Patent Publication Number: US-2007101290-A1

Title: Display apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application is based on and incorporates herein by reference Japanese Patent Application No. 2005-315745 filed on Oct. 31, 2005.  
     FIELD OF THE INVENTION  
      The present invention relates to a display apparatus. More specifically, the invention relates to a display apparatus capable of displaying multiple pieces of information on a display screen.  
     BACKGROUND OF THE INVENTION  
      There is widely known a display apparatus for displaying multiple pieces of information on a display screen such as a display apparatus provided for a car navigation system. When the display screen displays multiple pieces of information, it may take time to determine which information is currently needed. A user may miss a chance to recognize the necessary information.  
      When a vehicle stops or runs at a low speed, the navigation system described in patent document 1 displays a detailed map on the display screen. When the vehicle runs at a specified speed or more, the system displays a less detailed map to fast understand the map information needed during running.  
      Patent Document 1: JP-2667383 B2  
      It may be possible to display multiple windows on the display screen as needed and allow the windows to display different information. Also in this case, however, the user may miss a chance to recognize the information in the simultaneously displayed respective windows. When the windows partially or completely overlap with each other, the user may highly possibly miss a chance to recognize the information displayed in the underlying window.  
      Even when display areas such as windows do not overlap with each other, the use of multiple display areas makes it difficult to find where the important information is displayed. As a result, there is a possibility to miss a chance to recognize the information.  
     SUMMARY OF THE INVENTION  
      The present invention has been made in consideration of the foregoing. It is therefore an object of the present invention to provide a display apparatus that facilitates fast recognition of necessary information.  
      According to an aspect of the present invention, a display apparatus is provided as follows. Screen determination means determines information that includes a number of windows to be displayed in a display screen, a display range in each window, and a display content in each window. Image generation means generates an overall display image for the display screen based on information determined by the screen determination means and displays the generated image on the display screen. Priority determination means determines a display priority of a window based on a display content included in information determined by the screen determination means. When the screen determination means determines displaying a plurality of windows having display ranges to overlap with each other, the image generation means generates an overall image by determining an order of overlapping the plurality of windows based on display priorities determined by the priority determination means.  
      Under the above structure, when multiple windows are overlapped with each other to generate an overall image, a display priority is determined based on a display content and determines the order of the overlapping windows. A window may be displayed second or later in the order of overlapping windows before the display content is changed. Changing the display content may assign the highest display priority to the window. In this case, the window is displayed at the top, which makes it possible to easily view information in the window. A user can promptly and easily recognize the necessary information.  
      According to another aspect of the present invention, a display apparatus in a vehicle is provided as follows. A plurality of display areas are included as a display screen for simultaneously displaying information. A display control unit is included for controlling displaying information in the display screen. When normal information displayed in a certain display area of the plurality of display areas changes to predetermined abnormal information, the display control unit changes a display mode for the certain display area.  
      Under the above structure, when information displayed in the display area changes from normal to abnormal, the display area may be provided with a display mode that differs from the previous one. In this manner, a driver can easily notice a change in the display content of the display area and more promptly find abnormal information.  
      According to yet another aspect of the present invention, a method for displaying information is provided with the following: determining information that includes a number of windows to be displayed in a display screen, a display range in each window, and a display content in each window; determining a display priority of each window based on a display content of each window, when a plurality of windows having display ranges to overlap with each other are determined to be displayed; generating an overall display image for the display screen by determining an order of overlapping the plurality of windows based on display priorities determined; and displaying the generated image on the display screen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram showing a construction of a display apparatus according to a first embodiment of the invention;  
       FIG. 2  is a block diagram showing in detail a construction of an information collection unit;  
       FIG. 3  is a block diagram showing in detail a function of a control unit as a display control unit;  
       FIG. 4  exemplifies a virtual screen generated in a rendering unit of  FIG. 3  and a synthesized screen generated in a synthesized screen generation unit thereof;  
       FIG. 5  exemplifies part of a priority conversion table used in a priority determination unit of  FIG. 3 ;  
       FIG. 6  shows a synthesized screen different from that shown in  FIG. 4 ;  
       FIG. 7  shows a synthesized screen different from those shown in  FIGS. 4 and 6 ;  
       FIG. 8  is a block diagram showing in detail a function of a control unit as a display control unit according to a second embodiment;  
       FIG. 9  shows an example of a highlight table used in a highlight unit in  FIG. 8 ;  
       FIG. 10  shows a highlighted display frame in a vehicle information window;  
       FIG. 11  shows a highlight table used for a third embodiment;  
       FIG. 12  shows how a vehicle information window is enlarged to 200% and its display frame is highlighted;  
       FIG. 13  is a block diagram showing a construction of a display apparatus according to a fourth embodiment;  
       FIG. 14  is a block diagram showing in detail a control function of a control unit as a display control unit in  FIG. 13 ;  
       FIG. 15  is a flowchart showing a process of a synthesized screen generation unit in  FIG. 14 ;  
       FIG. 16  exemplifies a screen displayed on the display apparatus according to the fourth embodiment;  
       FIG. 17  exemplifies another screen displayed on the display apparatus according to the fourth embodiment, an example different from that shown in  FIG. 16 ;  
       FIG. 18  is a block diagram showing a construction of a display apparatus according to a fifth embodiment;  
       FIG. 19  is a block diagram showing in detail a control function of a control unit as a display control unit in  FIG. 18 ;  
       FIG. 20  exemplifies a display scale table in  FIG. 19 ;  
       FIG. 21  exemplifies an overall image displayed on the display apparatus according to the fifth embodiment;  
       FIG. 22  is a block diagram showing a construction of a display apparatus according to a sixth embodiment;  
       FIG. 23  is a block diagram showing a function of a control unit as a display control unit in  FIG. 22 ;  
       FIG. 24  exemplifies an overall image displayed on the display apparatus according to the sixth embodiment;  
       FIG. 25  exemplifies another overall image displayed on the display apparatus according to the sixth embodiment, an example different from that shown in  FIG. 24 ;  
       FIG. 26  exemplifies another overall image displayed on the display apparatus according to the sixth embodiment, an example different from those shown in  FIGS. 24 and 25 ;  
       FIG. 27  is a block diagram showing a construction of a display apparatus according to a seventh embodiment;  
       FIG. 28  shows the display unit in  FIG. 27 ;  
       FIG. 29  is a flowchart showing processes in a state information reception unit, an error state determination unit, and an error information display determination unit of  FIG. 27 ;  
       FIG. 30  shows a display example in a display area;  
       FIG. 31  shows a display example in the display area during the processes in  FIG. 29 ;  
       FIG. 32  exemplifies an error information priority table used during the processes in  FIG. 29 ; and  
       FIG. 33  shows an example displayed in the display area during the processes in  FIG. 29  when an engine system information icon is selected.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Embodiments of the present invention will be described in further detail with reference to the accompanying drawings.  
     First Embodiment  
       FIG. 1  is a block diagram showing the construction of a display apparatus  10  according to a first embodiment of the invention.  
      A display apparatus  10  mounted on a vehicle has an information collection unit  100  for collecting various information about the inside and the outside of the vehicle. Information collected in the information collection unit  100  is supplied to an information selection unit  12 . The information selection unit  12  selects information needed for the navigation unit  14  and information processing units  16 ,  18 ,  20 , and  22  from a variety of information supplied from the information collection unit  100 . The information selection unit  12  outputs the selected information to the navigation unit  14  and the information processing units  16 ,  18 ,  20 , and  22 .  
       FIG. 2  is a block diagram showing in detail the construction of the information collection unit  100 . The information collection unit  100  includes a GPS receiver  102 , a map information input device  104 , a gyroscope  106 , a vehicle speed sensor  108 , a steering sensor  110 , a fuel level sensor  112 , a tire inflation pressure sensor  114 , a brake switch  116 , a throttle angle sensor  118 , an onboard computer error monitoring apparatus  120 , a vicinity monitoring camera  122 , an obstacle sensor  124 , an indoor camera  126 , a biologic information sensor  127 , a VICS transceiver  128 , an Internet communication apparatus  130 , a radio set  132 , a TV set  134 , and an audiovisual reproducing apparatus  136 .  
      The GPS receiver  102  is used for the global positioning system (GPS) that measures vehicle positions based on radio waves from satellites. The map information input device  104  is provided with a storage medium such as DVD-ROM or CD-ROM. The map information input device  104  reads map information stored in the storage medium and supplies the information to the information selection unit  12 . The gyroscope  106  detects a relative orientation of the vehicle. The GPS receiver  102 , the map information input device  104 , and the gyroscope  106  collect the vehicle&#39;s position information.  
      The vehicle speed sensor  108  detects wheel revolutions to detect a vehicle speed. The steering sensor  110  detects a steering wheel angle. The fuel level sensor  112  detects the amount of fuel remaining in a fuel tank. The tire inflation pressure sensor  114  detects a tire inflation pressure. The brake switch  116  detects that a foot brake is operated. The throttle angle sensor  118  detects a throttle valve angle. The onboard computer error monitoring apparatus  120  monitors errors of various computers mounted in the vehicle. The onboard computer error monitoring apparatus  120  includes a diagnosis program stored in the computer of the apparatus itself or another computer. The vehicle speed sensor  108 , the steering sensor  110 , the fuel level sensor  112 , the tire inflation pressure sensor  114 , the brake switch  116 , the throttle angle sensor  118 , and the onboard computer error monitoring apparatus  120  collect the vehicle information.  
      The vicinity monitoring camera  122  is provided at a position capable of capturing a specified direction around the vehicle. The obstacle sensor  124  is provided to detect an obstacle in all directions, i.e., at 360 degrees, around the vehicle. The obstacle sensor  124  includes a specified number of sensors, e.g., four sensors to detect the front, rear, right side, and left side of the vehicle. The obstacle sensor  124  represents an ultrasonic sensor or a laser radar sensor. The obstacle sensor is also used to detect a distance between the vehicle and an obstacle. When another vehicle is assumed to be an obstacle, the obstacle sensor also functions as an inter-vehicle gap sensor. The vicinity monitoring camera  122  and the obstacle sensor  124  collect information around the vehicle.  
      The indoor camera  126  collects driver information. The indoor camera  126  is provided at a specified position in a vehicle compartment (e.g., on the ceiling at the front end of the compartment and at the center of the vehicle width direction). The indoor camera  126  chronologically (or time-sequentially) captures situations in the vehicle compartment, especially driver&#39;s situations. The biologic information sensor  127  also acquires the driver information. For example, the biologic information sensor  127  detects the driver&#39;s biologic information such as a heart rate and a breathing rate.  
      The VICS transceiver  128  receives information from a VICS (Vehicle Information and Communication System) (registered trademark) center via beacons installed on roads and local FM broadcasting stations. The VICS center provides information about road traffic, weather, date, facility, and advertisement. The Internet communication apparatus  130  is a wireless communication apparatus connectable to a public telephone line and connects to the Internet network via the public telephone line. The VICS transceiver  128  and the Internet communication apparatus  130  collect wide area information. That is, the VICS transceiver  128  and the Internet communication apparatus  130  collect information about an area wider than the vehicle vicinity about which information the vicinity monitoring camera  122  and the obstacle sensor  124  collect.  
      The audiovisual reproducing apparatus  136  can reproduce a music CD or a DVD that stores video such as movies. The audiovisual reproducing apparatus  136 , the radio set  132 , and the TV set  134  are mainly used to collect amusement information.  
      Referring back to  FIG. 1 , the navigation unit  14  processes the route guidance. Via the information selection unit  12 , the navigation unit  14  is supplied with information from the GPS receiver  102 , the map information input device  104 , the gyroscope  106 , and the vehicle speed sensor  108 . A user operates a user input apparatus  40  to supply information about a destination and the like. This information is supplied to the navigation unit  14  via the control unit  30 .  
      A vehicle information processing unit  16  determines the vehicle&#39;s running states such as an onboard device error and a running speed. Via the information selection unit  12 , the vehicle information processing unit  16  is supplied with information from the vehicle speed sensor  108 , the steering sensor  110 , the fuel level sensor  112 , the tire inflation pressure sensor  114 , the brake switch  116 , the throttle angle sensor  118 , and the onboard computer error monitoring apparatus  120 .  
      A wide-area information processing unit  18  processes the above-mentioned wide area information. Via the information selection unit  12 , the wide-area information processing unit  18  is supplied with information from the VICS transceiver  128  and the Internet communication apparatus  130 .  
      A circumference information processing unit  20  collects and processes information around the vehicle. Via the information selection unit  12 , the circumference information processing unit  20  is supplied with information from the vicinity monitoring camera  122  and the obstacle sensor  124 . The circumference information processing unit  20  is also supplied with vehicle information from the vehicle speed sensor  108 .  
      The audiovisual information processing unit  22  processes signals from the radio set  132 , the TV set  134 , and the audiovisual reproducing apparatus  136 . The audiovisual information processing unit  22  then determines a display content to be displayed on a display unit  42 . The display content to be determined includes an operation screen for each apparatus and a motion picture.  
      The navigation unit  14  and the information processing units  16 ,  18 ,  20 , and  22  each output a display instruction signal to the control unit  30  when determining display of information on the display unit  42 . The display instruction signal instructs the display unit  42  to display the information.  
      The user input apparatus  40  includes a key input apparatus and a voice input apparatus. The key input apparatus enables user&#39;s manual input operation using a mechanical key or the like. The voice input apparatus has a voice input apparatus including a microphone and a voice recognition unit that analyzes voice supplied from the microphone.  
      According to the embodiment, the display unit  42  includes a first display unit  42   a  and a second display unit  42   b . The following description simply concerns the display unit  42  unless distinguished specifically. The display unit  42  represents a liquid crystal display, for example. The first display unit  42   a  is provided in an instrument panel at the middle between a driver&#39;s seat and a passenger seat and displays a road map and the like. The second display unit  42   b  is provided in the instrument panel ahead of the driver&#39;s seat and displays a vehicle speed and the like.  
      The control unit  30  functions as a display control unit. The control unit  30  follows signals from the navigation unit  14  and the information processing units  16 ,  18 ,  20 , and  22 . Based on display contents determined by these units, the control unit  30  generates an overall image to be displayed on the display unit  42  and displays it on the display unit  42 . The control unit  30  also functions as an output sound control unit. The control unit  30  follows signals from the navigation unit  14  and the information processing units  16 ,  18 ,  20 , and  22  and allows the speaker  44  to output a specified sound.  
       FIG. 3  is a block diagram showing in detail one of control functions of the control unit  30  as the display control unit. As shown in  FIG. 3 , the control unit  30  includes a rendering unit  31 , a priority determination unit  32 , and a synthesis unit  33  functioning as image generation means. Further, the synthesis unit  33  includes a display priority temporary storage unit  34  and a synthesized screen generation unit  35 .  
      The rendering unit  31  functions as screen determination means. The rendering unit  31  follows display instruction signals from the outside, i.e., from the navigation unit  14  and the information processing units  16 ,  18 ,  20 , and  22  to determine the necessary number of virtual screens. The virtual screen provides an image for the entire displayable range of the display unit  42  (one of the first display unit  42   a  and the second display unit  42   b ). As shown in  FIG. 4 , for example, the rendering unit  31  determines (renders) three virtual screens  1  through  3 .  
      According to a display instruction signal from the navigation unit  14 , the virtual screen  1  uses part of the displayable range to render a map window  46  showing a road map. The remaining part of the displayable range is filled with a background color. According to a display instruction signal from the audiovisual information processing unit  22 , the virtual screen  2  uses part of the displayable range to render an audio operation window  48  for audio operation. The remaining part of the displayable range is filled with a background color. According to a display instruction signal from the vehicle information processing unit  16 , the virtual screen  3  uses part of the displayable range to render a vehicle information window for displaying vehicle information. The remaining part of the displayable range is filled with a background color.  
      The rendering unit  31  determines the virtual screens as exemplified in  FIG. 4 . The rendering unit  31  determines the number of windows to be displayed on the display unit  42 , a display range, and a display content in each window. In the example of  FIG. 4 , one virtual screen corresponds to one of the navigation unit  14  and the information processing units  16 ,  18 ,  20 , and  22 . Further, one virtual screen may render information about the multiple processing units  16 ,  18 ,  20 , and  22 , or the navigation unit  14 .  
      The priority determination unit  32  functions as priority determination means. The priority determination unit  32  uses a pre-stored priority conversion table to determine a display priority for the virtual screen determined by the rendering unit  31 .  
       FIG. 5  exemplifies part of the priority conversion table. As shown in  FIG. 5 , the priority conversion table defines display priorities corresponding to notification contents (display contents displayed in the windows) of the processing units (the navigation unit  14  and the information processing units  16 ,  18 ,  20 , and  22 ). Here, a larger number corresponds to a higher display priority. For instance, “30” is given the highest display priority and “1” is given the lowest display priority within the examples shown in  FIG. 5 . The priority conversion table in  FIG. 5  may be used as follows. When the map window  46  in the virtual screen  1  of  FIG. 4  contains a display content to be displayed during route guidance, the virtual screen  1  is assigned display priority  10 . When the audio operation window  48  in the virtual screen  2  contains a display content to be displayed during music reproduction, the virtual screen  2  is assigned display priority  3 . When the vehicle information window  50  in the virtual screen  3  shows no error, the virtual screen  3  is assigned display priority  1 .  
      Referring back to  FIG. 3 , the display priority temporary storage unit  34  represents a temporary storage such as RAM. The display priority temporary storage unit  34  temporarily stores each virtual screen&#39;s display priority determined by the priority determination unit  32 .  
      The synthesized screen generation unit  35  synthesizes all the virtual screens determined by the rendering unit  31  to generate a synthesized screen. At this time, window display ranges may overlap with each other. The synthesized screen generation unit  35  determines the order of overlapping windows so that the window having the highest display priority is displayed at the top, then the window having the next highest display priority is displayed next to the top window, and so on. For example, the synthesized screen generation unit  35  generates the synthesized screen as shown at the top in  FIG. 4 . The synthesized screen generation unit  35  outputs screen data for the synthesized screen to the display unit  42 . In this manner, the display unit  42  displays the synthesized screen.  
      Let us suppose that the display contents of the map window  46  and the audio operation window  48  are unchanged, but the vehicle information window  50  changes its display content from “no error” to “abnormal air pressure.” In this case, the display priority for the vehicle information window changes to  30 . As a result, the vehicle information window  50  is assigned the highest display priority. The order of three overlapping windows  46 ,  48 , and  50  changes. The overall image generated by the synthesized screen generation unit  35  changes from the one displayed at the top of  FIG. 4  to the one as shown in  FIG. 6 . That is, the vehicle information window  50  showing “abnormal air pressure” is displayed at the top for easy recognition. A driver can promptly notice the detection of abnormal air pressure.  
      Let us suppose that a change is made to the display content of the map window  46  in the screen of  FIG. 6  and the display priority for the map window  46  changes from 10 to 30. As a result, the same display priority is assigned to the map window  46  and the vehicle information window  50 . The highest display priority is assigned to the two windows. The rendering unit  31  determines the display ranges of the two windows  46  and  50  so that they overlap with each other. In this case, however, the synthesized screen generation unit  35  changes the display ranges determined by the rendering unit  31 . As shown in  FIG. 7 , the synthesized screen generation unit  35  generates a synthesized screen so that the display ranges of the two windows  46  and  50  do not overlap with each other. Broken lines indicate the display ranges of the windows  46  and  50  before changing the display ranges (i.e., the display ranges of the windows  46  and  50  in  FIG. 6 ).  
      Since the display ranges change, the user can simultaneously view all the windows  46  and  50  having the same display priority without needing to change the order of overlapping windows  46  and  50  or change the display positions thereof. Instead of changing the display ranges, different display times may be assigned to the windows so that they do not overlap with each other. Also in this case, the user can view all the windows having the same display priority without needing to switch between the windows.  
      When multiple windows overlap with each other to generate an overall image, the above-mentioned embodiment determines the order of overlapping windows using display priorities determined based on the display contents. When a window is displayed second or later in terms of the order of overlapping windows without changing the display content, changing the display content may assign the highest display priority to that window. The window is displayed at the top, making it easy to view the information in the window. Consequently, the user can promptly and easily recognize the necessary information.  
     Second Embodiment  
      The following describes a second embodiment of the invention. The mutually corresponding parts in the second and first embodiments are designated by the same reference numerals and a detailed description is omitted for simplicity.  
      As shown in  FIG. 8 , the apparatus according to the second embodiment differs from that according to the first embodiment in that the synthesized screen generation unit  35  includes a highlight unit  36 . The highlight unit  36  functions as highlight means. The top window may change to another when the display unit  42  displays multiple windows overlapping with each other. The highlight unit  36  determines whether or not the new top window displays a content with high urgency. That is, the highlight unit  36  determines whether or not the display priority for the window is greater than or equal to a predetermined value. The display priority is determined by the window&#39;s display content and the priority conversion table in  FIG. 5 .  
       FIG. 9  exemplifies a highlight table used for the determination. The highlight unit  36  uses the highlight table in  FIG. 9  to determine whether or not the display content is assigned high urgency. Specifically, the highlight unit  36  determines whether or not the window is assigned a display priority greater than 16. When the highlight table in  FIG. 9  is used, the display content urgency is classified into three categories instead of simply two, high or low.  
      As a result of the determination using the highlight table in  FIG. 9 , the display content may be assumed to be highly urgent, i.e., the display priority may be assumed to be 16 or more. In this case, the highlight unit  36  highlights the window newly positioned at the top in highlight mode specified correspondingly to the display priority in the highlight table.  
      This will be further explained below using the same example as the first embodiment. Since the vehicle information window  50  contains the display content indicating “no error,” the synthesized screen is displayed at the top as shown in  FIG. 4 . Let us suppose that the display content of the vehicle information window  50  changes to “abnormal air pressure” and the display priority of the window  50  changes to 30 from 1.  
      In this case, the vehicle information window  50  is displayed at the top. Since the highlight unit  36  references the table in  FIG. 9 , the vehicle information window  50  highlights the display frame ten seconds.  FIG. 10  shows the highlighted display frame of the vehicle information window  50 . The display frame is thicker than that in  FIG. 4 .  
      The order of overlapping windows may be changed to newly display the topmost window having a highly urgent display content. In such case, the second embodiment highlights the display frame of the topmost window. The user can easily pay attention to that window. Accordingly, the user can quickly notice that the window shows the highly urgent information.  
      Let us assume that the new topmost window may be assigned display priority 31 or more. As shown in the highlight table of  FIG. 9 , the window&#39;s display frame is highlighted ten seconds and the speaker  44  generates a specified audible alarm. Accordingly, the user can more easily notice the highly urgent information.  
     Third Embodiment  
      The following describes a third embodiment of the invention. The third embodiment differs from the second embodiment only in the use of a highlight table instead of the highlight table in  FIG. 9 .  
      According to the highlight table in  FIG. 9 , the audible alarm is provided depending on display priorities but the window highlight mode is unchanged. The highlight table in  FIG. 11  also provides different window highlight modes depending on display priorities.  
      Let us suppose that the display priority ranging from 16 to 30 is assigned to the window that references the highlight table in  FIG. 11 . The highlight unit  36  highlights the window&#39;s display frame ten seconds and increases a display scale 150% compared to that used for the display content before change. When the display priority is 31 or more, the highlight unit  36  highlights the display frame ten seconds. Further, the highlight unit  36  increases the display scale 200% compared to that used for the display content before change and allows the speaker  44  to generate a specified audible alarm.  
      This will be explained using the same example as the first embodiment. Since the vehicle information window  50  contains the display content indicating “no error,” the synthesized screen is displayed at the top as shown in  FIG. 4 . Let us suppose that the display content of the vehicle information window  50  changes to the display content with display priority  31  or higher. In this case, the vehicle information window  50  is displayed at the top. Since the highlight unit  36  references the table in  FIG. 11 , the vehicle information window  50  highlights its display frame ten seconds. In addition, the vehicle information window  50  is enlarged 200%.  FIG. 12  shows this state. Further, the speaker  44  generates a specified audible alarm.  
      The third embodiment uses different highlighting mode (i.e., display scales in this third embodiment) depending on display contents. More urgent information becomes more remarkable than less urgent information. When especially highly urgent information is displayed, the user can more easily notice that information  
     Fourth Embodiment  
      The following describes a fourth embodiment of the invention.  FIG. 13  is a block diagram showing the construction of a display apparatus  200  according to the fourth embodiment. The display apparatus  200  differs from the display apparatus  10  in that the former has a maximum value setup unit  202 . The function of a control unit  210  partly differs from the display apparatus  10 . The other parts of the construction are the same as those in  FIG. 1 .  
      The maximum value setup unit  202  functions as maximum value setup means. For example, the maximum value setup unit  202  includes a computer having CPU, ROM, and RAM. The maximum value setup unit  202  is supplied with a specific value indicating the maximum number of windows displayed on the display unit  42 . The maximum number of windows is supplied from the user input apparatus  40 . When the value is input, the maximum value setup unit  202  specifies the value as a maximum display count of windows displayed on the display unit  42 . The maximum value setup unit  202  outputs the specified maximum display count to the control unit  210 . According to the embodiment, the maximum display count is a numeric value specifying the maximum number of windows displayed on the one display unit  42 . The maximum display count may specify the maximum number of windows displayed on part (specified display range) of the display screen of the display unit  42 .  
       FIG. 14  is a block diagram showing in detail one of control functions of the control unit  210  in  FIG. 13  as the display control unit. When  FIGS. 14 and 3  are compared, there is only a difference between functions of the synthesized screen generation units  212  and  35  in  FIGS. 14 and 3 , respectively. The synthesized screen generation unit  212  has a maximum display count storage unit  214  for storing a maximum display count specified by the maximum value setup unit  202 .  
       FIG. 15  is a flowchart showing a process of the synthesized screen generation unit  212 . The process shown in the flowchart of  FIG. 15  is performed when the rendering unit  31  changes the content of at least one virtual screen.  
      At Step S 10 , the synthesized screen generation unit  212  determines whether or not the priority determination unit  32  changed the display priority of the window having its display content changed. When the result of the determination at Step S 10  is negative, the display priority is unchanged. In this case, at Step S 20 , synthesized screen generation unit  212  determines not to change the number of display windows and the order of overlapping windows. At Step S 30 , the synthesized screen generation unit  212  generates the overall image by changing only the window&#39;s display content without changing the type of window to be displayed and the order of overlapping windows.  
      When the result of the determination at Step S 10  is affirmative, the process proceeds to Step S 40 . At Step S 40 , the synthesized screen generation unit  212  determines whether or not the number of windows to be displayed on the display unit  42  exceeds the maximum display count stored in the maximum display count storage unit  214 . In this case, the rendering unit  31  determines the number of windows to be displayed on the display unit  42 . When the result of the determination at Step S 40  is negative, the process proceeds to Step S 50 . At Step S 50 , the synthesized screen generation unit  212  uses all the virtual screens determined by the rendering unit  31  to generate an overall image so as to display the window with a higher display priority stored in the display priority temporary storage unit  34 .  
      When the result of the determination at Step S 40  is affirmative, the process proceeds to Step S 60 . At Step S 60 , the synthesized screen generation unit  212  determines a virtual screen used for generation of the overall image based on the display priority stored in the display priority temporary storage unit  34 . For example, let us suppose that the display count determined by the rendering unit  31  is by one greater than the maximum display count stored in the maximum display count storage unit  214 . In this case, the synthesized screen generation unit  212  determines a virtual screen to be used for generation of the overall image so that the virtual screen is other than the one containing the window assigned the lowest display priority. At Step S 70 , the synthesized screen generation unit  212  generates the overall image by overlaying virtual screens determined at Step S 60  in the order of display priorities stored in the display priority temporary storage unit  34 .  
      At Step S 80 , the synthesized screen generation unit  212  supplies the display unit  42  with the overall images generated at Step S 30 ,  50 , and  70 .  
      The following describes the display screen displayed on the display unit  42  according to the fourth embodiment using the same example as the first embodiment. While the virtual screens  1  to  3  are generated as shown in  FIG. 4 , the maximum display count may be set to 2. In this case, virtual screen  3  is not displayed based on the display priority. Only virtual screens  1  and  2  are used to generate the overall image. The display unit  42  displays the screen as shown in  FIG. 16 .  
      In this state, let us suppose that the vehicle information window  50  changes its display content with display priority  1  to the one with display priority  30 . The generation of the overall image uses the vehicle information window  50  instead of the audio operation window  48 . In addition, the vehicle information window  50  is higher than the map window  46  in terms of the order of overlapping windows. The display unit  42  displays the screen as shown in  FIG. 17 .  
      As mentioned above, the fourth embodiment limits the number of windows displayed on the one display unit  42 . This improves visibility of all the displayed windows. The number of displayed windows is limited even when a specified window is determined to display important information with high display priority and is displayed on the top. This improves visibility of the important information.  
     Fifth Embodiment  
      The following describes a fifth embodiment of the invention.  FIG. 18  is a block diagram showing the construction of a display apparatus  300  according to the fifth embodiment. The display apparatus  300  differs from the display apparatus  10  in  FIG. 1  in that the former includes a driver characteristics acquisition unit  302 . The function of a control unit  310  partly differs from the display apparatus  10 . The other parts of the construction are the same as those in  FIG. 1 .  
      The driver characteristics acquisition unit  302  acquires driver characteristics information, i.e., information about driver characteristics. A driver operates the vehicle-mounted user input apparatus  40  to input a signal. Based on this input signal, the driver characteristics acquisition unit  302  according to the embodiment acquires the driver characteristics information. The embodiment acquires the driver&#39;s gender and age as the driver characteristics information.  
       FIG. 19  is a block diagram showing in detail one of control functions of the control unit  310  in  FIG. 18  as the display control unit. When  FIGS. 19 and 3  are compared,  FIG. 19  differs from  FIG. 3  in that  FIG. 19  includes a display enlargement determination unit  312  and a screen enlarging unit  316 .  
      The display enlargement determination unit  312  includes a display scale table  314 . Using the display scale table  314 , the display enlargement determination unit  312  determines whether or not to enlarge each virtual screen created in the rendering unit  31  according to the driver characteristics information acquired by the driver characteristics acquisition unit  302 . The display enlargement determination unit  312  also determines an enlargement factor of the virtual screen.  
       FIG. 20  is an example of the display scale table  314 . The display scale table defines display enlargement factors corresponding to the processing units (i.e., the navigation unit  14  and the information processing units  16 ,  18 ,  20 , and  22 ), their notification contents (display contents displayed in the windows), and the driver characteristics information. For example, the display scale table in  FIG. 20  notifies an abnormal air pressure based on the display mode for a male driver aged  50  or younger. The display enlargement factor is multiplied 1.4 times for a male driver aged  51  or older. The display enlargement factor is multiplied 1.3 times for a female driver aged  40  or younger. The display enlargement factor is doubled for a female driver aged  41  or older.  
      The display enlargement factor is configured based on the fact that a female driver generally cannot afford to pay sufficient attention to the display screen of the display unit  42  than a male driver. In addition, an older driver needs a relatively long time to confirm the content of a small display. An enlarged display is used to fast notify the driver of highly urgent contents. The driver can easily understand the highly urgent information.  
      The screen enlarging unit  316  functions as highlight means. When the rendering unit  31  determines a virtual screen, the screen enlarging unit  316  enlarges that virtual screen with an enlargement factor determined by the display enlargement determination unit  312 . The screen enlarging unit  316  supplies the enlarged screen to the synthesized screen generation unit  35 .  
      The following describes the display screen displayed on the display unit  42  according to the fifth embodiment using the same example as the first embodiment. At a given time point, let us suppose that virtual screens  1  through  3  are generated as shown in  FIG. 4  and the windows  46 ,  48 , and  50  provide the same notification contents as those for the first embodiment. The display enlargement factor is determined based on the display scale table and is set to 1 for all the windows  46 ,  48 , and  50  irrespectively of the contents of the driver characteristics information. Accordingly, the overall image is generated as shown at the top in  FIG. 4 .  
      When the content of the vehicle information window  50  changes to “abnormal air pressure,” the vehicle information window  50  is assigned the highest display priority. The overall image is changed so that the vehicle information window  50  is displayed at the top. When the driver characteristics acquisition unit  302  acquires the driver characteristics information about a male driver aged  50  or younger, the display enlargement factor remains 1 for all the windows  46 ,  48 , and  50 . The overall image is changed only as to the order of the overlapping windows  46 ,  48 , and  50 . The overall image is displayed as shown in  FIG. 6 .  
      When the driver characteristics acquisition unit  302  acquires the driver characteristics information about a female driver aged  41  or older, the display enlargement factor changes to 2 for the vehicle information window  50 . The vehicle information window  50  is positioned at the top and is doubled in size.  FIG. 21  exemplifies the overall image at this time.  
      The fifth embodiment uses different window enlargement factors for important display contents depending on the driver characteristics information. The top window is enlarged for display when the driver is generally considered to be less experienced and not to afford to pay sufficient attention to the display screen. The driver can acquire important information in a short period of time.  
     Sixth Embodiment  
      The following describes a sixth embodiment of the invention.  FIG. 22  is a block diagram showing the construction of a display apparatus  400  according to the sixth embodiment. The display apparatus  400  differs from the first through fifth embodiments in that the display apparatus  400  further includes a tension determination unit  402  as the information processing unit. The function of a control unit  410  partly differs from the first through fifth embodiments. The other parts of the construction are the same as those in  FIG. 1 .  
      The tension determination unit  402  functions as tension determination means. The tension determination unit  402  is supplied with a signal from the biologic information sensor  127  via the information selection unit  12 . The tension determination unit  402  uses the supplied signal to chronologically detect the driver&#39;s heart rate. Based on a change in the heart rate, the tension determination unit  402  determines whether or not the driver is tense. To do this determination, for example, the tension determination unit  402  finds an average heart rate as a reference in a stable state where a range of heart rate variations is smaller than a specified value. When the heart rate increases for a specified value or specified rate from the reference, the tension determination unit  402  determines that the driver is tense. The determination result is input to the control unit  410 .  
       FIG. 23  is a block diagram showing in detail one of control functions of the control unit  410  in  FIG. 22  as the display control unit. In  FIG. 23 , a process in the synthesis unit  412  differs from that in the preceding embodiments. The synthesis unit  412  includes order change disable means  414  and a synthesized screen generation unit  416  in addition to the above-mentioned display priority temporary storage unit  34 .  
      The tension determination unit  402  may determine that the driver is tense. Further, the user may operate the user input apparatus  40  to control the window displayed at the top of the display screen. In such cases, the order change disable means  414  determines to inhibit a change in the order of overlapping windows. The order change disable means  414  supplies the synthesized screen generation unit  416  with an instruction for inhibiting the order of overlapping windows from being changed. The driver may be then relieved from the tense state. Alternatively, the user may complete the operation concerning the topmost window. In such cases, the order change disable means  414  supplies the synthesized screen generation unit  416  with an instruction to release the instruction for inhibiting the order of overlapping windows from being changed.  
      The synthesized screen generation unit  416  is supplied with a virtual screen from the rendering unit  31  via the screen enlarging unit  316 . The synthesized screen generation unit  416  generates an overall image by overlapping one or more supplied virtual screens in the order of display priorities stored in the display priority temporary storage unit  34 . A change may be made to the display priority stored in the display priority temporary storage unit  34  to necessitate a change in the order of overlapping virtual screens. In this case, the synthesized screen generation unit  416  determines whether or not an order change disabling state takes effect. When the order change disabling state is inactive, the synthesized screen generation unit  416  regenerates the overall image by changing the order of overlapping virtual screens based on the updated display priority. The order change disabling state takes effect during a period from when the order change disable means  414  issues the instruction for inhibiting the order of overlapping windows from being changed to when the order change disable means  414  issues the instruction for releasing that inhibiting instruction.  
      The order change disabling state may be active even when there is a need for changing the order of overlapping virtual screens. In such case, the synthesized screen generation unit  416  generates the overall image by overlapping the virtual screens without changing the overlapping order.  
      The order change disabling state may be inactive even when the rendering unit  31  generates an increased number of virtual screens. In such case, the synthesized screen generation unit  416  generates the overall image by determining the order of overlapping virtual screens based on the display priority of an added virtual screen and the display priorities of the remaining virtual screens. When the order change disabling state is active, the synthesized screen generation unit  416  does not add a virtual screen until the order change disabling state is released.  
      The following uses an example to describe the display screen displayed on the display unit  42  according to the sixth embodiment. At a given time point, let us suppose that the map window  46  and the vehicle information window  50  are displayed as shown in  FIG. 24 . The map window  46  and the vehicle information window  50  are assigned display priorities  10  and  1 , respectively.  
      The circumference information processing unit  20  detects an error around the vehicle. Based on the detection result, the rendering unit  31  may generate an additional virtual screen containing a circumference information window  52  (see  FIG. 25 ) for notifying the error around the vehicle. In this case, the display unit  42  displays the screen as shown in  FIG. 25 . On the screen in  FIG. 25 , the circumference information window  52  is assigned display priority  30 . Therefore, the circumference information window  52  is displayed at the top.  
       FIG. 25  shows an example of a male driver aged  50  or younger. The display enlargement factor is set to 1 as shown in the display scale table of  FIG. 20 . When the driver is female aged  41  or older, the screen in  FIG. 26  is displayed instead of the screen in  FIG. 25 . The circumference information window  52  in  FIG. 26  is enlarged twice as large as that in  FIG. 25 .  
      The example in  FIG. 26  displays an enlarged version of the circumference information window  52 . When the display positions of the map window  46  and the vehicle information window  50  are unchanged, these windows are hardly viewed. To solve this problem, the display positions of the windows  46  and  50  are moved so that these windows overlap with the topmost circumference information window  52  as hardly as possible.  
      When the topmost window is manipulated, the sixth embodiment temporarily inhibits a change in the order of overlapping windows. While a window is being manipulated, the sixth embodiment prevents that window from being hidden from the other windows. When the driver is assumed to be tense, the embodiment also inhibits a change in the order of overlapping windows. When the driver is too tense to control driving, a change in the order of overlapping windows may draw the driver&#39;s attention to the display screen and may cause careless driving. The embodiment can decrease such possibility.  
     Seventh Embodiment  
      The following describes a seventh embodiment of the invention.  FIG. 27  is a block diagram showing the construction of a display apparatus  500  according to the seventh embodiment. The display apparatus  500  differs from the display apparatus  10  according to the first embodiment in that the former further includes a state information reception unit  502 , an error state determination unit  504 , an error information display determination unit  506 , and a memory unit  508 . As another difference, the display unit  510  is provided under a windshield as shown in  FIG. 28  and is approximately as long as the vehicle compartment in the width direction. The display unit  510  represents a liquid crystal display and includes many display areas  511  through  528 . The display areas  511  through  528  display various information such as a speedometer, a fuel gauge, a tachometer, an image around the vehicle, a traffic regulation indication, a route guidance indication, traffic congestion information, and vehicle anomaly information as needed. It is possible to vary the number of display areas  511  through  528 , their sizes, and types of information displayed on them as needed.  
      The state information reception unit  502  receives predetermined information out of the information output from the information collection unit  100 . The received information is used to determine a vehicle error such as a vehicle failure. For example, the state information reception unit  502  receives the same information as for the vehicle information processing unit  16 . In addition to the information collection unit  100  as shown in  FIG. 2 , there are further provided a battery voltage sensor, an exhaust gas sensor, an air suspension sensor, a water temperature sensor, an engine oil sensor, and a boost sensor (boost pressure sensor). The state information reception unit  502  may receive values output from these sensors.  
      The error state determination unit  504  determines a vehicle error based on the information received by the state information reception unit  502 . When the error state determination unit  504  determines the vehicle error, the error information display determination unit  506  supplies the control unit  30  with specified screen data for notifying the error content. Based on a signal from the error information display determination unit  506 , the control unit  30  displays a determination result from the error state determination unit  504  on the corresponding display areas  511  through  528  in the display unit  510 .  
      For example, the display area  523  displays a determination result from the error state determination unit  504 . It is difficult to find where urgent information such as a vehicle anomaly is displayed on the many display areas  511  through  528  of the display unit  510  as shown in  FIG. 28 . When the error state determination unit  504  determines the vehicle anomaly, the error information display determination unit  506  highlights a display mode more intensely than a case where no vehicle anomaly is determined. In this case, the error information display determination unit  506  references an error information priority table stored in the memory unit  508  to determine the display mode.  
       FIG. 29  is a flowchart showing processes in the state information reception unit  502 , the error state determination unit  504 , and the error information display determination unit  506 . In  FIG. 29 , Step S 100  corresponds to the process in the state information reception unit  502 . Step S 110  corresponds to the process in the error state determination unit  504 . Step S 120  and later correspond to the process in the error information display determination unit  506 .  
      At Step S 100 , the state information reception unit  502  acquires (receives) sensor information from a specified sensor. At Step S 110 , the error state determination unit  504  uses the sensor information acquired at Step S 100  to determine a vehicle anomaly. When the result of the determination at Step S 110  is negative, Step S 100  and later are repeated.  
      When the result of the determination at Step S 110  is affirmative, the process proceeds to Step S 120 . At Step S 120 , the error information display determination unit  506  blinks the background of a specified display area (display area  523  in this example) for displaying the vehicle anomaly.  
       FIG. 30  is a display example of the display area  523 . The display area  523  includes small display areas for showing a title display area  530  and various icons such as a browser icon  531 , a mail icon  532 , a setup icon  533 , and an abnormal information icon  534 . In the display area  523 , a part other than the small display areas is the background. At Step S 120 , the background blinks.  
      At Step S 130 , the error information display determination unit  506  audibly indicates the position of the display area  523 . At Step S 140 , the error information display determination unit  506  highlights the abnormal information icon  534 .  FIG. 30  shows an example of the display area  523  after execution of Step S 140 . In  FIG. 30 , the abnormal information icon  534  is displayed larger and brighter than the other icons  531  through  533 . In a normal state where no vehicle anomaly is determined, the abnormal information icon  534  is displayed with the same size and brightness as the other icons  531  through  533 . The highlight mode is not limited to the example in  FIG. 30  and may be provided as changing the color, blinking, or changing the display frame.  
      Since the abnormal information icon  534  is highlighted at Step S 140 , the driver can be notified that a vehicle anomaly is detected. The embodiment further blinks the periphery of the abnormal information icon  534  and audibly indicates the display position. The driver can be fast notified of the vehicle anomaly and the display position of the abnormal information icon  534 .  
      The error information display determination unit  506  highlights the abnormal information icon  534  at Step S 140  and then determines at Step S 150  whether or not the abnormal information icon  534  is selected. To perform this determination, a touch switch is integrated with the display unit  510  and detects that the driver presses the abnormal information icon  534 .  
      When the result of the determination at Step S 150  is negative, the process at Step S 150  is repeated. When the result of the determination at Step S 150  is negative, the error information display determination unit  506  displays the next screen at Step S 160 .  FIG. 31  shows a display example in the display area  523  after execution of Step S 160 .  
      The display area  523  in  FIG. 31  displays icons indicative of abnormal information corresponding to respective systems. The icons include the engine system information icon  540 , an electric system information icon  541 , a suspension system information icon  542 , and an exhaust system information icon  543 . The exhaust system information icon  543  is displayed in a display mode indicating that the exhaust system is normal. When no error is determined, the other icons  540 ,  541 , and  542  are also displayed in the same size and brightness as the exhaust system information icon  543 .  
      In  FIG. 31 , however, the engine system information icon  540 , the electric system information icon  541 , and the suspension system information icon  542  are displayed in a mode different from the display mode for the exhaust system information icon  543 . That is, the icons  540 ,  541 , and  542  are displayed larger and brighter than the exhaust system information icon  543 . This indicates that anomalies are detected in the engine, electric, and suspension systems.  
      The icons  540 ,  541 , and  542  are sized based on the error information priority table stored in the memory unit  508 .  FIG. 32  exemplifies the error information priority table. The error information priority table in  FIG. 32  defines the priority and the size of the icon corresponding to the abnormal system. The engine system has the highest priority and uses the largest icon. The priority decreases in the order of the suspension, exhaust, and electric systems. When an anomaly is determined, the icon size decreases in this order.  
      Referring back to  FIG. 29 , the error information display determination unit  506  displays the display area as shown in  FIG. 31  at Step S 160 . At Step S 170 , the error information display determination unit  506  then determines whether or not the icon indicative of anomaly detection is selected. (That is, such icon is one of the engine system information icon  540 , the electric system information icon  541 , and the suspension system information icon  542  in the example of  FIG. 31 .)  
      When the result of the determination at Step S 170  is negative, the process at Step S 170  is repeated. When the result of the determination at Step S 170  is affirmative, the error information display determination unit  506  uses a predetermined risk determination table to determine the risk of all anomaly contents defined for the system indicated by the selected icon at Step S 180 . The risk determination table classifies anomaly contents into (1) anomaly immediately affecting running, (2) anomaly not immediately affecting running, and (3) parts replacement.  
      After the risk determination at Step S 180 , the process proceeds to Step S 190 . At Step S 190 , the display area  523  displays the next screen that highlights a specific anomaly content corresponding to the risk of the anomaly content.  FIG. 33  shows a display example of the display area  523  corresponding to Step S 190  when the engine system information icon  540  is selected.  
      The example in  FIG. 33  shows three engine system anomalies correspondingly to the top, middle, and bottom. The top corresponds to the above-mentioned anomaly (1). The middle corresponds to the above-mentioned anomaly (2). The bottom corresponds to the above-mentioned anomaly (3). The anomaly (1) is indicated with a letter double as large as that for the anomalies (2) and (3). The anomaly (2) is indicated in boldface. The risk may be indicated in a variety of colors in addition to or instead of the size and thickness of letters. For example, the anomaly (1) may be indicated in red, (2) in yellow, and (3) in blue.  
      The driver may take specified action for the anomaly or repair or replace parts so as not to detect the anomaly. In such case, the display content of the display area  523  returns to the normal display content. (That is, the screen in  FIG. 30  will contain the abnormal information icon  534  resized to the other icons in  FIG. 30 .)  
      (Modifications)  
      For example, the sixth embodiment allows the user to input the driver characteristics information. Further, a storage apparatus may be used to store the driver characteristics information about multiple driver candidates. A camera may be used to capture a driver&#39;s image to identify the driver. It may be preferable to determine the actual driver&#39;s driver characteristics information from the driver characteristics information about multiple driver candidates stored in the storage apparatus. The driver characteristics information may further include a driving experience as well as the above.  
      The fourth embodiment may use the storage apparatus to store the relationship between the driver characteristics information and the maximum display count. The driver characteristics information can be determined based on a user&#39;s input operation as described in the sixth embodiment. Alternatively, the driver characteristics information can be determined from the driver characteristics information about multiple driver candidates based on the image recognition as mentioned above. The maximum display count may be configured according to the determined driver characteristics information and the above-mentioned relationship.  
      The seventh embodiment determines the driver&#39;s tense state based on a change in the heart rate. It may be preferable to determine the driver&#39;s tense state based on a change in the blood pressure instead of or in addition to the heart rate.  
      Each or any combination of processes, steps, or means explained in the above can be achieved as a software unit (e.g., subroutine) and/or a hardware unit (e.g., circuit or integrated circuit), including or not including a function of a related device; furthermore, the hardware unit can be constructed inside of a microcomputer.  
      Furthermore, the software unit or any combinations of multiple software units can be included in a software program, which can be contained in a computer-readable storage media or can be downloaded and installed in a computer via a communications network.  
      It will be obvious to those skilled in the art that various changes may be made in the above-described embodiments of the present invention. However, the scope of the present invention should be determined by the following claims.