Full-waveform data preprocessing method based on airborne laser radar

Abstract

The invention provides a full-waveform data preprocessing method based on an airborne laser radar, and relates to the technical field of data processing, and the method specifically comprises the following steps: calculating the number of sampling points according to the flight height of an unmanned aerial vehicle during working, and determining a specified data interception range; initializing acquisition card configuration; starting a data acquisition cycle, waiting for hardware triggering time, and acquiring original data; dynamically intercepting a specified range in the data buffer area; and writing the file, storing the file in segments, and when the detection record number is greater than or equal to N, closing the current file and creating a new file. According to the technical scheme, the problems that in the prior art, the full-waveform data processing efficiency is low, and the real-time performance is low are solved.

Description

Technical Field

[0001] The present invention relates to the field of data processing, and more particularly to a preprocessing method for airborne lidar full waveform data. Background Art

[0002] The waveform of the full waveform lidar refers to the function of the energy of the laser emission pulse or the received pulse changing with time. The full waveform lidar system can perform intensity sampling at small time intervals on the backscattered echo pulse reflected after contact and interaction with the same target, digitally quantify the intensity, and record the intensity value of the backscattered pulse. The full waveform lidar samples both the emission pulse and the backscattered echo pulse at small intervals, and the original data obtained is a set of two-dimensional data with the horizontal axis being the sampling points and the vertical axis being the echo intensity, which can almost record the entire backscattered echo waveform.

[0003] Due to the limited flight altitude of the airborne lidar, its working flight range is generally within 50 - 100 m at low altitude, the measured water depth is generally limited to the range of 0 - 50 m, and in most cases it works in land and shallow sea areas of 0 - 5 m. Its data form is saved in the form of.out files, and part of the data graph is displayed by converting the code into decimal data. A one-minute data has 300,000 rows of data, and each row of data has 16,384 columns. At present, the amount of airborne lidar full waveform data is very large, and 9.6 G of data can be collected per minute. Each flight generally lasts for 20 - 30 minutes, and when collecting data for more than ten minutes, the data volume fluctuates according to the acquisition card model and the ground object features collected, but the data volume is large.

[0004] The sampling rate of the high-speed acquisition card is 10 GHz. Taking a set of near-point scan data as an example, the effective data of its echo waveform is concentrated in a certain part of the waveform collected in each segment, depending on the distance from the laser to the target, and there are many invalid signals in each segment of the waveform. If not processed during acquisition, a large amount of invalid data will be collected into the original data together, thus increasing the data volume of the original data.

[0005] In the prior art, an effective vibration data interception method based on waveform feature statistics is based on the waveform features of the vibration signal, and filters out the noise peaks and intercepts the vibration signal by statistically analyzing the waveform features of the collected data. The above method first collects and stores a large amount of original full waveform data, and then processes the data after copying. Copying a large amount of data will increase the processing burden of the computer and reduce the processing efficiency. The amount of data collected itself is not effectively reduced, and then the effective data is extracted according to the waveform features. The whole process is an operation after obtaining the data, which belongs to post-processing and the real-time performance will be reduced.

[0006] Therefore, there is a need for a preprocessing method for airborne lidar full waveform data with higher processing efficiency and higher real-time performance. Summary of the Invention

[0007] The main object of the present invention is to provide a preprocessing method for airborne lidar full-waveform data to solve the problems of low processing efficiency and low real-time performance of full-waveform data in the prior art.

[0008] To achieve the above object, the present invention provides a preprocessing method for airborne lidar full-waveform data, which specifically includes the following steps: S1. Calculate the number of sampling points according to the flight altitude of the unmanned aerial vehicle (UAV) during operation, and determine the specified data range to be intercepted.

[0009] S2. Initialize the acquisition card configuration.

[0010] S3. Start the data acquisition loop, wait for the hardware trigger time, and acquire the raw data.

[0011] S4. Dynamically intercept the specified range in the data buffer.

[0012] S5. Write to a file and store the file in segments. When the detected record number is greater than or equal to N, close the current file and create a new file.

[0013] Further, step S1 specifically includes the following steps: S1.1. Calculate the sampling point distance interval : ; ; where the speed of light is 3× m / s, is the sampling rate, is the sampling period.

[0014] S1.2. Calculate the maximum acquisition distance of the acquisition card : ; where the total sampling time =N× , and N is the total number of sampling points.

[0015] S1.3. The mirror rotation scanning angle is , and the actual acquisition distance is , where is the flight altitude of the UAV, and the relationship between the actual acquisition distance and the maximum acquisition distance is: .

[0016] S1.4. The actual number of sampling points is : ; Wherein, is the actual acquisition distance, is the sampling point distance interval.

[0017] Furthermore, step S2 specifically includes the following steps: S2.1, calculate the actual number of sampling points according to the actual working height of the UAV , and according to set the intercept point parameters.

[0018] S2.2, configure the acquisition card parameters, including: sampling rate, trigger mode and original record length.

[0019] Furthermore, in step S2.1, according to setting the intercept point parameters specifically means: setting the intercept start point START_SAMPLE and the number of sampling points SAMPLES_TO_SAVE for sampling intercept.

[0020] Furthermore, step S3 is specifically: respond to an external trigger signal and acquire complete waveform data.

[0021] Furthermore, step S4 is specifically: S4.1, check whether the intercept start point exceeds the total number of sampling points, calculate the theoretical end point, compare it with the buffer boundary, and judge whether the end point is out of bounds. If it is out of bounds, automatically adjust it to the valid range.

[0022] Calculate the intercept end point end: end = min(START_SAMPLE + SAMPLES_TO_SAVE, total_samples); Wherein, total_samples is the total number of sampling points, and min is the minimum value function.

[0023] If the intercept start point exceeds the buffer range, reset it to 0 and discard the record. If the intercept end point exceeds the buffer range, intercept it to the end of the buffer.

[0024] S4.2, when the data spans Extradata and the current buffer, splice the intercept range, calculate the effective data length of each segment, including the available length of Extradata and the length to be supplemented in the current buffer, and then write the data intercepted from Extradata and the data supplemented from the current buffer in segments, giving priority to intercepting from the Extradata buffer, and making up the remaining part from the current buffer.

[0025] S4.3. Dynamically calculate the actual intercepted length and determine the final length based on the boundary protection result to ensure that the actual intercepted length does not exceed SAMPLES_TO_SAVE.

[0026] Further, step S5 is specifically as follows: S5.1. Use a global counter to count the number of records written to the current file; after accumulating N = 300,000 intercepted data, close the current file and generate a new file.

[0027] S5.2. The file name is named according to the channel and time, and the header file retains the original acquisition naming rule according to time; The file size is: 300000 × SAMPLES_TO_SAVE × 2 bytes.

[0028] The present invention has the following beneficial effects: 1. The present invention adopts a preprocessing method instead of a postprocessing method, greatly increasing the real-time performance of the acquisition program.

[0029] 2. Directly operate on the original data in the buffer area, avoiding dynamic memory allocation and frequent writing and reading, improving the processing efficiency, and effectively reducing the overall data volume size.

[0030] 3. By configuring parameters in advance, the complexity of calculation in the algorithm is reduced, and the whole process is simplified.

[0031] 4. Support seamless interception across buffer areas, ensure data integrity under high-frequency triggering, and avoid memory out-of-bounds and invalid access, enhancing the system robustness. Description of the Drawings

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. In the drawings: Figure 1 Shows a flowchart of a method for preprocessing airborne lidar full-waveform data according to the present invention.

[0033] Figure 2 Shows a waveform diagram after directly preprocessing the data.

[0034] Figure 3 Shows a waveform diagram after preprocessing the data using the method provided by the present invention. Detailed Embodiments

[0035] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] Embodiment 1 As Figure 1 shown, a preprocessing method for airborne lidar full waveform data specifically includes the following steps: S1. Calculate the number of sampling points according to the flight altitude of the unmanned aerial vehicle (UAV) during operation, and determine the intercepted specified data range.

[0037] S2. Initialize the acquisition card configuration.

[0038] S3. Start the data acquisition loop, wait for the hardware trigger time, and acquire the raw data.

[0039] S4. Dynamically intercept the specified range in the data buffer.

[0040] S5. Write to a file and store the file in segments. When the detected record number is greater than or equal to N, close the current file and create a new file.

[0041] Specifically, step S1 specifically includes the following steps: S1.1. Calculate the sampling point distance interval : ; ; where the speed of light is 3 × m / s, is the sampling rate, and is the sampling period.

[0042] S1.2. Calculate the farthest acquisition distance of the acquisition card : ; where the total sampling time = N × , and N is the total number of sampling points.

[0043] S1.3. The rotating mirror scanning angle is , and the actual acquisition distance is . Among them, is the flight altitude of the UAV, and the relationship between the actual acquisition distance and the farthest acquisition distance is: .

[0044] S1.4, the actual number of sampling points is , ; Among them, is the actual acquisition distance, is the sampling point distance interval.

[0045] Specifically, step S2 specifically includes the following steps: S2.1, calculate the actual number of sampling points according to the actual working height of the UAV , and according to set the intercept point parameters.

[0046] S2.2, configure the acquisition card parameters, including: basic sampling information such as sampling rate, trigger mode (external trigger), and original record length (16384 points), etc.

[0047] Specifically, in step S2.1, according to the set intercept point parameters are specifically: set the intercept start point START_SAMPLE and the number of sampling points SAMPLES_TO_SAVE for sampling intercept.

[0048] Specifically, step S3 is specifically: respond to the external trigger signal and collect the complete waveform data.

[0049] Specifically, step S4 is specifically: S4.1, boundary protection, check whether the intercept start point exceeds the total number of sampling points, calculate the theoretical end point, compare it with the buffer boundary, and judge whether the end point is out of bounds. If it is out of bounds, automatically adjust it to the valid range;

[0050] Calculate the intercept end point end: end = min(START_SAMPLE + SAMPLES_TO_SAVE, total_samples); Among them, total_samples is the total number of sampling points, and min is the minimum value function.

[0051] If the intercept start point exceeds the buffer range, reset it to 0 and discard the record. If the intercept end point exceeds the buffer range, intercept it to the end of the buffer.

[0052] S4.2, data merging, when the data crosses Extradata and the current buffer, splice the intercept range, calculate the effective data length of each segment, including the available length of Extradata and the length to be supplemented in the current buffer, and then write the data intercepted from Extradata and the data supplemented from the current buffer in segments, giving priority to intercepting from the Extradata buffer, and supplementing the remaining part from the current buffer.

[0053] S4.3, Length correction, dynamically calculate the actual intercepted length and determine the final length according to the boundary protection result to ensure that the actual intercepted length does not exceed SAMPLES_TO_SAVE.

[0054] Specifically, step S5 is as follows: S5.1, Use a global counter (file_record_count) to count the number of records written to the current file; After every N = 300,000 intercepted data are accumulated, close the current file and generate a new file.

[0055] S5.2, The file name is named according to the channel and time (such as dataA-0715-153045123.out), and the header file retains the original acquisition naming rule according to time (such as headerA-0715-153045123.out);

[0056] The file size is: 300000 × SAMPLES_TO_SAVE × 2 bytes; The original trigger timestamp and record length are retained in the header file and are not modified due to the interception operation.

[0057] Therefore, the file data volume is reduced from originally storing 16384 sampling points per line to storing SAMPLES TO SAVE sampling points per line, and the data volume is reduced by 16384 / SAMPLES TO SAVE times.

[0058] Embodiment 2 Use the ADQ7DC acquisition card of TELEDYNE SP DEVICES company to acquire full waveform data. The sampling frequency of the acquisition card is 10GHz, and the sampling rate of the analog-to-digital conversion ADC is set to 16834hz in the system. Its streaming transmission originally acquires, transmits and saves 300,000 rows and 16384 columns of data per minute as a 9.6Gb.out file. Due to the working environment conditions of the airborne lidar, the effective data is mainly concentrated in a certain part of the complete sampling waveform (depending on the actual sampling distance). By intercepting the effective data part of the complete waveform data, the specific method is to determine the number of sampling points according to the relationship between the flight altitude of the unmanned aerial vehicle, the laser scanning angle and the distance to the measurement target, as well as the sampling frequency. The specific formula is as follows:

[0059] Calculate the distance (spatial resolution) between each sampling point: The time interval of each sampling point is the sampling period: , the laser round-trip time is , so the sampling point distance interval is: ; where the speed of light is 3× m / s, the sampling rate = 10 GHz. Substituting into the formula gives: = 1.5 cm; At this sampling rate, the maximum distance that the acquisition card can collect is:

[0060] In the formula, the total sampling time = × .

[0061] Since the drone flies at the same altitude and the rotating mirror scanning angle is fixed at , the actual acquisition distance , where is the flight altitude of the drone, and the relationship between the actual acquisition distance and the maximum acquisition distance is: ; In the formula, the laser scanning angle is = 7.5°, that is, when the flight altitude of the drone is known, the range of the actual acquisition distance can be calculated, but it cannot exceed .

[0062] If the number of sampling points is 16384, then = 245.76 m, that is, the points within the range of 245.76 m from the ground point to the laser can be collected. If the drone-mounted lidar works at an altitude of 100 m, the actual acquisition distance = 100.86 m.

[0063] And during one operation, it will work at the same altitude and will not change the working altitude. The depth of the shallow water area is 5 - 10 m. Then the effective data of the original waveform is mainly concentrated in the middle part. First, the sampling points of the radar can be adjusted to 8192 according to the working altitude of the drone, reducing the data volume by half. Then = 122.88 m. The effective data is mainly concentrated between 100 ± 5 m, plus there may be a floating range of 5 m due to environmental factors. According to the calculation, the effective waveform is concentrated within the range of 6666 ± 333 of the sampling points. If the influence of the drone vibration is considered and the angle deviation is 7.5° ± 2.5°, then the effective data is concentrated at 100.38 m - 101.54 m (that is, the sampling points are concentrated at 6692 - 6769). The working state of the acquisition card is continuous trigger acquisition, and the frequency is 5000 hz.

[0064] The method provided by the present invention first collects data. When each triggered data collection is stored in the buffer but not yet written to the hard disk, the data in the buffer is directly processed. Before flight, some parameters are manually set. The sampling points in the buffer are intercepted for part of the buffer data from 5500 to 8000, which is stored in the hard disk, and the remaining part is discarded. This operation effectively reduces the overall data volume of the original data, and is more efficient. It does not require data replication to increase the input and output volume of processing, nor does it reduce the sampling speed. It directly operates on the original data, avoiding dynamic memory allocation. This preprocessing is completed during the collection process, which is beneficial to the subsequent efficient processing of data.

[0065] To verify the method provided by the present invention, a comparative experiment is carried out. Under the same collection time, the experimental results are as Figure 2 and Figure 3 shown. Figure 2 For the original waveform extracted by directly preprocessing one line of data in a 9.6 GB original data file, with the same collection time, Figure 2 the data volume in Figure 3 is very large. After preprocessing, the effective waveforms are mainly concentrated around the sampling point position of about 1500, and the other waveforms are all invalid information. And Figure 1 the size of the data file in

[0066] is reduced to 600 MB. The effective information is the same, and the data volume is reduced by about 16 times. The data of 1024 sampling points in the middle of the sampling point positions from 1024 to 2048 is intercepted, and a section of noise at the front end and a large amount of invalid data at the rear end in Figure 1 are intercepted, and only the effective data components are collected and retained. Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preprocessing full waveform data based on airborne laser radar, characterized in that: The specific steps include: S1, according to the flight altitude of the UAV, calculate the number of sampling points and determine the interception of the specified data range; S2, initialize the acquisition card configuration; S3, start the data acquisition cycle, wait for the hardware trigger time, and collect raw data; S4, dynamically intercepting a specified range in the data buffer; S5, write the file and store the file in segments. When the number of detection records is greater than or equal to N, close the current file and create a new file.

2. The method for preprocessing full waveform data based on airborne laser radar according to claim 1, characterized in that: Step S1 specifically includes the following steps: S1.1, calculate the distance interval of sampling points : ； ； Among them, the speed of light 3× m / s, is the sampling rate, is the sampling period; S1.2, calculate the maximum acquisition distance of the acquisition card : ； The total sampling time =N× , N is the total number of sampling points; S1.3, the scanning angle of the rotating mirror is , actual acquisition distance ,in, is the flight altitude of the drone, and the relationship between the actual collection distance and the maximum collection distance is: ； S1.4, the actual number of sampling points is , ； in, is the actual acquisition distance, is the sampling point distance interval.

3. The method for preprocessing full waveform data based on airborne laser radar according to claim 1, characterized in that: Step S2 specifically includes the following steps: S2.1, calculate the actual number of sampling points according to the actual UAV working altitude , and according to Set intercept point parameters; S2.2, configure the acquisition card parameters, including: sampling rate, trigger mode and original record length.

4. The method for preprocessing full waveform data based on airborne laser radar according to claim 3 is characterized in that: In step S2.1, according to The specific parameters for setting the interception point are: setting the interception starting point START_SAMPLE and the number of sampling points SAMPLES_TO_SAVE for sampling interception.

5. The method for preprocessing full waveform data based on airborne laser radar according to claim 1, characterized in that: Step S3 specifically includes: responding to an external trigger signal and collecting complete waveform data.

6. The method for preprocessing full waveform data based on airborne laser radar according to claim 1, characterized in that: Step S4 is specifically as follows: S4.1, check whether the interception starting point exceeds the total number of sampling points, calculate the theoretical end point, and compare it with the buffer boundary to determine whether the end point is out of bounds. If it is out of bounds, it is automatically adjusted to the valid range; Calculate the end point of the interception: end=min(START_SAMPLE+SAMPLES_TO_SAVE,total_samples); Among them, total_samples is the total number of sampling points, and min is the minimum value function; If the interception start point exceeds the buffer range, it is reset to 0 and the record is discarded. If the interception end point exceeds the buffer range, it is intercepted to the end of the buffer. S4.2, when the data spans the Extradata and the current buffer, the interception range is concatenated, the effective data length of each segment is calculated, including the available length of the Extradata and the length to be supplemented in the current buffer, and then the data intercepted from the Extradata and the data supplemented from the current buffer are written in segments, with priority given to intercepting from the Extradata buffer and the remaining part supplemented from the current buffer; S4.3, dynamically calculate the actual interception length and determine the final length based on the boundary protection result to ensure that the actual interception length does not exceed SAMPLES_TO_SAVE.

7. The method for preprocessing full waveform data based on airborne laser radar according to claim 1, characterized in that: Step S5 is specifically as follows: S5.1, use the global counter to count the number of records written to the current file; after accumulating N=300,000 intercepted data, close the current file and generate a new file; S5.2, the file name is named according to the channel and time, and the header file retains the original acquisition naming rule by time; The file size is: 300000 × SAMPLES_TO_SAVE × 2 bytes.

Images