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CN112461223B - A Method for Generating Magnetic Field Fingerprint Library Independent of Magnetometer Bias - Google Patents

A Method for Generating Magnetic Field Fingerprint Library Independent of Magnetometer Bias Download PDF

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CN112461223B
CN112461223B CN202011247148.7A CN202011247148A CN112461223B CN 112461223 B CN112461223 B CN 112461223B CN 202011247148 A CN202011247148 A CN 202011247148A CN 112461223 B CN112461223 B CN 112461223B
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magnetometer
grid
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field strength
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旷俭
牛小骥
李泰宇
刘韬
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Wuhan University WHU
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    • G—PHYSICS
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    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
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Abstract

一种磁力计零偏无关的磁场指纹库生成方法。本发明基于局部区域地磁场强度分量相同且磁场干扰的均值为零的假设，提供一种栅格形式的磁场指纹库生成方法。本发明与现有建库技术相比，简单高效，对手机姿态无要求，无需标定磁力计零偏，无需复杂的模型建立及计算方法，可以很好的解决由于磁力计零偏存在造成磁场数据库不准确的问题，使得磁场数据库更加准确。

Figure 202011247148

A method for generating a magnetic field fingerprint library independent of the zero bias of a magnetometer. Based on the assumption that the intensity components of the geomagnetic field in the local area are the same and the mean value of the magnetic field interference is zero, the invention provides a method for generating a magnetic field fingerprint database in the form of a grid. Compared with the existing database building technology, the present invention is simple and efficient, does not require the posture of the mobile phone, does not need to calibrate the bias of the magnetometer, and does not need complex model establishment and calculation methods, and can well solve the problem of the magnetic field database caused by the bias of the magnetometer. The inaccuracy problem makes the magnetic field database more accurate.

Figure 202011247148

Description

Magnetometer zero-bias independent magnetic field fingerprint database generation method
Technical Field
The invention belongs to the technical field of indoor positioning, and particularly relates to a magnetic field fingerprint database generation method.
Background
The magnetic field matching positioning is widely concerned in the navigation positioning field due to the characteristics of being ubiquitous, not needing extra arrangement, having good concealment and the like, and has been developed in the military field for decades. In recent years, due to the popularization of sensors based on micro-electro-mechanical systems technology and the increase of demand of people for location services in indoor scenes, indoor positioning systems based on magnetic field fingerprint matching are rapidly developed. The higher the magnetic field information dimension is, the larger the amount of information contained, and the higher the magnetic field matching positioning accuracy is. In the actual construction work of the magnetic field fingerprint database, the magnetic field fingerprint database is often inaccurate due to the fact that magnetometer calibration is forgotten to be performed, the magnetometer calibration result is inaccurate, and the like. Therefore, how to quickly and efficiently construct an accurate magnetic field fingerprint database is a key point and an urgent problem to be solved.
According to limited research, the method for establishing the magnetic field fingerprint database mainly comprises point-by-point acquisition and walking acquisition respectively. The point-by-point acquisition is carried out on a plurality of positions through static acquisition and interpolation to obtain a magnetic field database, the fingerprint database has high precision but low database building efficiency and cannot reflect whether zero offset of the magnetic field database is correctly compensated or not; the walking acquisition and warehouse building efficiency is high, but the calibration work of the magnetometer is complicated. Both the two database building methods have certain disadvantages, and a method for building the magnetic field fingerprint database with both accuracy and efficiency meeting requirements still needs to be provided.
In summary, a library construction method capable of simultaneously satisfying the efficiency and accuracy of magnetic fingerprint library construction is urgently needed. The invention establishes the grid magnetic field database under the condition of knowing the walking track coordinates and the attitude angles during library establishment, does not need to calibrate the magnetometer in advance, and provides a quick and efficient high-dimensional magnetic field fingerprint database generation method including but not limited to the application scene.
Disclosure of Invention
The invention provides a magnetometer null-bias irrelevant magnetic field fingerprint database generation method, which aims at solving the problem of complicated magnetometer calibration in an ambulatory acquisition database building method. And respectively obtaining the reference magnetic field intensity under the local coordinate system and the magnetometer observation true value under the carrier coordinate system through attitude angle projection, and then obtaining the zero offset of the magnetometer. And after the observation value of the compensation magnetometer obtains the accurate environment magnetic field intensity observation value of the known position, establishing a grid magnetic field fingerprint database by combining data acquisition track coordinates. The method does not need any external equipment or parameter setting, is simple and efficient, has good universality, and can meet the requirements of high-precision and high-dimensionality fingerprint libraries.
The invention adopts the following technical scheme: a magnetometer null-bias independent magnetic field fingerprint library generation method requires that the course angle of a walking track traverses different directions (such as a walking closed rectangular track or a S-shaped track), obtains the magnetometer null bias through attitude projection under the assumption that the local region-based geomagnetic field intensity components are the same and the mean value of magnetic field interference is zero, and establishes a magnetic field fingerprint library; the technical scheme comprises the following steps:
step 1, traversing tracks in different directions at a region walking course angle for establishing a magnetic field fingerprint library, and obtaining coordinates, high-precision attitude angles and magnetic field information of all positions in the walking tracks through sensor data acquired by intelligent equipment;
step 2, projecting the magnetometer original observed values of all positions to a local horizontal coordinate system by using the sensor attitude angles obtained in the step 1, and averaging the magnetic field projection components of all positions to obtain the reference magnetic field strength in the local horizontal coordinate system;
step 3, projecting the reference magnetic field strength to a carrier coordinate system by combining the reference magnetic field strength and the sensor attitude angle to obtain a magnetometer reference observation value; the original observed values and the reference observed values of the magnetometers at all positions are subjected to difference, and the difference value of each position is averaged to obtain the zero offset of the magnetometers; using the acquired magnetometer zero offset to compensate the magnetometer original observed values, and acquiring accurate environment magnetic field intensity observed values of all positions;
step 4, setting a minimum matrix covering a magnetic field database area based on the acquired track coordinates, dividing the minimum matrix into grids with equal size, and smoothing the magnetic field intensity in the same grid; and (4) performing interpolation filling on the non-collected region by using the magnetic field intensity values of the surrounding grids, and finally establishing a magnetic field grid fingerprint database under a local coordinate system.
Further, the positions in the step 1 are three-dimensional positions, namely a north position, an east position and a vertical position; and the attitude angle is a roll angle, a pitch angle and a course angle.
Further, the implementation of step 2 comprises the following sub-steps,
21) projecting the magnetic field intensity of all the positions in the carrier coordinate to a local coordinate system to obtain the magnetic field intensity of each position in the local coordinate system,
Figure BDA0002770388080000021
22) based on the assumption that the average value of the magnetic field interference formed by the manual facilities and the equipment in the local area is zero, the average value of the magnetic field intensity of each position in the local coordinate system is used as the reference magnetic field intensity,
Figure BDA0002770388080000022
in the above formula, the subscript n represents a local coordinate n system, the n system takes the inertial sensor IMU phase center as an origin, the x axis is parallel to the local horizontal plane and points to true north, the y axis is parallel to the local horizontal plane and points to true east, the z axis is perpendicular to the local horizontal plane and points downwards, and the three form a right-handed system; b represents a system b of a carrier coordinate system, the system b takes an inertial sensor IMU phase center as an origin, an x axis points to the advancing direction of the carrier, a y axis is perpendicular to the x axis and points to the right side of the carrier, and a z axis is perpendicular to the x axis and the y axis and forms a right-hand system; i represents the ith position, and j is total;
Figure BDA0002770388080000023
an attitude rotation matrix from the local coordinate system to the carrier coordinate system for each position; mn,iRepresenting the magnetic field strength of the ith position under the n system; mb,iRepresenting the magnetic field intensity of the ith position under the b system; mn_refRepresenting the reference magnetic field strength in the local coordinate system n.
Further, in step 3, the magnetometer original observation value is the fusion magnetic field strength of the magnetometer zero offset, the earth magnetic field and the magnetic field interference formed by the artificial equipment or facilities; the reference magnetic field strength is a projection value of the earth magnetic field strength under a local horizontal coordinate system; the magnetometer reference observed value is a projection value of the earth magnetic field under the carrier coordinate.
Further, the implementation of step 3 comprises the following sub-steps,
31) projecting the reference magnetic field intensity to a magnetometer reference observation value of each position in a carrier coordinate system through an attitude angle,
Figure BDA0002770388080000031
Mn_refrepresenting the reference magnetic field strength under a local coordinate system n system;
32) taking the mean value of the difference between the reference observation value of the magnetometer and the original observation value of the magnetometer in the carrier coordinate system as the zero offset of the magnetometer, and compensating the observation value of the magnetometer to obtain the accurate magnetic field intensity; the specific calculation method is as follows:
Figure BDA0002770388080000032
Figure BDA0002770388080000033
in the formula (I), the compound is shown in the specification,
Figure BDA0002770388080000034
representing the reference observation of the magnetometer under system b, Mb,iA raw output representing the magnetometer at the ith position; bias represents the zero bias error of the magnetometer;
Figure BDA0002770388080000035
represents the magnetometer observations after the i-th position compensation zero offset.
Further, in step 4, the magnetic field strength in the same grid is smoothed, and the smoothing method includes: averaging, weighted averaging, median, maximum-minimum averaging, averaging after eliminating the maximum and minimum, and gaussian model.
Further, in step 4, the non-collected region is interpolated and filled by using the magnetic field intensity values of the surrounding grids, and the interpolation method includes a linear interpolation method, a bilinear interpolation method, a cubic spline interpolation method, a nearest neighbor method, a gaussian model method and a kriging method.
Further, the specific implementation manner of step 4 includes the following sub-steps,
41) projecting the magnetometer observation value after compensating zero offset to a local coordinate system through an attitude angle;
42) dividing the reservoir building area into uniform grids according to the east-west direction and the south-north direction under a local coordinate system, and building a local coordinate system;
43) projecting the three-dimensional position information of the acquisition track into a local coordinate system, and recording a grid corresponding to each position point on the acquisition track;
44) averaging the magnetic field information of all position points in a single grid to obtain high-dimensional magnetic field information of the grid, and forming a magnetic field fingerprint together with the positions of the grid;
45) traversing all the grids, if a certain grid does not contain magnetic field information, interpolating by using the magnetic field information of surrounding grids to fill the magnetic field information of the grid, wherein the interpolation method specifically comprises the following steps:
a) drawing a circle by taking the center of a grid to be interpolated as the center of a circle and n meters as the radius, wherein the grid completely contained in the circle is taken as a grid to be selected, and the grid containing magnetic field information in the grid to be selected is taken as an effective grid;
b) traversing 8 directions of the grid to be interpolated, namely true east, true west, true south, true north, east south, east north, west south and west north, if and only if an effective grid exists in the true east and true west direction or an effective grid exists in the true south and north direction, allowing interpolation operation, and if not, considering the grid to be interpolated as an invalid region in the magnetic field fingerprint library;
c) if the interpolation operation can be carried out, respectively taking out the effective grids which are closest to the grid to be interpolated in 8 directions; if no effective grid exists in a certain direction, the grid in the opposite direction is determined to be ineffective;
d) carrying out weighted average processing on the magnetic field information in the effective grid, wherein the weight is the reciprocal of the distance from the center of the effective grid to the center of the grid to be interpolated, and carrying out normalization processing on the weight to obtain the magnetic field information in the effective grid;
at this point, the generation of the magnetic field fingerprint library is completed.
The invention has the following beneficial effects:
(1) the invention constructs the high-dimensional magnetic field fingerprint database in the north direction, the east direction and the height direction by the walking acquisition method, has high database construction efficiency, simple and easy operation and high information dimensionality of the fingerprint database.
(2) According to the invention, magnetometer calibration is not required to be carried out in advance, and the zero offset of the magnetometer is obtained through attitude projection under the assumption that the components of the magnetic field intensity in a local area are the same and the mean value of magnetic field interference is zero, so that the complicated magnetometer calibration process is omitted, the calibration effect is good, and the operation is further simplified.
(3) The method is simple to operate, easy to realize, simple and feasible, has good universality, does not need any external equipment or parameter setting, and can meet the requirements of a high-precision magnetic field fingerprint library.
Drawings
Fig. 1 is a schematic diagram of a walking track.
FIG. 2 is a diagram of linear interpolation of a magnetic fingerprint library.
Detailed Description
The technical solution of the present invention is further explained with reference to the drawings and the embodiments.
Step 1, holding the mobile phone in a random initial posture, and traversing tracks in different directions (0-360 degrees) at a walking course angle in a region for establishing a magnetic field library. For example, in an open area, walking the route (S-shaped track) in the shape of (a) and (b) in the attached figure 1, and determining the track interval according to the interpolation distance during library building; for a long and narrow corridor, a circle of walking is needed to go along the outer circle of the corridor, if the width of the corridor is larger, an acquisition route is needed to be added in the middle according to the interpolation distance during library building, and the walking tracks are as shown in (c) and (d) (rectangular tracks) in the attached figure 1. Acquiring coordinates of each position in a line-shaped track by using the method of the patent 'acquisition method of indoor positioning fingerprints'; acquiring high-precision attitude angles of the mobile phone at various positions in the walking process by the method of the MEMS gyroscope automatic calibration method; keeping the mobile phone posture stable during the library building period, and completing the acquisition of magnetic field information;
step 2, obtaining the reference magnetic field intensity under the local coordinate system through attitude projection according to the attitude angle obtained in the step 1;
furthermore, the implementation of step 2 comprises the following sub-steps,
21) projecting the magnetic field intensity of all the positions in the carrier coordinate to a local coordinate system to obtain the magnetic field intensity of each position in the local coordinate system,
Figure BDA0002770388080000051
22) based on the assumption that the average value of the magnetic field interference formed by the manual facilities and the equipment in the local area is zero, taking the average value of the magnetic field intensity of each position in the local coordinate system as the reference magnetic field intensity,
Figure BDA0002770388080000052
in the above formula, the subscript n represents a local coordinate n system, the n system takes the inertial sensor IMU phase center as an origin, the x axis is parallel to the local horizontal plane and points to true north, the y axis is parallel to the local horizontal plane and points to true east, the z axis is perpendicular to the local horizontal plane and points downwards, and the three form a right-handed system; b represents a system b of a carrier coordinate system, the system b takes an inertial sensor IMU phase center as an origin, an x axis points to the advancing direction of the carrier, a y axis is perpendicular to the x axis and points to the right side of the carrier, and a z axis is perpendicular to the x axis and the y axis and forms a right-hand system; i represents the ith position, and j is total;
Figure BDA0002770388080000053
an attitude rotation matrix from the local coordinate system to the carrier coordinate system for each position; mn,iRepresenting the magnetic field strength of the ith position under the n system; mb,iA raw output representing the magnetometer at the ith position; mn_refRepresenting the reference magnetic field strength in the local coordinate system n.
Step 3, obtaining a magnetometer reference observation value according to the reference magnetic field intensity in the local horizontal coordinate system obtained in the step 2, solving the magnetometer zero bias and compensating the magnetometer observation value;
furthermore, the implementation of step 3 comprises the following sub-steps,
31) projecting the reference magnetic field intensity to a magnetometer reference observation value of each position in a carrier coordinate system through an attitude angle,
Figure BDA0002770388080000054
in the formula (I), the compound is shown in the specification,
Figure BDA0002770388080000055
is the attitude rotation matrix from the local coordinate system to the carrier coordinate system.
32) And taking the mean value of the difference between the reference observation value of the magnetometer and the original observation value of the magnetometer in the carrier coordinate system as the zero offset of the magnetometer, and compensating the observation value of the magnetometer to obtain the accurate magnetic field intensity. The specific calculation method is as follows:
Figure BDA0002770388080000061
Figure BDA0002770388080000062
in the formula (I), the compound is shown in the specification,
Figure BDA0002770388080000063
representing magnetometer reference observations under system b; bias represents the zero bias error of the magnetometer;
Figure BDA0002770388080000064
represents the magnetometer observations after the i-th position compensation zero offset.
Therefore, a relatively accurate magnetometer observed value is obtained.
And 4, setting a minimum matrix covering the magnetic field database area according to the data acquisition track coordinates, and dividing the reservoir building area into grids with equal size. Averaging the magnetic field intensity in the grids, interpolating the magnetic field intensity of the adjacent grids in the area where the magnetic field intensity is not acquired, and establishing a magnetic field grid fingerprint database under a local coordinate system;
furthermore, the implementation of step 4 comprises the following sub-steps,
41) projecting the magnetometer observation value after compensating zero offset to a local coordinate system through an attitude angle;
42) dividing the reservoir building area into uniform grids according to the east-west direction and the south-north direction under a local coordinate system, and building a local coordinate system;
43) projecting the three-dimensional position information of the acquisition track into a local coordinate system, and recording a grid corresponding to each position point on the acquisition track;
44) averaging the magnetic field information of all position points in a single grid to obtain high-dimensional magnetic field information of the grid, and forming a magnetic field fingerprint together with the positions of the grid;
45) traversing all the grids, if a certain grid does not contain magnetic field information, interpolating by using the magnetic field information of surrounding grids to fill the magnetic field information of the grid, wherein the interpolation method specifically comprises the following steps:
a) the center of the grid to be interpolated is taken as the center of a circle, a circle is drawn by taking 1.5 meters as the radius, the grid completely contained in the circle is taken as a grid to be selected, and the grid containing magnetic field information in the grid to be selected is taken as an effective grid. Assuming the central non-numbered gray grid in fig. 2 as the grid to be interpolated, the radius of the circle is 1.5 m. The grids 1 to 8 are candidate grids, wherein the grids 1 to 6 with gray numbers contain magnetic field information and are effective grids; the grids 7 to 8 with black numbers do not contain magnetic field information and are invalid grids.
b) And traversing 8 directions of the grid to be interpolated, namely true east, true west, true south, true north, east south, east north, west south and west north, if and only if an effective grid exists in the true east and true west direction or an effective grid exists in the true south and north direction, allowing the interpolation operation, and if not, considering the grid to be interpolated as an invalid region in the magnetic field fingerprint library. Grid 2 (due north) and grid 6 (due south) in fig. 2 are both active grids and interpolation operations can be performed.
c) If the interpolation operation can be carried out, respectively taking out the effective grids which are closest to the grid to be interpolated in 8 directions; if no valid grid exists in a certain direction, the grid in the opposite direction is considered invalid. In FIG. 2, grids 1-6 contain magnetic field information, but according to the rule in c, grids 1, 2, 5, 6 satisfy the relative relationship, and are effective grids; the grids 7 and 8 corresponding to the grids 3 and 4 are invalid grids, and do not satisfy the relative relationship, so that the grids are removed from the valid grids.
d) And carrying out weighted average processing on the magnetic field information in the effective grid, wherein the weight is the reciprocal of the distance from the center of the effective grid to the center of the grid to be interpolated. And carrying out normalization processing on the weight to obtain the magnetic field information in the effective grid.
At this point, the generation of the magnetic field fingerprint library is completed.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Claims (8)

1.一种磁力计零偏无关的磁场指纹库生成方法，其特征在于，包括以下步骤：1. a magnetic field fingerprint library generation method irrelevant to the zero bias of a magnetometer, is characterized in that, comprises the following steps: 步骤1，在建立磁场指纹库的区域行走，每次数据采集行走的轨迹，其航向角遍历不同方向，通过智能设备采集的传感器数据得到行走轨迹中各个位置的坐标、高精度姿态角及磁场信息；Step 1: Walk in the area where the magnetic fingerprint database is established. Each time the data is collected for the walking trajectory, its heading angle traverses different directions, and the coordinates, high-precision attitude angle and magnetic field information of each position in the walking trajectory are obtained through the sensor data collected by the smart device. ; 步骤2，使用步骤1获得的姿态角将所有位置的磁力计原始观测值投影到当地水平坐标系下，并对所有位置的磁场投影分量进行平均，获得当地水平坐标系下的参考磁场强度；Step 2, use the attitude angle obtained in step 1 to project the original observation values of the magnetometers at all positions into the local horizontal coordinate system, and average the magnetic field projection components at all positions to obtain the reference magnetic field strength in the local horizontal coordinate system; 步骤3，结合参考磁场强度和姿态角，将参考磁场强度投影到载体坐标系下，获得磁力计参考观测值；并对所有位置的磁力计原始观测值和参考观测值做差，对每个位置的差值求平均获得磁力计零偏；使用获得的磁力计零偏补偿磁力计原始观测值，获得所有位置准确的环境磁场强度观测值；Step 3: Combine the reference magnetic field strength and attitude angle, project the reference magnetic field strength to the carrier coordinate system, and obtain the magnetometer reference observation value; Average the difference of the magnetometer to obtain the zero bias of the magnetometer; use the obtained zero bias of the magnetometer to compensate the original observation value of the magnetometer, and obtain the accurate observation value of the environmental magnetic field strength at all locations; 步骤4，基于行走的轨迹坐标，设置覆盖磁场数据库区域的最小矩阵，并划分为等大小的栅格，对同一栅格内的磁场强度进行平滑处理；对未采集的区域，使用周围栅格的磁场强度值进行插值填充，建立当地坐标系下的磁场栅格指纹库。Step 4: Based on the walking trajectory coordinates, set the minimum matrix covering the magnetic field database area, and divide it into grids of equal size, and smooth the magnetic field strength in the same grid; for the uncollected area, use the surrounding grids. The magnetic field strength value is interpolated and filled, and the magnetic field grid fingerprint library in the local coordinate system is established. 2.根据权利要求1所述一种磁力计零偏无关的磁场指纹库生成方法，其特征在于：步骤1中所述位置为三维位置，即北向位置、东向位置和垂向位置；姿态角，即为横滚角、俯仰角和航向角。2. a kind of magnetic field fingerprint library generation method independent of magnetometer zero bias according to claim 1, is characterized in that: the position described in step 1 is three-dimensional position, namely northward position, eastward position and vertical position; Attitude angle , namely the roll angle, pitch angle and heading angle. 3.根据权利要求1所述一种磁力计零偏无关的磁场指纹库生成方法，其特征在于：步骤2的实现方式包括以下子步骤，3. The method for generating a magnetic field fingerprint library independent of the zero bias of a magnetometer according to claim 1, wherein the implementation of step 2 comprises the following sub-steps, 21)将所有位置在载体坐标系的磁场强度投影到当地坐标系下，得到每个位置在当地坐标系下的磁场强度，21) Project the magnetic field strength of all positions in the carrier coordinate system to the local coordinate system, and obtain the magnetic field strength of each position in the local coordinate system,
Figure FDA0003124302940000011
Figure FDA0003124302940000011
 22)基于局部区域内人工设施和设备所形成的磁场干扰平均值为零的假设，将所有位置在当地坐标系下的磁场强度的均值作为参考磁场强度，22) Based on the assumption that the average value of the magnetic field interference formed by artificial facilities and equipment in the local area is zero, the average value of the magnetic field strength of all locations in the local coordinate system is used as the reference magnetic field strength,
Figure FDA0003124302940000012
Figure FDA0003124302940000012
 上式中，下标n表示当地坐标n系，n系是以惯性传感器IMU相位中心为原点，x轴平行于当地水平面指向正北，y轴平行于当地水平面指向正东，z轴垂直于当地水平面向下，三者构成右手系；b表示载体坐标系b系，b系是以惯性传感器IMU相位中心为原点，x轴指向载体前进方向，y轴垂直于x轴指向载体右侧，z轴与x轴和y轴垂直并构成右手系；i表示第i个位置，共计j个；
Figure FDA0003124302940000021
为第i个位置从当地坐标系到载体坐标系的姿态旋转矩阵；Mn，i表示第i个位置在n系下的磁场强度；Mb，i表示磁力计在第i个位置的原始输出；Mn_ref表示当地坐标系n系下的参考磁场强度。In the above formula, the subscript n represents the local coordinate n system, the n system is based on the inertial sensor IMU phase center as the origin, the x-axis is parallel to the local horizontal plane and points to the north, the y-axis is parallel to the local horizontal plane and points to the east, and the z-axis is perpendicular to the local The horizontal plane is downward, and the three constitute a right-handed system; b represents the carrier coordinate system b system, which is based on the inertial sensor IMU phase center as the origin, the x-axis points to the forward direction of the carrier, the y-axis is perpendicular to the x-axis and points to the right side of the carrier, and the z-axis points to the right side of the carrier. It is perpendicular to the x-axis and the y-axis and forms a right-handed system; i represents the i-th position, totaling j;
Figure FDA0003124302940000021
is the attitude rotation matrix of the ith position from the local coordinate system to the carrier coordinate system; M n, i represents the magnetic field strength of the ith position in the n system; M b, i represents the original output of the magnetometer at the ith position ; Mn_ref represents the reference magnetic field strength in the local coordinate system n. 4.根据权利要求1所述一种磁力计零偏无关的磁场指纹库生成方法，其特征在于：步骤3中，磁力计原始观测值为磁力计零偏、地球磁场和人工设备或设施形成的磁场干扰的融合磁场强度；参考磁场强度为地球磁场强度在当地水平坐标系下的投影值；磁力计参考观测值为地球磁场在载体器坐标下的投影值。4. a kind of magnetic field fingerprint library generation method irrelevant to magnetometer bias according to claim 1, is characterized in that: in step 3, the original observation value of magnetometer is formed by the bias of magnetometer, earth's magnetic field and artificial equipment or facility. The fusion magnetic field strength of the magnetic field interference; the reference magnetic field strength is the projection value of the earth's magnetic field strength under the local horizontal coordinate system; the magnetometer reference observation value is the projection value of the earth's magnetic field under the coordinates of the carrier. 5.根据权利要求1所述一种磁力计零偏无关的磁场指纹库生成方法，其特征在于：步骤3的实现方式包括以下子步骤，5. The method for generating a magnetic field fingerprint database independent of the zero bias of a magnetometer according to claim 1, wherein the implementation of step 3 comprises the following sub-steps, 31)将参考磁场强度通过姿态角投影到载体坐标系下的得到各个位置在载体坐标系下的磁力计参考观测值，31) Projecting the reference magnetic field intensity to the carrier coordinate system through the attitude angle to obtain the magnetometer reference observation values of each position in the carrier coordinate system,
Figure FDA0003124302940000022
Figure FDA0003124302940000022
 Mn_ref表示当地坐标系n系下的参考磁场强度；M n_ref represents the reference magnetic field strength in the local coordinate system n; 32)将载体坐标系下的磁力计参考观测值与原始磁力计观测值之差的均值作为磁力计零偏，补偿磁力计观测值获得准确的磁场强度；具体计算方式如下：32) Take the mean value of the difference between the magnetometer reference observation value and the original magnetometer observation value under the carrier coordinate system as the magnetometer zero offset, and compensate the magnetometer observation value to obtain an accurate magnetic field strength; the specific calculation method is as follows:
Figure FDA0003124302940000023
Figure FDA0003124302940000023
Figure FDA0003124302940000024
Figure FDA0003124302940000024
 式中，
Figure FDA0003124302940000025
表示载体坐标b系下的磁力计参考观测值，Mb，i表示磁力计在第i个位置的原始输出；bias表示磁力计的零偏误差；
Figure FDA0003124302940000026
表示第i个位置补偿零偏后的磁力计观测值。In the formula,
Figure FDA0003124302940000025
represents the reference observation value of the magnetometer in the carrier coordinate system b, M b, i represents the original output of the magnetometer at the ith position; bias represents the zero bias error of the magnetometer;
Figure FDA0003124302940000026
Indicates the magnetometer observation value after the ith position is compensated for zero offset. 6.根据权利要求1所述一种磁力计零偏无关的磁场指纹库生成方法，其特征在于：步骤4中，对同一栅格内的磁场强度进行平滑处理，平滑方法包括：平均法、加权平均法、中位值法、最大最小值平均法、去掉最大最小值后平均法、高斯模型法。6. The method for generating a magnetic field fingerprint database independent of the zero bias of a magnetometer according to claim 1, wherein in step 4, smoothing is performed on the magnetic field intensity in the same grid, and the smoothing method comprises: averaging, weighting Average method, median method, maximum and minimum average method, average method after removing the maximum and minimum values, Gaussian model method. 7.根据权利要求1所述一种磁力计零偏无关的磁场指纹库生成方法，其特征在于：步骤4中，对未采集的区域，使用周围栅格的磁场强度值进行插值填充，插值方法包括线性内插法、双线性内插法、三次样条内插法、最邻近元法、高斯模型法、克里金法。7. The method for generating a magnetic field fingerprint database independent of the zero bias of a magnetometer according to claim 1, characterized in that: in step 4, for the uncollected area, use the magnetic field strength value of the surrounding grid to perform interpolation filling, and the interpolation method Including linear interpolation, bilinear interpolation, cubic spline interpolation, nearest neighbor method, Gaussian model method, kriging method. 8.根据权利要求1所述一种磁力计零偏无关的磁场指纹库生成方法，其特征在于：步骤4的具体实现方式包括以下子步骤，8. The method for generating a magnetic field fingerprint database independent of the zero bias of a magnetometer according to claim 1, wherein the specific implementation of step 4 comprises the following sub-steps: 41)通过姿态角将补偿零偏后的磁力计观测值投影到当地坐标系；41) Project the magnetometer observation value after compensation of zero offset to the local coordinate system through the attitude angle; 42)将建库区域按照当地坐标系下的东西方向、南北方向划分为均匀的网格，并建立局部坐标系；42) Divide the building area into uniform grids according to the east-west and north-south directions under the local coordinate system, and establish a local coordinate system; 43)将采集轨迹的三维位置信息，投影至局部坐标系中，并记录采集轨迹上每个位置点所对应的网格；43) Project the three-dimensional position information of the collection track into the local coordinate system, and record the grid corresponding to each position point on the collection track; 44)对单个网格内所有位置点的磁场信息进行平均处理，得到该网格的高维磁场信息，与该网格的位置共同组成磁场指纹；44) Averaging the magnetic field information of all position points in a single grid to obtain the high-dimensional magnetic field information of the grid, which together with the position of the grid constitutes a magnetic field fingerprint; 45)遍历所有网格，若某一网格内不包含磁场信息，利用周围网格的磁场信息进行内插，填补该网格的磁场信息，内插方法具体如下：45) Traverse all grids, if a grid does not contain magnetic field information, use the magnetic field information of the surrounding grids to interpolate to fill the magnetic field information of the grid. The interpolation method is as follows: a)以需要内插的网格中心为圆心，以n米为半径画圆，完全包含在圆圈内的网格为待选网格，待选网格中含有磁场信息的网格为有效网格；a) Draw a circle with the center of the grid to be interpolated as the center, and draw a circle with a radius of n meters. The grid completely contained in the circle is the grid to be selected, and the grid containing the magnetic field information in the grid to be selected is the effective grid ; b)遍历待内插网格的8个方向，即正东、正西、正南、正北、东南、东北、西南、西北，当且仅当正东、正西方向存在有效网格或正南、正北方向存在有效网格时，允许进行内插操作，否则认为待内插网格为磁场指纹库中无效区域；b) Traverse the 8 directions of the grid to be interpolated, namely due east, due west, due south, due north, southeast, northeast, southwest, and northwest, if and only if there is a valid grid in due east and due west When there are valid grids in the south and true north directions, the interpolation operation is allowed, otherwise the grid to be interpolated is considered to be an invalid area in the magnetic field fingerprint database; c)若判断可以进行内插操作，分别取出8个方向上与待内插网格距离最近的有效网格；若某个方向上不存在有效网格，认定与其相对方向上的网格也无效；c) If it is judged that the interpolation operation can be performed, take out the valid grids in the 8 directions with the closest distance to the grid to be interpolated; if there is no valid grid in a certain direction, it is determined that the grid in the opposite direction is also invalid. ; d)将有效网格中的磁场信息进行加权平均处理，权重为有效网格中心到待内插网格中心距离的倒数，将权重进行归一化处理后，得到有效网格中的磁场信息。d) Perform weighted average processing on the magnetic field information in the effective grid, where the weight is the reciprocal of the distance from the center of the effective grid to the center of the grid to be interpolated, and normalize the weight to obtain the magnetic field information in the effective grid.
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