1. An unmanned aerial vehicle autonomous take-off and landing cruise method based on digital twins is characterized by comprising the following steps:

step 1, building a 3D model and a scene of an unmanned aerial vehicle

Establishing a 3D unmanned aerial vehicle model, a sensor model and an indoor and outdoor scene model by using a simulation end, labeling the established unmanned aerial vehicle model, setting a 3D rigid body and a role controller of a building of the unmanned aerial vehicle model and the indoor and outdoor scene, setting positions and coloring backgrounds for all scenes, adding a collider for the unmanned aerial vehicle model, setting a rotor wing, and performing position distribution control and local rendering and mapping of the unmanned aerial vehicle model;

step 2, designing the takeoff and landing of the unmanned aerial vehicle

Designing take-off and landing aiming at the established unmanned aerial vehicle model, compiling a Script to control the unmanned aerial vehicle model, compiling the Script according to the mark of the unmanned aerial vehicle model and the mark, defining keyboard keys in the Script and focusing a mouse, thereby more conveniently controlling the air route of the unmanned aerial vehicle and completing the movement and switching of a virtual field of view in the established scene by a virtual roaming program;

step 3, simulating the sensor under the simulation end

In the simulation end, an infrared sensor is used for infrared obstacle avoidance and information transmission; ultrasonic obstacle avoidance is carried out by utilizing an ultrasonic sensor; simulating machine vision by using a common camera sensor; acquiring environmental depth information by using a depth camera sensor and a laser radar sensor, and performing autonomous positioning navigation; acquiring attitude information and operation information of the unmanned aerial vehicle by using an IMU sensor; acquiring height information and speed information of the unmanned aerial vehicle by using a height sensor; acquiring the sensing range of the unmanned aerial vehicle by using the contact sensor, and completing the construction of a digital twin model through the steps 1 to 3;

step 4, self-organizing network communication of unmanned aerial vehicle model

Based on the existing mobile ad hoc network system structure, carrying out ad hoc network communication; the deviation of the unmanned aerial vehicle path is subjected to error elimination by adopting a gradient descent method, and the difference between the current position and the planned path is subjected to gradient descent, so that the position of the unmanned aerial vehicle is closer to the planned path;

step 5, carrying out real-time interaction by utilizing a digital twinning technology

The method comprises the steps of modeling a real-life scene by adopting a three-dimensional modeling method and a rendering engine technology in an analog end, realizing remote issuing of a command to an unmanned aerial vehicle in the actual scene by a cloud end by utilizing the existing 4G and 5G modules, an Alice cloud service and a network communication technology, and realizing virtual reality synchronization by butting with the scene of the analog end; collecting unmanned aerial vehicle data in an actual scene by using a big data cloud platform, and optimizing an unmanned aerial vehicle model in a simulation end; the unmanned aerial vehicle in an actual scene is combined with the Internet of things platform, visual intelligent monitoring is realized by virtual geographic environment, multi-source data fusion and analog simulation, the information resource allocation operation efficiency and value are improved, the cloud platform release detection level is comprehensively upgraded and optimized, and a better control effect is achieved;

step 6, starting a cloud command on a computer webpage, managing resources of the Aliskian by executing a Linux command, and remotely issuing a command to the unmanned aerial vehicle in an actual scene;

step 7, utilizing the cloud platform to carry out self-organizing network communication on the unmanned aerial vehicle in the actual scene so as to carry out real virtual synchronization: the unmanned aerial vehicle model is subjected to autonomous take-off and landing cruise at the simulation end, and the actual unmanned aerial vehicle also realizes the autonomous take-off and landing cruise to realize synchronization.

2. The unmanned aerial vehicle autonomous take-off and landing cruise method based on the digital twin, according to claim 1, is characterized in that the construction of the digital twin model is carried out from two aspects of multi-domain model construction and 'geometric-physics-behavior-rule' multi-dimensional model construction;

when the model building object is relatively complex, the hierarchical relation of the model needs to be built and the assembly sequence of the model is determined so as to avoid the situation of difficult assembly, and the constraint relations such as angle constraint, contact constraint, offset constraint and the like among parts need to be built and added, then model fusion is carried out, aiming at some system-level twin model building, the model assembly of the control dimension can not meet the requirements of the physical object, and further fusion needs to be carried out, namely the fusion among different fields of different disciplines is realized; and finally, verifying the model, namely verifying the model after the model is constructed, assembled and fused to ensure the correctness and the validity of the model, and verifying whether the output of the model is consistent with the output of the physical object or not according to different requirements during model verification.

3. The unmanned aerial vehicle autonomous take-off and landing cruising method based on the digital twin as claimed in claim 1, is characterized in that a cognitive plane is provided for cognitive reasoning, control and configuration of dynamic information of the unmanned aerial vehicle communication network, corresponding dynamic parameters of the unmanned aerial vehicle network are guided, measured and repaired, the cognition of the more complex dynamic information and the main management control are separated from a single plane, and the data plane is guaranteed to transmit data efficiently in real time.

4. The cruise method for autonomous take-off and landing of unmanned aerial vehicle based on digital twin as claimed in claim 1, wherein under the known condition provided by the cognitive plane movement measurement, the direct link status and path weight calculation method between unmanned aerial vehicles is as follows:

in the formulaLink weight for i to its immediate neighbors; rho_MACi∈[0,1]Reflecting the busy and idle of a channel for the MAC duty ratio, and transmitting local MAC statistics from a beacon; gamma-shaped_iIs a receiver threshold;

f_map(SINR_i,i+1) As a relative mapping function:

in the formula P_RXiIs i maximum received power; d₀Is far field distance, d is the distance between two unmanned planes, the value of gamma is 2-6,source power, N, representing interference to node j_oIs the noise power;

link aggregation is a path, and the end-to-end weight is defined as:

thus, a single link failure results in the failure of the entire source path, requiring a re-routing and re-calculation of weights.

5. The unmanned aerial vehicle autonomous take-off and landing cruise method based on the digital twin as claimed in claim 1, wherein the analog end employs a Unity platform.

Background

With the progress of the times and the development of technologies, unmanned planes are widely applied to various fields, and simultaneously, a emerging digital twin technology gradually enriches the lives of people, and the digital twin technology integrates the simulation processes of multiple disciplines, multiple physical quantities, multiple scales and multiple probabilities by fully utilizing data such as physical models, sensor updating, operation histories and the like, and completes mapping in a virtual space so as to reflect the full life cycle process of corresponding entity equipment. Digital twinning is an beyond-realistic concept that can be viewed as a digital mapping system of one or more important, interdependent equipment systems. The digital twin is a generally-adapted theoretical technical system, can be applied to a plurality of fields, and is more applied to the fields of product design, product manufacturing, medical analysis, engineering construction and the like at present. At present, the most deep application in China is in the field of engineering construction, the highest attention and the hottest research are in the field of intelligent manufacturing. In industry, the logistics service industry often needs a remote unmanned aerial vehicle to autonomously complete a task, which is a difficult task, and a conventional unmanned aerial vehicle control process is as follows:

(1) firstly, the control end designs a flight route aiming at a control task, sends a command and transmits the command to the unmanned aerial vehicle. (2) Secondly, the unmanned aerial vehicle receives the signal that the control end transmitted, carries out the flight task. (3) Furthermore, the unmanned aerial vehicle transmits uninterrupted transmission information to the terminal. (4) And finally, the terminal feeds back the information to the control end, the control end compares the information and transmits the command to the unmanned aerial vehicle again to form negative feedback.

At present, along with the development of control technology, a plurality of excellent algorithms are applied to autonomous take-off and landing of an unmanned aerial vehicle, and a very good effect is achieved in experimental verification, but the autonomous take-off and landing cruise of the unmanned aerial vehicle is carried out in a real environment, the requirements of manpower and material resources are greatly reduced, the current requirements cannot be met by severe weather aiming at complex terrains, great hidden dangers exist in the aspects of safety and efficiency, and self-correction and self-learning are difficult to carry out aiming at some complex geographic environments which are relatively narrow and difficult to utilize a tracking detection algorithm.

Secondly, although the further development of the algorithm, the application of the SLAM technology and the development of robust control filtering in recent years enable the effect of the unmanned aerial vehicle in the aspect of control to be obviously improved, the unmanned aerial vehicle is directed to environmental strain, object identification and a large amount of calculation borne by the unmanned aerial vehicle, and has great problems in the aspects of autonomous taking off and landing and fixed-point cruising.

Disclosure of Invention

The invention aims to provide an unmanned aerial vehicle autonomous take-off and landing cruise method based on a digital twin, which is characterized in that a cloud platform is built by utilizing the digital twin technology, and an unmanned aerial vehicle group is controlled at the cloud end to remotely perform autonomous take-off, landing and cruise.

In order to realize the task, the invention adopts the following technical scheme:

an unmanned aerial vehicle autonomous take-off and landing cruise method based on digital twins comprises the following steps:

step 1, building an unmanned aerial vehicle 3D model and a scene.

Establishing a 3D unmanned aerial vehicle model, a sensor model and an indoor and outdoor scene model by using a simulation end, labeling the established unmanned aerial vehicle model, setting a 3D rigid body and a role controller of a building of the unmanned aerial vehicle model and the indoor and outdoor scene, setting positions and coloring backgrounds for all scenes, adding a collider for the unmanned aerial vehicle model, setting a rotor wing, and performing position distribution control and local rendering and mapping of the unmanned aerial vehicle model;

step 2, designing the takeoff and landing of the unmanned aerial vehicle

Designing take-off and landing aiming at the established unmanned aerial vehicle model, compiling a Script to control the unmanned aerial vehicle model, compiling the Script according to the mark of the unmanned aerial vehicle model and the mark, defining keyboard keys in the Script and focusing a mouse, thereby more conveniently controlling the air route of the unmanned aerial vehicle and completing the movement and switching of a virtual field of view in the established scene by a virtual roaming program;

step 3, simulating the sensor under the simulation end

In the simulation end, an infrared sensor is used for infrared obstacle avoidance and information transmission; ultrasonic obstacle avoidance is carried out by utilizing an ultrasonic sensor; simulating machine vision by using a common camera sensor; acquiring environmental depth information by using a depth camera sensor and a laser radar sensor, and performing autonomous positioning navigation; acquiring attitude information and operation information of the unmanned aerial vehicle by using an IMU sensor; acquiring height information and speed information of the unmanned aerial vehicle by using a height sensor; acquiring the sensing range of the unmanned aerial vehicle by using the contact sensor, and completing the construction of a digital twin model through the steps 1 to 3;

step 4, self-organizing network communication of unmanned aerial vehicle model

Based on the existing mobile ad hoc network system structure, carrying out ad hoc network communication; the deviation of the unmanned aerial vehicle path is subjected to error elimination by adopting a gradient descent method, and the difference between the current position and the planned path is subjected to gradient descent, so that the position of the unmanned aerial vehicle is closer to the planned path;

step 5, carrying out real-time interaction by utilizing a digital twinning technology

Modeling a real-life scene by adopting a three-dimensional modeling method and a rendering engine technology in a simulation end, and establishing a high-precision model, namely a high-immersion scene; meanwhile, the existing 4G and 5G modules and the Ali cloud service are utilized, the network communication technology is used for realizing that the cloud end remotely issues an instruction to the unmanned aerial vehicle in an actual scene, and meanwhile, the unmanned aerial vehicle is in butt joint with a simulation end scene, so that virtual reality synchronization is realized; collecting unmanned aerial vehicle data in an actual scene by using a big data cloud platform, and optimizing an unmanned aerial vehicle model in a simulation end; the unmanned aerial vehicle in an actual scene is combined with the Internet of things platform, visual intelligent monitoring is realized by virtual geographic environment, multi-source data fusion and analog simulation, the information resource allocation operation efficiency and value are improved, the cloud platform release detection level is comprehensively upgraded and optimized, and a better control effect is achieved;

step 6, starting a cloud command on a computer webpage, managing resources of the Aliskian by executing a Linux command, and remotely issuing a command to the unmanned aerial vehicle in an actual scene;

step 7, utilizing the cloud platform to carry out self-organizing network communication on the unmanned aerial vehicle in the actual scene so as to carry out real virtual synchronization: the unmanned aerial vehicle model is subjected to autonomous take-off and landing cruise at the simulation end, and the actual unmanned aerial vehicle also realizes the autonomous take-off and landing cruise to realize synchronization.

Further, constructing a digital twin model from two aspects of multi-domain model construction and 'geometry-physics-behavior-rule' multi-dimensional model construction;

when the model building object is relatively complex, the hierarchical relation of the model needs to be built and the assembly sequence of the model is determined so as to avoid the situation of difficult assembly, and the constraint relations such as angle constraint, contact constraint, offset constraint and the like among parts need to be built and added, then model fusion is carried out, the model fusion is built aiming at some system-level twin models, the model assembly of the control dimensionality cannot meet the requirements of the physical object, and further fusion is needed, namely the fusion among different fields of different disciplines is realized; and finally, verifying the model, namely verifying the model after the model is constructed, assembled and fused to ensure the correctness and the validity of the model, and verifying whether the output of the model is consistent with the output of the physical object or not according to different requirements during model verification.

Furthermore, the cognitive plane is used for cognitive reasoning, control and configuration of dynamic information of the unmanned aerial vehicle communication network, corresponding dynamic parameters of the unmanned aerial vehicle network are guided, measured and repaired, the complex dynamic information cognition and main management control are separated from a single plane, and the data plane is guaranteed to transmit data efficiently in real time.

Further, under the known condition provided by the cognitive plane mobility measurement, the direct link state and path weight calculation method between the drones is as follows:

in the formulaLink weight for i to its immediate neighbors; rho_MACi∈[0,1]Reflecting the busy and idle of a channel for the MAC duty ratio, and transmitting local MAC statistics from a beacon; gamma-shaped_iIs a receiver threshold;

f_map(SINR_i,i+1) As a relative mapping function:

in the formula P_RXiIs i maximum received power; d₀Is far field distance, d is the distance between two unmanned planes, the value of gamma is 2-6,source power, N, representing interference to node j_oIs the noise power;

link aggregation is a path, and the end-to-end weight is defined as:

thus, a single link failure results in the failure of the entire source path, requiring a re-routing and re-calculation of weights.

Further, the analog end adopts a Unity platform.

Compared with the prior art, the invention has the following technical characteristics:

1. through using the twin technology of digit, further promote the efficiency of execution of unmanned aerial vehicle task, in some complicated geographic environment, under the bad weather and on the carrier of the motion of descending, traditional unmanned aerial vehicle takes off and land the location can not be fine satisfy the requirement of reality, can not accomplish accurate taking off and land, the virtual reality that adopts the twin of digit to go on is alternately carried out unmanned aerial vehicle taking off and land, as long as the high accuracy model emulation that goes on can reach the index, the unmanned aerial vehicle that corresponds in the reality can also reach.

2. The multi-sensor fusion achieves more real virtual reality interaction, accurate interaction is achieved, simulation corresponds to reality, an ultra wide band UWB wireless positioning technology is added on the basis of a GPS/vision multi-sensor fusion positioning algorithm by combining the mainstream combined Kalman filtering technology at present, and the defect that the GPS and the vision sensor cannot provide effective position data is overcome. In order to ensure the fault tolerance and robustness of the multi-sensor fusion algorithm, the validity of the sensor data is checked by adopting chi-square test based on the Mahalanobis distance between the Kalman filtering measurement value and the predicted value.

3. A big data cloud platform is built through a digital twin technology, a real scene is deeply rendered, model optimization and rendering are carried out, data remote transmission is carried out through 4G and 5G modules, an unmanned aerial vehicle kernel at a virtual end and a real unmanned aerial vehicle flight control set are integrated, the cloud platform remotely issues ROS instruction transmission and issues commands by using perfect butt joint Ubuntu systems such as network communication Unity-Unity, Unity-ROS and Unity-All, the unmanned aerial vehicle aerial remote sensing and remote sensing image automatic processing technology, oblique photography three-dimensional modeling, geographic information system technology (GIS), Building Information Model (BIM), big data application and other interdisciplines are deeply fused, air-ground integration is built, and a perfect system of data acquisition, processing and decision auxiliary analysis is integrated, so that the unmanned aerial vehicle becomes accurate, efficient and high in cost.

Drawings

Fig. 1 is a schematic diagram of a 3D model of an unmanned aerial vehicle and a scene;

FIG. 2 is a schematic diagram of a Unity platform sensor simulation;

FIG. 3 is a schematic diagram of a model architecture framework of the present invention;

FIG. 4 illustrates the independent take-off and landing implemented by Unity simulation;

fig. 5 is a schematic diagram of autonomous landing of a real drone;

fig. 6 is a schematic diagram of autonomous cruising of an unmanned aerial vehicle in reality.

Detailed Description

Referring to the attached drawings, the invention provides an unmanned aerial vehicle autonomous take-off and landing cruise method based on digital twins, which comprises the following steps:

step 1, building an unmanned aerial vehicle 3D model and a scene.

An unmanned aerial vehicle 3D model and a scene in simulation are shown in figure 1, a simulation end Unity is used for establishing a 3D unmanned aerial vehicle model, a sensor model and an indoor and outdoor scene model, the established unmanned aerial vehicle model is labeled, a 3D rigid body Rigiddbody and a role Controller of a building of the unmanned aerial vehicle model and the indoor and outdoor scene are set, positions and colors of all scenes are set, a rotor wing is set aiming at the unmanned aerial vehicle model and a collision device, position distribution and local rendering and mapping of the unmanned aerial vehicle model are carried out on the unmanned aerial vehicle model, the unmanned aerial vehicle model has more scientific and technological senses and realistic senses, the Unity scene is attractive, and the scene is close to a real scene.

And 2, designing the takeoff and landing of the unmanned aerial vehicle.

Designing take-off and landing aiming at the unmanned aerial vehicle model established in the step 1, writing a Script based on C # under Project because the established unmanned aerial vehicle model is in a Unity 3D scene, controlling the unmanned aerial vehicle model, usually linking the model in the scene, writing the Script according to the mark of the prior unmanned aerial vehicle model, wherein the Script runs under Visual Studio, and in addition, keyboard keys and mouse focusing can be further defined in the Script, so that the air route of the unmanned aerial vehicle is more conveniently controlled, and the virtual roaming program is completed to realize the movement and switching of the virtual Visual field in the established scene.

And 3, simulating the sensor under the simulation end.

In this step, sensor simulation may be implemented, for example, using an analog-end Unity platform, as shown in fig. 3: in the simulation end, an infrared sensor is used for infrared obstacle avoidance and information transmission; ultrasonic obstacle avoidance is carried out by utilizing an ultrasonic sensor; simulating machine vision by using a common camera sensor; acquiring environmental depth information by using a depth camera sensor and a laser radar sensor, and performing autonomous positioning navigation; acquiring attitude information and operation information of the unmanned aerial vehicle by using an IMU sensor; acquiring height information and speed information of the unmanned aerial vehicle by using a height sensor; and (3) acquiring the sensing range of the unmanned aerial vehicle by using the contact sensor, so that the construction of the digital twin model is completed through the steps 1 to 3, as shown in fig. 3.

The model construction refers to the construction of a model of a basic unit of a physical object, the construction of a digital twin model can be carried out from two aspects of multi-domain model construction and geometric-physical-behavior-rule multi-dimensional model construction, the digital twin model covers the multi-dimensional and multi-domain models, so that the comprehensive real depiction and description of the physical object are realized, when the model construction object is relatively complex, the hierarchical relationship of the model is required to be constructed and the assembly sequence of the model is clear, so as to avoid the situation of difficult assembly, and the constraint relationships such as angle constraint, contact constraint, offset constraint and the like among parts are required to be constructed and added, and then the model fusion is carried out, the model fusion is the construction of some system level or complex system level twin models, the assembly of the model with the control dimension can not meet the depiction requirement of the physical object, and further fusion is required, namely, the fusion between different subjects and different fields is realized. And finally, verifying the model, namely verifying the model after the model is constructed, assembled and fused to ensure the correctness and the validity of the model, and verifying whether the output of the model is consistent with the output of the physical object or not according to different requirements during model verification.

Step 4, self-organizing network communication of unmanned aerial vehicle model

The existing mobile ad hoc networks (MAENTs) TCP/IP five-layer system structure is combined with a novel communication system structure of the unmanned aerial vehicle ad hoc network to carry out ad hoc network communication. The most important TCP/IP five-layer system of INTERNET has the greatest success in the flexibility in multiple aspects brought by modular protocol layering and network transparency, a cognitive plane is set for cognitive reasoning, controlling and configuring corresponding dynamic parameters of an unmanned aerial vehicle communication network, and guiding, measuring and repairing a data plane, the cognition of more complex dynamic information and the main management control are separated from a single plane, the data plane is ensured to transmit data efficiently and in real time, the cognitive plane finds a guidance protocol most important, and under the condition that the cognitive plane movement measurement provides known conditions, a direct link state and path weight calculation method among unmanned aerial vehicles is as follows:

in the formulaLink weight for i to its immediate neighbors; rho_MACi∈[0,1]Reflecting the busy and idle of a channel for the MAC duty ratio, and transmitting local MAC statistics from a beacon; gamma-shaped_iIs the receiver threshold.

f_map(SINR_i,i+1) Is relative toMapping function, and deriving:

in the formula P_RXiIs i maximum received power; d₀Is far field distance, d is the distance between two unmanned planes, the value of gamma is 2-6,source power, N, representing interference to j_oIs the noise power.

Link aggregation is a path, and the end-to-end weight is defined as:

the above equation shows that the failure of a single link results in the failure of the whole source path, the path needs to be changed and the weight needs to be recalculated, and the link quality depends on the "comparison" of the high-priority management parameters of the nodes at both ends of the link, that is: signal to noise ratio (SINR) (maximum value corresponds to instantaneous maximum rate of reception), maximum transmission rate, acceptance threshold (reliable transmission considering bi-directionality), channel access busy, idle, etc.

Then on the basis, a gradient descent method is adopted for error elimination aiming at the deviation of the unmanned aerial vehicle path, and gradient descent is carried out on the difference value between the current position and the planned path, so that the position of the unmanned aerial vehicle is closer to the planned path.

And 5, carrying out real-time interaction by using a digital twinning technology.

The method comprises the steps of aiming at finishing interaction of virtual reality, modeling a scene of real life by adopting a three-dimensional modeling method and a rendering engine technology in the Unity of a simulation end, and establishing a high-precision model, namely a high-immersion scene; meanwhile, the existing 4G and 5G modules and the Ali cloud service are utilized, the network communication technology is used for realizing the cloud remote issuing of instructions to the airplane, the instructions are transmitted in real time by high-real-time bidirectional interaction data, meanwhile, the instructions are butted with a simulation end Unity scene, the virtual reality synchronization is realized, in addition, the existing machine learning and the development of deep learning are realized, the big data cloud platform is utilized for collecting unmanned aerial vehicle data in an actual scene, and the unmanned aerial vehicle model in the simulation end is optimized. The unmanned aerial vehicle in the actual scene is combined with the Internet of things platform, visual intelligent monitoring is realized by adding virtual geographic environment, multi-source data fusion and analog simulation, the information resource configuration operation efficiency and value are improved, the cloud platform release detection level is comprehensively upgraded and optimized, and a better control effect is achieved.

And 6, starting a cloud command on a computer webpage, managing resources of the Alice cloud by executing a Linux command, and remotely issuing a command to the unmanned aerial vehicle in an actual scene.

Step 7, utilizing the cloud platform to carry out self-organizing network communication on the unmanned aerial vehicle in the actual scene so as to carry out real virtual synchronization: the unmanned aerial vehicle model is subjected to autonomous take-off and landing cruise on the simulation end Unity platform, and the actual unmanned aerial vehicle also achieves the autonomous take-off and landing cruise, so that synchronization is achieved, and data transmission and data acquisition are completed.

The unmanned aerial vehicle autonomous take-off and landing cruise based on the digital twin technology is designed, real virtual interaction is realized, real virtual is achieved, digital cloning bodies are realized and established on an information platform, and therefore the unmanned aerial vehicle can take off and land autonomously under the condition that detection and positioning cannot be realized; the method has the advantages that the big data cloud platform is introduced to perform online optimization on the established scene model, the internet of things is introduced for online upgrade of services, real-time efficient real-time interaction between information of the unmanned aerial vehicle in reality and the unmanned aerial vehicle in a virtual scene is realized, and the core problem that the unmanned aerial vehicle is promoted to develop intelligently due to the fact that phenomena that the degree of informatization of the unmanned aerial vehicle is low, data acquisition has delay, and decision making is performed by depending on flight experience of a control hand too much is solved. Realize the human-computer interaction of high accuracy, realize that the multisensor fuses and carry out information processing, reach long-range high accuracy and handle unmanned aerial vehicle information, reduce the calculated amount of unmanned aerial vehicle itself for unmanned aerial vehicle is safer, high-efficient.

The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.