Abstract:
A method for displaying the vehicle safety distance, which is executed under the basic structure of a vehicle safety warning device, the vehicle safety warning device at least includes a display module and an image recognition module. The method displays various virtual icons of different situations on the road, to display in advance and warn the lane departure situation, to thereby ensure traffic safety.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     A method for displaying the vehicle safety distance and, more particularly, to a method for displaying the vehicle safety distance with predictive display and lane departure warning functions, to thereby warn the driver of the lane departure situation timely, to ensure traffic safety. 
     2. Brief Description of the Related Art 
     For the vehicle equipments, safety is most important. In recent years, image recognition and wireless detection technology become more sophisticated, a lot of technology is applied on vehicle safety, such as the functions of suggesting safety distance to the front car and lane departure warning in response to market demand. 
     Currently, there are two kinds of lane departure warning systems. In one of the two systems, a photoreceptor is set on the location near the two front wheels under the car. When the photoreceptor senses the ground color near the wheels changed, the displayed color of the display unit may change to white or yellow from black, and the system determines that the car departures the lane. The cost of the method is low, but malfunction may be occurred easily. In another system, a camera lens is installed in front of the car, usually in a high place inside the windshield for capturing the image in front of the car, which includes the lane line. An image recognition method is used to extract the lane line in the image and determine the shift amount of the lane line. When the lane line is shifted to the predetermined location, the system determines as lane departure. The cost of the method is high, but the probability of malfunction is low. 
     There are also two kinds of vehicle safety distance warning systems. In one of the two systems, a millimeter-wave radar (30 GHz˜300 GHz) with high frequency or a laser radar is used to perform the determination of the vehicle safety distance, the weathering resistance and the distance performance distance are both excellent, but the cost is high, and the system cannot identify whether the car is in the same lane or in the roadside fence, thus malfunction may be occurred easily. In another system using an image recognition method, the forward object is shot by an image camera lens with fixed angle. The extraction of the forward object is converted into the distance by the elevation angle of the image relative to the image lens. The cost is low, and the same camera lens may be shared with the lane departure warning system to thereby share the cost, but the weathering resistance is bad, and its determination for the front car may be affected by the reasons, such as night, fog, heavy rain. 
     The above vehicle safety distance warning systems using radar wave are usually installed in the high-priced cars, some of the systems are further connected to the actuator system to start the brakes for assisting brake when necessary. Since the cost of the vehicle safety distance warning systems is high and a lot of components are involved in, it cannot be installed in the common price cars, and it is more difficult for the car owners to install the system by themselves after buying the car. 
     In the commercially available vehicle safety distance warning systems, the high-end products may drive the brake and the actuator system of the car after determining the front vehicle distance, and may automatically adjust the car speed according to the front vehicle distance to keep an appropriate distance from the front vehicle. Some low-end products may mark the front vehicle distance on the screen after determining it, but the drivers do not have intuitive feelings about this kind of vehicle distance data, thus it is not helpful to the drivers. Another kind of the low-end products warn the driver by images or sounds when the front vehicle distance is too short, the drivers cannot receive enough information to keep the vehicle safety distance before being warned. 
     If the traditional lane departure warning device does not detect the lane, it does not warn to drivers even when the car has already departed the lane. Similarly, if the vehicle safety distance warning device cannot detect the front car, it does not warn to drivers even when the front vehicle distance is too short. If encounter these situations, instead of improving traffic, this kind of safety devices may let drivers feel safe and not pay attention on the road. 
     In order to solve the drawbacks of the above vehicle safety systems and warning devices, the industry disclose various related technology continuously, such as the patent reference, such as the patent reference with TW publication no. 200951892 (hereafter called the cited reference), which is a typical representative (as  FIG. 1 ). The portable electronic device  11  of the cited reference is consisted of a camera lens  12 , a speaker  13 , a computing unit  14 , a display unit  15  and a vibration unit  16 . The speaker  13  is set on the portable electronic device  11 ; the camera lens  12  is set on the portable electronic device  11  for capturing a real-time road image  121 ; the display unit  15  is set on the portable electronic device  11  for displaying the above real-time road image  121 . The computing unit  14  is set inside the portable electronic device  11 , which includes an image analysis software  141 , which judges whether the vehicle is located in the lane according to the traffic markings in the real-time road image  121 , the speaker  13  sends out a warning signal  131  to remind the driver that the vehicle is departed the lane if the vehicle is not located inside the lane. If the portable electronic device  11  is set to silent mode, the driver may be reminded that the vehicle is departed the lane by the vibration of the vibration unit  16 . The driver may further use the API system to turn on the camera lens  12  to shot the real-time road message, also may open the camera function originally set by the portable electronic device  11  directly to obtain the real-time road image  121 , and the shot image may be transmitting to the display unit  15  for displaying by instant transmission technology. 
     The steps of the operation method of the cited reference (as shown in  FIG. 2 ), the portable electronic device  11  is started to a driving safety mode, in the step  21 , a camera lens  12  is used to get the real-time road image  121  actually; and then in the step  22 , the real-time road image  121  is sent to the computing unit  14  and displayed on the display unit  15 ; and then in the step  23 , the computing unit  14  is used to analyze the real-time road image  121  by using an image analysis software  141 . In step  24 , judging whether the vehicle is departed the lane according to the location of the lane on the road in the real-time road image  121 . For example, judging whether there is only one or a little part of the strip whose color similar to the two lane lines on the real-time road image  121 , if yes, the computing unit  14  judges that the vehicle has already departed the lane; if there are two strips whose color similar to the lane lines on the real-time road image  121 , the computing unit  14  judges that the vehicle is in a safe driving condition. If the computing unit  14  judges that the vehicle departs the lane, in step  25 , the portable electronic device  11  make a sound to remind the driver that the vehicle maybe departs the lane. If not, repeat executing step  21 . 
     Although the cited reference solved the drawbacks of the traditional vehicle safety systems, the real-time road image  121  shot by the camera lens  12  is a virtual image, which is not as clear as marked lines in visual appearance to impressive the driver. The driver may not easily be aware of the impending driving danger from the images in advance before the vibration or the warning sound starts. 
     SUMMARY OF THE INVENTION 
     In view of this, the inventor finally completed the method for displaying the vehicle safety distance of the present invention after numerous improvements, namely, the object of the present invention is to provide a method for displaying the vehicle safety distance with predictive display and lane departure warning functions, to thereby warn the driver of the lane departure situation timely, to achieve advanced prevention to ensure traffic safety. 
     In order to achieve the above purpose, the first embodiment of the displaying method for vehicle safety warning of the present invention includes a vehicle safety warning device, the vehicle safety warning device has a display module and an image recognition module; different icons are used to be displayed on the display module to show different situations on the road, the displaying steps includes: 
     A. a double vertical line is displayed on the display module; 
     B. a first vehicle location icon is displayed on the display module, the first vehicle location icon represents the location of the vehicle, the first vehicle location icon is placed in the middle of the double vertical line, the first vehicle location icon moves left and right according to the actual location in the lane detected by the image recognition module; 
     C. when the first vehicle location icon displayed on the display module is overlapped on the double vertical line, it means the lane departure, at this time, the double vertical line is showed by a warning icon for caution. 
     The displaying step A, when the image recognition module cannot detect the lane line, the double vertical line is hidden without being displayed. 
     The displaying step C, the warning icon is provided to warn by flashing the double vertical line. 
     The displaying step C, the warning icon is provided to warn by changing the color of the double vertical line. 
     The second embodiment of the displaying method for vehicle safety warning of the present invention includes a vehicle safety warning device, the vehicle safety warning device has a display module, an image recognition module and a distance detection module; different icons are used to be displayed on the display module to show different situations on the road, the displaying steps includes: 
     A. a double vertical line is displayed on the display module; 
     B. a first vehicle location icon is displayed on the display module, the first vehicle location icon represents the location of the present vehicle, the first vehicle location icon is placed in the middle of the double vertical line, the first vehicle location icon moves left and right according to the actual location in the lane detected by the image recognition module; 
     C. when the first vehicle location icon displayed on the display module is overlapped on the double vertical line, it means the lane departure, at this time, the double vertical line is showed by a warning icon for caution; 
     D. a second vehicle location icon displayed on the display module is located above the first vehicle location icon in the middle of the double vertical line, the second vehicle location icon represents the location of the front vehicle, the second vehicle location icon moves up and down according to the front vehicle distance detected by the distance detection module. 
     The displaying step A, when the image recognition module cannot detect the lane line, the double vertical line is hidden without being displayed. 
     The displaying step C, the warning icon is provided to warn by flashing the double vertical line. 
     The displaying step C, the warning icon is provided to warn by changing the color of the double vertical line. 
     The displaying step D, wherein when the distance detection module detects that the front vehicle is too far or there is no vehicle, the second vehicle location icon is hidden without being displayed. 
     The displaying step D, wherein when the detection environment is not good for the distance detection module to accurately determine the location of the front vehicle, the second vehicle location icon is replaced by other marked icon, the marked icon is a question mark or a dotted line icon. 
     The above method for displaying the vehicle safety distance further includes a displaying step E, the first vehicle location icon is increased upwards or shortened with the change of the car speed. 
     The displaying step E, wherein if the first vehicle location icon increased to contact the second vehicle location icon, it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the first vehicle location icon flashes or changes its color as a warning. 
     The above method for displaying the vehicle safety distance, further includes a displaying step E, wherein the first vehicle location icon is increased upwards or shortened with the change of the car speed, if the first vehicle location icon is increased to contact the second vehicle location icon, it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the vehicle safety warning device further includes a speaker module, which is provide to send out a sound signal as a warning. 
     The third embodiment of the displaying method for vehicle safety warning of the present invention, which includes a vehicle safety warning device, the vehicle safety warning device has a display module, an image recognition module, a distance detection module and a car speed detection module; different icons are used to be displayed on the display module to show different situations on the road, the displaying steps includes: 
     A. a double vertical line is displayed on the display module; 
     B. a first vehicle location icon is displayed on the display module, the first vehicle location icon represents the location of the vehicle, the first vehicle location icon is placed in the middle of the double vertical line, the first vehicle location icon moves left and right according to the actual location in the lane detected by the image recognition module; 
     C. when the first vehicle location icon displayed on the display module is overlapped on the double vertical line, it means the lane departure, at this time, the double vertical line is showed by a warning icon flashing or changing color for caution; 
     D. a second vehicle location icon displayed on the display module is located above the first vehicle location icon in the middle of the double vertical line, the second vehicle location icon represents the location of the front vehicle, the second vehicle location icon moves up and down according to the front vehicle distance detected by the distance detection module; 
     E. a safe vehicle distance icon is displayed on the display module, which is set between the first vehicle location icon and the second vehicle location icon, the length of the safe vehicle distance icon is changed according to the car speed detected by the car speed detection module. 
     The displaying step A, when the image recognition module cannot detect the lane line, the double vertical line is hidden without being displayed. 
     The displaying step C, the warning icon is provided to warn by flashing the double vertical line. 
     The displaying step C, the warning icon is provided to warn by changing the color of the double vertical line. 
     The displaying step D, wherein when the distance detection module detects that the front vehicle is too far or there is no vehicle, the second vehicle location icon is hidden without being displayed. 
     The displaying step D, wherein when the detection environment is not good for the distance detection module to accurately determine the location of the front vehicle, the second vehicle location icon is replaced by other marked icon, the marked icon is a question mark or a dotted line icon. 
     The displaying step E, wherein, the safe vehicle distance icon with the second vehicle location icon as its top end is increased upwards or shortened with the change of the car speed. 
     The displaying step E, wherein if the first vehicle location icon is increased to contact the second vehicle location icon, it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the first vehicle location icon flashes or changes its color as a warning. 
     The displaying step E, wherein the safe vehicle distance icon with the second vehicle location icon as its top end is increased upwards or shortened with the change of the car speed, if the first vehicle location icon is increased to contact the second vehicle location icon, it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the vehicle safety warning device further includes a speaker module, which is provide to send out a sound signal as a warning. 
     The displaying step E, wherein, the safe vehicle distance icon with the first vehicle location icon as its bottom end is increased upwards or shortened with the change of the car speed. 
     The displaying step E, wherein if the first vehicle location icon increased to contact the second vehicle location icon, it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the first vehicle location icon flashes or changes its color as a warning. 
     The displaying step E, wherein the safe vehicle distance icon with the first vehicle location icon as its bottom end is increased upwards or shortened with the change of the car speed, if the first vehicle location icon is increased to contact the second vehicle location icon, it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the vehicle safety warning device further includes a speaker module, which is provide to send out a sound signal as a warning. 
    
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
       The detail structure, the applied principle, the function and the effectiveness of the present invention can be more fully understood with reference to the following description and accompanying drawings, in which: 
         FIG. 1  is a block diagram of the prior art; 
         FIG. 2  is an implementation flowchart of the operation method of the prior art; 
         FIG. 3  is an implementation flowchart of the first embodiment of the present invention; 
         FIG. 4  is a block diagram of the first embodiment of the present invention; 
         FIG. 5  is a schematic diagram (1) of the displaying image of the present invention; 
         FIG. 6  is a schematic diagram (2) of the displaying image of the present invention; 
         FIG. 7  is an implementation flowchart of the second embodiment of the present invention; 
         FIG. 8  is a block diagram of the second embodiment of the present invention; 
         FIG. 9  is a schematic diagram (3) of the displaying image of the present invention; 
         FIG. 10  is a schematic diagram (4) of the displaying image of the present invention; 
         FIG. 11  is a schematic diagram (5) of the displaying image of the present invention; 
         FIG. 12  is an implementation flowchart of the third embodiment of the present invention; 
         FIG. 13  is a block diagram of the third embodiment of the present invention; 
         FIG. 14  is a schematic diagram (6) of the displaying image of the present invention; and 
         FIG. 15  is a schematic diagram (7) of the displaying image of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention. 
     As shown in  FIG. 3 ,  FIG. 4 , it is the first embodiment of the present invention, which includes a vehicle safety warning device  4  electrically connected to a microprocessor P, the vehicle safety warning device  4  has a display module  41  and an image recognition module  42 . 
     The display module  41 , different icons are used to be displayed on the display module  41  to show different situations on the road, the image D displayed on the display device  41  is the virtual illustration drawn by the vehicle safety warning device  4  (as shown in  FIG. 5 ), not drawn the icons on the realistic images shot by the camera lens  421 . 
     The image recognition module  42  includes a camera lens  421  and a image recognition software  422 , the image recognition software  422  is used to recognize images based on the images shot by the camera lens  421 . If the image recognition software  422  does not detect the two lane lines, but only detect one way lane line, another lane line is estimated by the width of a normal lane. 
     Under the basic structure of the vehicle safety warning device  4 , the displaying steps (as shown in  FIG. 3 ) of the method for displaying the vehicle safety distance  3  of the present invention, includes: 
     In step  31 , a double vertical line  51  is displayed on the display module  41  (as shown in  FIG. 5 ); the double vertical line  51  represents the lane lines on both sides of the present car (which means the car driven by the driver), the double vertical line  51  is not limited to a line, but a virtual icon drawn according to the lane lines of the actual road. When the lane line of the actual road is a curve, the double vertical line  51  is a curve correspondingly; 
     in step  32 , a first vehicle location icon  52  is displayed on the display module  41 , the first vehicle location icon  52  represents the location of the present vehicle, the first vehicle location icon  52  is placed in the middle of the double vertical line  51 , the first vehicle location icon  52  moves left and right according to the actual location in the lane detected by the image recognition module  42 ; 
     in step  33 , when the first vehicle location icon  52  displayed on the display module  41  is overlapped on the double vertical line  51  (as shown in  FIG. 6 ), it means the lane departure, at this time, the double vertical line  51  is showed by a warning icon for caution. 
     The displaying step  31 , when the image recognition module  42  cannot detect the lane line, the double vertical line  51  is hidden without being displayed. 
     The displaying step  33 , the warning icon is provided to warn by flashing the double vertical line  51 . 
     The displaying step  33 , the warning icon is provided to warn by changing the color of the double vertical line  51 . 
     As shown in  FIG. 7 ,  FIG. 8 , it is the second embodiment of the present invention, which includes a vehicle safety warning device  7  electrically connected to a microprocessor P, the vehicle safety warning device  7  has a display module  71 , an image recognition module  72  and a distance detection module  73 . 
     The display module  71 , different icons are used to be displayed on the display module  71  to show different situations on the road, the image D displayed on the display device  41  is the virtual illustration drawn by the vehicle safety warning device  7  (as shown in  FIG. 5 ), not drawn the icons on the realistic images shot by the camera lens  721 . 
     The image recognition module  72  includes a camera lens  721  and a image recognition software  722 , the image recognition software  722  is used to recognize images based on the images shot by the camera lens  721 . If the image recognition software  722  does not detect the two lane lines, but only detect one way lane line, another lane line is estimated by the width of a normal lane. 
     The distance detection module  73 , which is provided to detect the distance between the present car and the front car, the detection method is an image ranging, a radar ranging or an infrared ranging detection technology. 
     The vehicle safety warning device  7  further includes a speaker module  74 . 
     Under the structure of the vehicle safety warning device  7 , the displaying steps (as shown in  FIG. 7 ) of the method for displaying the vehicle safety distance  6  of the present invention, includes: 
     In step  61 , a double vertical line  51  is displayed on the display module  71  (as shown in  FIG. 5 ); the double vertical line  51  represents the lane lines on both sides of the present car (which means the car driven by the driver), the double vertical line  51  is not limited to a line, but a virtual icon drawn according to the lane lines of the actual road. When the lane line of the actual road is a curve, the double vertical line  51  is a curve correspondingly; 
     in step  62 , a first vehicle location icon  52  is displayed on the display module  71 , the first vehicle location icon  52  represents the location of the present vehicle, the first vehicle location icon  52  is placed in the middle of the double vertical line  51 , the first vehicle location icon  52  moves left and right according to the actual location in the lane detected by the image recognition module  72 ; 
     in step  63 , when the first vehicle location icon  52  displayed on the display module  71  is overlapped on the double vertical line  51  (as shown in  FIG. 6 ), it means the lane departure, at this time, the double vertical line  51  is showed by a warning icon for caution; 
     in step  64 , a second vehicle location icon  53  is displayed on the display module  71 , which is located above the first vehicle location icon  52  in the middle of the double vertical line  51  (as shown in  FIG. 9 ), the second vehicle location icon  53  represents the location of the front car, and the second vehicle location icon  53  moves up and down according to the front vehicle distance detected by the distance detection module  73 . 
     The displaying step  61 , when the image recognition module  72  cannot detect the lane line, the double vertical line  51  is hidden without being displayed. 
     The displaying step  63 , the warning icon is provided to warn by flashing the double vertical line  51 . 
     The displaying step  63 , the warning icon is provided to warn by changing the color of the double vertical line  51 . 
     The displaying step  64 , wherein when the distance detection module  73  detects that the front vehicle is too far or there is no vehicle, the second vehicle location icon  53  is hidden without being displayed. 
     The displaying step  64 , wherein when the detection environment is not good for the distance detection module  73  to accurately determine the location of the front vehicle, the second vehicle location icon  53  is replaced by other marked icon, the marked icon is a question mark or a dotted line icon. 
     The above method for displaying the vehicle safety distance  6  of the present invention further includes a step  65 , the first vehicle location icon  52  is increased upwards or shortened with the change of the car speed (as shown in  FIG. 10 ). 
     The displaying step  65 , wherein if the first vehicle location icon  52  is increased to contact the second vehicle location icon  53  (as shown in  FIG. 11 ), it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the first vehicle location icon  52  flashes or changes its color as a warning, the speaker module  74  is further used to send out a sound signal (such as voice or beep) as a warning. 
     As shown in  FIG. 12 ,  FIG. 13 , it is the third embodiment of the present invention, which includes a vehicle safety warning device  9  electrically connected to a microprocessor P, the vehicle safety warning device  9  has a display module  91 , an image recognition module  92 , a distance detection module  93  and a car speed detection module  95 . 
     The display module  91 , different icons are used to be displayed on the display module  91  to show different situations on the road, the image D displayed on the display device  91  is the virtual illustration drawn by the vehicle safety warning device  9  (as shown in  FIG. 5 ), not drawn the icons on the realistic images shot by the camera lens  921 . 
     The image recognition module  92  includes a camera lens  921  and a image recognition software  922 , the image recognition software  922  is used to recognize images based on the images shot by the camera lens  921 . If the image recognition software  922  does not detect the two lane lines, but only detect one way lane line, another lane line is estimated by the width of a normal lane. 
     The distance detection module  93 , which is provided to detect the distance between the present car and the front car, the detection method is an image ranging, a radar ranging or an infrared ranging detection technology. 
     The car speed detection module  95 , which is used to detect the car speed of the present vehicle, the detection method is receiving a car speed signal provided by the car, or a detection technology, such as the GPS speed detection. 
     The vehicle safety warning device  9  further includes a speaker module  94 . 
     Under the structure of the vehicle safety warning device  9 , the displaying steps (as shown in  FIG. 12 ) of the method for displaying the vehicle safety distance  8  of the present invention, includes: 
     In step  81 , a double vertical line  51  is displayed on the display module  91  (as shown in  FIG. 5 ); the double vertical line  51  represents the lane lines on both sides of the present car (which means the car driven by the driver), the double vertical line  51  is not limited to a line, but a virtual icon drawn according to the lane lines of the actual road. When the lane line of the actual road is a curve, the double vertical line  51  is a curve correspondingly; 
     in step  82 , a first vehicle location icon  52  is displayed on the display module  91 , the first vehicle location icon  52  represents the location of the present vehicle, the first vehicle location icon  52  is placed in the middle of the double vertical line  51 , the first vehicle location icon  52  moves left and right according to the actual location in the lane detected by the image recognition module  92 ; 
     in step  83 , when the first vehicle location icon  52  displayed on the display module  91  is overlapped on the double vertical line  51  (as shown in  FIG. 6 ), it means the lane departure, at this time, the double vertical line  51  is showed by a warning icon for caution; 
     in step  84 , a second vehicle location icon  53  is displayed on the display module  91 , which is located above the first vehicle location icon  52  in the middle of the double vertical line  51  (as shown in  FIG. 9 ), the second vehicle location icon  53  represents the location of the front car, and the second vehicle location icon  53  moves up and down according to the front vehicle distance detected by the distance detection module  93 . 
     Step  85 , a safe vehicle distance icon  54  (as shown in  FIG. 14 ) is displayed on the display module  91 , which is set between the first vehicle location icon  52  and the second vehicle location icon  53 , the length of the safe vehicle distance icon  54  is changed according to the car speed detected by the car speed detection module. 
     In the displaying step  81 , wherein the double vertical line  51  is hidden without being displayed when the image recognition module  92  cannot detect the lane line. 
     The displaying step  83 , the warning icon is provided to warn by flashing the double vertical line  51 . 
     The displaying step  83 , the warning icon is provided to warn by changing the color of the double vertical line  51 . 
     In the displaying step  84 , wherein the double vertical line  51  is hidden without being displayed when the distance detection module  93  detects that the front car is too far or there is no car, the second vehicle location icon  53  is hidden without being displayed. 
     The displaying step  84 , wherein when the detection environment is not good for the distance detection module  93  to accurately determine the location of the front vehicle, the second vehicle location icon  53  is replaced by other marked icon, the marked icon is a question mark or a dotted line icon. 
     The displaying step  85 , wherein the safe vehicle distance  54  with the second vehicle location icon  53  as its top end (as shown in  FIG. 14 ) is increased upwards or shortened with the change of the car speed. 
     The displaying step  85 , wherein if the safe vehicle distance icon  54  is increased to contact the first vehicle location icon  52 , it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the safe vehicle distance icon  54  flashes or changes its color as a warning, the speaker module  94  is further used to send out a sound signal (such as voice or beep) as a warning. 
     In the displaying step  85 , wherein the safe vehicle distance  54  with the first vehicle location icon  52  as its bottom end is increased upwards or shortened with the change of the car speed (as shown in  FIG. 15 ). 
     The displaying step  85 , wherein if the safe vehicle distance icon  54  is increased upwards to contact the second vehicle location icon  53 , it represents that the front vehicle distance is too short and the present vehicle is in an unsafe condition; the safe vehicle distance icon  54  flashes or changes its color as a warning, the speaker module  94  is further used to send out a sound signal (such as voice or beep) as a warning.