CN113376645A - Method and device for improving laser ranging precision - Google Patents
Method and device for improving laser ranging precision Download PDFInfo
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- CN113376645A CN113376645A CN202110937698.XA CN202110937698A CN113376645A CN 113376645 A CN113376645 A CN 113376645A CN 202110937698 A CN202110937698 A CN 202110937698A CN 113376645 A CN113376645 A CN 113376645A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/4802—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
Abstract
The invention discloses a method and a device for improving laser ranging precision, when detecting that a concave point exists above a signal threshold in the waveform of an echo signal, entering a specific echo calculation process: creating a virtual echo of a second echo by taking the first echo as a center, and determining the rough flight time of the virtual echo based on a first function; obtaining the initial flight time T of the second echo according to the initial flight time of the virtual echo, the peak value corresponding time of the virtual echo and the peak value corresponding time of the second echo; calculating the echo intensity of the superposed hidden part in the second echo according to the initial flight time of the second echo, the corresponding time of the last pit and the peak height of the last pit; the first function is a functional relationship between the rising edge time width and the peak height of the normal echo. By the aid of the scheme, the distance measurement process in a scene with interference sources such as rain, snow, dust and the like can be guaranteed not to be affected by the interference sources, and the target distance can be accurately and stably calculated.
Description
Technical Field
The invention belongs to the technical field of laser ranging, and particularly relates to a method and a device for improving laser ranging precision.
Background
The laser radar can be used for detecting three-dimensional space information of surrounding environment and completing reconstruction of a three-dimensional point cloud system, and has wide application in multiple fields and a plurality of specific application scenes. Meanwhile, the laser radar can be applied to various environments, and most of the laser radar is applied to outdoor environments particularly in the industrial field. The outdoor environment is comparatively abominable, receives the interference of interference sources such as sleet dust very easily to influence laser radar's normal detection.
At present, the technical means of removing the influence of rain, snow, dust and the like by the laser radar is to adopt a multi-echo technology, namely, echoes caused by interference sources such as rain, snow, dust and the like and target effective echoes are detected together, and screening and filtering are carried out through a system. Taking an interference source as an example of raindrops, as shown in fig. 1, when the raindrops are far away from a target, an interference echo and a target echo are separated on a time axis, and the interference echo can be effectively identified and filtered through a multi-echo algorithm, so that the target can be clearly and stably detected.
However, if the distance between the interference source and the target is too close and the interference source and the target are both close to the laser radar device, the transmission distance of the detection echo transmitted by the laser radar device in the space is not far, the light intensity is not attenuated too much, the divergence size of the light spot is not large, and at the moment, the echoes generated by the interference source and the target cannot be effectively separated. As shown in fig. 2, when the raindrops are close to the target, the interference echoes caused by the raindrops overlap with the target echoes, and at this time, the multi-echo algorithm cannot effectively identify and filter the interference echoes, so that the laser radar is affected by interference sources such as rain, snow, dust and the like in some special applications.
In view of the above, it is an urgent problem in the art to overcome the above-mentioned drawbacks of the prior art.
Disclosure of Invention
The invention provides a method and a device for improving laser ranging precision, aiming at solving the technical problem that in some special application scenes, a multi-echo technology cannot effectively identify and filter the influence of interference sources such as rain, snow, dust and the like on a laser radar.
In order to achieve the above object, according to an aspect of the present invention, a method for improving laser ranging accuracy is provided, when a pit is detected in a waveform of an echo signal above a signal threshold, a specific echo calculation process is performed, specifically:
creating a virtual echo of a second echo by taking a first echo as a center, enabling the corresponding time of the virtual echo to be consistent with the corresponding time of the peak value of the first echo, and determining the initial flight time Tx of the virtual echo based on a first function;
obtaining the initial flight time T of the second echo according to the initial flight time Tx of the virtual echo, the time T1 corresponding to the peak value of the virtual echo and the time T2 corresponding to the peak value of the second echo;
calculating the echo intensity S2 of the superimposed hidden part in the second echo according to the initial flight time T of the second echo, the corresponding time T3 of the last pit and the peak height H3 of the last pit, and finally obtaining the total echo intensity S of the second echo;
the first echo is a first received echo signal, the second echo is a last received echo signal, and the first function is a functional relation between a rising edge time width and a peak height of a normal echo.
Preferably, in the flow of computing the specific echo, the first function is determined by scaling, specifically:
collecting a plurality of normal echoes to further obtain a plurality of groups of rising edge time widths and corresponding peak heights; wherein the peak positions of the plurality of normal echoes are the same;
based on the multiple groups of data of the rising edge time width and the corresponding peak value height, calibrating to obtain the first function for representing the relation between the rising edge time width and the peak value height;
the rising edge time width refers to a time width from an initial flight time of the echo signal to a peak value corresponding time.
Preferably, the creating a virtual echo of the second echo with the first echo as the center, making the virtual echo coincide with the peak corresponding time of the first echo, and determining the initial flight time Tx of the virtual echo based on a first function specifically is:
creating a virtual echo of a second echo on a time axis by taking the first echo as a center, and enabling the time corresponding to the peak value of the virtual echo to be consistent with the time corresponding to the peak value of the first echo;
calculating a rising edge time width W2 of the virtual echo based on the first function and a peak height H2 of the virtual echo;
and calculating the initial flight time Tx of the virtual echo by combining the calculated rising edge time width W2 of the virtual echo and the peak value corresponding time T1 of the virtual echo.
Preferably, when determining the rough time of flight Tx of the virtual echo based on the first function, the method further comprises:
calculating a rising edge time width W1 of the first echo based on the first function and a peak height H1 of the first echo;
calculating a squeezing error E1 by combining the calculated rising edge time width W1 of the first echo, the peak corresponding time T1 of the first echo and the initial flight time T0 of the first echo;
after calculating the initial flight time Tx of the virtual echo, the calculated initial flight time Tx is compensated and corrected by the extrusion error E1.
Preferably, the obtaining the initial flight time T of the second echo according to the initial flight time Tx of the virtual echo, the peak value corresponding time T1 of the virtual echo, and the peak value corresponding time T2 of the second echo includes:
calculating a deviation E2 between the initial flight time Tx of the virtual echo and the initial flight time T of the second echo according to the peak value corresponding time T1 of the virtual echo and the peak value corresponding time T2 of the second echo;
and calculating the initial flight time T of the second echo according to the deviation E2 and the initial flight time Tx of the virtual echo.
Preferably, the echo intensity S2 of the superimposed concealed portion in the second echo is calculated according to the initial flight time T of the second echo, the corresponding time T3 of the last pit, and the peak height H3 of the last pit, and the total echo intensity S of the second echo is finally obtained, specifically:
calculating the echo intensity S2 of the superimposed hidden part in the second echo according to a triangle area formula based on the initial flight time T of the second echo, the corresponding time T3 of the last pit and the peak height H3 of the last pit;
calculating echo intensities of the non-superimposed concealed portions of the second echo according to a fitting function of the second echo based on a corresponding time T3 of a last pit and an ending flight time T4 of the second echo S1;
and adding the echo intensity S2 of the superimposed hidden part and the echo intensity S1 of the non-superimposed hidden part in the second echo to obtain the total echo intensity S of the second echo.
Preferably, after calculating the echo intensity S2 of the superimposed hidden part in the second echo according to the initial flight time T of the second echo, the corresponding time T3 of the last pit and the peak height H3 of the last pit, and finally obtaining the total echo intensity S of the second echo, the method further comprises:
and calculating the distance between the target and the laser radar according to the initial flight time T of the second echo and the total echo intensity S of the second echo.
Preferably, the calculating a distance between the target and the laser radar according to the rough flight time T of the second echo and the total echo intensity S of the second echo includes:
calculating a corresponding time calibration value according to the total echo intensity S of the second echo;
calculating the laser flight time according to the initial flight time T of the second echo and the time calibration value;
and calculating the distance between the target and the laser radar according to the laser flight time and the light speed.
Preferably, when it is detected that the waveform of the echo signal does not have a pit above the signal threshold, a normal echo calculation process is performed, specifically:
and obtaining the total echo intensity of the target echo according to the initial flight time of the target echo, the ending flight time of the target echo and the fitting function of the normal echo.
According to another aspect of the present invention, there is provided an apparatus for improving laser ranging accuracy, comprising at least one processor and a memory, the at least one processor and the memory being connected via a data bus, the memory storing instructions executable by the at least one processor, the instructions being configured to perform the method for improving laser ranging accuracy according to the first aspect after being executed by the processor.
Generally, compared with the prior art, the technical scheme of the invention has the following beneficial effects: according to the scheme for improving the laser ranging precision, the specific echo can be identified based on whether the waveform has the pits or not, the specific echo calculation process is entered, the time width-peak height function relation of the normal echo is skillfully utilized during calculation, the initial flight time of the target echo is obtained by means of the initial flight time of the interference echo, the time corresponding to the peak value of the interference echo, the virtual echo of the target echo and the like, the echo intensity of the superposed and hidden part in the target echo is further calculated, the total echo intensity of the target echo is finally obtained, and the distance calculation is carried out. By the scheme, in a scene with interference sources such as rain, snow, dust and the like, the distance measurement process can be guaranteed not to be affected by the interference sources, and the distance of the target echo in multi-echo superposition, namely the distance between the target and the laser radar, can be accurately and stably calculated.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly described below. It is obvious that the drawings described below are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a diagram illustrating an echo signal when a raindrop interference source is far away from a target;
FIG. 2 is a schematic diagram of echo signal superposition when a raindrop interference source is close to a target;
FIG. 3 is a schematic diagram of waveforms of multiple groups of normal echoes at the same distance according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating waveforms of specific echoes in the presence of an interference source according to an embodiment of the present invention;
FIG. 5 is a waveform diagram of a specific echo in the presence of multiple interference sources according to an embodiment of the present invention;
FIG. 6 is a flow chart of a flow of computing a differential echo according to an embodiment of the present invention;
FIG. 7 is a diagram illustrating an echo signal when a smoke-like interference source is far away from a target;
FIG. 8 is a schematic diagram of the superposition of echo signals when the smoke interference source is close to the target;
FIG. 9 is a waveform diagram of a specific echo in the presence of a smoke-like interference source according to an embodiment of the present invention;
FIG. 10 is a flow chart of another flow of computing the idiosyncratic echo according to an embodiment of the present invention;
fig. 11 is a diagram of an apparatus architecture for improving laser ranging accuracy according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the description of the present invention, the terms "inside", "outside", "longitudinal", "lateral", "upper", "lower", "top", "bottom", "left", "right", "front", "rear", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of describing the present invention but do not require that the present invention must be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
In the embodiments of the present invention, the symbol "/" indicates the meaning of having both functions, and the symbol "a and/or B" indicates that the combination between the preceding and following objects connected by the symbol includes three cases of "a", "B", "a and B".
In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other. The invention will be described in detail below with reference to the figures and examples.
Example 1
In an application scene with interference sources such as rain, snow, dust and the like, when a laser signal reaches a target and the interference sources, the laser signal is reflected to generate an echo signal. If echo signals of the target and the interference source are superposed, the laser ranging is affected, and at the moment, the influence of the interference source on the laser radar cannot be effectively identified and filtered by the multi-echo technology. In order to solve the above problem, an embodiment of the present invention provides a method for improving laser ranging accuracy, where:
after receiving the echo signal, firstly detecting whether the waveform of the echo signal has a pit above a signal threshold. If the pits exist, the received echo signals are proved to be specific echoes caused by the existence of interference sources such as rain, snow, dust and the like, and the echoes of the target and the interference sources are superposed, and then a specific echo calculation process is carried out; if the pit does not exist, the received echo signal is proved to be a normal echo, namely, the interference source does not exist or the interference source exists but the echoes of the target and the interference source are not superposed, and then a normal echo calculation process is carried out. For the sake of understanding, before the description of the flow of computing the peculiar echo and the flow of computing the normal echo, the following description is first made:
under the same detection distance, a plurality of normal echoes acquired aiming at targets with different reflectivities are shown in fig. 3, and have the following characteristics from the view of rising edge waveforms alone: the higher the peak height H, the wider the corresponding rising edge time width W, which is approximately linear with the peak height H, and the peak positions of the plurality of normal echoes are the same (i.e., the peaks are on the same time axis). The rising edge time width W refers to a time width from an initial flight time of the echo signal to a time corresponding to a peak value, and the initial flight time refers to a time intersection point of the rising edge of the echo and a signal threshold. For example, A, B, C, D, E in fig. 3 corresponds to the time points of the first flight times of the echo signals 1, 2, 3, 4, and 5, respectively, O is the time corresponding to the peak of each echo, AO, BO, CO, DO, and EO are the rising edge time widths of the echo signals 1, 2, 3, 4, and 5, respectively; since the echo signal gradually increases in peak height H in the order of 1, 2, 3, 4, and 5, the rise time widths AO, BO, CO, DO, and EO increase in sequence.
According to the above features, the specific echo calculation procedure may first obtain, through scaling, a first function W = f1(H) for characterizing a relationship between a rising edge time width W and a peak height H in a normal echo, specifically: firstly, collecting a plurality of normal echoes reflected by targets with different reflectivity at the same detection distance, and further obtaining a plurality of groups of rising edge time widths W and corresponding peak heights H, namely a plurality of groups of (W, H) data; then, based on the rising edge time width W and the sets of (W, H) data corresponding to the peak height H, a first function for characterizing the relationship between the rising edge time width W and the peak height H is obtained by fitting scaling. As can be seen from fig. 3, the rising edge time width W and the peak height H are substantially linear, and accordingly, the first function W = f1(H) is a linear function.
When laser generated by the laser radar first hits an interference source to generate reflection and then hits a target to generate reflection, the obtained echo signal includes two overlapped echoes as shown in fig. 4, and it is obvious that the first echo on the time axis is an interference echo and the second echo is a target echo. When laser generated by the laser radar first hits multiple interference sources to generate reflection and then hits a target to generate reflection, the obtained echo signal includes multiple overlapped echoes as shown in fig. 5, obviously, the last echo on the time axis is a target echo, and all echoes before the target echo are interference echoes. For convenience of description, marking a received first echo signal as a first echo, wherein the first echo corresponds to an interference echo; and recording the last received echo signal as a second echo, namely a target echo.
In fig. 4 and 5, T0 is the time intersection of the rising edge of the first echo and the signal threshold, i.e. the initial flight time of the first echo; t1 is the peak corresponding time of the first echo, T2 is the peak corresponding time of the second echo; t3 is the corresponding time of the last pit; t4 is the time intersection of the falling edge of the second echo with the signal threshold, i.e. the ending time of flight of the second echo; h1 is the peak height of the first echo, H2 is the peak height of the second echo; h3 is the peak height of the last pit, and all the above parameters can be directly obtained from the waveform of the echo signal. And extending the rising edge of the second echo reversely to obtain a time intersection point T of the rising edge of the second echo and a signal threshold, namely the initial flight time of the second echo. As can be seen from the figure, the waveform of the second echo is hidden from superposition from T to T3, and if the echo intensity of the second echo is to be acquired, the initial flight time T of the second echo needs to be calculated.
As shown in fig. 6, based on the above description, the flow of computing the distinctive echo is specifically as follows:
First, a virtual echo of a second echo is created on a time axis with the first echo as a center, and both the time corresponding to the peak of the virtual echo and the time corresponding to the peak of the first echo are T1, that is, the peak of the virtual echo and the peak of the first echo are coaxial. With reference to fig. 4 and 5, the rising edge of the virtual echo is shown as a dashed waveform, and the waveform of the virtual echo is the same as that of the second echo; the time intersection point of the rising edge of the virtual echo and the signal threshold is Tx, namely the initial flight time of the virtual echo is Tx.
Then, based on the first function and the peak height H2 of the virtual echo, the rising edge time width W2 of the virtual echo is calculated. Wherein, according to the first function W = f1(H), the rising edge time width W2= T1-Tx = f1(H2) of the virtual echo can be obtained.
Finally, the calculated rising edge time width W2 of the virtual echo and the peak corresponding time T1 of the virtual echo are combined to calculate the initial flight time Tx of the virtual echo. Specifically, from W2= T1-Tx = f1(H2), Tx = T1-f1(H2) can be obtained.
Further, taking the first echo as an example, according to the first function, there is T1-T0= f1(H1), but since there is a plurality of peaks, there occurs squeezing between peaks, which are not strictly equal, i.e., T1-T0 ≠ f1(H1), there exists a certain squeezing error. To ensure the accuracy of the calculation of the rough time of flight Tx, the extrusion error is also considered when determining the rough time of flight Tx, which is as follows:
first, based on the first function and the peak height H1 of the first echo, the rising edge time width W1 of the first echo is calculated: w1= f1 (H1). Then, the calculated rising edge time width W1 of the first echo, the peak corresponding time T1 of the first echo, and the rough flight time T0 of the first echo are combined to calculate a squeezing error E1: e1= T1-T0-W1= T1-T0-f1 (H1). After calculating the initial flight time Tx of the virtual echo, the calculated initial flight time Tx is compensated and corrected by the extrusion error E1, and the final Tx can be obtained as follows: tx = T1-f1(H2) + E1= T1-f1(H2) + T1-T0-f1(H1) =2T1-T0-f1(H1) -f1 (H2).
And 102, obtaining the initial flight time T of the second echo according to the initial flight time Tx of the virtual echo, the time T1 corresponding to the peak value of the virtual echo and the time T2 corresponding to the peak value of the second echo.
The waveform of the virtual echo is the same as the waveform of the second echo, so the rough flight time T of the second echo can be determined by the rough flight time Tx of the virtual echo, as follows: first, a deviation E2 between the initial flight time Tx of the virtual echo and the initial flight time T of the second echo is calculated from the peak corresponding time T1 of the virtual echo and the peak corresponding time T2 of the second echo: e2= T-Tx = T2-T1. Then, the initial flight time T of the second echo is calculated from the deviation E2 and the initial flight time Tx of the virtual echo: t = T2-T1+ Tx. When Tx =2T1-T0-f1(H1) -f1(H2), T = T2+ T1-T0-f1(H1) -f1 (H2).
The total echo intensity S of the second echo is the echo intensity from T to T4, wherein the echo intensity S1 from T3 to T4 can be directly obtained according to the waveform, the part from T to T3 has no waveform, the waveform from T to T3 can be approximated to a straight line with the height from 0 to H3, the echo intensity S2 from T to T3 is calculated, and the two parts of echo intensities are added to obtain the total echo intensity S. The specific process is as follows:
first, based on the rough flight time T of the second echo, the corresponding time T3 of the last pit, and the peak height H3 of the last pit, the echo intensity S2 of the superimposed hidden portion of the second echo is calculated according to the triangle area formula. Since the waveform of the time period from T to T3 is approximated to a straight line, the corresponding region is approximated to a triangle, and therefore, the corresponding echo intensity S2, i.e., S2= (T-T3) × H3/2, can be calculated by a triangle area formula.
Then, based on the corresponding time T3 of the last pit and the ending flight time T4 of the second echo, the echo intensity S1 of the non-superimposed hidden portion of the second echo is calculated according to the fitted function of the second echo. The normal echoes are all in a parabolic shape, the second echoes are also in a parabolic shape, the corresponding fitting function can be obtained by performing curve fitting on a plurality of echo signal data sampled in a time period from T3 to T4, and then the echo intensity S1 in the time period from T3 to T4 can be obtained according to the fitting function.
Finally, the echo intensity S2 of the superimposed hidden portion and the echo intensity S1 of the non-superimposed hidden portion in the second echo are added to obtain the total echo intensity S of the second echo, i.e., S = S1+ S2.
And 104, calculating the distance between the target and the laser radar according to the initial flight time T of the second echo and the total echo intensity S of the second echo.
First, a corresponding time calibration value, i.e. f2(S), is calculated from the total echo intensity S of the second echo, where f2 is a time calibration function based on echo intensity, and can be obtained by scaling.
Then, the laser flight time T ', i.e., T' = [ T + f2(S) ]/2 is calculated from the initial flight time T of the second echo and the time calibration value f2(S), and the division by 2 is the time elapsed by 2 times since the time of T is from the start of laser emission to the end of laser emission.
Finally, the distance L between the target and the laser radar is calculated according to the laser flight time T 'and the speed of light c, i.e. L = T' × c = [ T + f2(S) ] × c/2.
In the flow of computing the peculiar echo, the echo intensity S2 of the superimposed hidden part in the second echo is directly obtained according to a triangle area computing formula. In an alternative embodiment, as shown in fig. 4 and 5, a point with height H3 is found on the rising edge of the first echo, and the time Ty corresponding to the height H3 is determined on the rising edge of the first echo; after Ty is determined, an echo intensity for a time period T0 to Ty in the first echo may be calculated according to a fit function of the first echo S2'; according to the triangle area proportion relation, S2 '/S2 = (Ty-T0)/(T3-T), so S2= S2' (T3-T)/(Ty-T0) can be obtained. Wherein the fitting function of the first echo is obtained by curve fitting a plurality of echo signal data sampled in a time period from T0 to T3. In another alternative embodiment, the echo intensity may also be calculated from a fitted function of the second echoes based directly on T and T3S 2. Compared with simulation calculation, the difference between the S2 calculated by different methods is small, so that different methods can be selected for calculation according to actual requirements.
It should be noted that, when the first method is adopted to calculate S2, the waveform of the second echo in the time period from T to T3 is approximated to a triangle, that is, the rising edge of the second echo is approximated to a straight line. However, the rising edge in the actual waveform still has a certain radian and is not a complete straight line, so that a certain error still exists after approximation; in order to reduce the error, certain hardware circuit design or software design can be carried out during laser emission, so that the rising edge of the received echo signal is as close to a straight line as possible. The closer the rising edge of the actual waveform is to a straight line, the more accurate the echo intensity calculated when the waveform is approximated to a triangle, and the higher the final ranging accuracy.
It should be noted that, in the case that a plurality of interference sources exist in fig. 5 and a plurality of interference echoes are generated, a plurality of pits exist in the waveform, and at this time, when calculating the initial flight time T and the total echo intensity S of the second echo (i.e., the target echo), only the rising edge and the last pit of the first interference echo need to be used, and the specific calculation method is the same as that when one interference source exists, and is performed in the order of step 101 to step 104.
Further, when the received echo signal is a normal echo, only one target echo is present on the time axis, or there are multiple echoes but the target echo can be clearly distinguished, and at this time, the corresponding normal echo calculation process specifically includes: and directly obtaining the total echo intensity S of the target echo according to the initial flight time of the target echo, the ending flight time of the target echo and the fitting function of the normal echo.
In summary, the method provided in the embodiment of the present invention can identify the specific echo based on whether the waveform has a pit or not, and enter the specific echo calculation process, and when calculating, skillfully utilize the rising edge time width-peak height function relation of the normal echo, obtain the initial flight time T of the target echo by using the initial flight time of the interference echo, the time corresponding to the peak of the interference echo, the virtual echo of the target echo, and the like, further calculate the echo intensity of the superimposed and hidden portion in the target echo, finally obtain the total echo intensity T of the target echo, and perform distance calculation. By the scheme, in a scene with interference sources such as rain, snow, dust and the like, the distance measurement process can be guaranteed not to be affected by the interference sources, and the distance of the target echo in multi-echo superposition, namely the distance between the target and the laser radar, can be accurately and stably calculated.
Example 2
In the above embodiment 1, there is an application scenario where there are interference sources such as rain, snow, dust, etc., and the thickness of such interference sources is small, so that the waveforms of the generated interference echoes are similar to the target echoes and have a sharp peak, as shown in fig. 1, and as shown in fig. 2, 4, and 5 after being overlapped. For the interference sources with certain thickness such as smoke and haze, the waveforms of the generated interference echoes are different, and there are no sharp peaks, but rather there are wider peaks as shown in fig. 7, and after overlapping, as shown in fig. 8 and 9. Aiming at the influence caused by the interference source with certain thickness, the embodiment of the invention further provides another method for improving the laser ranging precision:
after receiving the echo signal, firstly detecting the slope change of the rising edge of the echo signal above the signal threshold. If the slope of the rising edge of the echo signal above the signal threshold is detected to be within the minimum preset range for a preset time, the received echo signal is proved to be a specific echo caused by the existence of interference sources with certain thicknesses such as fog, haze and dust, and the echoes of the target and the interference sources are superposed, and then a specific echo calculation process is started; if the slope of the rising edge of the echo signal above the signal threshold is not detected to be within the minimum preset range for a preset time, the received echo signal is proved to be a normal echo, namely, no interference source exists or no interference source exists but the echoes of the target and the interference source are not superposed, and then a normal echo calculation process is carried out. The minimum preset range is within a certain fluctuation range of the minimum value of the slope, the minimum value of the slope is usually 0 or is close to 0, and when the slope of the rising edge is within the minimum preset range, the height change of the waveform is small and the waveform is in a gentle state; the preset time can be specifically taken according to actual experience, and when the slope of the rising edge is in the minimum preset range and lasts for the preset time, the echo is considered to be an interference echo corresponding to an interference source with a certain thickness.
For the sake of understanding, before describing the flow of computing the specific echo and the flow of computing the normal echo, the following description is first made with reference to fig. 9: recording a first received echo signal as a first echo, and corresponding to an interference echo; and recording the last received echo signal as a second echo, namely a target echo. T0 is the rough time of flight of the first echo; t1 is the time when the slope of the first echo enters a minimum preset range, i.e. the time corresponding to the peak of the rising edge; t2 is the peak corresponding time of the second echo; t3 is the time when the slope of the first echo leaves a minimum preset range; t4 is the end time of flight of the second echo; h1 is the height at which the slope of the first echo enters a minimum preset range; h2 is the peak height of the second echo; h3 is the height of the first echo when the slope is away from the minimum preset range, and all the above parameters can be directly obtained by the waveform of the echo signal. And extending the rising edge of the second echo reversely to obtain a time intersection point T of the rising edge of the second echo and a signal threshold, namely the initial flight time of the second echo. As can be seen from the figure, the waveform of the second echo is hidden from superposition from T to T3, and if the echo intensity of the second echo is to be acquired, the initial flight time T of the second echo needs to be calculated.
As shown in fig. 10, based on the above description, the flow of calculating the peculiar echo at this time is specifically as follows:
First, a virtual echo of a second echo is created on a time axis with the first echo as a center, and a time corresponding to a peak of the virtual echo is made to coincide with a time when a slope of the first echo falls within a minimum preset range, all of which are T1. With reference to fig. 9, the rising edge of the virtual echo is shown as a dashed waveform, and the waveform of the virtual echo is the same as that of the second echo; the time intersection point of the rising edge of the virtual echo and the signal threshold is Tx, namely the initial flight time of the virtual echo is Tx.
Then, based on the first function and the peak height H2 of the virtual echo, the rising edge time width W2 of the virtual echo is calculated. Wherein, according to the first function W = f1(H), the rising edge time width of the virtual echo rising edge is W2= T1-Tx = f1 (H2). The first function used here is the same as that used in example 1, and the scaling method is the same.
Finally, the calculated rising edge time width W2 of the virtual echo and the peak corresponding time T1 of the virtual echo are combined to calculate the initial flight time Tx of the virtual echo. Specifically, from W2= T1-Tx = f1(H2), Tx = T1-f1(H2) can be obtained.
Further, taking the first echo as an example, according to the first function, there is T1-T0= f1(H1), but since there is a plurality of peaks, there occurs squeezing between peaks, which are not strictly equal, i.e., T1-T0 ≠ f1(H1), there exists a certain squeezing error. To ensure the accuracy of the calculation of the rough time of flight Tx, the extrusion error is also considered when determining the rough time of flight Tx, which is as follows:
firstly, calculating a rising edge time width W1 of the first echo based on the first function and a height H1 when the slope of the first echo enters a minimum preset range; although the first echo has no sharp peak like that of the target echo, the rising edge time width W1 and the height H1 (corresponding to the peak height of the rising edge) have the same linear relationship as the normal echo, that is, the rising edge time width W1 and the height H1 still conform to the first function of the normal echo, and thus, there is W1= f1 (H1). Then, in combination with the calculated rising edge time width W1 of the first echo, the time T1 at which the slope of the first echo enters a minimum preset range, and the initial time of flight T0 of the first echo, a squeezing error E1 is calculated: e1= T1-T0-W1= T1-T0-f1 (H1). After calculating the initial flight time Tx of the virtual echo, the calculated initial flight time Tx is compensated and corrected by the extrusion error E1, and the final Tx can be obtained as follows: tx = T1-f1(H2) + E1= T1-f1(H2) + T1-T0-f1(H1) =2T1-T0-f1(H1) -f1 (H2).
The waveform of the virtual echo is the same as the waveform of the second echo, so the rough flight time T of the second echo can be determined by the rough flight time Tx of the virtual echo, as follows: first, a deviation E2 between the initial flight time Tx of the virtual echo and the initial flight time T of the second echo is calculated from the peak corresponding time T1 of the virtual echo and the peak corresponding time T2 of the second echo: e2= T-Tx = T2-T1. Then, the initial flight time T of the second echo is calculated from the deviation E2 and the initial flight time Tx of the virtual echo: t = T2-T1+ Tx. When Tx =2T1-T0-f1(H1) -f1(H2), T = T2+ T1-T0-f1(H1) -f1 (H2).
The total echo intensity S of the second echo is the echo intensity from T to T4, wherein the echo intensity S1 from T3 to T4 can be directly obtained according to the waveform, the part from T to T3 has no waveform, the waveform from T to T3 can be approximated to a straight line with the height from 0 to H3, the echo intensity S2 from T to T3 is calculated, and the two parts of echo intensities are added to obtain the total echo intensity S. The specific process is as follows:
firstly, the echo intensity of the superimposed hidden part in the second echo is calculated by means of a triangular area proportional relation according to the echo intensity S0 of the first echo before the slope enters a minimum preset range and the rough flight time T of the second echo, and S2 is calculated. The specific calculation process will be described later, and will not be described herein.
Then, based on the time T3 when the slope of the first echo leaves the minimum preset range and the end flight time T4 of the second echo, the echo intensity S1 of the non-superimposed hidden portion in the second echo is calculated according to the fitting function of the second echo. The normal echoes are all in a parabolic shape, the second echoes are also in a parabolic shape, the corresponding fitting function can be obtained by performing curve fitting on a plurality of echo signal data sampled in a time period from T3 to T4, and then the echo intensity S1 in the time period from T3 to T4 can be obtained according to the fitting function.
Finally, the echo intensity S2 of the superimposed hidden portion and the echo intensity S1 of the non-superimposed hidden portion in the second echo are added to obtain the total echo intensity S of the second echo, i.e., S = S1+ S2.
And 204, calculating the distance between the target and the laser radar according to the initial flight time T of the second echo, the total echo intensity S of the second echo, the duration T3-T1 of the slope of the first echo in the minimum preset range and the minimum value M of the slope of the first echo.
First, a corresponding first time calibration value, i.e. f2(S), is calculated from the total echo intensity S of the second echo, where f2 is a time calibration function based on echo intensity, and can be obtained by scaling.
Secondly, a second time calibration value, i.e. f3(T3-T1, M), is calculated from the duration T3-T1 of the slope of the first echo within a minimum preset range and the minimum value M of the slope of the first echo. Since the interference source is fragmented so that the energy loss is not negligible, the first echo needs to be used to calibrate the laser time of flight from the slope into the minimum preset range to the width (T3-T1) out of the minimum preset range; meanwhile, when the slope is less than 0, the position of H1 is not the peak value of the first echo, so the laser flight time needs to be calibrated by using the minimum slope value. Where f3 is a time calibration function based on duration (T3-T1) and slope minimum M, which can be obtained by scaling. Of course, if the minimum slope value is 0, the calibration value corresponding to the minimum slope value M is 0, and at this time, the second time calibration value is calculated by using only the duration (T3-T1) of the rising edge slope of the first echo within the minimum preset range.
Then, from the initial time-of-flight T of the second echo, the first time calibration value f2(S), and the second time calibration value f3(T3-T1, M), the laser time-of-flight T 'is calculated, i.e., T' = [ T + f2(S) + f3(T3-T1, M) ]/2, and the division by 2 is a time that is 2 times elapsed since the time of T is from the start of laser emission to the end of laser emission.
Finally, the distance L between the target and the laser radar is calculated according to the laser flight time T 'and the speed of light c, i.e. L = T' × c = [ T + f2(S) + f3(T3-T1, M) ] × c/2.
With further reference to fig. 9, since the rising edge time width W of the waveform is substantially linear with the peak height H, the waveform region of the first echo in the period from T0 to T1 (i.e. the waveform of the first echo before the slope enters the minimum preset range) may be approximated as a triangle, which is denoted as a first triangle; the waveform of the second echo in the time period from T to T3 (i.e. the waveform of the second echo superimposed with the hidden part) may also be approximated to a triangle, which is denoted as a second triangle. In step 203, the calculation method of the echo intensity S2 is specifically as follows:
firstly, according to the initial flight time T and the rest echo parameters of the second echo, calculating the ratio of the echo intensity S0 of the first echo before the slope enters the minimum preset range to the echo intensity S2 of the superimposed hidden part in the second echo by means of a triangular area proportional relation; wherein the remaining echo parameters include an initial flight time T0 of the first echo, a time T1 when the slope of the first echo enters a minimum preset range, an altitude H1 when the slope of the first echo enters the minimum preset range, a time T3 when the slope of the first echo leaves the minimum preset range, and an altitude H3 when the slope of the first echo leaves the minimum preset range. Specifically, with reference to fig. 4, the base of the first triangle is T1-T0, and the height is H1; the base of the second triangle is T3-T, and the height of the second triangle is H3. For calculation, a transition triangle can be created, and the base of the transition triangle is the same as that of the second triangle, namely T3-T; the height is the same as the height of the first triangle, H1, whose area can be denoted as S0'. The echo intensity in the corresponding time period area is expressed by the area of the triangle, and according to the proportional relation of the area of the triangle, the following relation is approximately realized: S0/S0 '= (T1-T0)/(T3-T), S2/S0' = H3/H1, whereby S0/S2= [ (T1-T0)/(T3-T) ] (H1/H3) can be obtained.
Then, based on the rough flight time T0 of the first echo and the time T1 when the slope of the first echo enters a minimum preset range, the echo intensity S0 of the first echo before the slope enters the minimum preset range, that is, the area of the parabolic waveform region in the period from T0 to T1, is calculated according to the fitting function of the rising edge of the first echo. Wherein the fitting function of the first echo rising edge can be obtained by curve fitting of a plurality of echo signal data sampled in the time period from T0 to T1.
Finally, according to the calculated echo intensity ratio S0/S2 and the echo intensity S0 of the first echo before the slope enters the minimum preset range, the echo intensity S2 of the superimposed hidden part in the second echo is calculated. Wherein S2= S0 [ (T3-T)/(T1-T0) ] (H3/H1).
By the method, the echo intensity S2 of the superimposed hidden part in the second echo can be calculated relatively accurately. In addition, in an alternative embodiment, to further simplify the calculation, S2 may also be calculated by using a triangle area formula directly according to T, T3 and H3, that is, S2= (T3-T) × H3/2; alternatively, the echo intensity S2 may also be calculated from a fit function of the second echoes directly based on T and T3. However, both methods do not use the real waveform of the first echo, but directly calculate the waveform of the superimposed hidden part in the second echo, so that compared with the first method, the method is coarser, the accuracy is reduced, but the method has the advantages of faster and simpler calculation, and the method can be used for fast calculation under the condition of lower error requirement.
It should be noted that, when calculating S2 by the first two methods, the waveform of the second echo in the time period from T to T3 is approximated to a triangle, that is, the rising edge of the second echo is approximated to a straight line. However, the rising edge in the actual waveform still has a certain radian and is not a complete straight line, so that a certain error still exists after approximation; in order to reduce the error, certain hardware circuit design or software design can be carried out during laser emission, so that the rising edge of the received echo signal is as close to a straight line as possible. The closer the rising edge of the actual waveform is to a straight line, the more accurate the echo intensity calculated when the waveform is approximated to a triangle, and the higher the final ranging accuracy.
Further, when the received echo signal is a normal echo, only one target echo is present on the time axis, or there are multiple echoes but the target echo can be clearly distinguished, and at this time, the corresponding normal echo calculation process specifically includes: and directly obtaining the total echo intensity S of the target echo according to the initial flight time of the target echo, the ending flight time of the target echo and the fitting function of the normal echo.
In summary, the method provided by the embodiment of the present invention can identify the specific echo based on the change of the slope of the waveform, and enter the specific echo calculation process, and when calculating, skillfully utilize the rising edge time width-peak height function relation of the normal echo, obtain the initial flight time T of the target echo by using the interference echo and the virtual echo of the target echo, further calculate the echo intensity of the superimposed and hidden portion in the target echo, finally obtain the total echo intensity T of the target echo, and perform distance calculation. Through the scheme, in a scene with interference sources such as fog, haze and dust, the distance measuring process can be guaranteed not to be affected by the interference sources, and the distance of the target echo in multi-echo superposition, namely the distance between the target and the laser radar, can be accurately and stably calculated.
Example 3
On the basis of the methods for improving the laser ranging accuracy provided in the foregoing embodiments 1 and 2, the present invention further provides a device for improving the laser ranging accuracy, which can be used for implementing the foregoing methods, and as shown in fig. 11, is a schematic structural diagram of the device in the embodiments of the present invention. The apparatus for improving the accuracy of laser ranging of the present embodiment includes one or more processors 21 and a memory 22. In fig. 11, one processor 21 is taken as an example.
The processor 21 and the memory 22 may be connected by a bus or other means, and fig. 11 illustrates the connection by a bus as an example.
The memory 22, which is a non-volatile computer-readable storage medium for a method of improving laser ranging accuracy, may be used to store non-volatile software programs, non-volatile computer-executable programs, and modules, such as the method of improving laser ranging accuracy in embodiment 1. The processor 21 executes various functional applications and data processing of the apparatus for improving laser ranging accuracy by executing the nonvolatile software program, instructions and modules stored in the memory 22, that is, implements the methods for improving laser ranging accuracy of embodiments 1 and 2.
The memory 22 may include high speed random access memory and may also include non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other non-volatile solid state storage device. In some embodiments, the memory 22 may optionally include memory located remotely from the processor 21, and these remote memories may be connected to the processor 21 via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
The program instructions/modules are stored in the memory 22 and, when executed by the one or more processors 21, perform the methods of improving laser ranging accuracy in embodiments 1 and 2 described above, for example, performing the various steps shown in fig. 6 and 10 described above.
Those of ordinary skill in the art will appreciate that all or part of the steps of the various methods of the embodiments may be implemented by associated hardware as instructed by a program, which may be stored on a computer-readable storage medium, which may include: read Only Memory (ROM), Random Access Memory (RAM), magnetic or optical disks, and the like.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A method for improving laser ranging accuracy is characterized in that when a concave point exists above a signal threshold in a waveform of an echo signal, a specific echo calculation process is started, and specifically:
creating a virtual echo of a second echo by taking a first echo as a center, enabling the corresponding time of the virtual echo to be consistent with the corresponding time of the peak value of the first echo, and determining the initial flight time Tx of the virtual echo based on a first function;
obtaining the initial flight time T of the second echo according to the initial flight time Tx of the virtual echo, the time T1 corresponding to the peak value of the virtual echo and the time T2 corresponding to the peak value of the second echo;
calculating the echo intensity S2 of the superimposed hidden part in the second echo according to the initial flight time T of the second echo, the corresponding time T3 of the last pit and the peak height H3 of the last pit, and finally obtaining the total echo intensity S of the second echo;
the first echo is a first received echo signal, the second echo is a last received echo signal, and the first function is a functional relation between a rising edge time width and a peak height of a normal echo.
2. The method for improving laser ranging accuracy according to claim 1, wherein in the specific echo calculation process, the first function is determined by scaling, specifically:
collecting a plurality of normal echoes to further obtain a plurality of groups of rising edge time widths and corresponding peak heights; wherein the peak positions of the plurality of normal echoes are the same;
based on the multiple groups of data of the rising edge time width and the corresponding peak value height, calibrating to obtain the first function for representing the relation between the rising edge time width and the peak value height;
the rising edge time width refers to a time width from an initial flight time of the echo signal to a peak value corresponding time.
3. The method according to claim 1, wherein the virtual echo of the second echo is created with the first echo as a center, the time corresponding to the peak of the virtual echo is consistent with the time corresponding to the peak of the first echo, and the initial flight time Tx of the virtual echo is determined based on a first function, specifically:
creating a virtual echo of a second echo on a time axis by taking the first echo as a center, and enabling the time corresponding to the peak value of the virtual echo to be consistent with the time corresponding to the peak value of the first echo;
calculating a rising edge time width W2 of the virtual echo based on the first function and a peak height H2 of the virtual echo;
and calculating the initial flight time Tx of the virtual echo by combining the calculated rising edge time width W2 of the virtual echo and the peak value corresponding time T1 of the virtual echo.
4. A method of improving laser ranging accuracy as defined in claim 3 wherein, in determining the rough time of flight Tx of the virtual echo based on the first function, the method further comprises:
calculating a rising edge time width W1 of the first echo based on the first function and a peak height H1 of the first echo;
calculating a squeezing error E1 by combining the calculated rising edge time width W1 of the first echo, the peak corresponding time T1 of the first echo and the initial flight time T0 of the first echo;
after calculating the initial flight time Tx of the virtual echo, the calculated initial flight time Tx is compensated and corrected by the extrusion error E1.
5. The method according to claim 1, wherein the obtaining the initial flight time T of the second echo according to the initial flight time Tx of the virtual echo, the peak value corresponding time T1 of the virtual echo, and the peak value corresponding time T2 of the second echo comprises:
calculating a deviation E2 between the initial flight time Tx of the virtual echo and the initial flight time T of the second echo according to the peak value corresponding time T1 of the virtual echo and the peak value corresponding time T2 of the second echo;
and calculating the initial flight time T of the second echo according to the deviation E2 and the initial flight time Tx of the virtual echo.
6. The method for improving laser ranging accuracy according to claim 1, wherein the echo intensity S2 of the superimposed hidden portion of the second echo is calculated according to the initial flight time T of the second echo, the corresponding time T3 of the last pit, and the peak height H3 of the last pit, and the total echo intensity S of the second echo is obtained by:
calculating the echo intensity S2 of the superimposed hidden part in the second echo according to a triangle area formula based on the initial flight time T of the second echo, the corresponding time T3 of the last pit and the peak height H3 of the last pit;
calculating echo intensities of the non-superimposed concealed portions of the second echo according to a fitting function of the second echo based on a corresponding time T3 of a last pit and an ending flight time T4 of the second echo S1;
and adding the echo intensity S2 of the superimposed hidden part and the echo intensity S1 of the non-superimposed hidden part in the second echo to obtain the total echo intensity S of the second echo.
7. The method of improving laser ranging accuracy of any one of claims 1 to 6, wherein after calculating echo intensity S2 of the superimposed hidden portion of the second echo according to the initial flight time T of the second echo, the corresponding time T3 of the last pit and the peak height H3 of the last pit, and finally obtaining the total echo intensity S of the second echo, the method further comprises:
and calculating the distance between the target and the laser radar according to the initial flight time T of the second echo and the total echo intensity S of the second echo.
8. The method of claim 7, wherein the distance between the target and the lidar is calculated according to the initial flight time T of the second echo and the total echo intensity S of the second echo, specifically:
calculating a corresponding time calibration value according to the total echo intensity S of the second echo;
calculating the laser flight time according to the initial flight time T of the second echo and the time calibration value;
and calculating the distance between the target and the laser radar according to the laser flight time and the light speed.
9. The method for improving laser ranging accuracy according to any one of claims 1 to 6, wherein when it is detected that the waveform of the echo signal does not have a pit above a signal threshold, a normal echo calculation procedure is performed, specifically:
and obtaining the total echo intensity of the target echo according to the initial flight time of the target echo, the ending flight time of the target echo and the fitting function of the normal echo.
10. An apparatus for improving laser ranging accuracy, comprising at least one processor and a memory, wherein the at least one processor and the memory are connected through a data bus, and the memory stores instructions executable by the at least one processor, and the instructions are used for completing the method for improving laser ranging accuracy according to any one of claims 1 to 9 after being executed by the processor.
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| CN112462356A (en) * | 2020-11-10 | 2021-03-09 | 西安电子工程研究所 | Method for improving radar ranging precision based on Gaussian interpolation |
| CN112525165A (en) * | 2020-11-18 | 2021-03-19 | 华中科技大学 | Multichannel laser radar ultra-shallow water sounding data processing method |
| CN113189606A (en) * | 2021-04-30 | 2021-07-30 | 深圳煜炜光学科技有限公司 | Method and device for improving distance measurement precision of targets with different reflectivities |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115616525A (en) * | 2022-12-06 | 2023-01-17 | 深圳煜炜光学科技有限公司 | Method, device and equipment for distinguishing reflected echo signals and storage medium |
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