CN111474532B - Time synchronization method and device for vehicle-mounted mobile laser radar measurement system - Google Patents
Time synchronization method and device for vehicle-mounted mobile laser radar measurement system Download PDFInfo
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Abstract
The invention discloses a time synchronization method of a vehicle-mounted mobile laser radar measurement system, wherein the mobile laser radar measurement system comprises a laser radar and a panoramic camera, the mobile laser radar measurement system also comprises a time synchronization device, the time synchronization device comprises a singlechip and a CAN controller, and the time synchronization method comprises the following steps: the method comprises the following steps that firstly, a single chip microcomputer receives a time signal and converts the time signal into a timestamp, meanwhile, the single chip microcomputer receives a pulse per second signal, and sends the timestamp at the rising edge moment in a digital signal mode in a rising edge triggering mode according to the pulse per second signal; and step two, the CAN controller receives the digital signal and transmits the digital signal to the laser radar and the panoramic camera through a CAN bus so that the laser radar and the panoramic camera respond at the same instant. The invention also discloses a time synchronization device of the vehicle-mounted mobile laser radar measurement system. The invention develops the time synchronizer, accurately obtains the data at the same instant moment and is convenient for subsequent application.
Description
Technical Field
The invention relates to the technical field of mobile measurement, in particular to a time synchronization method and a time synchronization device for a vehicle-mounted mobile laser radar measurement system.
Background
In recent years, with the progress of national science and technology, the surveying and mapping industry as the foundation of national infrastructure is also changing with the world. The vehicle-mounted PSLV system records data acquired by the sensor by selecting any time epoch in Beidou time, coordinated universal time UTC, POS time or a user-defined time system. The Beidou satellite provides a unified high-precision time reference for the world, and is a global time service system with higher precision at present. And it is convenient for obtaining, and the user only needs to install cheap big dipper receiver just can obtain required time information free of charge. The superiority of time service makes it used in electric power system more and more widely. The high-precision measurement of the vehicle-mounted mobile measurement system takes Beidou time as a measurement reference, the continuous motion state of the vehicle-mounted platform is accurately described, the position of the vehicle-mounted platform changes along with time, and when the position coordinate of a vehicle running track is given, the instant time of response must be given. The high-precision mobile measurement system is composed of a plurality of sensors, the working frequency and the form of each sensor are different, time synchronization is carried out through Beidou second pulse signals, the system is a link for complete working of the system, and the system is of great importance for data synchronization processing of a mobile three-dimensional imaging system. However, the operating frequencies of the sensor modules of the mobile measurement system are often inconsistent, and the output of the receiver is generally a pulse per second signal. Therefore, a time synchronization device is necessary to process the pulse-per-second signal to obtain a synchronous clock suitable for the application of the mobile measurement system, and the obtained synchronous clock is required to have high precision and high stability.
Disclosure of Invention
An object of the present invention is to solve at least the above problems and to provide at least the advantages described later.
The invention also aims to provide a time synchronization method and a time synchronization device for the mobile laser radar measurement system.
To achieve these objects and other advantages in accordance with the present invention, there is provided a time synchronization method for a vehicle-mounted mobile lidar measurement system, the mobile lidar measurement system including a lidar, a panoramic camera, and a time synchronization device including a single chip microcomputer and a CAN controller, the time synchronization method comprising the steps of:
the method comprises the following steps that firstly, a single chip microcomputer receives a time signal and converts the time signal into a timestamp, and meanwhile, the single chip microcomputer receives a pulse per second signal and sends the timestamp at a rising edge moment in a digital signal mode in a rising edge triggering mode according to the pulse per second signal;
and step two, the CAN controller receives the digital signal and transmits the digital signal to the laser radar and the panoramic camera through a CAN bus so that the laser radar and the panoramic camera respond at the same instant.
Preferably, the time signal and the pulse per second signal in the step one are both from a signal receiver of a Beidou satellite navigation positioning time service system, the signal receiver is connected with the single chip microcomputer through an RS232 serial port, a MAX232 chip is arranged in the single chip microcomputer, the signal receiver sends out the time signal, the time signal is a BDRMC data frame, the BDRMC data frame is converted into an RS232 signal through the RS232 serial port firstly and then is converted into a TTL signal through the MAX232 chip, the single chip microcomputer converts the TTL signal into a UNIX timestamp, and the CAN controller is connected with the laser radar and the panoramic camera through CAN buses.
Preferably, the mobile lidar measurement system further comprises: the system comprises an inertial navigation system, a panoramic camera and a control system, wherein the laser radar is used for collecting laser radar point cloud data of a target scene, the inertial navigation system is used for acquiring attitude data of a vehicle to generate POS data, and the panoramic camera is used for collecting panoramic image data of the target scene;
remove laser radar measurement system and host computer connection, the host computer includes: the device comprises a parameter setting module, a data input module, a data processing module and a data output module;
the time synchronization method further includes:
and thirdly, inputting the acquired laser radar point cloud data and POS data by a data input module, setting segmentation parameters and translation parameters of the input laser radar point cloud data and POS data by a parameter setting module, carrying out point cloud registration and coordinate conversion on the input laser radar point cloud data and POS data by a data processing module, and outputting final point cloud data of a target scene by a data output module.
Preferably, the upper computer further comprises a scanning operation module, wherein the scanning operation module is used for controlling the data processing process of the input laser radar point cloud data and the POS data, and the process comprises starting scanning, recording data, suspending scanning and finishing scanning.
Preferably, the CPU chip of the single chip microcomputer is STM32F103CBT6, and the chip of the CAN controller is MCP 2551.
Preferably, the satellite navigation system is a Beidou satellite navigation positioning time service system, and the time service mode is an RNSS unidirectional time service mode.
The invention also provides a time synchronization device of the vehicle-mounted mobile laser radar measurement system, the mobile laser radar measurement system comprises a panoramic camera and a laser radar, and the time synchronization device comprises: the single chip microcomputer receives the time signal, decodes the time signal and converts the time signal into the timestamp, meanwhile, the single chip microcomputer receives the second pulse signal and sends the timestamp at the rising edge moment in a digital signal mode in a rising edge triggering mode according to the second pulse signal, and the CAN controller receives the digital signal and transmits the digital signal to the laser radar and the panoramic camera through a CAN bus so that the laser radar and the panoramic camera CAN respond at the same instant moment.
Preferably, the time signal and the pulse per second signal are both from a signal receiver of a satellite navigation system, the signal receiver is connected with the single chip microcomputer through an RS232 serial port, a MAX232 chip is arranged in the single chip microcomputer, the signal receiver sends the time signal, the time signal is a BDRMC data frame, the BDRMC data frame is converted into the RS232 signal through the RS232 serial port firstly and then is converted into a TTL signal through the MAX232 chip, the single chip microcomputer converts the TTL signal into a UNIX timestamp, and the CAN controller is connected with the laser radar and the panoramic camera through a CAN bus.
Preferably, the CPU chip of the single chip microcomputer is STM32F103CBT6, and the chip of the CAN controller is MCP 2551.
Preferably, the satellite navigation system is a Beidou satellite navigation positioning time service system, and the time service mode is an RNSS unidirectional time service mode.
The invention at least comprises the following beneficial effects:
the vehicle-mounted mobile laser radar measuring system is used as a platform, and the time synchronization device is developed, so that all parts of the mobile laser radar measuring system can work coordinately, data at the same instant moment can be accurately acquired, and subsequent application is facilitated.
The invention provides a time synchronization device based on a Beidou satellite navigation positioning time service system, aiming at the problem that the time between sensors of all parts in a mobile laser radar measurement system cannot be synchronized. Experimental results prove that the coupling between the sensors of all parts of the vehicle-mounted mobile measuring system can be effectively improved through the set of device, the overall precision and the point cloud quality of the vehicle-mounted mobile laser radar measuring system are improved, and the device has high feasibility and economic benefits.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
Fig. 1 is a signal transmission flow chart for performing time synchronization according to one embodiment of the present invention;
FIG. 2 is a schematic diagram of a system according to one embodiment of the present invention;
fig. 3 is a chip structure diagram of the CAN controller according to one embodiment of the present invention;
FIG. 4 is a timing diagram of a CAN basic frame number according to one embodiment of the present invention;
fig. 5 is a software architecture diagram of the upper computer according to one embodiment of the present invention;
FIG. 6 is a diagram of a final point cloud data sample obtained after processing according to one embodiment of the present invention;
FIG. 7 is a diagram of an example of a point cloud data processed by time synchronization according to an embodiment of the present invention;
FIG. 8 is a diagram of a point cloud data sample with slightly advanced time synchronization according to one embodiment of the present invention;
FIG. 9 is a diagram of a sample point cloud with a slightly delayed time synchronization according to one embodiment of the present invention;
FIG. 10 is a diagram of a point cloud data analysis with slightly advanced time synchronization according to one embodiment of the present invention;
fig. 11 is a point cloud data analysis diagram with a little delay in time synchronization according to one embodiment of the present invention.
Detailed Description
The present invention is further described in detail below with reference to the drawings and examples so that those skilled in the art can practice the invention with reference to the description.
It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
The invention provides a time synchronization method of a vehicle-mounted mobile laser radar measurement system, wherein the mobile laser radar measurement system comprises a laser radar and a panoramic camera, the mobile laser radar measurement system also comprises a time synchronization device, the time synchronization device comprises a singlechip and a CAN controller, and the time synchronization method comprises the following steps:
the method comprises the following steps that firstly, a single chip microcomputer receives a time signal and converts the time signal into a timestamp, and meanwhile, the single chip microcomputer receives a pulse per second signal and sends the timestamp at a rising edge moment in a digital signal mode in a rising edge triggering mode according to the pulse per second signal;
and step two, the CAN controller receives the digital signal and transmits the digital signal to the laser radar and the panoramic camera through a CAN bus so that the laser radar and the panoramic camera respond at the same instant.
In practical application, the mobile laser radar measuring system further comprises: the inertial navigation system (prior art) is used for acquiring laser radar point cloud data of a target scene, acquiring attitude data of a vehicle, resolving and generating POS data by combining the attitude data of the vehicle with other data (such as acceleration and the like) according to the prior art, and acquiring panoramic image data of the target scene by the panoramic camera. According to the invention, both a time signal and a pulse per second signal are readable by a single chip microcomputer, the single chip microcomputer converts the time signal into a timestamp, the timestamp is sent as a digital signal at a rising edge moment by adopting a rising edge triggering mode according to the pulse per second signal, and a CAN controller transmits the digital signal to a laser radar and a panoramic camera, so that the laser radar and the panoramic camera respond at the same instant moment, namely the laser radar acquires point cloud data at the moment, the panoramic camera acquires panoramic image data at the moment, synchronous acquisition of the data is realized, and subsequent generation of accurate point cloud data and real-time panoramic images is facilitated. According to the time synchronization method, the real-time panoramic image can be accurately obtained by combining the technology for obtaining the real-time panoramic image in the prior art.
The vehicle-mounted mobile laser radar measuring system is used as a platform, and the time synchronization device is developed, so that all parts of the mobile laser radar measuring system can work coordinately, data at the same instant moment can be accurately acquired, and subsequent application is facilitated.
The time signal and the pulse per second signal are both from a satellite navigation system (namely, a global satellite navigation system) and are sent by a signal receiver of the satellite navigation system. The satellite navigation system can be a Beidou satellite navigation positioning time service system, and can also be other satellites providing time signals, such as a United states Global Positioning System (GPS), Russian GLONASS and the like, or the fusion of several satellite signals.
In another technical scheme, the time signal and the pulse per second signal in the step one are both from a signal receiver of a satellite navigation system, the signal receiver is connected with a MAX232 instrument through an RS232 serial port, the MAX232 instrument is connected with the single chip microcomputer through a TTL serial port, the signal receiver sends the time signal, the time signal is a BDRMC data frame, the BDRMC data frame is converted into an RS232 signal through the RS232 serial port, then is converted into a TTL signal through the MAX232 instrument, and is finally transmitted to the single chip microcomputer, and the CAN controller is connected with the laser radar and the panoramic camera through a CAN bus.
As shown in the figures 1-2, the CPU chip of the singlechip can adopt STM32F103CBT6, the chip belongs to a 32-bit microcontroller of Cortex-M3 series of ARM, and has abundant IO ports and bus peripheral equipment, the singlechip can work in a temperature range of-40 ℃ to +105 ℃, the power supply voltage is 2.0V to 3.6V, the singlechip has a power-saving mode to meet the requirement of low power consumption, and the singlechip can download programs and debug online through a JTAG interface. The time signal and the pulse per second signal are both from a signal receiver of the satellite navigation system, the signal receiver of the satellite navigation system can receive the BDRMC data frame and the PPS pulse per second data, the signal receiver transmits the time signal (BDRMC data frame) to the single chip microcomputer through an RS232 bus, and simultaneously transmits the PPS signal to a PA1 pin of an STM32F103CBT6, the time signal and the PPS pulse per second signal are configured into EXTI _ Mode _ Interrupt (Interrupt generation) in an external Interrupt Mode, and a rising edge trigger Mode is adopted. The STM32F103CBT6 realizes the mutual conversion of the RS232 level and the TTL level. STM32 converts time signal into UNIX time stamp, through PPS second pulse with the UNIX time stamp pass through the CAN bus transmission for inertial navigation system (inertial navigation system), laser radar and laser radar singlechip receive the time signal that signal receiver transmitted through the serial ports at the rising edge moment, decode required time information, convert the time stamp into. Meanwhile, edge alignment is carried out according to the pulse per second signal, and accurate data transmission once per second is completed through the interrupt function of the single chip microcomputer. The signal receiver in fig. 1 is a signal receiver of a Beidou satellite navigation positioning time service system. STM32 is STM32F103CBT 6. The satellite receiver in fig. 2 is a signal receiver of a satellite navigation system.
The chip of the CAN controller is MCP2551, and the MCP2551 is a fault-tolerant high-speed CAN device and CAN be used as a CAN protocol controller and a physical bus interface. MCP2551 CAN provide differential transceiving capacity for a CAN protocol controller, completely conforms to the ISO-11898 standard and comprises the capacity of meeting the 24V voltage requirement, the working speed of the MCP2551 reaches up to 1Mb/s, the bus is in a dominant state when the differential voltage between CANH and CANL is higher than 1.2V, the bus is in a stealth state when the differential voltage is lower than 0V, the low level and the high level of a TXD input pin correspond to the dominant state and the recessive state of the bus, and the Rs pin CAN select three operation modes of high speed, slope control and standby. The CAN controller MCP2551 CAN control the state of the bus for sending and receiving data, and converts a digital signal sent by the STM32 into a signal suitable for CAN bus transmission. The data frame of the CAN protocol is used by the sending unit and used for sending information to the receiving unit, and when the high-speed CAN bus transmits a dominant signal (0), the CAN _ H end is lifted to a high level of 5V, and the CAN _ L is pulled to a low level of 0V. When the recessive signal (1) is transmitted, the CAN _ H or CAN _ L end is not driven. The standard + Frame of the CAN protocol consists of 7 fields, namely Start of Frame, Arbitration Field, Control Field, Data Field, CRC Field, ACK Field and End of Frame, and the timing diagram of the basic Frame is shown in FIG. 4. All frames consist of a single dominant bit with the start bit (SOF) as the start of the information transmission and the end of the frame consists of 7 consecutive hidden bits. Each node has a different frame ID, and the IDE can set the reception object of the frame by setting the control field. The data field is used for storing data to be sent, and UNIX time stamps are converted into 16-system data to be sequentially placed in the data field during time transmission. The CRC field serves as a cyclic redundancy check to provide error correction for frame transmission. The ACK is used to confirm that the CAN frame is valid, and when the ACK is at an explicit level, the frame is a valid frame, otherwise, the frame is an invalid frame.
UTC Time (Universal Time Coordinated), which is also known as Universal Time, is the most common Time standard in the world. The UNIX timestamp is the number of seconds elapsed since 1/1970 (midnight of UTC/GMT), not considering leap seconds. STM32 receives the UTC time and converts it to a UNIX timestamp. The time difference between the beijing time and the UTC time is +8, so that the beijing time is UTC + 8. The time information format received by the receiver is typically $ BDRMC, <1>, <2>, <3>, <4>, <5>, <6>, <7>, <8>, <9>, <10>, <11>, <12 >. h < CR > < LF > where the <1> and <9> information is the time minute second and the month and day of UTC time, respectively, the 6 sets of data are taken out of the time minus the start of the UNIX timestamp, and the time difference of 8 hours is added to account for the leap year and the leap second to obtain the timestamp seconds of the current time. For example, $ BDRMC,030551.000, a,3906.2586, N,11720.3131, E,0.00,138.07,150719, a × 6B extracts information <1> and <9> from the frame, and obtains UTC time of 3 hours, 5 minutes and 51 seconds of 7 months, 15 days, and 2019, and adds 8 hours of time difference to obtain beijing time of 5 minutes and 51 seconds of 11 hours, 7 months, 15 days, and 2019 at this moment. The corresponding UNIX timestamp is thus obtained as 1563159951, which is converted into 16-ary to obtain 5D2B ED8F, which is stored in the CAN data frames awaiting transmission.
The time conversion algorithm pseudo-code is illustrated as follows:
inputting year, month, day, hour, minute, second → Y, M, D, H, Mi, S
In another aspect, the mobile lidar measurement system further comprises: the system comprises an inertial navigation system, a panoramic camera and a control system, wherein the laser radar is used for collecting laser radar point cloud data of a target scene, the inertial navigation system is used for acquiring attitude data of a vehicle to generate POS data, the POS data can be generated by resolving the attitude data of the vehicle in combination with other data (such as acceleration and the like) according to the prior art, and the panoramic camera is used for collecting panoramic image data of the target scene;
remove laser radar measurement system and host computer connection, as shown in fig. 5, the host computer includes: the device comprises a parameter setting module, a data input module, a data processing module and a data output module;
the time synchronization method further includes:
and thirdly, inputting the acquired laser radar point cloud data and POS data by a data input module, setting segmentation parameters and translation parameters of the input laser radar point cloud data and POS data by a parameter setting module, carrying out point cloud registration and coordinate conversion on the input laser radar point cloud data and POS data by a data processing module, and outputting final point cloud data of a target scene by a data output module.
The vehicle-mounted mobile laser radar measuring system consists of a hardware integrated system (laser radar, a panoramic camera and the like) and an upper computer software system. The hardware system integrates various devices to simultaneously acquire laser radar point cloud data and panoramic image data, and the upper computer software system realizes control of the laser radar and space-time registration calculation of the laser radar point cloud data. The software system adopts a Visual Studio compiling platform, designs a system interface by using a C #. net language, and designs a dynamic link library of an algorithm by using a C + +. net language to complete the functions of surveying and mapping sensor control, data acquisition, data checking, data processing, input and output and the like of the system.
In another technical scheme, the upper computer further comprises a scanning operation module, and the scanning operation module is used for controlling the data processing process of the input laser radar point cloud data and POS data, and comprises the steps of starting scanning, recording data, suspending scanning and ending scanning.
When the upper computer software is controlled, the scanning operation module is accessed, various scanning operations are selected according to different operation types, such as starting scanning, recording data, suspending scanning, ending scanning and the like, and the collected data stored in the high-speed SD card can be checked in real time in the scanning process by utilizing the wireless storage technology to check whether the scanning data is increased or not. And clicking the scanning operation after the scanning is finished, finishing the scanning and stopping the scanning work. And when the acquisition is finished, the scanning is finished, the vehicle stands for about 2 minutes, the track recording is stopped, the software is closed, and the base station is recovered. The collected data of various measuring sensors are imported into software for processing to generate complete point cloud data, as shown in fig. 6.
In another technical scheme, a CPU chip of the single chip microcomputer is STM32F103CBT6, and a chip of the CAN controller is MCP 2551.
In another technical scheme, the satellite navigation system is a Beidou satellite navigation positioning time service system, and the time service mode is an RNSS unidirectional time service mode.
The Beidou time service principle can be divided into unidirectional time service and bidirectional time service. The unidirectional time service is divided into two modes of RNSS unidirectional time service and RDSS unidirectional time service. The RDSS (radio Determination Satellite service) one-way time service principle is that an atomic clock of a ground central station generates accurate time information to be sent to a Satellite, the accurate time information is sent to a receiving terminal after being coded by the Satellite, and the receiving terminal decodes the time information to complete time service. The RDSS bidirectional time service system performs round-trip measurement with the ground central station, and the central station obtains the time difference between the time service terminal and the ground central station, so that the time information is calculated. The RNSS one-way time service (Radio Navigation Satellite System) needs to receive measurement data of at least 4 satellites simultaneously, unknown information such as position, speed and time is solved through a equation set, the Beidou time service mode adopted by the invention is the RNSS one-way time service mode, a vehicle-mounted mobile measurement System needs to carry out accurate measurement in a complex and unknown geographic environment, and theoretically, the RNSS time service precision can reach 10ns according to a Navigation precision index UERE (user Equipment Range) of the Beidou Satellite, so that the vehicle-mounted mobile measurement System works in a high dynamic form in a global Range.
The invention also provides a time synchronization device of the vehicle-mounted mobile laser radar measurement system, the mobile laser radar measurement system comprises a laser radar and a panoramic camera, the laser radar is used for collecting laser radar point cloud data of a target scene, the panoramic camera is used for collecting panoramic image data of the target scene, and the time synchronization device comprises: the single chip microcomputer receives the time signal, decodes the time signal and converts the time signal into the timestamp, meanwhile, the single chip microcomputer receives the second pulse signal and sends the timestamp at the rising edge moment in a digital signal mode in a rising edge triggering mode according to the second pulse signal, and the CAN controller receives the digital signal and transmits the digital signal to the laser radar and the panoramic camera through a CAN bus so that the laser radar and the panoramic camera CAN respond at the same instant moment.
The mobile laser radar measuring system comprises a laser radar, a panoramic camera, a POS system and a time synchronization device, wherein the POS system comprises a GNSS and an INS, and the time synchronization device can adjust time errors generated between the laser radar and the panoramic camera according to time provided by the GNSS, so that time synchronization is realized, and the influence on the overall accuracy of the system and the poor quality of point cloud caused by the time errors is overcome. An Inertial Navigation System (INS) is used to obtain attitude data of the vehicle to generate POS data, which can be resolved by the attitude data of the vehicle in combination with other data (such as acceleration, etc.) according to the prior art.
According to the invention, both a time signal and a pulse per second signal are readable by a single chip microcomputer, the single chip microcomputer converts the time signal into a timestamp, the timestamp is sent as a digital signal at a rising edge moment by adopting a rising edge triggering mode according to the pulse per second signal, and a CAN controller transmits the digital signal to a laser radar and a panoramic camera, so that the laser radar and the panoramic camera respond at the same instant moment, namely, the laser radar acquires point cloud data of the laser radar at the moment, and the panoramic camera acquires panoramic image data at the moment, so that synchronous acquisition of the data is realized, and the subsequent generation of accurate three-dimensional integral point cloud data and real-time panoramic images is facilitated. According to the time synchronization method, the real-time panoramic image can be accurately obtained by combining the technology for obtaining the real-time panoramic image in the prior art.
The vehicle-mounted mobile laser radar measuring system is used as a platform, and the time synchronization device is developed, so that all parts of the mobile laser radar measuring system can work coordinately, data at the same instant moment can be accurately acquired, and subsequent application is facilitated.
In another technical scheme, the time signal and the pulse per second signal are both from a signal receiver of a satellite navigation system, the signal receiver is connected with the single chip microcomputer through an RS232 serial port, a MAX232 chip is arranged in the single chip microcomputer, the signal receiver sends out the time signal, the time signal is a BDRMC data frame, the BDRMC data frame is converted into the RS232 signal through the RS232 serial port firstly and then is converted into a TTL signal through the MAX232 chip, the single chip microcomputer converts the TTL signal into a UNIX timestamp, and the CAN controller is connected with the laser radar and the panoramic camera through a CAN bus.
The CPU chip of the singlechip in the invention can adopt STM32F103CBT 6. The time signal and the pulse per second signal are both from a signal receiver of a Beidou satellite navigation positioning time service system, the signal receiver of the Beidou satellite navigation positioning time service system can receive a BDRMC data frame and PPS pulse data, the signal receiver transmits the time signal (BDRMC data frame) to a single chip microcomputer through an RS232 bus, and simultaneously transmits the PPS signal to a PA1 pin of an STM32F103CBT6, an external Interrupt Mode is adopted to configure the time signal and the PPS pulse signal into EXTI _ Mode _ Interrupt (Interrupt generation), and a rising edge trigger Mode is adopted. The STM32F103CBT6 realizes the mutual conversion of the RS232 level and the TTL level. STM32 converts time signal into UNIX time stamp, through PPS second pulse with UNIX time stamp pass through the CAN bus transmission for inertial navigation system (inertial navigation system), laser radar at the rising edge moment, the time signal that the singlechip transmitted through serial ports receiving signal receiver decodes required time information, converts the time stamp into. Meanwhile, edge alignment is carried out according to the pulse per second signal, and accurate data transmission once per second is completed through the interrupt function of the single chip microcomputer. The chip of the CAN controller is MCP2551, the structure of which is shown in FIG. 3. The CAN controller MCP2551 CAN control the state of the bus for sending and receiving data, and converts the digital signals sent by the STM32 into signals suitable for CAN bus transmission.
In another technical scheme, a CPU chip of the single chip microcomputer is STM32F103CBT6, and a chip of the CAN controller is MCP 2551.
In another technical scheme, the satellite navigation system is a Beidou satellite navigation positioning time service system, and the time service mode is an RNSS unidirectional time service mode.
The overall system is tested and analyzed according to specific embodiments, and the influence of the system time synchronization problem on the point cloud quality is quantitatively analyzed to evaluate the effect of the time synchronization device.
The mobile laser radar measuring system comprises a laser radar, a panoramic camera, a POS system and a time synchronization device, wherein the POS system comprises a GNSS and an INS, and the time synchronization device can adjust time errors generated between the laser radar and the panoramic camera according to time provided by the GNSS, so that time synchronization is realized, and the influence on the overall accuracy of the system and the poor quality of point cloud caused by the time errors is overcome.
And (3) experimental test:
the time synchronizer is set to different time intervals, the time synchronizer after the parameter setting is used as a comparison group, two groups of experiments with slightly advanced and slightly retarded time synchronization are used as experiment groups to observe the result of point cloud calculation, and thus the necessity of the time synchronizer and the influence on the system precision are analyzed.
(1) The sensor synchronization time of the time synchronization device is adjusted to be an ideal state through upper computer software, a mobile laser radar measuring system is used for collecting data of a certain road, and the collected data are processed through the upper computer software to obtain the road surface point cloud shown in the figure 7.
(2) Adjusting the synchronization time of the sensor of the time synchronization device to a slightly advanced state, utilizing the original data acquired in the step (1), and processing to obtain the road surface point cloud as shown in fig. 8.
(3) Fig. 9 shows a road surface point cloud obtained by adjusting the synchronization time of the sensor of the time synchronizer to a slightly delayed state and using the raw data acquired in step (1) and processing the data.
And (3) data analysis:
as shown in fig. 10 to 11, by comparing the point cloud data at the same curve in the experiments (1), (2), and (3), it can be seen that the time synchronizer has a large influence on the result data. The difference is difficult to see at the position with few straight lines or features, but the difference is obvious at the position of a curve, the condition of turning ahead or delaying can occur, the point cloud can even be distorted, and the reality of the point cloud is influenced due to the great difference from the actual condition.
And (4) carrying out quantitative analysis on the point cloud data of the experiment. The point cloud difference of the experimental results of each group can be obtained by comparison and analysis by taking the first group of experiment (1) as a reference group and the second group (2) and the third group (3) as a control group, as shown in the following table 1.
TABLE 1
It can be seen from the above table that when the time synchronizer is adjusted to an ideal state one second earlier, the error of the point cloud reaches 3.28m, and when the time synchronizer is adjusted to an ideal state one second later, the error of the point cloud reaches 4.43m, so that the time synchronizer has a great influence on the point cloud result obtained by the mobile laser radar measurement system.
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable in various fields of endeavor to which the invention pertains, and further modifications may readily be made by those skilled in the art, it being understood that the invention is not limited to the details shown and described herein without departing from the general concept defined by the appended claims and their equivalents.
Claims (8)
1. The time synchronization method of the vehicle-mounted mobile laser radar measurement system is characterized in that the mobile laser radar measurement system further comprises a time synchronization device and an inertial navigation system, the laser radar is used for collecting laser radar point cloud data of a target scene, the inertial navigation system is used for obtaining attitude data of a vehicle to generate POS data, and the panoramic camera is used for collecting panoramic image data of the target scene; remove laser radar measurement system and host computer connection, the host computer includes: the device comprises a parameter setting module, a data input module, a data processing module and a data output module; the time synchronization device comprises a single chip microcomputer and a CAN controller, and the time synchronization method comprises the following steps:
the method comprises the following steps that firstly, a single chip microcomputer receives a time signal and converts the time signal into a timestamp, and meanwhile, the single chip microcomputer receives a pulse per second signal and sends the timestamp at a rising edge moment in a digital signal mode in a rising edge triggering mode according to the pulse per second signal; the time signal and the pulse per second signal are both from a signal receiver of a satellite navigation system, the signal receiver is connected with the single chip microcomputer through an RS232 serial port, an MAX232 chip is arranged in the single chip microcomputer, the signal receiver sends the time signal, the time signal is a BDRMC data frame, the BDRMC data frame is firstly converted into the RS232 signal through the RS232 serial port and then converted into a TTL signal through the MAX232 chip, the single chip microcomputer converts the TTL signal into a UNIX timestamp, and the CAN controller is connected with the laser radar and the panoramic camera through CAN buses;
secondly, the CAN controller receives the digital signal and transmits the digital signal to the laser radar and the panoramic camera through a CAN bus so that the laser radar and the panoramic camera respond at the same instant time;
and thirdly, inputting the acquired laser radar point cloud data and POS data by a data input module, setting segmentation parameters and translation parameters of the input laser radar point cloud data and POS data by a parameter setting module, carrying out point cloud registration and coordinate conversion on the input laser radar point cloud data and POS data by a data processing module, and outputting final point cloud data of a target scene by a data output module.
2. The time synchronization method for the vehicle-mounted mobile lidar measurement system of claim 1, wherein the upper computer further comprises a scanning operation module, and the scanning operation module is used for controlling the processes of data reprocessing of the input lidar point cloud data and the POS data, including starting scanning, recording data, suspending scanning and ending scanning.
3. The time synchronization method of the vehicle-mounted mobile laser radar measurement system as claimed in claim 1, wherein the CPU chip of the single chip microcomputer is STM32F103CBT6, and the chip of the CAN controller is MCP 2551.
4. The method according to claim 1, wherein the satellite navigation system is a beidou satellite navigation positioning time service system, and the time service mode is an RNSS one-way time service mode.
5. Time synchronization device of a vehicle-mounted mobile lidar measurement system for performing the synchronization method according to any of claims 1 to 4, the mobile lidar measurement system comprising a panoramic camera, a lidar, and comprising: the single chip microcomputer receives the time signal, decodes the time signal and converts the time signal into the timestamp, meanwhile, the single chip microcomputer receives the second pulse signal and sends the timestamp at the rising edge moment in a digital signal mode in a rising edge triggering mode according to the second pulse signal, and the CAN controller receives the digital signal and transmits the digital signal to the laser radar and the panoramic camera through a CAN bus so that the laser radar and the panoramic camera CAN respond at the same instant moment.
6. The time synchronizer of vehicle mounted mobile lidar measuring system of claim 5, wherein the time signal and the pulse per second signal are both from a signal receiver of a satellite navigation system, the signal receiver is connected to the single chip via an RS232 serial port, a MAX232 chip is provided in the single chip, the signal receiver sends out the time signal, the time signal is a BDRMC data frame, which is converted into an RS232 signal via the RS232 serial port and then into a TTL signal via the MAX232 chip, the single chip converts the TTL signal into a UNIX timestamp, and the CAN controller is connected to the lidar and the panoramic camera via a CAN bus.
7. The time synchronizer of the vehicle-mounted mobile lidar measurement system of claim 5, wherein the CPU chip of the single chip microcomputer is STM32F103CBT6, and the chip of the CAN controller is MCP 2551.
8. The device of claim 6, wherein the satellite navigation system is a Beidou satellite navigation positioning time service system, and the time service mode is an RNSS one-way time service mode.
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| CN112230240A (en) * | 2020-09-30 | 2021-01-15 | 深兰人工智能(深圳)有限公司 | Space-time synchronization system, device and readable medium for laser radar and camera data |
| CN112578367B (en) * | 2020-10-21 | 2023-01-06 | 上汽大众汽车有限公司 | System and method for measuring relative time of camera and laser radar in automatic driving system |
| CN112622928B (en) * | 2020-12-11 | 2022-07-15 | 上海商汤临港智能科技有限公司 | Automatic driving system and vehicle |
| CN112671497B (en) * | 2020-12-29 | 2022-12-06 | 苏州挚途科技有限公司 | Time synchronization method and device and electronic equipment |
| CN113099211A (en) * | 2021-03-31 | 2021-07-09 | 华南理工大学 | Stereoscopic vision data acquisition system and method with time synchronization |
| CN114413878B (en) * | 2021-12-24 | 2024-02-13 | 苏州浪潮智能科技有限公司 | Time calibration system, method, electronic equipment and storage medium |
| CN114754769B (en) * | 2022-06-15 | 2022-11-18 | 天津大学四川创新研究院 | Data synchronization time service system and method for laser radar and inertial sensor |
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