CN102508251A - Method for rapidly implementing sector conversion in multi-beam image sonar - Google Patents
Method for rapidly implementing sector conversion in multi-beam image sonar Download PDFInfo
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Abstract
The invention provides a method for rapidly implementing sector conversion in a multi-beam image sonar. An acoustic signal is radiated by a transmitting transducer by using the multi-beam image sonar; a target echo is received by a receiving transducer; beam forming processing is performed on the echo data to acquire a target scene image output in a polar coordinate mode; and a sector conversion module is used for conversing the acoustic image of the polar coordinate into the acoustic image of a rectangular coordinate to conform to the visual sense habit. When the sector conversion is realized on the image sonar based on the beam forming, triangular function operation or anti-trigonometric function operation is not needed in the hardware such as field programmable gata array (FPGA). The method comprises the steps of: (1) identifying the resolution ratio of a display used for displaying the acoustic image of a rectangular coordinate; (2) calculating the resolution ratio of horizontal and vertical distances of the image of the rectangular coordinate according to the actual range of the horizontal and vertical distances of the image sonar; (3) calculating the values of the horizontal and vertical coordinates of the polar coordinate corresponding to some point according to the horizontal and vertical coordinates at the point of the image of the rectangular coordinate; (4) obtaining an index value of the horizontal and vertical coordinates of the polar coordinate of the point according to a beam forming principle; (5) storing the image of the polar coordinate image into a memory, reading the corresponding pixel amplitude value according to the index value of the horizontal and vertical coordinates of the polar coordinate, and assigning the value to the position corresponding to the rectangular coordinate; and (6) completing mapping between each point and the polar coordinate under the rectangular coordinate to obtain the acoustic image of the rectangular coordinate.
Description
Technical field
The invention belongs to image sonar field, relate generally to the implementation method of image sonar middle fan fractal transform.
Background technology
Multi-beam image sonar often adopts active mode work; Utilize transmitting transducer to give off acoustical signal, through receiving transducer receiving target echo, echo data forms to handle through wave beam and obtains the object scene image; Image is exported with polar form; Fan-shaped conversion module then is used for the polar coordinates acoustic image is converted into the rectangular coordinate acoustic image, so that the graphoscope demonstration is suitable for user's visual custom.
The polar plot that wave beam forms module output similarly is to be horizontal ordinate with target to the oblique distance r of receiving transducer, is ordinate with target with respect to the orientation angles θ of receiving transducer.Fan-shaped conversion can (r, (r, θ) (x, y) (x forms between y) and shines upon the image pixel value f under θ), obtains the rectangular coordinate acoustic image at last for following image pixel value g with rectangular coordinate with polar coordinates.The rectangular coordinate acoustic image is generally shown on the display, carries out the target information interpretation for the soundman.Like figure (1), the transformation relation between coordinate does
Fan-shaped conversion can have two kinds of mapping modes.A kind of is that (r, θ) (x, y) conversion that is to say polar coordinates (r to polar coordinates to rectangular coordinate
0, θ
0) pixel amplitude f (r
0, θ
0) equal rectangular coordinate
The pixel amplitude
Under pixel amplitude f (r
0, θ
0), then need calculate the arctan trigonometric function value.Because the rectangular coordinate acoustic image is presented on the display, its horizontal ordinate x utilizes the display horizontal resolution, and ordinate y utilizes the display vertical resolution.Because the sampling number on the polar coordinates acoustic image r direction (being the oblique distance direction) is high more a lot of than display vertical resolution; If adopt the method for polar coordinates to rectangular coordinates transformation; Every bit under the polar coordinates all will be done the mapping of a rectangular coordinate conversion; The phenomenon that polar multiple spot all is mapped to the same point of rectangular coordinate can occur, and calculated amount can be very big, so often adopt the method for rectangular coordinates transformation to the polar coordinates relevant position value of reaching.
When the receiver of image sonar utilized FPGA to carry out real-time fan-shaped conversion, the most consuming time what account for hardware resource most was exactly trigonometric function operation, and the calculating of trigonometric function value has two kinds of processing modes, and a kind of is that the trigonometric function value that calculated in advance is good is stored in hardware and deposits g (x
0, y
0), need to calculate the trigonometric function value of sin and cos this moment; Another kind is that (x, (r, θ) sites value that is to say rectangular coordinate (x y) to transform to polar coordinates with rectangular coordinate
0, y
0) under pixel amplitude g (x
0, y
0) equal directly to call when needing in the polar coordinates reservoir, but need to consume very big hardware resource like this.Chen Jingyu [Chen Jingyu, conversion of high-resolution radar displaing coordinate and relevant design, marine electronic antagonism, 2001] utilizes the periodicity and the symmetry of trigonometric function, deposits the carry value of first quartile in EPROM, reduces the capacity requirement of storer with the method.Store but still need to consume hardware resource, the system configuration that has can't satisfy the demands; Another kind of mode is to utilize iterative approach algorithm (cordic algorithm) to calculate trigonometric function value; For example the long root of poplar is at master thesis [Yang Changgen; Based on acoustic imaging algorithm research and the realization of FPGA, Harbin: Harbin Engineering University's master thesis (CNKI), 2006] utilize cordic algorithm that the fan-shaped conversion of image sonar is realized; But in order to obtain high-precision trigonometric function value, often required iterations is very big.For example talk and people [Tan Yiyu such as should educate; Bian Wenbing, a kind of coordinate conversion circuit, data acquisition and processing based on cordic algorithm; 2001] utilize cordic algorithm that the fan-shaped conversion of B ultrasonic image is realized equally, but operational precision need high data-measuring figure place to guarantee.And the realization of cordic algorithm need carry out the program design based on streamline, and the developer is had certain requirement.
Summary of the invention
The object of the present invention is to provide a kind of Fast implementation of multi-beam image sonar middle fan fractal transform of the real-time that can largely improve fan-shaped conversion.This method makes the image sonar that forms based on wave beam when realizing fan-shaped conversion, and hardware such as FPGA need not loaded down with trivial details triangle or inverse trigonometric function computing, can largely improve the real-time of fan-shaped conversion.
The objective of the invention is to realize like this: the monitor resolution of rectangular coordinate acoustic image is confirmed to be used for showing in (1); (2), calculate rectangular coordinate image level and vertical range resolution according to image sonar real standard and vertical distance range; (3), calculate the corresponding horizontal ordinate value of polar coordinates of this point according to the horizontal ordinate value of the rectangular coordinate of certain point; (4) form principle according to wave beam and obtain the horizontal ordinate index value of polar coordinates; (5) polar coordinate image is stored in the storer, reads the respective pixel amplitude according to polar horizontal ordinate index value, and assignment is given the rectangular coordinate correspondence position; (6) accomplish every bit and polar mapping under the rectangular coordinate system, obtain the rectangular coordinate acoustic image.
Each pixel intensity of image is reflected by pixel amplitude size.Can know rectangular coordinate (x by formula (1)
0, y
0) under the pixel amplitude equal polar coordinates
Under the pixel amplitude.Polar pixel amplitude is stored in SDRAM or other storeies, be from SDRAM correct values, need not know θ in fact
0And r
0What specifically is, and need knows this θ
0Horizontal ordinate in polar coordinates (angle) index value (promptly 0,1,2.), r
0Also like this, like this could be according to the address table value of tabling look-up.And with this value assignment to rectangular coordinate correspondence position (x
0, y
0), at this moment also must know x
0, y
0Index value.
Generally, the method for acquisition coordinated indexing value is respectively under polar coordinates and rectangular coordinate system
Wherein θ _ index and r_index are respectively polar coordinates lower angles and apart from index value;
and
is respectively angle and distance resolution, confirmed by image sonar performance; X_index and y_index are respectively level and vertical range index values under the rectangular coordinate;
and
is respectively level and vertical range resolution, counts definite by sonar range and the display picture element that is used to show.It is the most complicated wherein to find the solution θ _ index, because according to formula (1), needs to accomplish the computing of arctan arctan function, just can know azimuth angle theta
0The present invention is primarily aimed at θ _ index and finds the solution and simplify.
Multi-beam image sonar utilizes basic matrix receiving target echo, obtains the polar coordinates acoustic image through processing such as wave beam formation.The wavelength of supposing echoed signal is λ, is spaced apart the uniformly-spaced linear base of d for N unit, and when the plane wave incident direction was θ, normalization battle array output amplitude did
Can know by formula (3); On the position of
, get maximum value, get on sin θ axle for
maximum value the position of principal maximum.Form principle according to wave beam, between adjacent array element, insert phase shift ξ, make the position changeable of principal maximum do
So, as incident direction θ
0When unknown,, form then exportable different amplitude through wave beam if insert different phase shifts or time delay between adjacent array element.Battle array output can reach principal maximum, by the corresponding horizontal ordinate sin θ of principal maximum
0Can obtain the incident orientation angle.For the image sonar; All carry out wave beam to each sampling instant and form processing; Then can form a width of cloth is horizontal ordinate with target with respect to the azimuth angle theta (in fact with sin θ) of receiving transducer; Is ordinate with target to the oblique distance r of receiving transducer, is the two-dimentional polar coordinate image of pixel amplitude with the battle array output amplitude.
The two-dimensional coordinate of polar coordinate image is that (sin θ r), forms example with nn point DFT wave beam, supposes that the time domain waveform sampling rate is fs, and the velocity of sound is c, and the collection duration is T, owing to be active sonar, then the distance between neighbouring sample point is c/2f
s, according to formula (4), the horizontal ordinate of polar each coordinate points of image does
So the horizontal ordinate index value of each coordinate points of polar coordinates does
Exactly because the image horizontal ordinate that forms based on wave beam is sin θ (i.e.
); There is simple linear relationship between it and the horizontal ordinate index value θ _ index (i.e.
), can obtains horizontal ordinate (being angle) index value at once.When this value is non-integer, can round with the mode of interpolation or neighborhood average, but this is not the emphasis that the present invention studies.Can know by above-mentioned analysis, no longer need utilize the arctan function value earlier
Calculated theta
0, calculate the angle index value again and realized fan-shaped conversion.
By above-mentioned analysis, may be summarized as follows: by wave beam form obtain be
If the polar coordinate image that A λ D in the zone is ordered is will be at R
xλ R
yForm the rectangular coordinate image that M λ N is ordered on the zone, so horizontal range resolution
Vertical range resolution
Can formula (6) be rewritten into
Just can know right angle image coordinate point (x_index, pixel amplitude g y_index) (x_index, y_index); Equal polar coordinate image coordinate points (θ _ index; R_index) (θ _ index r_index), can form the rectangular coordinate image that view picture M λ N is ordered to pixel amplitude f like this.
Principal feature of the present invention is embodied in:
1, according to under the rectangular coordinate have a few that (x, (r, θ) mode of sites value is carried out fan-shaped conversion y) to be transformed into polar coordinates.
2, need not trigonometric function operation is carried out program design, can accomplish the mapping of coordinated indexing value between rectangular coordinate and the polar coordinates.
3, need not the trigonometric function value that calculated in advance is good is stored in the hardware memory.
4, utilize beam-forming technology, the horizontal ordinate of the polar coordinate image that sonar obtains is sin θ, avoids finding the solution θ during fan-shaped conversion and specifically what equals, and directly finds the solution the horizontal ordinate index value.
5, because there is simple linear relationship in the principle that wave beam forms between the horizontal ordinate sin θ of polar coordinate image and the horizontal ordinate index value θ _ index, can obtain the horizontal ordinate index value at once.
Description of drawings
Fig. 1 is the conversion synoptic diagram between polar coordinate image and the rectangular coordinate image.
Embodiment
The function of fan-shaped conversion is the mapping of accomplishing between the address table of polar coordinate image and rectangular coordinate image, the mapping between the horizontal ordinate index value of image just.Again because the horizontal ordinate of the polar coordinate image that the image sonar that forms based on wave beam obtains is sin θ; Through deriving, there is simple linear relationship between it and polar angle index value, so can not need calculate triangle or inverse trigonometric function is realized fan-shaped conversion; According to (the x that has a few under the rectangular coordinate; Y) be transformed into polar coordinates (r, θ) mode of sites value is carried out fan-shaped conversion, concrete implementation method is following:
(1) confirms to be used for showing the monitor resolution M λ N of rectangular coordinate acoustic image, obtain the span of the horizontal ordinate index value of rectangular coordinate image: 0}x_index
TMM, 0}y_index
TMN;
(2) distance parameter that is provided with according to system (supposing that the horizontal range scope is for
vertical distance range is
), calculating rectangular coordinate image level (being horizontal ordinate) range resolution
and vertical (being ordinate) range resolution
(3) under rectangular coordinate system, calculate certain put horizontal ordinate value
so that calculate horizontal ordinate value under the polar coordinates of this point (sin θ, r);
(4) calculate polar horizontal ordinate index value according to
formula: θ _ index, r_index; If non-integer rounds according to the mode of interpolation or neighborhood average;
(5) polar coordinate image is stored in the storer, according to (θ _ index r_index) reads corresponding pixel amplitude, and assignment is given (x_index, y_index) the pixel amplitude of correspondence under the rectangular coordinate image.
(6) repeat (3)～(5) step and accomplish every bit and polar mapping under the rectangular coordinate system, obtain a complete rectangular coordinate acoustic image at last.
Claims (5)
1. the Fast implementation of multi-beam image sonar middle fan fractal transform makes the image sonar that forms based on wave beam when realizing fan-shaped conversion, and hardware such as FPGA need not loaded down with trivial details triangle or inverse trigonometric function computing, can largely improve the real-time of fan-shaped conversion.It is characterized in that: the monitor resolution of rectangular coordinate acoustic image is confirmed to be used for showing in (1); (2), calculate rectangular coordinate image level and vertical range resolution according to image sonar real standard and vertical distance range; (3), calculate the corresponding horizontal ordinate value of polar coordinates of this point according to the horizontal ordinate value of the rectangular coordinate of certain point; (4) form principle according to wave beam and obtain the horizontal ordinate index value of polar coordinates; (5) polar coordinate image is stored in the storer, reads the respective pixel amplitude according to polar horizontal ordinate index value, and assignment is given the rectangular coordinate correspondence position; (6) accomplish every bit and polar mapping under the rectangular coordinate system, obtain the rectangular coordinate acoustic image.
2. the Fast implementation of multi-beam image sonar middle fan fractal transform according to claim 1; It is characterized in that: said according to image sonar real standard and vertical distance range calculating rectangular coordinate image level and vertical range resolution, if the horizontal range scope is then calculated rectangular coordinate image horizontal range resolution
and vertical range resolution
for
vertical distance range for
3. the Fast implementation of multi-beam image sonar middle fan fractal transform according to claim 2; It is characterized in that: the horizontal ordinate value of the rectangular coordinate of said certain point for
so that calculate horizontal ordinate value under the polar coordinates of this point (sin θ, r).
4. the Fast implementation of multi-beam image sonar middle fan fractal transform according to claim 3 is characterized in that: the relation between the horizontal ordinate index value of said rectangular coordinate index value and polar coordinates is
5. the Fast implementation of multi-beam image sonar middle fan fractal transform according to claim 4; It is characterized in that: polar coordinate image is stored in the storer; Read the respective pixel amplitude according to described polar horizontal ordinate index value θ _ index and r_index, and assignment is given the rectangular coordinate correspondence position.
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Cited By (7)
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| CN103954967A (en) * | 2014-05-19 | 2014-07-30 | 么彬 | Near-field sonar image quick imaging method for image sonar |
| CN106707265A (en) * | 2016-12-26 | 2017-05-24 | 江苏中海达海洋信息技术有限公司 | Conversion updating method for sonar sector diagram |
| CN108508446A (en) * | 2018-03-28 | 2018-09-07 | 青岛海洋地质研究所 | Fan-shaped transform method based on cold seepage imaging data |
| CN108802738A (en) * | 2018-03-14 | 2018-11-13 | 浙江大学 | Three-dimensional sonar data imaging method and system based on adaptive distance resolution |
| CN109239709A (en) * | 2018-08-02 | 2019-01-18 | 哈尔滨工程大学 | A kind of autonomous construction method of local environment map of unmanned boat |
| CN111103588A (en) * | 2019-12-31 | 2020-05-05 | 哈尔滨工程大学 | Triangular wave multi-target identification method by utilizing signal energy |
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Cited By (11)
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| CN109239709A (en) * | 2018-08-02 | 2019-01-18 | 哈尔滨工程大学 | A kind of autonomous construction method of local environment map of unmanned boat |
| CN109239709B (en) * | 2018-08-02 | 2022-06-17 | 哈尔滨工程大学 | Autonomous construction method for local environment map of unmanned ship |
| CN111103588A (en) * | 2019-12-31 | 2020-05-05 | 哈尔滨工程大学 | Triangular wave multi-target identification method by utilizing signal energy |
| CN111401377A (en) * | 2020-03-13 | 2020-07-10 | 北京市商汤科技开发有限公司 | Instrument data reading method and device, electronic equipment and storage medium |
| CN111401377B (en) * | 2020-03-13 | 2024-03-08 | 北京市商汤科技开发有限公司 | Meter data reading method and device, electronic equipment and storage medium |
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