A design method for afterglow trails of marine navigation radar

Abstract

The present invention discloses a method for designing afterglow trails for a marine navigation radar, comprising the following steps: (1) checking whether echo data from the marine navigation radar is received, and if so, proceeding to the next step; (2) obtaining currently set parameters, including afterglow attenuation modes and parameters associated therewith, and transmitting the obtained currently set parameters to a GPU via OpenGL; (3) transmitting radar echo data received in real time to the GPU via OpenGL; (4) determining a triggering period for afterglow attenuation according to the currently set afterglow attenuation mode; (5) attenuating radar echo data outside an azimuth interval according to the currently selected afterglow attenuation mode; and starting OpenGL rendering when afterglow attenuation is triggered to obtain afterglow and its trails that extend over time. The present invention adopts an OpenGL-based afterglow design method for a marine navigation radar, which can design afterglow in modern marine navigation radars with high performance and can achieve afterglow attenuation at various speeds and in various modes.

Description

Technical Field

[0001] The invention belongs to the field of ship navigation, and in particular relates to a method for designing afterglow trails of a ship navigation radar. Background Art

[0002] Marine radar is a radar installed on ships for navigation avoidance, ship positioning, and narrow waterway piloting. It provides necessary observation means for sailors when visibility is poor.

[0003] Traditional radar display oscilloscopes mostly use monochrome cathode ray tubes (CRTs). Electrons bombard the display material with electrons to display the image. The inherent brightness decay of the display material causes an afterglow effect. This afterglow effect in traditional radars is an accidental result of display manufacturing characteristics and is not a purposely designed effect. The afterglow characteristic can effectively identify moving targets, especially the long afterglow resulting from the long tail phenomenon, which can effectively distinguish small moving targets from clutter. However, the afterglow effect in traditional radars is an undesigned byproduct and is rarely adjustable.

[0004] With the increasing automation and diversification of ship functions, the software supporting marine navigation radars is often integrated with bridge systems, moving away from the traditional oscilloscope display model and toward digital software simulation. Common implementations of marine navigation radar display and control software fall into two main categories: one based on dedicated circuits or systems-on-chips (SoCs); the other on PC platforms. The first approach utilizes high-speed computing units such as DSPs. While this approach can meet the requirements of large radar image data volumes, high refresh rates, and high real-time performance, it suffers from poor portability. System development, updates, and maintenance are limited by the hardware platform, making integration with other systems nearly impossible. The second approach allows for easier integration with other systems, but commonly uses operating system graphics device interfaces (GDI+), which significantly consume the PC's CPU resources and rarely meet rendering requirements.

[0005] Modern marine navigation radars generally lack a persistence function. Even if they do, they require specialized equipment such as a radar video information processing unit to implement it, significantly increasing the cost of the radar. When implemented, persistence and wakes typically employ two distinct design approaches. Afterglow uses a high-frequency method to reduce the brightness of the entire radar image, while wakes store historical data for comparison with current data. Both methods rely on CPU processing and require real-time processing of the entire radar image, placing significant demands on the computer's CPU and memory resources. Summary of the Invention

[0006] The present invention aims to overcome the above-mentioned deficiencies in the prior art by adopting a method for designing afterglow for a marine navigation radar based on the OpenGL software interface of GPU-based graphics hardware, combining afterglow and wake functions into one, and redesigning the afterglow and wake functions using OpenGL. This method can achieve high-performance design of afterglow in modern marine navigation radars and realize afterglow attenuation at various speeds and in various modes.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a method for designing afterglow trails of a marine navigation radar, comprising the following steps: (1) checking whether echo data from the marine navigation radar is received, and if so, proceeding to the next step; (2) obtaining currently set parameters, including afterglow attenuation mode and parameters associated therewith, and transmitting the currently set parameters obtained to a GPU via OpenGL; (3) transmitting the radar echo data received in real time to the GPU via OpenGL; (4) determining a trigger period of afterglow attenuation according to the currently set afterglow attenuation mode; (5) taking the azimuth of the marine navigation radar when the afterglow attenuation was triggered last time as a starting value, and The azimuth angle of the marine navigation radar when the secondary afterglow attenuation is triggered is used as the ending value, and the starting value and the ending value are transmitted to the fragment shader, and the starting value and the ending value are used as the left and right endpoints respectively to form an azimuth angle interval; in the fragment shader, the radar echo data within the azimuth angle interval adopts the latest scan value of the marine navigation radar, and the value of the alpha channel is set to the larger of the latest scanned echo intensity and the current attenuation value after the last refresh; the radar echo data outside the azimuth angle interval is attenuated according to the currently selected afterglow attenuation method; when the afterglow attenuation is triggered, OpenGL rendering is turned on to obtain the afterglow and its trail that stretches over time.

[0008] Furthermore, the afterglow attenuation mode in step (2) includes a time-based afterglow attenuation mode and an azimuth-based afterglow attenuation mode, the parameters associated with the time-based afterglow attenuation mode include an attenuation time constant, and the parameters associated with the azimuth-based afterglow attenuation mode include a minimum attenuation ratio.

[0009] Furthermore, the time-based persistence decay method adopts the following exponential decay model:

[0010]

[0011] Where I is the afterglow brightness, I0 is the echo intensity, k is the time decay constant, t is the decay time, t b For the afterglow time.

[0012] Furthermore, the afterglow time t bIt is the time required for the afterglow brightness to drop from 100% to the brightness ratio threshold, and the value range of the brightness ratio threshold is [5%, 20%].

[0013] Furthermore, the orientation-based afterglow attenuation method adopts the following linear attenuation model:

[0014]

[0015] Where I is the afterglow brightness, I0 is the echo intensity, k is the minimum attenuation ratio, and α is the angular displacement relative to the current scanning azimuth.

[0016] Furthermore, the refresh rate of the afterglow in step (5) is not less than 50 Hz.

[0017] Furthermore, the OpenGL rendering in step (5) is rendering to a texture.

[0018] Furthermore, the rendering to texture process is as follows: creating a frame buffer area, which allows rendering to be transferred from the window's frame buffer to one or more off-screen frame buffers created; creating a texture object as the rendering object of the frame buffer area, and binding the frame buffer area to the rendering pipeline.

[0019] Furthermore, after rendering to the texture, a copy of the texture is made.

[0020] Furthermore, after rendering to the texture, the vertex coordinates corresponding to the texture buffer are set on the screen, and the rendered texture is rendered to the screen to achieve an afterglow effect.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. It has two attenuation modes: time-based afterglow attenuation and azimuth-based afterglow attenuation. The time-based afterglow mode can achieve long tails and effectively detect moving targets. When users need to observe small targets, they can choose the time-based afterglow attenuation mode and adjust the parameter value according to the actual movement of the observed target. The azimuth-based afterglow mode can better distinguish between clutter and targets. When in high-clutter sea conditions, the azimuth-based afterglow mode can better distinguish targets from clutter.

[0023] 2. The implementation method of afterglow of marine navigation radar based on OpenGL is to use OpenGL to transmit radar echo data to GPU for processing, thereby simulating the afterglow effect under the electron tube radar system. It can also provide two afterglow modes and adjustable afterglow parameters, which is conducive to enhancing the observation of targets.

[0024] 3. Using GPU instead of CPU can significantly reduce CPU load and improve system fluency. At the same time, it can ensure a high refresh rate of radar video under the premise of low CPU load.

[0025] 4. Using OpenGL render-to-texture technology, the image after the last attenuation process is saved in the GPU. The entire processing process is confined to the GPU, reducing the data exchange between the CPU and GPU and significantly improving the operating efficiency of the CPU and GPU. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flowchart of an embodiment of the present invention;

[0027] Figure 2 This is a flowchart of rendering to texture in one embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 and Figure 2 As shown, an embodiment of the method for designing afterglow trails for marine navigation radars of the present invention implements two types of afterglow based on OpenGL's render-to-texture technology, and utilizes the afterglow to realize the function of long target trails. The algorithm includes the following steps:

[0030] The first step is to enable the function request;

[0031] The second step is to check whether the echo data of the marine navigation radar can be received. If the echo data of the marine navigation radar cannot be received, turn off the function. If it can be received, proceed to the next step.

[0032] The third step is to obtain the currently set parameters, including the persistence attenuation method set by the user, the attenuation time constant (used in the time-based attenuation method), and the minimum attenuation ratio (used in the direction-based attenuation method). The obtained currently set parameters are transferred to the GPU through OpenGL.

[0033] The fourth step is to transmit the real-time radar echo data to the GPU through OpenGL.

[0034] Radar echo data is two-dimensional data, and a two-dimensional texture buffer needs to be created in the video memory through OpenGL;

[0035] The OpenGL method for creating a texture buffer is as follows:

[0036] glGenTextures(GLsizei n,GLuint*textures)

[0037] glTexImage2D(GLenum target,GLint level,GLenum internalformat,GLsizeiwidth,GLsizei height,GLint border,GLenum format,GLenum type,const void*pixels);

[0038] Similarly, a memory area of ​​the same size as the radar echo data needs to be created in memory to store the radar image transferred from the previous process. This is then transferred to the video memory via OpenGL.

[0039] The method of transferring data from OpenGL memory to video memory is as follows:

[0040] void glTexSubImage2D(GLenum target,GLint level,GLint xoffset,GLintyoffset,GLsizei width,GLsizei height,GLenum format,GLenum type,const GLvoid*data);

[0041] Step 5: Determine the triggering time for persistence attenuation based on the currently configured persistence attenuation mode. For time-based persistence attenuation, triggering should be performed periodically, typically no more than 20ms apart, ensuring a persistence refresh rate of at least 50Hz. For azimuth-based persistence attenuation, set the antenna rotation period to 2.5s and trigger at least every 2.88°, ensuring a persistence refresh rate of at least 50Hz.

[0042] OpenGL provides the glutTimerFunc function as a timer;

[0043] Step 6: When attenuation is triggered, start OpenGL rendering;

[0044] Step 7: Pass the start and end values ​​of the radar's updated position between the last trigger and the current trigger to the fragment shader. For example, if the antenna rotated from 45° to 47.3° between the last trigger and the current trigger, the start value would be 45° and the end value would be 47.3°.

[0045] Use programmable fragment shader. Programmable fragment shader uses glsl language. You can use glCreateProgram() to create a programmable shader program and use glGetUniformLocation to bind the shader program.

[0046] Step 8. In the fragment shader, the values ​​between the start and end values ​​use the latest values. The alpha channel value is set to the latest scanned echo intensity or the current attenuation value after the last refresh, whichever is greater. If the start value is 45°, the end value is 47.3°, and the azimuth angle interval is [45°, 47.3°], then the echo data within the interval, that is, the echo data between 45° and 47.3°, uses the latest scanned value of the radar.

[0047] In the ninth step, values ​​outside the start and end values ​​are attenuated according to the selected persistence attenuation model. For example, if the start value is 45° and the end value is 47.3°, and the azimuth interval is [45°, 47.3°], covering an azimuth range of 2.3°, then the echo data outside the interval, that is, the echo data from 47.3° to 45° (covering an azimuth range of 357.7°, nearly the entire image), must be attenuated according to the attenuation model. Specifically, there are two types of persistence attenuation models: time-based and azimuth-based. The time-based persistence model enables long tails and effectively detects moving targets. When users need to observe small targets, they can select the time-based persistence attenuation method and adjust the parameter value according to the actual motion of the observed target. The azimuth-based persistence mode can better distinguish between clutter and targets. When in high-clutter sea conditions, using the azimuth-based persistence model can better distinguish targets from clutter.

[0048] The time-based afterglow decay model satisfies the exponential decay model, as shown in the formula:

[0049]

[0050] Where: I is the afterglow brightness, I0 is the echo intensity, k is the time decay constant, and t is the decay time.

[0051] Persistence decreases over time, so a timer is needed to periodically reduce the value of the alpha channel in the entire PPI display.

[0052] The afterglow time (e.g. the time when the afterglow brightness drops to 10%) is taken as t b , the time decay constant can be calculated based on the linear decay curve equation. 10% is an empirical value and is generally recommended. A value above 10% increases the residual value after echo disappearance, making it suitable for strong target echoes and low clutter intensity. A value below 10% allows for better observation of weak targets.

[0053]

[0054] t b The smaller it is, the more drastic the decay curve is and the shorter the afterglow is.

[0055] If the afterglow time (e.g. the time it takes for the afterglow brightness to drop to 10%) is 2s, then

[0056]

[0057] Therefore, the afterglow decay equation is

[0058]

[0059] If the echo intensity is 100, it will decay to

[0060]

[0061] The afterglow is prolonged, forming an afterglow trail, which is helpful for observing the movement trend of small moving targets. When the afterglow decay time exceeds the scanning period of the marine navigation radar (usually 2 seconds), it is necessary to compare it with the echo intensity of the most recent scanning of the navigation radar, and take the larger of the two.

[0062] If the afterglow time (e.g. the time it takes for the afterglow brightness to drop to 10%) is 10s, then

[0063]

[0064] Therefore, the afterglow decay equation is

[0065]

[0066] If the echo intensity is 100, it will decay to

[0067]

[0068] At this time, the new echo intensity may be stronger than the attenuation value, and the larger one is selected.

[0069] The azimuth-based persistence attenuation model satisfies the linear attenuation model, as shown in the formula:

[0070]

[0071] Where: I is the afterglow brightness, I0 is the echo intensity, k is the minimum attenuation ratio, and α is the azimuth distance from the current scanning azimuth.

[0072] For example, if the current scan line orientation is 45°, the minimum attenuation ratio is k = 0.01 (the minimum attenuated brightness is 1% of the initial brightness). For the echo at the 50° position, if its original intensity is I0 = 100, the current value after attenuation is

[0073]

[0074] For the echo at the 44° position, if its original intensity is I0=100, the current value after attenuation is

[0075]

[0076] Afterglow decreases with azimuth. Every time the antenna scans a certain azimuth, it needs to trigger a afterglow attenuation calculation. After the trigger, the value of the Alpha channel in the entire PPI display is reduced.

[0077] The attenuation of afterglow generally does not decay to 0. Attenuation to 0 may cause the intensity of small targets to drop rapidly, making it difficult for users to detect small targets and affecting navigation safety.

[0078] The attenuation value of this afterglow can be calculated. The attenuation value of this time can be obtained by subtracting the attenuation value of this time from the result after the last attenuation.

[0079] The tenth step is to create a frame buffer (FBO), which allows the rendering to be transferred from the window's frame buffer to one or more off-screen frame buffers created.

[0080] OpenGL creates a frame buffer as follows:

[0081] void glGenFramebuffers(GLsizei n,GLuint*ids);

[0082] void glFramebufferTexture2D(GLenum target,GLenum attachment,GLenumtextarget,GLuint texture,GLint level);

[0083] Step 11: Create a texture object as the rendering object of the frame buffer and bind the frame buffer to the rendering pipeline.

[0084] The frame buffer is bound to the rendering pipeline as follows:

[0085] void glBindFramebuffer(GLenum target,GLuint framebuffer);

[0086] Step 12. In the fragment shader, the destination texture and the texture used in rendering cannot be the same texture, so after rendering to the texture, you need to copy the texture;

[0087] Step 13: Set the texture cache on the screen to the corresponding vertex coordinates, and render the rendered texture to the screen, so that the afterglow effect can be achieved on the radar.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for designing afterglow trails of marine navigation radar, characterized in that: The steps include: (1) Check whether the echo data from the ship navigation radar is received. If so, proceed to the next step; (2) obtaining the currently set parameters, including the persistence attenuation mode and its associated parameters, and transmitting the obtained currently set parameters to the GPU via OpenGL; (3) Transmitting the real-time received radar echo data to the GPU via OpenGL; (4) Determine the trigger period of afterglow decay according to the currently set afterglow decay mode; (5) The azimuth angle of the ship navigation radar when the last afterglow attenuation is triggered is used as the starting value, and the azimuth angle of the ship navigation radar when the current afterglow attenuation is triggered is used as the ending value. The starting value and the ending value are transmitted to the fragment shader, and the starting value and the ending value are used as the left and right endpoints respectively to form an azimuth angle interval; in the fragment shader, the radar echo data within the azimuth angle interval uses the latest scan value of the ship navigation radar, and the value of the alpha channel is set to the larger of the latest scanned echo intensity and the current attenuation value after the last refresh; the radar echo data outside the azimuth angle interval is attenuated according to the currently selected afterglow attenuation method; when the afterglow attenuation is triggered, OpenGL rendering is turned on to obtain the afterglow and its trail that stretches over time.

2. The marine navigation radar afterglow trail design method according to claim 1, characterized in that: The afterglow attenuation mode in step (2) includes a time-based afterglow attenuation mode and an azimuth-based afterglow attenuation mode. The parameters associated with the time-based afterglow attenuation mode include an attenuation time constant, and the parameters associated with the azimuth-based afterglow attenuation mode include a minimum attenuation ratio.

3. The method for designing afterglow trails of marine navigation radar according to claim 2, characterized in that: The time-based afterglow decay method adopts the following exponential decay model: Where I is the afterglow brightness, I0 is the echo intensity, k is the time decay constant, t is the decay time, t b For the afterglow time.

4. The marine navigation radar afterglow trail design method according to claim 3, characterized in that: The afterglow time t b It is the time required for the afterglow brightness to drop from 100% to the brightness ratio threshold, and the value range of the brightness ratio threshold is [5%, 20%].

5. The method for designing afterglow trails of marine navigation radar according to claim 2, characterized in that: The azimuth-based afterglow attenuation method adopts the following linear attenuation model: Where I is the afterglow brightness, I0 is the echo intensity, k is the minimum attenuation ratio, and α is the angular displacement relative to the current scanning azimuth.

6. The marine navigation radar afterglow trail design method according to claim 1, characterized in that: The refresh rate of the afterglow in step (5) is not less than 50 Hz.

7. The method for designing afterglow trails of marine navigation radar according to claim 1, characterized in that: The OpenGL rendering in step (5) is rendering to a texture.

8. The method for designing afterglow trails of marine navigation radar according to claim 7, characterized in that: The rendering to texture process is as follows: creating a frame buffer that allows rendering to be transferred from the window's frame buffer to one or more created off-screen frame buffers; Create a texture object as the render object of the frame buffer and bind the frame buffer to the rendering pipeline.

9. The method for designing afterglow trails of a marine navigation radar according to claim 7 or 8, characterized in that: After rendering to the texture, make a copy of the texture.

10. The method for designing afterglow trails of marine navigation radar according to claim 7, characterized in that: After rendering to the texture, set the vertex coordinates corresponding to the texture buffer on the screen, and render the rendered texture to the screen to achieve the afterglow effect.

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