JPH11174952A - Reading method for map data in lookahead and map scrolling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To read a current map sheet is lookahead and eight circumferential map sheets by effectively utilizing an idle time of a CPU. SOLUTION: This method is a reading method for map data in lookahead of a navigation device which prereads the center map sheet corresponding to the area that a vehicle belongs to and adjacent map sheets corresponding to peripheral areas of the above area. A prepared thread for reading the map data in lookahead is prepared in a program memory 32 and give low priority, an idle time of the CPU 20 is monitored, and the preread thread is started in the CPU idle time to read the current map sheet and circumferential map sheets out of a map recording medium 10 and store them in a main storage device 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prefetching method of map data and a map scrolling method, and more particularly to a prefetching method of map data and a map in a navigation device for displaying a map around a vehicle position on a screen as the vehicle moves. Regarding scrolling method.

[0002]

2. Description of the Related Art A navigation device that provides guidance for driving a vehicle so that a driver can easily reach a desired destination can be obtained by detecting the position of the vehicle and using a map recording medium (for example, a CD).
-ROM) to read map data around the vehicle position,
The map image is drawn on the display screen, and the vehicle position mark is also drawn. In such a navigation device, the vehicle position mark is fixedly displayed at a predetermined position on a display screen, and the map is usually scrolled according to the movement of the vehicle, so that the map around the vehicle position can always be seen at a glance. . For this reason, in the navigation device, it is necessary to read the map data corresponding to the vehicle position from the map recording medium in a timely manner so that the map can be smoothly scrolled.

[0003] Map data is created by dividing a map into leaf units and recorded and managed on a map recording medium. This leaf is sufficiently larger than the size of a screen that can be generally displayed. In such a method of loading only data for one map leaf into the memory, new map data needs to be updated when the vehicle approaches the boundary of the current map leaf. FIG. 18 is an explanatory diagram of such map data update timing, where 4 is a figure corresponding to the area to which the vehicle currently belongs, 0 to 8 (except 4) are adjacent figures around, and WD is one screen around the vehicle. Is a window according to the size of. Window W according to vehicle movement
When D reaches the border of the adjacent map, new map data needs to be updated. However, in such a map data updating method, it takes time to update the map data in a portion beyond the boundary, the map scroll becomes discontinuous, and the screen appears to flicker.

Therefore, a method is conceivable in which an adjacent area where a vehicle enters next is predicted, and map data of an adjacent map is prefetched from a map recording medium before the vehicle actually enters the adjacent area. For example, a method in which the road is extended in the direction in which the vehicle is currently traveling to read ahead the adjacent map leaf that is in contact with the boundary of the center map leaf, or dividing the center map leaf into four triangles diagonally, A method of predicting a corresponding adjacent map based on whether the own vehicle is running inside the vehicle and prefetching the map is conceivable. However, the road network in Japan is rarely the same as the United States, where vertical and horizontal roads are laid in a grid pattern.
Most roads are distorted even in relatively narrow areas. In other words, even if an attempt is made to predict the next figure leaf using the method described above, reliable prediction cannot be performed. If the prediction is erroneous, it is necessary to perform another prediction each time. Will prefetch most of the adjacent map leaves. In this case, a large amount of calculation time required for the prediction is wasted, and the efficiency is low.
U) reduces the throughput.

[0005] In computer systems, there is a bias in the timing at which the CPU executes arithmetic processing based on a program, and frequent arithmetic operations and idle idle time are mixed. In the map scroll display of the navigation device, the time during which the CPU is actively calculating is said to be 30% of the total CPU time, and the remaining 70% is the idle time, and the CPU is not active. On the other hand, in the map scroll display, the time for reading the map data from the map recording medium becomes a bottleneck, and it feels physically slow. This is a CD
-The speed at which the map data is read into the main memory by accessing the map recording medium such as the ROM is lower than that of the hard disk or the like.

[0006]

As described above, in the conventional map data look-ahead method, the CPU processing is useless,
In addition, there is a problem that the CPU has a long idle time.
Further, in the conventional map scroll method, the map scroll is discontinuous, and there is a flicker problem on the screen. Furthermore, in the conventional map scrolling method, the data update in the map scroll display is very heavy compared to other processes, and the execution of other important processes is delayed due to a long data update time, and the request from the user cannot be accepted, There was a problem that the execution speed of the route search was extremely reduced.

Therefore, an object of the present invention is to make use of the idle time of the CPU effectively without predicting an adjacent map, so that the current map and eight surrounding maps can be read ahead in the idle time. is there. Another object of the present invention is to provide a data update thread, a map drawing thread, and a screen display thread that can be executed by parallel processing, dynamically assign the priority of these threads according to the situation, and
The change is to enable smooth map scrolling. Another object of the present invention is to provide a map rendering algorithm using pre-reading and dynamically assignable priorities so that when the load on the CPU is not so large, data is updated in a thread set to a low priority,
It is an object of the present invention to avoid a large load temporarily generated at the time of updating data for redrawing so that execution of other important processing is not delayed.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided a map data of a navigation apparatus for prefetching, in a memory, a central map leaf corresponding to an area to which a vehicle belongs and an adjacent map leaf corresponding to a peripheral area of the area. In the prefetching method of (1), a prefetching thread for prefetching the map data is prepared and the priority of the prefetching thread is lowered, (2) the idle time of the CPU is monitored, and (3) the prefetching is performed at the idle time of the CPU. This is achieved by a prefetching method in which a thread is started, and (4) a prefetching thread reads a center map leaf and peripheral neighboring maps from a map recording medium and stores them in a memory. According to such a look-ahead method, it is possible to effectively use the idle time of the CPU without predicting the adjacent map, and to read ahead the center map and the peripheral map at the idle time.

According to the present invention, there is provided a map scrolling method for a navigation device for displaying a map around a position of a vehicle on a screen as the vehicle moves. (1) Map data is read from a map recording medium and a map buffer is read. Data update control for updating data stored in the map buffer, map drawing control for generating a map image based on the map data stored in the map buffer and drawing it in the VRAM, VRA
A data update thread, a map drawing thread, and a screen display thread are prepared, which can execute a screen display control for cutting out a map image around the vehicle position from M and displaying the screen image on a screen in parallel. (2) Priority of these threads Before the data update is completed, the priority of the data update thread among the above threads is made highest, and after the data update is completed and before the map drawing is completed, the priority of the map drawing thread is made the highest, and the map drawing is performed. After the completion and before the completion of the screen display, the priority of the screen display thread is set to the highest priority, and (3) the map scrolling method is executed by executing the thread having the highest priority in the map scroll processing.

According to this method, smooth scrolling can be performed by giving the thread which plays the most important role at each stage of the map scroll control the highest priority. By using the concept of the thread priority, the car navigation developer does not need to perform the scheduling based on the careful load calculation between the controls (data update control, map drawing control, screen display control). In addition, (1) a look-ahead thread is prepared for eight adjacent figures adjacent to the center figure corresponding to the area to which the vehicle belongs, and (2) a look-ahead thread of the adjacent figure that the vehicle enters enters the data update thread. (3) For the map leaf adjacent to the map leaf that the vehicle has entered, the map data is read ahead by a look-ahead thread that has a lower priority set than the data update thread, the map drawing thread, and the screen display thread. By doing so, the data of the figure into which the vehicle has entered can be read with the highest priority, and as a result, a map image around the vehicle position can be displayed at high speed, and the map can be scrolled smoothly.

Further, by lowering the priority of a look-ahead thread for preparing data necessary for map scrolling,
Pre-reading of map data is performed when the load is light, and as a result, it is possible to prevent the delay of other processing due to a temporary large load at the time of redrawing, greatly increasing the efficiency of the entire system. Can be improved. In this case, (1) the center map leaf corresponding to the area to which the vehicle belongs is divided into four parts, (2) which divided area the center point displayed on the screen belongs to is determined, and (3) Set the priority of the prefetch thread of the adjacent map leaf according to the area adjacent to the divided area to be higher than the priority of the prefetch thread of the other adjacent map leaf, and (4) prefetch ahead of the adjacent map leaf having the higher priority. According to this configuration, since the adjacent map having a high possibility of the vehicle entering next can be read ahead of time, the map image around the vehicle position can be reliably displayed, and the map can be smoothly scrolled. Further, by pre-reading only the adjacent map leaf other than the adjacent map leaf already read in the map buffer, the load of the pre-read can be reduced, the time required for the pre-read can be reduced, and the center map leaf and the eight peripheral areas can be surely read. Adjacent maps can be read ahead and stored in the map buffer.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Pre-reading of map data (first
Embodiment) (a) The drawing method of the present invention The Java language is used as an implementation language, and a thread with a low priority (for example, the lowest priority) is automatically activated in the idle time of the CPU. Is added. As a result, a prefetch thread that automatically prefetches map data at the idle time of the CPU and buffers the map data in the main memory is realized. The threads execute processing in parallel. Since the look-ahead thread has a low priority, even if it starts, it has little effect on the responsiveness of the system.

(B) Map data management As shown by the solid line in FIG. 1A, 3 × 3 (= 9) sheets consisting of a center figure leaf and adjacent figures are numbered 0 to 8, and The map data is managed using the leaf numbers. That is,
Hashtables with leaf numbers 0 to 8 are provided, and map data is managed by the Hashtable. For this reason, when the vehicle moves and enters the adjacent map, the map number needs to be changed.
For example, as shown in FIG. 1A, when the own vehicle moves and enters the leaf of the adjacent leaf number 7 directly below the central leaf, the central leaf is updated to the leaf of the adjacent leaf number 7. Is done. At this time, the original center leaf 4 is adjacent leaf number 1 as shown in FIG.
Figure leaves. In addition, the figure of the original adjacent figure number 3 becomes 0, 5 becomes 2, 6 becomes 3, 7 becomes 4, and 8 becomes 5. That is, when the vehicle moves and enters the leaf of the adjacent leaf number 7 immediately below the center leaf, it is necessary to change the old leaf number to the new leaf number as shown in FIG. In general, if the old leaf number of the leaf into which the vehicle has entered is C, the old leaf number of the leaf of interest is B, and the new leaf number of the leaf of interest is A, Formula A = B + (4-C) (1) is established. In the case of FIG. 1 (c), the new figure leaf number A is obtained by calculating the equation (1) with C = 7.

By the way, as shown in FIG. 1 (a), when the own vehicle enters a leaf having an adjacent leaf number 7 immediately below the center leaf, an old map (map data) which can be used even after entering. The leaf numbers are 3,4,5,6,7,8, and the new leaf numbers (map data) that must be read ahead after entering are 6,
7, 8 (FIG. 1 (d)). That is, if equation (1) is applied to the old map numbers 3, 4, 5, 6, 7, and 8 and the map numbers are changed to the new map numbers, it is not necessary to newly read map data. It is sufficient to pre-read only the figures 6, 7 and 8 (map data). If the relationship shown in FIG. 1D is known, the efficiency of the transfer process to the new leaf number and the prefetching process can be improved. Accordingly, an array AR1 of the old leaf numbers of the leaves (map data) that can be used even after the entry and corresponding to the old leaf number C of the adjacent leaf into which the vehicle enters, Map data)
Of the new map leaf number AR1
To reduce the computational cost of changing operations. FIG. 2 shows C and AR
1 is a table showing the relationship C = {AR1}, {AR2}.

FIG. 3 is an explanatory diagram of a hash table.
In the state shown by the solid line in FIG.
It is in response to the map mesh numbers 0-8 as shown in FIG. 3 (a) and associates the G ₀ ~G ₈ as the map data u. In this state, when the own vehicle enters the leaf of the adjacent leaf number 7 immediately below the center leaf, the hash table HT is updated as shown in FIG. That, and associates the G ₃ ~G ₈ as the map data u corresponding to Shinzuha number 0-5. Also,
Since the map data corresponding to the new leaf numbers 6 to 8 has not been read out to the main storage device, u = 0.

(C) Main Configuration of Navigation Device FIG. 4 is a functional configuration diagram of a drawing system of the navigation device. 10 is a map recording medium (for example, a CD-ROM) for storing map data. CD-R based on
A map readout control unit that reads out predetermined map data from the OM 10 and calculates a screen center position on a map displayed on a display screen according to the position of the vehicle;
A map buffer for storing map data read from the OM, 13 a map drawing unit for generating a map image using map information stored in the map buffer, 14 a VRAM for storing a map image, 15 Is the map reading control unit 11
A map cutout control unit that cuts out a map image for one screen from the VRAM 14 based on the screen center position input from the
6 is a display device, and 17 is a position measuring device for measuring the position of the own vehicle. Map reading control unit 11, map drawing unit 1
3. The map extraction control unit 15 is actually configured by a CPU (FIG. 5).

FIG. 5 is a block diagram of a navigation device having a CPU configuration, and the same parts as those in FIG. 4 are denoted by the same reference numerals. 10 is a map recording medium (CD-ROM), 14 is a VRAM, 16 is a display device, 17 is a position measuring device, and 20 is a processor (CP) for performing navigation control.
U), 21 are a CD-ROM control unit, 22 is a remote control interface unit, 23 is an external memory, and 24 is a bus.
In the CPU 20, 31 is an arithmetic processing hardware unit,
32 is a program memory (ROM) for storing various programs for navigation control (programs for route guidance control, map matching control, map scroll control, etc.), and 33 is a main storage device (RAM), which is a CD-RO.
It stores map data read from M, a hash table, and other processing results. The map scrolling program is programmed to perform map reading control, map drawing control, and map clipping control shown in FIG.

(D) Prefetch algorithm FIG. 6 is a flowchart of the prefetch control process of the present invention.
Is a main processing flow, and (b) is a processing flow of a prefetch thread. The priority of the look-ahead thread is set to the lowest, and the look-ahead thread is activated to perform the look-ahead only when the CPU becomes empty. Even if the priority of the prefetch thread is minimized, the idle time of the CPU is 70% of the total CPU time. Therefore, the map data of the adjacent map can be read from the CD-ROM 11 and stored in the main storage device 33 with a margin. .

The CPU 20 executes the main navigation process under the control of the management program, and monitors whether the CPU 20 is free (steps 101 to 102). If it becomes vacant, it is checked whether map prefetching is necessary, that is, whether the vehicle enters an adjacent area and map prefetching is necessary (step 103). If pre-reading is unnecessary because the vehicle has not entered the adjacent area, the process returns to step 101. On the other hand, if prefetching is necessary, a prefetch thread is started (step 1).
04), and thereafter wait for occurrence of a high-priority event (step 105). If a high-priority event occurs, that is, if the CPU becomes free, the prefetch thread is stopped (step 106) and the main processing is executed (step 101).

The prefetch thread is initialized when started (step 201). Next, it is checked whether or not the CPU is empty. If the CPU is not empty, a predetermined time (for example, 1 second) is waited, and the empty of the CPU is checked (steps 202 to 2)
03). If the CPU is vacant, that is, if the stop is not instructed, the hash table HT (FIG. 3) is referred to to identify the adjacent map to be pre-read, and the adjacent map is set to C.
The data is read from the D-ROM 10 and stored in the main storage device 33 (step 204). Thereafter, it is checked whether reading of all adjacent maps has been completed (step 205). If not completed, the processing from step 202 onward is repeated, and if reading of all adjacent maps has been completed, the pre-reading processing ends.

The following is a program of the algorithm of the look-ahead thread. (1). If (CPU is idle) (2). For (for adjacent figure u) u (3). If (read-ahead thread of adjacent figure u is not initialized) (4). Initialize the look-ahead thread for figure u (5). If (reading of map data for adjacent figure u is not finished) (6). Start look-ahead thread for figure u adjacent (7). Else (8) Stop prefetch thread (9). Wait 1 second In (1), it is checked whether the CPU has free time. When the CPU is idle, (2) to (6) are executed. First, it is checked whether or not the prefetch thread has been initialized for the corresponding eight adjacent figures (3). Initialize the prefetch thread if it has not been initialized
(Four). If the corresponding look-ahead thread has already been initialized and the look-ahead has not been completed yet (5), start the look-ahead thread and execute the look-ahead of the adjacent figure leaf.
(6). If there is no idle time in the CPU, the prefetch thread is suspended for one second.

In the above, the description has been made with emphasis on pre-reading (data updating) of map data. However, in the case of map scrolling, map drawing control and screen display control are necessary in addition to data update control. In the following, an embodiment will be described in which threads are prepared for these controls and they are processed in parallel.

(B) Parallel Drawing Control of Map Using Multithread (Second Embodiment) (a) Outline In a general map drawing method, a large load is temporarily applied to the CPU at the time of redrawing. As a result, not only redrawing but also performance of the entire system is reduced.
As a result, as a result, the screen flickers or the system goes down, and the operation from the user is temporarily stopped. In order to solve such a problem, it is effective to pre-read the map data of a portion required at the time of redrawing before redrawing is called, and this is described in (A). By the way, in order to draw a map on a screen, (1) update control of map data by prefetching (data update control), (2) drawing control of a map image in a VRAM (map drawing control), and (3) from a VRAM Control for reading a map image and displaying it on a screen (screen display control) is required, and it is necessary to coordinate these controls to efficiently scroll and display the map on the screen. Therefore, in (B), map scroll display is realized by parallel processing based on thread programming. Thread programming is for realizing parallel processing, and is supported by a multitask OS. In the following, a description will be given using a Java language that can easily set the priority of parallel processing.

When prefetching the map data during a time when the load on the CPU is relatively small (for example, idle time), for example, "how much calculation is required if this task and that task are performed at the same time ..." Thus, it is very difficult for a programmer to make a tight scheduling of CPU usage in advance. On the other hand, using the concept of thread priority, a task A
For the other task B, scheduling of CPU use is automatically performed only by giving a relative numerical value. The programmer only needs to specify the priority of the task without having to think about its execution scheduling. In other words, A can only use the CPU for 10 times as long as B by simply declaring A to be priority 10 and B to be priority 1. The present invention uses the above thread priorities, dynamically changes the priorities as necessary, and prefetches the map data at a low priority. Improve overall system performance.

(B) Drawing Method Using Multi-Threads To draw a map on a screen using map data in a navigation device (see FIG. 4), the following three steps are required. step 1: The map data is read from the storage medium 10 in which the map data is stored, and loaded into the memory (map buffer) 12 (data update). step 2: Off-screen processing so that the data loaded in the memory 12 can be displayed on the screen as a map. That is, a bit image map image is drawn in the VRAM 14 using the map data (map drawing). step 3: A map is displayed on the screen (screen) 16 using the image data drawn in the VRAM in step 2 (screen display).

Generally, the relationship between the processing costs of these steps is as follows: step 3 << step 2 <step 1 When comparing the processing time of step 1 and step 2, st
It has been confirmed by experiments that ep 1 requires about 1.5 times as long as step 2. Also, compared to step 1 and step 2
Step 3 requires negligible processing time.
As described above, instead of executing the above three steps only when there is a drawing request from the system, step 1 is processed in advance in the spare time of the CPU.
(Look-ahead) is effective. This processing method will be described later. First, a basic drawing portion excluding prefetching will be described.

(C) Drawing Model In order to perform drawing, first consider a drawing model as shown in FIG. In this model, threads represented by the Java language are used, and the following four threads are executed simultaneously. Reference numeral 41 denotes a data management thread which manages a group of drawing threads (a data updating thread, a map drawing thread, and a screen display thread). Specifically, the priority of the drawing thread group is dynamically changed according to the situation. assign. 42
A data update thread reads map data from a storage medium (CD-ROM) 10 storing map data and loads the map data into a map buffer 12. This data update thread corresponds to the map reading control unit 11 in FIG. Reference numeral 43 denotes a map drawing thread which generates a bit image map image using the map data loaded in the map buffer 12 and stores it in the VRAM 14. This map drawing thread corresponds to the map drawing unit 13 in FIG. Reference numeral 44 denotes a screen display thread, which cuts out a map portion corresponding to the position of the vehicle from the map drawn in the VRAM 14 by the map drawing thread, and
To be displayed. The map drawing thread 44 corresponds to the map cutout control unit 15 in FIG.

The data management thread 41 is a thread for managing everything related to drawing, and must be executed with the highest priority. Under this data management thread 41, a drawing thread group corresponding to the above-described steps 1 to 3
(A data update thread 42, a map drawing thread 43, and a screen display thread 44). The drawing threads do not operate in a chain, but operate independently and in parallel by multithreading. This enables a parallel operation in which the map drawing thread 43 draws the updated portion while the data update thread 42 collects data. However, if you do not set any rules, each thread will try to perform its task independently. For this reason, V by the map drawing thread 43
Contention between threads may occur, such as when the screen display thread 44 tries to cut out the map and display the screen even though the map drawing on the RAM 14 is not completed.

Therefore, in the present invention, when a drawing command is issued, the priorities of the drawing thread groups 42 to 44 can be dynamically assigned and changed according to the situation under the control of the data management thread 41. In this case, it is natural that the priority of the drawing thread groups 42 to 44 is lower than the priority of the data management thread 41. or,
The priority of each thread is set low so as to be executed when the load on the CPU is low. FIG. 8 is an explanatory diagram showing the situation of such priorities. The priority is for changing the CPU occupation time between threads. That is, the higher the priority, the easier the execution is, and the lower the priority, the later the execution. By utilizing this characteristic, it becomes possible to cause necessary processing to be performed preferentially, and to perform other processing during idle time of the CPU. Hereinafter, a method of redrawing a map using this priority assignment will be described.

(D) Dynamic Priority Assignment When the data management thread 41 assigns dynamic priorities to the drawing thread groups 42 to 44, the following situation must be considered. Situation 1: Whether or not the data update of the part necessary for drawing has been completed. Situation 2: Whether or not map drawing is completed. Situation 3: Whether or not the screen display has been completed. There are a total of eight combinations of these situations. However, considering that the drawing process proceeds in the steps of data update → map drawing → screen display, for example, there is no situation in which the map drawing is completed even though the data update is not completed. Remains. Situation 1: Data update, map drawing, and screen display are not all completed. Situation 2: Data update has been completed, but map drawing and screen display have not been completed. Situation 3: Data update and map drawing have been completed, but screen display has not been completed. Situation 4: Data update, map drawing, and screen display have all been completed.

There is also a temporal relationship between these four situations. In other words, the situation before the situation 4 is only the situation 3, the situation before the situation 3 is only the situation 2, and the situation 2 is the situation 1 before the situation 2. Therefore, the processing algorithm at that time may be checked in the order of the situation 1 → the situation 2 → the situation 3 → the situation 4, and the dynamic priority may be assigned. The priority assignment criteria at that time are:
9A to 9D.

FIG. 9A shows a priority assignment criterion in the situation 1. The priority is set in the order of the data update thread 42> the map drawing thread 43> the screen display thread 44. FIG.
(B) is a priority assignment criterion in situation 2, where the priority is set in the order of the map drawing thread 43> the screen display thread 44> the data update thread 42. FIG. 9C shows the priority allocation criterion in the situation 3, where the priority is the screen display thread 44> the data update thread 42> the map drawing thread 4.
Repeat in the order of 3. FIG. 9D shows the priority assignment criterion in Situation 4, and the priorities are set as data update thread 42 = map drawing thread 43 = screen display thread 44. As described above, by dynamically assigning the priority of each thread according to each situation, it is possible to perform map scroll control without contradiction and efficiently.

From the above, the dynamic priority assignment algorithm of the drawing thread groups 42 to 44 by the data management thread 41 is as shown in FIG. In this algorithm,
The structure is based on the fact that the status changes in the order of status 1 → status 2 → status 3 → status 4. In other words, “data update of drawing part is not completed” corresponds to situation 1, “map drawing not completed” corresponds to situation 2, “screen display not completed” corresponds to situation 3, and “screen display completed” corresponds to situation 1. 4 is supported. In the algorithm, for example, when a redraw command is newly generated, first, the data management thread 41 checks whether or not the data of the drawing portion has already been updated (step 301). If it has been updated, the process proceeds to the next stage. If it is an update process, the data update thread 42 has the highest priority, and the map drawing thread 43 and the screen display thread 44 are assigned priorities in this order. When the data update is completed (steps 302 and 303), it is checked whether the drawing of the map is completed (step 3).
04), if not finished, change the priority with the highest priority on the map drawing thread 42 (step 30).
5, 306). In this way, the thread that plays the most important role in each drawing stage is given the highest priority, thereby avoiding contention without synchronizing the threads.

(E) Introduction of Look-Ahead to Drawing A map can be drawn temporarily by the above method. But,
Data updating requires a very large processing cost compared to map drawing and screen display. Even if the user interacts with the multi-thread (remote control interface control),
Even if GPS data acquisition, route search, etc. are implemented, data update in map scroll display is very heavy compared to other processes, and the execution speed of other threads is delayed due to a long data update time. As a result, the request from the user is not accepted, or the execution speed of the route search is extremely reduced.

When a request for redrawing a map has not been issued in order to solve such a problem, that is, when there is room in the CPU, it is anticipated that a request for redrawing a map will be issued in advance, and preparations for that will be made. Prefetching is effective. At the time of map scroll display, the data update cost is the highest, and as long as the data can be updated, map drawing and screen display can be realized at a small cost. Therefore, data storage for updating the map, which is the most expensive, is prepared and performed in advance. Preserving this data is nothing more than reading the digital data of the unknown map portion ahead of the CD-ROM. First, the portion of the map to be prefetched will be described, and the prefetching method and the position of prefetching in the entire system will be clarified.

(E-1) Parts to be Pre-Readed Map data such as navigation is created by dividing a map into map units and stored and managed in a map recording medium such as a CD-ROM. This map leaf is sufficiently large compared to the size of a screen that can be generally displayed, and in a method of loading only data of one map leaf into a memory, a request for updating new map data is generated in FIG. It is time to reach the border of the figure leaf as shown. Then, it takes time to update the data in a portion beyond the boundary, and as a result, the screen looks flickering. Therefore, in the present invention,
The data of eight plots (adjacent plots) adjacent to the plot (center plot) that includes the center point of the part currently displayed on the screen is pre-read. Exactly this part shows the adjacent figures 1, 2, 3, 4, 5, 6, 7, 8 of FIG.

(E-2) Pre-reading method In pre-reading, one pre-reading thread is prepared for each adjacent figure. That is, there are a total of eight prefetch threads. The concept of priority described above is also used for this look-ahead thread. In other words, of these eight pieces of leaf data, a leaf having a higher possibility of being drawn next has a higher priority. Specifically, as shown in FIG. 12, the priorities of eight prefetch threads are determined. That is, the center map is divided into four regions, and the priority of the prefetch thread of each adjacent map is determined based on where the center point of the portion currently displayed on the screen is included in this region. FIG. 13 is an explanatory chart showing the relationship between the area to which the center of the screen display portion belongs and the priority of each adjacent figure. By assigning the priority to the prefetch thread of the adjacent drawing in this way, it is possible to preferentially read the data of the drawing which is particularly likely to be used in the prefetching and save the data early.

(E-3) Positioning of Priority of Look-Ahead Thread The look-ahead thread plays an auxiliary role, and its priority is a data management thread 41, a data update thread 42, a map drawing thread 43, and a screen display thread. 44
Must be lower priority. FIG. 14 is an explanatory diagram of the positioning of the priority of the prefetch thread. The data update thread 42 and the prefetch threads 51 to 58 are functionally the same. However, not all of the prefetch threads 51 to 58 are activated when the data update thread 41 is activated. Only when data of a portion to be displayed next is not prepared by the prefetch thread at the time of redrawing, the prefetch thread that prefetches the data is treated as the data update thread 42. The other prefetch threads are executed at a lower priority than the other thread groups 43 and 44. That is, when the vehicle enters a predetermined area, the prefetch thread of the adjacent map corresponding to the area is executed as the data update thread 42, and thereafter, the map drawing thread 4 is executed.
3. Execute the screen display thread 44, and execute these thread 4
After the completion of the execution of steps 3 and 44, another prefetch thread is activated to prefetch another adjacent leaf.

(E-4) Improvement of Efficiency of Prefetching by Using Difference Information A thread for prefetching map data of a new adjacent eight plots every time the center plot changes due to the movement of the own vehicle. Here, a method for improving the efficiency at that time will be described. For example, assume that there are leaves from 1 to 25 as shown in FIG. 15 and the center leaf of the own vehicle has moved from 9 to 13. Already when my car was at figure 9, figure 3, 4, 5,
The map data of 8, 9, 10, 13, 14, and 15, if not complete, is partially stored in the map buffer 12 (FIG. 7) by pre-reading and data updating (only 9 is read by data updating). . Next, when the vehicle moves to the map 13, the prefetch thread of the map 13 is treated as the data update thread 41, and the map 7, 8, 9, 12, 1 is newly added.
Prefetch threads for 4, 17, 18, and 19 are prepared.

However, out of the prefetch threads,
9 and 14, the map data should have been taken into the map buffer 12 to some extent when the center map leaf was already 9. That is, the parts to be prefetched in the new center map leaf 13 are the maps 8, 9, and 14 already stored to some extent in the map buffer 12, and the new prefetch thread 7,
12, 17, 18, 19, respectively. To summarize the above, when the center map leaf is changed from p to c, (a part of the data already in the map buffer in the prefetch part of c) = (prefetch part of c) ∩ (prefetch part of p) (2) (the part where c prepares a new prefetch thread) (3) = (the prefetch part of c) ∩ (the part other than the prefetch of p). By using such difference information, the pre-reading time can be reduced.

[0041] FIG. 16 is a flowchart of a redrawing algorithm using difference information, which is an algorithm in which the algorithm of FIG. 10 is slightly modified. In step 401 in the algorithm, the map satisfying the expression (3) (the look-ahead portion for the previous center map p and the new center map c
And prepare a new look-ahead thread only for the part that is the difference from the look-ahead part. For a figure satisfying the expression (2) (the overlapping part), the previous look-ahead thread is used as it is. As described above, according to the drawing algorithm for the car navigation system using the pre-reading and the dynamic priority (FIG. 16), the priority temporarily set at the time of updating the data for redrawing is set to a low priority when the load on the CPU is not so large. It can be avoided by updating in a thread.

(C) Evaluation experiment In order to show the effectiveness of this method, a commercially available Naviken CD
-Use the ROM to scroll the screen in a certain direction to force redrawing, and compare the required processing time for data update, map drawing, and map display with and without prefetching. went. Evaluation is Sun Ultr
went on al. FIGS. 17A and 17B are graphs of experimental results, in which FIG. 17A shows a case where prefetching is not performed, and FIG. 17B shows a case where prefetching is performed. Regardless of whether there is pre-reading or not, the map drawing time in the VRAM in redrawing during scrolling, V
The map display time read from the RAM and displayed on the screen falls within a certain range, and there is no great difference. However, CD-
The data update time for reading and updating map data from the ROM is af in the case of redrawing without prefetching.
It protrudes as shown by. This means that a very large load is temporarily applied to the CPU. On the other hand, when there is pre-reading, the protrusion is eliminated, and the data update time is almost inconspicuous (in the graph, the value is substantially close to 0). This means that the temporarily prominent CPU load is uniformly distributed when no prefetching is performed, and the advantage of prefetching is apparent. As described above, the processing cost at the time of redrawing is dispersed by pre-reading, whereby the temporary load on the system at the time of redrawing can be reduced.

Next, FIG. 17C shows the improvement of the performance of the whole system when the prefetch is used. Compared with the case where there is no prefetching, when there is prefetching, not only the load on the system is dispersed, but also the performance at the time of redrawing is improved by about 23% as a whole. That is, prefetching can improve not only load distribution but also the performance of the entire system. As described above, the present invention has been described with reference to the embodiments. However, the present invention can be variously modified in accordance with the gist of the present invention described in the claims, and the present invention does not exclude these.

[0044]

As described above, according to the present invention, (1) preparing a prefetch thread for prefetching map data, lowering the priority of the prefetch thread, (2) monitoring the idle time of the CPU, and (3) (4) The prefetch thread is started during the idle time of the CPU, and (4) the center map leaf and the neighboring map leaf are read from the map recording medium and stored in the memory by the prefetch thread. No need to
In addition, the idle time of the CPU can be effectively used, and the center figure and the surrounding figures can be prefetched into the map buffer at the idle time.

According to the present invention, (1) data update control for reading map data from a map recording medium and updating data already stored in the map buffer, and performing map updating based on the map data stored in the map buffer. A data update thread, a map drawing thread, and a screen display capable of executing, by parallel processing, a map drawing control for generating an image and drawing the map image in a VRAM, and a screen display control for cutting out a map image around a vehicle position from the VRAM and displaying the map image on a screen. Prepare threads and (2) lower the priority of these threads, and prior to the completion of data update, set the priority of the data update thread to the highest among the above threads, and after the completion of data update and before the completion of map drawing Makes the map drawing thread the highest priority, and after the map drawing is completed but before the screen display is completed, the screen display thread has priority (3) Since the thread with the highest priority is executed during the map scrolling process, the thread that plays the most important role in each drawing stage of the map scrolling control can be executed with the highest priority. Avoiding conflicts among threads without synchronization, enabling smooth map scrolling.

Further, according to the present invention, (1) a look-ahead thread is prepared corresponding to eight adjacent maps adjacent to the center map corresponding to the area to which the vehicle belongs, and (2) the adjacent thread into which the vehicle has entered. The prefetch thread of the map leaf is used as the data update thread to prefetch the adjacent map leaf, and (3) the priority of the prefetch thread according to the other adjacent map leaf is set lower than the map drawing thread and the screen display thread. Since the other adjacent map is pre-read, the adjacent map into which the vehicle has entered can be read ahead with the highest priority, so that the map image around the vehicle position can be reliably displayed and the map can be scrolled smoothly. .

Further, according to the present invention, the priority of the data update thread required for map scrolling is reduced, and the map data is prefetched when the CPU load is low. Large temporary loads can sometimes be avoided, thereby preventing delays in other important processes and greatly improving system efficiency. Also,
According to the present invention, (1) the center map leaf corresponding to the region to which the vehicle belongs is divided into four, and (2) which divided region the center point displayed on the screen belongs to is determined. The priority of the prefetch thread of the adjacent map leaf corresponding to the area adjacent to the belonging division area is set higher than the priority of the prefetch thread of the other adjacent map leaf, and (4) the prefetch thread of the adjacent map leaf having a higher priority is earlier. With this configuration, it is possible to pre-read the adjacent map having a high possibility that the vehicle will enter next, so that the map image around the vehicle position can be reliably displayed, and the map can be smoothly scrolled.

Further, according to the present invention, since only the adjacent map leaf (difference map) other than the adjacent map leaf already read into the map buffer is prefetched, the load of the prefetch can be reduced, and the prefetching can be performed. The required time can be shortened, and the center map and the eight neighboring maps can be reliably read ahead and stored in the map buffer.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of map data management.

FIG. 2 is a correspondence table of an old leaf number C of an entry destination, an old leaf number array AR1 usable after entry, and a new leaf array AR2 requiring prefetching after entry.

FIG. 3 is a diagram illustrating the contents of a hash table.

FIG. 4 is a configuration diagram of a main part of the navigation device.

FIG. 5 is a configuration diagram of a navigation device including a CPU.

FIG. 6 is a prefetch control processing flow.

FIG. 7 is an explanatory diagram of a drawing model using multi-threading.

FIG. 8 is an explanatory diagram of positioning regarding the priority between threads.

FIG. 9 is an explanatory diagram of priority assignment in each situation.

FIG. 10 is a flowchart of a dynamic priority assignment process.

FIG. 11 is an explanatory diagram of a timing at which a data update request is generated.

FIG. 12 is an explanatory diagram of a divided area obtained by dividing a central map leaf into four for prediction.

FIG. 13 is an explanatory diagram of priority assignment between prefetch threads.

FIG. 14 is an explanatory diagram of the positioning of the priority of a prefetch thread.

FIG. 15 is an explanatory diagram of a difference in prefetching.

FIG. 16 shows a re-drawing algorithm using difference information.

FIG. 17 is an explanatory diagram of an evaluation experiment result.

FIG. 18 is an explanatory diagram of a conventional map data update timing.

[Explanation of symbols]

 10. Map recording medium (CD-ROM) 14. VRAM 16. Display device 17. Position measuring device 20. Processor (CPU) 31. Arithmetic processing hardware unit 32. Program memory 33. Storage device

Claims (5)

[Claims] 1. A pre-reading thread for pre-reading map data in a map data pre-reading method of a navigation device for pre-reading in a memory a central map leaf corresponding to a region to which a vehicle belongs and an adjacent map leaf corresponding to a peripheral region of the region. And lowering the priority of the prefetch thread, monitoring the idle time of the CPU, activating the prefetch thread during the idle time of the CPU, and using the prefetch thread to read the center map leaf and the neighboring neighboring map leaf from the map recording medium. A prefetching method of map data, which is read out and stored in a memory. 2. A map scrolling method for a navigation device for displaying a map around a vehicle position on a screen as the vehicle moves, reading map data from a map recording medium and updating data already stored in a map buffer. Data update control, map drawing control for generating a map image based on the map data stored in the map buffer and drawing it in the VRAM, and screen display control for cutting out the map image around the vehicle position from the VRAM and displaying it on the screen Prepare a data update thread, a map drawing thread, and a screen display thread that can be executed by parallel processing, lower the priority of these threads, and set the priority of the data update thread among the above threads before the data update is completed. Highest, and after the data update is completed and before the map drawing is completed, the map drawing Prior to the completion of map drawing and before the completion of screen display, the highest priority is given to the screen display thread, and the thread with the highest priority is executed during map scroll processing. Map scroll method. 3. A read-ahead thread is prepared for eight adjacent map leaves adjacent to a center map leaf corresponding to an area to which a vehicle belongs, and a pre-read thread of the adjacent map leaf where the vehicle has entered is treated as the data update thread. The map data is read in advance by using a prefetch thread set to have a lower priority than the map update thread, the map drawing thread, and the screen display thread for the map leaf adjacent to the map into which the vehicle has entered. 3. The map scrolling method according to claim 2, wherein: 4. A center map leaf is divided into four parts, a central point displayed on the screen belongs to which divided area, and a pre-read thread of an adjacent figure leaf according to an area adjacent to the belonging divided area is determined. 4. The map scrolling method according to claim 3, wherein the priority is set higher than the priority of the look-ahead thread of the other adjacent map, and the adjacent map having the higher priority is read ahead earlier. 5. The map scrolling method according to claim 3, wherein only the adjacent map other than the adjacent map already read into the map buffer is pre-read.