overall level of the tilt angle when the elevation angle of the magnetic field is known. The tilt angle can be expressed as:

[0142]

[0143] According to one embodiment, the method further comprises:

[0144] - estimating the horizontal displacement of the rotating apparatus using at least one of the flight time, the release speed, the initial altitude and the height of the rotating apparatus relative to the ground; and

[0145] -Determine the position of a rotating device relative to a specified target by combining the direction of the rotating device's spin axis with the horizontal displacement.

[0146] Therefore, the horizontal displacement of the rotating equipment can be estimated. The horizontal displacement can be estimated using at least one of the flight time, release speed, initial height and height of the rotating equipment relative to the ground. As an example, if the flight time of the ball is 2 seconds and the speed (if friction is not considered, the release speed can be considered as speed) is 3.5 meters per second, the horizontal displacement is 7 meters. In addition, the position of the rotating equipment relative to the specified target can be determined by combining the direction of the spin axis of the rotating equipment with the horizontal displacement. An example of a specified target is the basket of a basketball court (with a long side in the east-west direction). For example, if the direction of the spin axis is determined to be north, we can determine that the projectile is 7 meters away from the basket in the long side direction (i.e., outside the 3-point line), i.e., the position where the basketball is located when the projectile is performed. That is, assuming that the long side of the court is in the east-west direction, the spin axis pointing north indicates that the projectile is performed in the direction of the long side. This is because in the given example, there is a gap of about 90 degrees between the spin axis and the projectile direction. This position information is very useful when analyzing the game. In addition, the method / equipment can be used to derive the position without the need for using external beacons or cameras or other systems through the method. In another example, in a rugby game, the direction of the spin axis is determined to be east. The rugby field is east-west oriented. The ball hits a specific target in the goal (e.g., detected with an optional accelerometer). If the horizontal displacement is 30 meters, the location where the shot was made can be determined. Therefore, the present method automatically determines the relative position of the rotating equipment relative to the specified target.

[0147] In practice, in football, the spin axis of a straight shot (commonly referred to as a pass or kick in American football) is rarely horizontal, but rather closer to the vertical, or a combination of horizontal and vertical displacements. In this case, the angle between the spin axis and the horizontal ground plane can be used to enhance the determination of position. For a pass / projection that rolls and / or bounces on the ground, the spin axis is closer to the horizontal spin axis.

[0148] According to yet another embodiment, the overall direction of the magnetic field is determined by: firing the rotating equipment at least once along a trajectory of known horizontal direction; using geographic information related to at least one local environment; or using a second sensor. As an example, we know that the rotating equipment was fired (thrown in the case of a ball) to the north. The known direction to the north is provided to the control module. Alternatively, the known direction can be provided to a smartphone that receives information from the control module of the rotating equipment. In addition, geographic information related to at least one local environment can be used.

[0149] As an example, if we know the direction of the long side of a basketball court, we can use this as information to determine the overall direction. In addition, the overall direction can be determined by using a second sensor, such as a sensor of a smart phone.

[0150] According to yet another embodiment, the method includes using an accelerometer of the rotating equipment to detect whether the rotating equipment is launched (thrown) on a ballistic trajectory. If the rotating equipment is detected to be on a ballistic trajectory, the XYZ magnetic field sensor is activated. Therefore, the method optionally employs an accelerometer that is attached to or otherwise fixed to the interior of the rotating equipment.

[0151] When a rotating device is used, an accelerometer can be used to detect the acceleration of the rotating device. As an example, the accelerometer can detect when the rotating device is on a trajectory. For example, when the rotating device is a ball, when the ball is thrown, the ball will follow a path under the action of the force from the throwing motion. For example, such a throwing motion can also include passing or projecting.

[0152] According to one embodiment, if the rotating equipment is detected to be in a ballistic trajectory, the accelerometer activates the XYZ magnetic field sensor, thereby reducing the power consumption of the rotating equipment. When the rotating equipment is in a ballistic trajectory, it is in a "free fall" state from the perspective of the accelerometer, that is, the accelerometer reading is actually zero (or the reading can be used to infer whether the rotating equipment is in a "free fall state"). Please note that the accelerometer reading can also include reading values ​​caused by or generated by the rotation. This reduces power consumption because the direction of the spin axis is mainly required when a rotating projectile is thrown into a trajectory, such as a ballistic trajectory. In this way, the spin axis direction can be used to measure the position where the projectile (such as a basketball) is thrown. Alternatively, the accelerometer can detect the movement of a projectile such as a hockey puck and activate the XYZ magnetic field sensor when the movement of the hockey puck is detected.

[0153] The optional accelerometer and XYZ magnetic field sensor communicate measured data, such as acceleration data, and multiple magnetic field values ​​of the rotating equipment to the control module.

[0154] According to yet another embodiment, the direction of the spin axis is determined during the time interval when the rotating device is on the ballistic trajectory. In this way, the power consumption of the electronic components of the rotating device can be reduced when the spin axis direction can only be determined when the ball is determined to be on the trajectory. The magnetic field sensor can be kept off at other times (such as during storage, non-use or when the rotating device is handheld).

[0155] In an alternative embodiment, the direction of the spin axis of a rotating device including an XYZ magnetic field sensor and a gyroscope is determined. First, the overall direction of the magnetic field is determined. Then, the rotating device is provided with a rotation around the spin axis, wherein the spin axis is defined along a line that includes a point in three-dimensional space that remains fixed during the rotation of the rotating device. When the rotating device rotates around the spin axis, at least one magnetic field value is measured using the XYZ magnetic field sensor. The gyroscope is used to measure at least one angular velocity value and an orientation value. The direction of the spin axis is determined using the measured at least one magnetic field value, at least one angular velocity value, the orientation value, and the overall direction of the determined magnetic field.

[0156] The gyroscope values ​​can be used to determine the spin axis. In this embodiment, the angle between the gyroscope and the magnetic field sensor is known. Therefore, the magnetic field measurement provides information about the direction of the spin axis relative to the local magnetic field that can be determined. This information is compared to the global direction to determine the direction of the spin axis.

[0157] The direction of the spin axis can be used to determine the position of the rotating equipment, for example, as discussed previously. In addition, if the rotating equipment includes an accelerometer, the accelerometer reading can be used to turn on the gyroscope during the time when the rotating equipment is in a ballistic trajectory to save power.

[0158] In an example embodiment, when the rotating equipment is a football, when the football rolls on the ground, the XYZ magnetic field sensor of the football is optionally used to measure multiple magnetic field values. The football is equipped with an XYZ magnetic sensor, and optionally, the XYZ magnetic field sensor is configured to turn on only when the football is in a ballistic trajectory (i.e., shooting, passing or kicking) or rolling on the ground. By limiting the time when the XYZ magnetic sensor is used, the power consumption of electronic components in the football can be reduced.

[0159] Aspects of the disclosed embodiments provide an apparatus comprising:

[0160] -main body;

[0161] - an XYZ magnetic field sensor arranged inside the body and configured to measure at least one magnetic field value varying with time when the body rotates around the spin axis; and

[0162] - a control module disposed inside the body and communicatively connected to the XYZ magnetic field sensor, wherein the control module is configured to:

[0163] - receiving at least one measured magnetic field value;

[0164] - calculating a magnetic field component of at least one measured magnetic field value in the direction of the local body coordinates of the spin axis of the body from the received at least one measured magnetic field value; and

[0165] - Determining the direction of the subject's spin axis using the calculated magnetic field components of the magnetic field and the determined overall direction of the magnetic field.

[0166] The direction of the spin axis of the determined subject can be used to analyze, for example, the trajectory of a rotating device. For example, many sports activities require this to provide meaningful statistics or provide feedback on athletic performance. In essence, the direction of the spin axis can be used as an indication of the direction in which the rotating device is traveling at a given moment. The magnetic field sensor (and other components) are arranged inside the device body. As an example, the sensor can be arranged in a compact package with other components (such as a controller and associated battery + communication device and an optional accelerometer). The compact package is attached to the inner surface of the body. In the case of a basketball, the inner surface of the body is the same as the inner surface of the ball.

[0167] In one embodiment, the XYZ magnetic field sensor is a device that detects and measures the strength and direction of magnetic flux and / or magnetic field at a specific location. The XYZ magnetic field sensor is optionally a three-axis magnetometer. In one embodiment, the XYZ magnetic field sensor is optionally attached to the inner surface of the rotating equipment. In another embodiment, the XYZ magnetic field sensor is optionally attached to the outer surface of the rotating equipment. The rotating equipment is optionally a basketball with an XYZ magnetic field sensor and a control module attached. The rotating equipment is optionally a rugby, football, baseball, ice hockey or other sports object that includes the XYZ magnetic field sensor and the control module.

[0168] In one embodiment, the rotating equipment is communicatively connected to a server or user device via a wired or wireless network. The server optionally receives a plurality of measured magnetic field values ​​from the rotating equipment. The server may include a processor that determines the direction of the spin axis of the rotating equipment. In one embodiment, the processor of the server optionally performs one or more steps of the control module. The server optionally includes a personal computer, a tablet computer, a laptop computer, or an electronic notebook. The components of the rotating equipment communicate via a communication network, which is optionally a wired network or a wireless network. The user device optionally includes a personal computer, a smart phone, a tablet computer, a laptop computer, or an electronic notebook.

[0169] In one embodiment, the rotating device optionally communicates the determined direction of the spin axis to a server. The server stores the determined direction of the spin axis in a database. In one embodiment, the server is optionally a cloud service.

[0170] According to one embodiment, the rotating device further includes a gyroscope disposed inside the body of the rotating device.

[0171] According to another embodiment, the rotating equipment further comprises an accelerometer. The accelerometer is arranged inside the rotating equipment. As an example, the accelerometer can be embedded in a compact package (as described above) mounted on the inner surface of the body, the accelerometer is configured to provide accelerometer measurements to the control module, and the control module is configured to:

[0172] - detecting from the accelerometer measurements provided whether the spinning material is launched on a ballistic trajectory (i.e. passed, thrown or projected); and

[0173] - If it is detected that the rotating equipment is in a ballistic trajectory, providing an activation signal to the XYZ magnetic field sensor to activate the XYZ magnetic field sensor to perform magnetic field measurement.

[0174] The present disclosure provides a system for determining the position of a rotating device, wherein the rotating device is configured to

[0175] - Determine the direction of the spin axis of the rotating device;

[0176] - Estimating the horizontal displacement of the rotating device from the location where the rotating device was ejected to the specified target; and

[0177] - providing the determined direction of the spin axis and the estimated horizontal displacement to a portable computing device,

[0178] The portable computing device is configured to use the provided direction and displacement values ​​to determine a position of the rotating equipment relative to a designated target.

[0179] As previously mentioned, the position of a rotating device can be used to analyze, for example, a basketball game. The position in the example is the position of the ball relative to a target such as a basket. Since the position, orientation, and basket position relative to the basket are known, a rendered view (on the user's device) of a shot taken during a game or practice can be provided to the user.

[0180] Therefore, the advantages of the present system are the same as those disclosed above in conjunction with the present method, and the embodiments listed above in conjunction with the present method are also applicable to the system with necessary modifications.

[0181] Embodiments of the present disclosure can more accurately determine the direction of the spin axis of a rotating device. Embodiments of the present disclosure can determine the relative position of a rotating device relative to a specified target. Embodiments of the present disclosure can beneficially reduce the power consumption of a rotating device by turning on an XYZ magnetic field sensor only when the rotating device moves along a track. Embodiments of the present disclosure can determine the rotation speed of a rotating device without a gyroscope sensor that consumes more power.

[0182] Figure 11 is a schematic diagram of a rotating device 102 according to an embodiment of the present disclosure. The rotating device 102 rotates around or with a spin axis 106. The rotating device 102 (e.g., a basketball or a football) includes an XYZ magnetic field sensor 104, which is attached to a surface (e.g., an inner surface or an outer surface) of the rotating device 102. In one embodiment, when the rotating device 102 rotates around the spin axis 106, the XYZ magnetic field sensor 104 rotates around the spin axis 106 at the same rotation speed as the rotating device 102. The functions of these components have been described above.

[0183] Figure 2 2 is a schematic diagram of a system according to an embodiment of the present disclosure. The system includes a rotating device 202 (such as a ball), an XYZ magnetic field sensor 204A, a control module 204B, and a communication module 204C. The control module 204B is communicatively connected to a user device 206 via wireless communication. The user device can provide information to a server 210 via a network 208. The server 210 includes a database 212. The functions of these components have been described above.

[0184] Reference Figure 1 , Figure 3 According to an embodiment of the present disclosure, Figure 1 Schematic diagram of a rotating device 302 viewed from a direction B of the spin axis 106 (in the direction B of the spin axis 106). The rotating device 302 rotates around the spin axis 306. The rotating device 302 includes an XYZ magnetic field sensor 304, which is attached to the inner surface or structure of the rotating device 302. The XYZ magnetic field sensor 304 rotates around the spin axis 306 at an angular velocity (w) 308. The functions of these components have been described above.

[0185] Figure 4 400 is a schematic diagram of a playing field or court 400 according to an embodiment of the present disclosure. The playing field 400 (e.g., a basketball court) includes a basket 408. In one embodiment, a first ball (e.g., a first spinning device) 402A and a second ball (e.g., a second spinning device) 402B are launched toward and / or thrown into the basket 408 by a user.

[0186] In one embodiment, first ball 402A rotates or spins along or about first spin axis 406A by launching first ball 402A toward basket 408. First ball 402A includes first XYZ magnetic field sensor 404A attached to an inner surface of first ball 402A that rotates about first spin axis 406A.

[0187] In one embodiment, when second ball 402B is thrown or launched, second ball 402B rotates along or around second spin axis 406B. Second ball 402B includes second XYZ magnetic field sensor 404B that rotates around second spin axis 406B.

[0188] The flight direction or trajectory of first ball 402A and / or second ball 402B is determined by determining the direction of the spin axis using the balls' respective XYZ magnetic field sensors. In one embodiment, an accelerometer and a timer are used to measure the flight time of first ball 402A and the flight time of second ball 402B.

[0189] In the exemplary embodiment, the magnetic field parameters of the playing field 400 are calculated based on the parameters magEle (i.e., the horizontal direction of the local magnetic field relative to the x-axis of the global magnetic field) and magAz (i.e., the vertical direction of the local magnetic field relative to the local horizontal plane), which convert the obtained spin axis (b sa ) is converted into a more tangible direction estimate. In one embodiment, b is calculated sa values ​​to determine the magnetic field parameters for multiple throws from a known throw direction. In another embodiment, a thrower / user with the ability to consistently throw with a horizontal spin axis can generate a consistent b for each direction. sa value.

[0190] In yet another embodiment, an optimization process is performed to determine a pair of magnetic field parameters. In one embodiment, the correct magnetic field parameter estimates are determined by validating the calculated magEle values ​​with a geomagnetic database.

[0191] In one embodiment, first ball 402A and second ball 402B are rolled on the ground from multiple different directions toward playing field 408. In one embodiment, a set of projectiles including projectiles from different directions is used to determine magnetic field parameters / values ​​generated by the set of projectiles and projectile direction estimates, which are calculated based on the magnetic field parameters / values ​​generated by the set of projectiles. In the range of d is the spin direction of the first ball 402A or the second ball 402B. This method does not require the direction of each projectile, but rather requires groups of projectiles from different directions.

[0192] In addition, a process may be implemented to use the sa (excluding possible outliers) to determine magEle by the maximum absolute value obtained so that |b sa | max = cos(magEle). Then, use magAz to convert the spin direction value (s d ) are set within the expected range.

[0193] Figure 5 It is a diagram of the acceleration of the projectile measured by the accelerometer attached to the rotating equipment according to an embodiment of the present disclosure. The diagram depicts acceleration graphs 504A, 504B, 504C based on the acceleration data detected by the accelerometer during the release of the rotating equipment. Graph 504A is a diagram of the situation where the rotating equipment (ball) is projected but before it is released from the hand. When the rotating equipment is in the air or flying, the accelerometer reading 504C is 0 because the rotating equipment is in free fall from the perspective of the accelerometer. When the rotating equipment hits the target or the ground, the accelerometer reading 504B provides a reading related to the impact. The accelerometer detects whether the rotating equipment is ejected onto a ballistic trajectory, and if it is detected that the rotating equipment is in a ballistic trajectory, the XYZ magnetic field sensor is activated. The magnetic field value / data is sensed only when the rotating equipment is in a ballistic trajectory and rotates around the spin axis, thereby reducing the power consumption of the rotating equipment.

[0194] During the flight time, the magnetic field values ​​collected by the XYZ magnetic field sensor are represented by lines 502A, 502B, and 502C. During the flight of the rotating equipment, the XYZ magnetic field sensor data on each of the three axes are displayed as sinusoidal curves, and the axis of each XYZ magnetic field sensor has arbitrary offset, amplitude, frequency, and phase shift values. If the magnetic field is uniform, these magnetic field values ​​will be coupled together.

[0195] Figure 6 is a diagram of the values ​​of magnetic field components according to an embodiment of the present disclosure. sa The overall behavior for different values ​​of is depicted as a contour plot, which shows that b sa The shape of the constant value of changes as the spin axis orientation changes in the surrounding magnetic field. The diagram also depicts a horizontal rotation of the spin axis corresponding to the horizontal direction, and a vertical rotation of the spin axis corresponding to the horizontal direction. The diagram shows a line 602 representing the spin axis without any constraints.

[0196] For example, in basketball, a technically correct jump shot (ignoring layups, dunks, etc.) is one in which the angle between the horizontal ground plane and the spin axis is zero. This corresponds to the line β sa=0, which is shown as line 602 in the figure. With this constraint on the spin axis, the horizontal direction of the spin axis retains two results, for example, approximately ±40° from the magnetic south direction towards the east and west, respectively. The diagram shows line 604, which indicates the extreme value of the magnetic field component along the horizontal spin axis, which is indicated by cos(magEle) (i.e., the magnitude of the horizontal component of the magnetic field). The two possible results (both) are reduced to the same direction, namely at least one of (i) north or (ii) south. When line 602 is outside the "obstacle", the problem manifested in this form has no real value and / or physical result for any horizontal spin axis. In fact, this line 602 may appear when magEle approaches ±90° and / or the direction of the spin axis is close to the north or south direction, especially for inexperienced shooters. This also shows that there is a clear dependency between the accuracy of the horizontal spin axis and magEle: cos(magEle), cos(magEle) stipulates b sa A range of physically meaningful values ​​of , and this range decreases with increasing |magEle|, thus making the result more reliable than the obtained b sa The value is becoming more sensitive.

[0197] In one embodiment, the practical limit of reasonable accuracy of the horizontal spin axis is about ±80°, which depends primarily on the quality of the XYZ magnetic field sensor and the thrower / athlete. In one embodiment, for inexperienced throwers, the accuracy of the direction estimate decreases faster as |magEle| increases.

[0198] Figure 7 704 is a flow chart showing an exemplary process flow of a method for determining the direction of a spin axis of a rotating device according to various aspects of the disclosed embodiments. In step 702, the overall direction of the magnetic field is determined. In step 704, a rotation of the rotating device around the spin axis is provided. The spin axis includes a line that includes a point in three-dimensional space that remains fixed during the spinning of the rotating device. In step 706, when the rotating device rotates around the spin axis or around the spin axis, a plurality of magnetic field values ​​that vary over time are measured using an XYZ magnetic field sensor. Typically, the spin axis passes through the center of the rotating device (for example, in the case of a sphere).

[0199] At step 708, a magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating device is calculated from the measured plurality of magnetic field values. At step 710, the direction of the spin axis is determined using the calculated magnetic field component of the magnetic field and the determined global direction of the magnetic field.

[0200] The embodiments of the present disclosure described above may be modified without departing from the scope of the present disclosure as defined by the appended claims. Expressions used to describe and claim the present disclosure, such as "comprises," "includes," "incorporates," "has," "is," are intended to be interpreted in a non-exclusive manner, i.e., also allowing for the presence of items, parts, or elements that are not explicitly described. References to the singular should also be interpreted as referring to the plural.

Claims

1. A method for determining the direction of a spin axis (106, 306, 406A, 406B) of a rotating moving object (102, 202, 302, 402A, 402B), the moving object comprising an XYZ magnetic field sensor (104, 204A, 304, 404A, 404B), a control module (204B), and an accelerometer disposed inside a body of the moving object, the method comprising: detecting, by means of the accelerometer, whether the moving object is ejected onto a ballistic trajectory; When it is detected that the moving object is ejected onto the ballistic trajectory, activating the XYZ magnetic field sensor (104, 204A, 304, 404A, 404B) disposed inside the body of the moving object (102, 202, 302, 402A, 402B); Determine the overall direction of the magnetic field; providing the moving object with rotation about the spin axis, wherein the spin axis is defined along a line including a point in three-dimensional space that remains stationary during the spinning of the moving object; When the moving object rotates around the spin axis, using the XYZ magnetic field sensor to measure a plurality of magnetic field values ​​that vary with time; According to the measured multiple magnetic field values, the magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating moving object is calculated, wherein the magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating moving object is determined by the following mathematical formula: Among them, b sa is the magnetic field in the direction of the spin axis, magEle is the vertical direction of the magnetic field or the inclination angle of the magnetic field relative to the local horizontal plane, α is the angle between the spin axis and the horizontal ground plane; and Determining the direction of the spin axis using the calculated magnetic field components of the magnetic field and the determined overall direction of the magnetic field, wherein determining the direction of the spin axis comprises: determining the angle of the spin axis relative to a horizontal ground plane; and The angle of the horizontal component of the projectile direction relative to the spin axis is determined.

2. The method according to claim 1, further comprising: determining an angle between the spin axis (106, 306, 406A, 406B) and a horizontal ground plane; as well as The determined angle is used to enhance the determined direction of the spin axis (106, 306, 406A, 406B).

3. The method according to claim 1 or 2, wherein: Determining the direction of the spin axis (106, 306, 406A, 406B) further includes: Finding a direction that minimizes the variance of the plurality of measured magnetic field values; Resolving a sign ambiguity associated with the direction found that minimizes a variance of the measured plurality of magnetic field values ​​by comparing two consecutively measured magnetic field values ​​of the measured plurality of magnetic field values ​​to each other; and The found direction with the resolved sign is used as the direction of the spin axis.

4. The method according to claim 1 or 2, wherein: The method further comprises: estimating a horizontal displacement of the moving object using at least one of a flight time, a release speed, an initial height, and a height of the moving object relative to the ground; and The position of the moving object relative to a designated target is determined by combining the direction of the spin axis of the moving object with the horizontal displacement.

5. The method according to claim 1 or 2, wherein: The overall direction of the magnetic field is determined by: ejecting the moving object at least once along a trajectory in a known horizontal direction; Use geographic information related to at least one local environment; or Use a second sensor.

6. The method according to claim 1 or 2, wherein: The direction of the spin axis is determined during a time interval when the moving object is on the ballistic trajectory.

7. A moving object (102, 202, 302, 402A, 402B), the moving object comprising: main body; an XYZ magnetic field sensor (104, 204A, 304, 404A, 404B) disposed inside the body and configured to measure at least one magnetic field value that varies with time when the moving object (102, 202, 302, 402A, 402B) rotates around a spin axis (106, 306, 406A, 406B); an accelerometer disposed inside the body of the moving object and configured to detect whether the moving object is ejected onto a ballistic trajectory; as well as a control module (204B) disposed inside the body and communicatively connected to the XYZ magnetic field sensor (104, 204A, 304, 404A, 404B), wherein the control module (204B) is configured to: receiving at least one measured magnetic field value; The magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating moving object is calculated according to the received at least one measured magnetic field value, wherein the magnetic field component of the magnetic field in the direction of the local body coordinates of the spin axis of the rotating moving object is determined by the following mathematical formula: Among them, b sa is the magnetic field in the direction of the spin axis, magEle is the vertical direction of the magnetic field or the inclination angle of the magnetic field relative to the local horizontal plane, α is the angle between the spin axis and the horizontal ground plane; and The direction of the spin axis is determined using the calculated magnetic field components of the magnetic field and the overall direction of the magnetic field, wherein, to further determine the direction of the spin axis, the control module is configured to determine the angle of the spin axis relative to a horizontal ground plane; and determine the angle of the projection direction relative to the horizontal component of the spin axis. 8 . The moving object according to claim 7 , further comprising a gyroscope disposed inside the main body of the moving object.

9. The moving object according to claim 7 or 8, further comprising an accelerometer, wherein the accelerometer is arranged inside the moving object, wherein: The accelerometer is configured to provide accelerometer measurements to the control module (204B), and the control module (204B) is configured to: detecting from the provided accelerometer measurements whether the moving object is ejected onto a ballistic trajectory, and If it is detected that the moving object is in the ballistic trajectory, an activation signal is provided to the XYZ magnetic field sensor (104, 204A, 304, 404A, 404B) to activate the XYZ magnetic field sensor to perform magnetic field measurement.

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