Navigation device

Abstract: In a navigation device, the map information read by a map information reproduction device (4) is displayed on the display device (5), and an intersection which the vehicle approaches is enlarged. The enlarged display of an intersection is continued if the speed of the vehicle is not more than a predetermined value even when the vehicle is moving away from the intersection. A place at which the classification of road changes may be treated like an intersection. An exclusion key (95) may be provided for designating, during simulation, an intersection to be excluded from the enlarged display. During simulation, the vehicle may be slowed, or stopped when it is near an intersection to permit full examination. A multi-disk reproduction device (4) may be used to selectively reproduce map information from a first disk (41) for storing map information of a first area, and a second disk (42) for storing map information of a second area. If, in the state in which the first disk is selected, the vehicle moves to the second area, the disk storing map information of the second area is automatically selected.

Description: BACKGROUND OF THE INVENTION The present invention relates to a navigation device for performing enlarged display of an intersection. The present invention also relates to a navigation device for performing guidance of a route. It is important for a navigation system mounted on a vehicle to provide information about intersections. As one of the methods of providing this information, enlarged display of an area near the intersection (fork) a vehicle is approaching is disclosed in Japanese Unexamined Patent Publication 4-127015. In this method of performing enlarged display of the intersection, when a vehicle approaches to within a predetermined distance of the intersection, the enlarged display of the intersection is initiated, and when the vehicle moves away from the intersection, the enlarged display is terminated. However, when a current position detector position measurement errors, the enlarged display may intermittently appear and disappear while a vehicle is making a temporary stop near a boundary at which the enlarged display of the intersection is to be initiated. In the case of GPS position detector by which radio waves are received from the GPS (Global Positioning System) satellites, the error in the position measurement may lead to an error in the speed measurement of substantially two kilo meters per hour at the maximum. For this reason, when a vehicle makes a temporary stop due to a traffic jam near a boundary at which the enlarged display is to be initiated, the enlarged display may intermittently appear and disappear. This is not satisfactory. Further, when there is the error in the position measurement, even while the vehicle is making a stop at the intersection, erroneous determination that the vehicle is moving away is sometimes made. It sometimes happens, for example, when an enlarged view of an intersection is not provided while waiting for the traffic lights to change. Moreover, the enlarged display of an intersection (giving details of the intersection) is carried out automatically with the movement of the vehicle, and the information is not obtained readily when the user desires it at other times. Another navigation device disclosed in Japanese Utility Model Kokai Publication 5-84975 has a route guidance function. The user sets a planned route by entering a starting point, a destination, and one ore more points on the route as required prior to the actual travel, and display of the set route, guidance for turning by voice, and the like are performed during the actual travel. In addition, recognition or examination of the route by means of simulation can also be performed. Another navigation device disclosed in Japanese Patent Kokai Publication 5-53500 combines the function of enlarged display of an area near an intersection (fork) with the function of route guidance. However, there are places where classification of road changes. In Japan, for example, the roads are classified into eight classifications, namely: automotive expressways, metropolitan expressways, national highways, principal local roads, prefectural roads, standard roads having a width of 5.5 m or more, other roads (narrow roads), and ferry routes. The place where this classification of roads changes may be a boundary of prefectures or cities, a boundary at which the restrictions of the road traffic law such as one on speed limits change, or a boundary at which a condition of a road such as the width of a road, the number of lanes, or the type of surface changes. Since a navigation device for notifying or emphasizing the classification of roads was not available in the past, the above-mentioned boundary could not be known in advance. Another problem is that enlarged display is performed for all the intersections. However, enlarged display of an intersection which the user does not want only reduces the useful range of the display screen. A further problem is that the time for which the enlarged display is made during simulation is sometimes insufficient for the recognition or examination of an intersection, particularly when the vehicle is moving fast. Thus, intersections which need not be enlarged are also enlarged, and intersections which need to be enlarged for recognition or examination cannot be enlarged for a sufficient time. SUMMARY OF THE INVENTION An object of the invention is to prevent erroneous termination of enlarged display of an intersection due to an error of a position detector while the vehicle is making a temporary stop near the intersection. According to the invention, there is provided a navigation device comprising: a current position detector (3) for detecting a current position of a vehicle; a map information reproduction device (4) for reading map information from a medium which stores the map information; a display device (5); and a control circuit (1) for causing the map information read by the map information reproduction device (4) to be displayed on the display device (5), initiating enlarged display of an intersection of which the vehicle approaches to within a predetermined distance, and terminating the enlarged display when a predetermined condition has been satisfied; wherein the control circuit (1) continues the enlarged display of the intersection if the speed of the vehicle is not more than a predetermined value, even though the predetermined condition has been satisfied. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the pertinent part of a first embodiment of the present invention; FIG. 2 is a flow chart showing the route setting operation of a control circuit according to the first embodiment ; FIG. 3 is a flow chart showing the simulating operation of a control circuit according to the first embodiment; FIG. 4 is a flow chart showing the enlarged display operation of an intersection by a control circuit according to the first embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing the pertinent part of a first embodiment of the present invention. A control circuit 1 operates according to the programs stored in a ROM 2 and exercises control over the entire device. A GPS position detector 3 receives radio waves from the GPS satellites, measures the current position, and supplies the measurement data to the control circuit 1. A CD-ROM reproduction device 4 reads map information from a CD-ROM on which map information is written and supplies it to the control circuit 1. A display device 5 displays a map, the current position, and the like under the control of the control circuit 1. A voice generator 6 generates voice for guiding the route, etc. under the control of the control circuit 1. A brake detector 7 is connected to the parking brake line of a vehicle, detects whether or not the parking brake is operating, and supplies the result to the control circuit 1. Reference numeral 8 indicates a RAM, which stores data needed for the operations of the control circuit 1 such as, for example, a current position (81), a position of the user's home indicated by reference numeral (82), a starting point (84), the position of a destination (85), and a point on the route (86) of a planned route (83). An input device 9 includes a scroll key 91 for scrolling the display in eight directions, an execution key 92 for executing data output to the control circuit 1, a route setting key 93 for setting a planned route, a simulation key 94 for directing simulation, an exclusion key 95 for excluding an undesired intersection from the enlarged display during the simulation, a user's home key 96 for designating the user's home as the starting point or the destination, and an intersection display key 97 for directing enlarged display of an intersection even when the vehicle is not coming closer to it. The fundamental operation of the system, i.e., reception of GPS radio waves and display of the current position of a vehicle on the map is next described. The detection of the current position is performed by the GPS position detector 3. When the power switch of the navigation device is turned ON for the first time, it takes several minutes to detect the position. However, when the position is detected continuously, new positional data is obtained at every second. After receiving new positional data, the control circuit 1 stores this data in the current position storage region 81 in the RAM 8 and updates the data. Then, the control circuit 1 updates the current position on the map displayed on the display device 5. Before the vehicle starts moving, it often happens that the current position is not located on the road due to an error of the GPS. When the vehicle begins moving, the distances to respective roads taking account of the moving direction are calculated, and by comparing these, one of the roads which the vehicle is most likely to be on is selected, and the data representing the position of the vehicle as stored in the RAM 8 is corrected to represent this position on the selected road, and the indication of the position of the vehicle on the display is moved onto the selected road. This operation is called map-matching. Next, the planned route setting operation is described. FIG. 2 is a flow chart showing the operation of the control circuit 1. When the route setting key 93 is depressed (S1), the control circuit 1 displays on the display device 5 a message prompting input of the starting point, such as "Enter the starting point." and a cross-shaped cursor representing the starting point (S2). Then, the control circuit comes into a waiting state in which it waits for input by the execution key 92, the user's home key 96, and the scroll key 91 (N at S3, N at S4, and N at S5). When the user's home key 96 is depressed, the position of the user's home which has been stored in advance by the input of the user is read from the RAM 8, the user's home is displayed (S6), and the position of the user's home is stored in the starting point storage region 84 in the RAM 8 (S7). When the starting point is not at the user's home, the display is scrolled by the operation of the scroll key 91 and the cursor is moved to the position which is desired to be the starting point (Y at S5, S8), and the execution key 92 is depressed (Y at S3). Then, the control circuit 1 stores in the starting point storage region 84 in the RAM 8 the position of the cursor at the time when the execution key 92 is depressed (S7). After the operation of S7, the control circuit 1 displays a message prompting the input of the destination, such as "Enter the destination." and the cross-shaped cursor representing the destination onto the display device 5 (S9). Then, in the manner similar to that with the input of the starting point (S3 - S7), using a one-touch operation by means of the user's home key 96 or the scroll operation, the designated position is stored in the destination storage region 85 (S10 - S15). Then, the control circuit displays a query as to whether or not input of one or more points on the route between the starting point and the destination is required. If it is required, the control circuit performs the process of the point on the route input and stores the point on the route onto the storage region of the point on the route in the RAM 8 (S16, S17). Next, the simulation, which is an operation for recognizing (or examining) the set route, is described. FIG. 3 is a flowchart showing the operation of the control circuit 1. When the simulation key 94 is depressed (Y at S20), the planned route 83 stored in the RAM 8 is read out, and the intersections in this route are detected (S21). The places at which the classification of the road changes are treated in the same way as the intersections (S22). This classification of the roads is written on the CD-ROM, and roads are classified into eight classes: automotive expressways, metropolitan expressways, national highways, principal local roads, prefectural highways, standard roads having a width of 5.5 m or more, other roads (narrow streets), and ferry routes. The place at which the width of a road changes is treated like an intersection. Next, a vehicle is subject to a simulated travel from the starting point to the destination at a predetermined speed. It is checked whether there is an intersection to which the vehicle is coming closer and whether it is within a predetermined distance. That is, it is checked whether to select the mode of enlarged display of the intersection (S23). If the enlarged display mode is not selected, the display is continued without enlargement and without changing the vehicle speed (S24), and the procedure proceeds to S29. If the enlarged display is selected, the enlarged display is performed, and the vehicle speed is lowered (S25, S26). If the exclusion key 95 is depressed, a flag indicating the exclusion is set for the intersection (or the places where the classification of road changes) being displayed (S27, S28). The intersection with this flag being set will not be displayed in the enlarged state during actual travel. Further, it is checked whether or not the parking brake is operating. While the parking brake is not operating, the simulation is interrupted (S29 - S31). The above-mentioned operations are performed until the vehicle reaches the destination (S32). In this way, the time for the recognition or examination of the intersection can be made sufficiently long without being restricted by the normal speed of the vehicle. Moreover, this gives the user sufficient time for consideration as to whether the enlarged display is to be effected for the intersection in question during actual travel (whether to designate the intersection as one which does not require enlarged display during the actual travel). Next, the operations during the actual travel of a vehicle are described. FIG. 4 is a flowchart showing the operations of the control circuit 1. The control circuit 1 reads the current position from the current position storage region 81 in the RAM 8 (S40). Based on the position which has been read, intersections which lie ahead in the route are detected (S41). The places at which the classification of the roads is changed are added to the intersections (S42), and the intersections (or the places at which the classification of road changes) which have been excluded from the enlarged display during the simulation are excluded (S43). If there are intersections obtained in this way (Y at S44), the intersection that lies ahead and is the closest to the current position is set to the intersection to be displayed in the enlarged state (S45). The current position is read again, and the distance to the intersection is calculated and displayed on the display (S46, S47). Then, it is checked whether the distance to the intersection which has been set is within 300 meters (S48), whether the intersection display key 97 is depressed (S49), and the intersection which lies ahead has been manually scrolled up to the predetermined central region on the display (S50). If all of the answers are NO, the procedure is returned to 546. When the distance to the intersection which has been set is within 300 meters at S48, the enlarged display of the intersection is performed (S51). Thereafter, it is checked whether the vehicle is moving away from the intersection which has been set at not less than five kilometers per hour (S52). If the answer is "NO", the procedure is returned to S46. If the answer is "YES", the procedure is returned to S40. When the intersection display key 97 is depressed at S49, the distance to the intersection which has been set is reported by the voice generator 6 (S53), the enlarged display of the intersection is performed for a predetermined time period (S54), and the procedure is returned to S46. When the intersection which lies ahead is manually scrolled up to the predetermined central region on the display at S50, the distance to the intersection which lies ahead is reported by the voice generator 6 (S53), the enlarged display of this intersection is performed for a predetermined time period (S54), and the procedure is returned to S46. As described above, enlarged display is performed for a place at which the classification of road changes as well as an intersection (fork). That is, a place where the width of the road changes, for example is also treated like an intersection. The current position detector according to this embodiment uses the GPS radio waves. This has an an error in the position measurement leading to an error in speed measurement of substantially two kilo meters at the maximum. For this reason, until now, while a vehicle is making a temporary stop near a boundary at which the vehicle initiates the enlarged display of the intersection, the enlarged display may intermittently appear and disappear. In addition, it sometimes happens that, when one wishes to look down at the enlarged diagram of an intersection while waiting for the traffic lights to change, he cannot do so because enlarged display is not performed due to erroneous recognition that the vehicle is moving away from the intersection. According to the present invention, enlarged display of an intersection is terminated when a vehicle is moving away from the intersection at not less than a predetermined speed (five kilometers per hour), and an erroneous termination of the enlarged display of the intersection due to an error of the position detector can be thereby prevented. Although the user's home key 96 is used for setting the starting point or the destination in the above-mentioned embodiment, it may also or alternatively be used for setting a point on the route. According to the embodiment described, erroneous termination of the enlarged display of an intersection due to an error of the position detector can be prevented. Moreover, by depressing a predetermined key associated with the information about an intersection or moving the intersection to a predetermined position on the screen by means of a cursor, enlarged display of the intersection and notification of a distance to the intersection by voice can be carried out. That is, detailed information about an intersection can be given when the user desires it. Furthermore, enlarged display of a boundary at which classification of roads changes is performed. Accordingly, information about a boundary of prefectures or cities, a boundary at which the restrictions of the road traffic law such as one on speed limits change, and a boundary at which a road condition such as the road width, the number of lanes, or the type of surface changes can be obtained advance. In addition, enlarged display is effected only for the intersections which the user wants to examine in detail. For this reason, the useful range of the display screen will not be reduced due to enlarged display of undesired intersections. During the actual travel, the display must follow the current position of a vehicle, so that the time for the enlargement of an intersection is limited. During the simulation, this limitation is not imposed. Thus, by lowering the moving speed of or by temporarily stopping the vehicle during the enlarged display of the intersection, in a simulation, the time for the enlargement of the intersection can be made sufficiently long. This gives the user sufficient time for consideration as to whether the enlarged display is to be effected for the intersection in question during actual travel (whether to designate the intersection as one which does not require enlarged display during the actual travel). In addition, setting of the user's home position can be performed by depressing the user's home key, i.e., without moving the cursor.

Claims: A navigation device comprising: a current positon detector (3) for detecting a current position of a vehicle; a map information reproduction device (4) for reading map information from a medium which stores the map information; a display device (5); and a control circuit (1) for causing the map information read by the map information reproduction device (4) to be displayed on the display device (5), initiating enlarged display of an intersection of which the vehicle approaches to within a predetermined distance, and terminating the enlarged display when a predetermined condition has been satisfied; unless the speed of the vehicle is not more than a predetermined value. The device according to claim 1, wherein said predetermined condition is that the vehicle moves away from the intersection farther than a predetermined distance. The device according to claim 1 or 2 wherein said control circuit (1) terminates the enlarged display when the vehicle moves at a speed greater that a predetermined speed, after pasing the intersection; or when a predetermined time has passed after the vehicle has passed the intersection.

Inventors: ABE YUICHI, ABE, YUICHI, Abe, Yuichi, c/o Tottori Sanyo Electric Co., Ltd.
Applicants: SANYO ELECTRIC CO, TOKYO SANYO ELECTRIC CO, SANYO ELECTRIC CO. LTD, TOTTORI SANYO ELECTRIC CO., LTD.
Application year: 1997
Main classification: G01C21
IPC codes: G08G1, G01C21