JP2012242737A - Device and method for determining bridge elevation value, computer program for determining the same, and recording medium recording the computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method for determining an elevation value of a bridge.SOLUTION: A method for determining an elevation value of a bridge includes: extracting a link including the bridge as a target link from a map data storage unit; determining a first gradient variation point adjacent to a first node corresponding to one end point of the target link and a second gradient variation point adjacent to a second node corresponding to the other end point of the target link by referring to an elevation data storage unit; calculating a first elevation value of the determined first gradient variation point and a second elevation value of the determined second gradient variation point; and determining the elevation value of the bridge on the basis of the calculated first elevation value and the calculated second elevation value.

Description

  The present invention relates to an apparatus for specifying an elevation value of a bridge and a method thereof.

2. Description of the Related Art In recent years, in navigation devices that perform route search, a technology for calculating the energy consumption amount using road gradient data has been proposed due to an increasing demand for route search technology considering energy consumption amount.
As such a technique, in Patent Document 1, a vehicle route for calculating an estimated fuel consumption in each link based on road gradient data stored for each link and performing an optimum route search using the calculated estimated fuel consumption. Search devices and the like have been proposed.
The road gradient data is generally determined based on elevation values of predetermined points (coordinates) on the link. Then, the altitude value of the predetermined point on the link is calculated based on reference altitude data (for example, 10 m mesh altitude data).

Japanese Patent No. 3551634

  Conventionally, the altitude value of a predetermined point on the link is specified by calculating based on mesh altitude data. Here, the mesh elevation data is elevation data provided by the Geospatial Information Authority of Japan, which can be obtained in the form of a recording medium such as a CD-ROM as with the navigation software. In general, linear interpolation is performed based on the altitude of four grid points (mesh elevation data) surrounding any given point in the map data, which is finely divided into small square areas of about 50m or 10m. It can be determined by the method. That is, the elevation value of the predetermined point is specified based on the mesh elevation data of the four lattice points surrounding the point.

However, since the above-mentioned mesh altitude data uses the altitude data of the ground surface, if the predetermined point exists on the ground surface, it is possible to calculate a certain altitude value, but like the bridge part etc. For a predetermined point not provided on the ground surface, the altitude value cannot be calculated correctly. This is because the elevation value of the water surface corresponding to the predetermined point is calculated.
On the other hand, there is a demand for more accurately obtaining the altitude value of a portion not provided on the ground surface such as a bridge included in the link.

FIG. 1 is a schematic diagram showing a relationship between a general road link including a bridge and the like and an altitude value calculated based on mesh altitude data.
As shown in FIG. 1A, a link including a bridge or the like (in the figure, symbol L) generally includes a bridge part (part A), a dike part (part B) provided near both ends of the bridge part, and And a surface road part (part C) connected to the dike part.

FIG. 1B is a schematic diagram showing an elevation value H1 obtained using 10 m mesh elevation data in the link L. FIG.
As described above, when the altitude value of the link L is calculated based on the 10 m mesh altitude data, the altitude value in the part C can be calculated accurately, but the parts A and B corresponding to the levee part and the bridge part are calculated. The current situation is that the altitude value cannot be calculated accurately. This is considered to be due to the following reasons.

  In other words, considering that the 10m mesh elevation data is the elevation data created based on the contour map data etc. of the topographic map, the bridge portion A is not reflected in the contour lines, so the elevation value of the water surface continuous to the ground surface is calculated. It will be calculated. In addition, since the levee portion B is continuous with the ground surface, its existence is reflected in the contour line, but the proportion of the area occupied by the levee portion in the area around the levee is small. The calculated altitude value will be equalized to the surrounding altitude values.

  In order to solve such a situation, in recent years, as an altitude database, 5 m mesh altitude data and the like have been prepared in some areas. In the altitude database based on the 5 m mesh altitude data, altitude values obtained based on altitude data acquired by aviation laser surveying are stored.

FIG. 1C is a schematic diagram showing an elevation value H2 using 5m mesh elevation data in the link L. FIG.
Thus, since the 5 m mesh elevation data reflects the levee portion B, the elevation value of the portion B can be obtained accurately. However, since the 5 m mesh elevation database is removed by filtering artificial structures such as bridges that shield the ground surface from the measured elevation data, as shown in FIG. There was a problem that an appropriate altitude value could not be acquired.

  Therefore, as a result of intensive studies to solve the above-mentioned problems, the present inventors paid attention to the characteristic elevation shape near the bridge, and determined the gradient change points adjacent to both end nodes of the link including the bridge. We thought that it was possible to calculate the altitude value of the bridge more accurately by connecting the altitude value corresponding to each gradient change point as a point.

The present invention has been made in view of the above-mentioned problems, and the first aspect is defined as follows. That is,
A target link extraction unit that extracts a link including a bridge as a target link from the map data storage unit;
Referring to the elevation data storage unit, adjacent to the first gradient change point adjacent to the first node corresponding to one end point of the target link and the second node corresponding to the other end point of the target link A gradient change point determination unit for determining a second gradient change point;
An altitude value calculator for calculating the determined first altitude value of the first gradient change point and the second altitude value of the second gradient change point;
An altitude value specifying unit for specifying an altitude value on the bridge based on the calculated first altitude value and the second altitude value;
Elevation value specifying device with bridge.

  According to the bridge elevation value specifying device of the first aspect defined as described above, the target links including the bridge that is the target of specifying the elevation value are extracted, and the first gradient adjacent to both end nodes of the target link, respectively. The change point and the second gradient change point (signs p and q shown in FIG. 1C) are determined, and the elevation value in the bridge is specified based on the elevation value of the gradient change point. In this way, by specifying the elevation value of the bridge by simulating the gradient change point on the target link as the start and end points of the bridge, the actual elevation value that is realistic and relevant to the bridge part located away from the ground surface Can be specified.

Here, the “link including a bridge” is a link including a bridge that exists away from the ground surface in the link, and is based on an attribute indicating that the bridge is attached to the link, or manually by the operator. Specified by. The link including the bridge is not limited to 1, and two or more adjacent links can be the target link.
The “end point of the target link” indicates a connection point between the target link and the link connected to the target link. When one link is extracted as the target link, both end nodes of the target link are the end points. It becomes. Further, when the first link and the second link are extracted as the target link, it is one node of the first link, and the connection point between the second link and another link, similarly , One node of the second link, and a connection point between the first link and another link is an end point of the target link.
The “gradient change point” indicates a point where the sign of the gradient value attached to the link is switched.

The second aspect of the present invention is defined as follows. That is,
In the bridge elevation value specifying device defined in the first aspect, a first elevation difference between the first elevation value and the elevation value of the first node, and the second elevation value and the second elevation value. A control unit that calculates a second elevation difference from the elevation value of the node, and activates the elevation value specifying unit when the first elevation difference and / or the second elevation difference is equal to or greater than a predetermined threshold; .
According to the bridge elevation value specifying device defined in the second aspect defined in this way, the elevation value at the slope change point simulated by the bridge start and end points is different from the elevation value of the node on the ground road by a predetermined threshold value or more. Since there is a specific process for determining the bridge altitude, the load on the processing apparatus can be reduced.

The third aspect of the present invention is defined as follows. That is,
In the bridge elevation value specifying device defined in the first or second aspect, the target link extraction unit includes the bridge, and extracts the continuous first link and second link as target links,
A node designating unit for designating a third node corresponding to a connection point between the first link and the second link;
A node position determination unit that determines whether or not the third node exists between the first gradient change point and the second gradient change point;
A node excluding unit that excludes the third node when the third node exists between the first gradient change point and the second gradient change point as a result of the determination;
According to the bridge elevation value specifying device defined in the third aspect defined in this way, the target link composed of two or more links is extracted, and the node connecting the two links is the first gradient change. When it exists between the point and the second gradient change point, the node is excluded. Since the altitude value calculated based on the mesh altitude data for the node cannot calculate the altitude value on the bridge, it is not suitable for specifying the bridge altitude value. Therefore, by excluding the node, it is possible to acquire a more likely elevation value for the bridge portion.

The fourth aspect of the present invention is defined as follows. That is,
A target link extraction step of extracting a link including a bridge as a target link from the map data storage unit;
Referring to the elevation data storage unit, adjacent to the first gradient change point adjacent to the first node corresponding to one end point of the target link and the second node corresponding to the other end point of the target link A gradient change point determining step for determining a second gradient change point;
An altitude value calculating step of calculating the determined first altitude value of the first gradient change point and the second altitude value of the second gradient change point;
An elevation value identifying step for identifying an elevation value on the bridge based on the calculated first elevation value and the second elevation value;
A method for identifying bridge elevation values.
According to the invention of the fourth aspect defined as described above, the same effect as that of the first aspect can be obtained.

The fifth aspect of the present invention is defined as follows. That is,
In the bridge elevation value specifying method defined in the fourth aspect, a first elevation difference between the first elevation value and the elevation value of the first node, and the second elevation value and the second elevation value. A control step of calculating a second elevation difference from the elevation value of the node, and operating the elevation value specifying step when the first elevation difference and / or the second elevation difference is equal to or greater than a predetermined threshold. .
According to the fifth aspect of the invention thus defined, the same effects as those of the second aspect can be achieved.

The sixth aspect of the present invention is defined as follows. That is,
In the bridge elevation value specifying method defined in the fourth or fifth aspect, the target link extraction step includes the bridge and extracts the continuous first link and second link as target links,
A node designating step of designating a third node corresponding to a connection point between the first link and the second link;
A node position determination step for determining whether or not the third node exists between the first gradient change point and the second gradient change point;
A node excluding step of excluding the third node when the third node exists between the first gradient change point and the second gradient change point as a result of the determination.
According to the sixth aspect of the invention thus defined, the same effect as the third aspect can be obtained.

Furthermore, the seventh aspect of the present invention is defined as follows. That is,
A computer program for specifying an elevation value of a bridge, comprising:
A target link extraction means for extracting a link including a bridge as a target link from the map data storage unit;
Referring to the elevation data storage unit, adjacent to the first gradient change point adjacent to the first node corresponding to one end point of the target link and the second node corresponding to the other end point of the target link A gradient change point determining means for determining a second gradient change point;
Altitude value calculating means for calculating the determined first altitude value of the first gradient change point and the second altitude value of the second gradient change point;
An altitude value specifying means for specifying an altitude value on the bridge based on the calculated first altitude value and the second altitude value;
As a computer program.
According to the seventh aspect of the invention thus defined, the same effect as the first aspect can be obtained.

The eighth aspect of the present invention is defined as follows. That is,
In the computer program defined in the seventh aspect, the computer is further
A first elevation difference between the first elevation value and the elevation value of the first node, and a second elevation difference between the second elevation value and the elevation value of the second node are calculated. Then, when the first altitude difference and / or the second altitude difference is equal to or greater than a predetermined threshold, the altitude value specifying means is operated as a control means.
According to the invention of the eighth aspect defined as described above, the same effect as that of the second aspect can be obtained.

The ninth aspect of the present invention is defined as follows. That is,
In the computer program defined in the seventh or eighth aspect, the computer further comprises:
The target link extracting means extracts the first and second links that include the bridge and are continuous as target links,
Node designating means for designating a third node corresponding to a connection point between the first link and the second link;
Node position determination means for determining whether or not the third node exists between the first gradient change point and the second gradient change point;
As a result of the determination, when the third node exists between the first gradient change point and the second gradient change point, the third node is caused to function as node exclusion means for excluding the third node.
According to the ninth aspect of the invention thus defined, the same effect as the third aspect can be obtained.

  A recording medium for recording a computer program defined in any of the seventh to ninth aspects is defined as a tenth aspect.

(A) is a schematic diagram showing an example of a link including a bridge, (B) is a schematic diagram showing an elevation value obtained using 10 m mesh elevation data, and (C) uses 5 m mesh elevation data. It is a schematic diagram which shows the altitude value acquired in this way. It is a block diagram which shows the structure of the bridge elevation value specific | identification apparatus of embodiment of this invention. It is a flowchart which shows operation | movement of the bridge elevation value specific | specification apparatus of embodiment of this invention. It is a block diagram which shows the structure of the bridge elevation value specific | specification apparatus of other embodiment of this invention. It is a block diagram which shows the structure of the bridge elevation value specific | specification apparatus of other embodiment of this invention. The computer program which comprises the altitude value specific | identification apparatus of embodiment of this invention is shown.

A bridge elevation value specifying device 1 according to an embodiment of the present invention will be described.
FIG. 2 shows a schematic configuration of the bridge elevation value specifying device 1.
As shown in FIG. 2, the bridge elevation value specifying device 1 includes a map data storage unit 3, an elevation data storage unit 4, a target link extraction unit 5, a first storage unit 6, a gradient change point determination unit 7, and a second storage. Unit 8, altitude value calculation unit 9, third storage unit 10, altitude value specifying unit 11, and fourth storage unit 12.

Map information is stored in the map data storage unit 3. The map information includes information on road elements for defining map information such as links and nodes, information drawn on the map, and the like.
The altitude data storage unit 4 stores altitude data associated with the map data. The altitude data may be data prepared in advance. In particular, the altitude data is preferably data that is expressed in units of areas divided into meshes of a predetermined size and to which altitude information on the topography is given. Examples of such data include mesh elevation data, and 5 m mesh elevation data is particularly preferable.

  The target link extraction unit 5 refers to the map data storage unit 3 and extracts, as the target link, a link including a bridge, which is an altitude value identification target. Although the extraction method is not particularly limited, for example, a link existing in a region arbitrarily selected from the map data can be automatically extracted. In this case, based on the link attribute indicating that the bridge is included, the link with the attribute can be extracted as the target link. As another method, it may be designed to allow the operator to manually extract the link.

  Further, the target link extraction unit 5 may extract both end nodes of the target link. The number of target links to be extracted is not limited to 1, and two or more adjacent links can be extracted as target links. When the target link extraction unit 5 extracts two or more links as target links, the gradient change point determination unit 7, the altitude value calculation unit 9, and the altitude value identification unit 11, which will be described later, unite the two or more links. Can be processed. The extracted target link is stored in the first storage unit 6.

  The gradient change point determination unit 7 refers to the elevation data storage unit 4 and the first storage unit 6 and determines the first gradient change point and the second gradient change point in the target link. That is, the first gradient change point adjacent to the first node corresponding to one end point of the target link stored in the first storage unit 6 and the second node corresponding to the other end point of the target link An adjacent second gradient change point is determined. The method of determining the gradient change point is not particularly limited as long as the gradient change point can be accurately determined. For example, the gradient change amount is calculated based on the gradient information given to the link, and the positive gradient change amount is calculated. And a negative gradient change amount can be obtained as a gradient change point. Similarly, a boundary point between a positive gradient value and a negative gradient value may be obtained as a gradient change point. As another method, a gradient change point can be obtained by calculating a gradient value based on the altitude data given to the link.

Furthermore, instead of the gradient change point, the peak of the target link elevation value can be determined. As the elevation vertices in the target link, for example, referring to the elevation data storage unit 4, the first elevation vertices adjacent to the first node and the second elevation vertices adjacent to the second node are Can be determined. The elevation vertex is a first curve having a positive gradient value connected to the first node (or the second node) and a second curve having a negative gradient value continuous to the first curve. It may be an intersection.
The determined first gradient change point and second gradient change point are stored in the second storage unit 8 in association with the coordinates.

  The elevation value calculation unit 9 refers to the elevation data storage unit 4 and the second storage unit 8 and calculates the first elevation value of the first gradient change point and the second elevation value of the second gradient change point. Calculate. The calculation method can be determined by a linear interpolation method based on four mesh elevation data surrounding the gradient change point. The calculated first elevation value and second elevation value are stored in the third storage unit 10 in association with the coordinates.

  The elevation value identification unit 11 refers to the third storage unit 10 and identifies the elevation value of the bridge portion. The specific method is not particularly limited as long as it can accurately specify the elevation value of the bridge. For example, it is specified by linearly interpolating the calculated first elevation value and second elevation value. be able to. The elevation value of the identified bridge part is stored in the fourth storage unit 12 in association with the coordinates of the part. When information indicating that the bridge and the road provided at the top of the embankment cross three-dimensionally is obtained, the altitude value specifying unit 11 changes the gradient calculated by the altitude value calculating unit 9 based on the information. A value obtained by adding a predetermined value (for example, 5 m) to the elevation value of the point can be specified as the elevation value of the bridge portion.

The operation of the bridge elevation value specifying device 1 shown in FIG. 2 will be described with reference to FIG.
First, in step 1, the map data storage unit 3 is referred to, and a link including a bridge for which an altitude value is specified is extracted and stored as a target link.
In step 3, the elevation data storage unit 4 and the first storage unit 6 are referred to, and the first gradient change point and the second gradient change point of the target link extracted in step 1 are determined and stored.

In step 5, the first elevation value of the first gradient change point and the second elevation value of the second gradient change point determined in step 3 are referred to the elevation data storage unit 4 and the second storage unit 8. Is calculated and saved.
In step 7, the elevation value of the bridge portion is specified and stored with reference to the third storage unit 10. The elevation value can be specified by linearly interpolating the first elevation value and the second elevation value calculated in step 5.

FIG. 4 shows a bridge elevation value specifying device 21 according to another embodiment. 4, the same elements as those in FIG. 2 are denoted by the same reference numerals, and the description thereof is partially omitted.
FIG. 4 shows a bridge elevation value specifying device 21 that can specify a bridge elevation value when a predetermined condition is satisfied. That is, the apparatus 21 further includes a control unit 23 in the bridge elevation value specifying apparatus 1 shown in FIG.
The control unit 23 includes an altitude difference calculation unit 25, a comparison unit 26, and a trigger unit 27, and outputs a signal to operate the altitude value specifying unit 11 when a predetermined condition is satisfied.

The elevation difference calculation unit 25 refers to the elevation data storage unit 4, the first storage unit 6, and the third storage unit 10, and calculates the first elevation difference between the first elevation value and the elevation value of the first node. calculate. Similarly, a second elevation difference between the second elevation value and the elevation value of the second node is calculated.
The comparison unit 26 compares the calculated first elevation difference with a preset threshold value. Similarly, the second elevation difference is compared with the threshold value.
The trigger unit 27 refers to the comparison result of the comparison unit 26 and outputs a trigger signal for operating the elevation value specifying unit 11 when the first elevation difference and / or the second elevation difference is equal to or greater than the threshold value. To do.

  As described above, in the bridge elevation value specifying device 21, the control unit 23 generates a trigger signal for operating the elevation value specifying unit 11 based on the elevation difference between the first elevation value and the elevation value of the first node. As another example, the trigger signal may be output based on the distance between the position associated with the first elevation value and the position of the first node. This is because the higher the distance, the higher the difference in elevation between the first elevation value and the elevation value of the first node.

FIG. 5 shows a bridge elevation value specifying device 31 according to another embodiment. 5, the same elements as those in FIGS. 2 and 4 are denoted by the same reference numerals, and the description thereof is partially omitted.
FIG. 5 shows a bridge altitude value specifying device 31 that specifies an altitude value of a bridge by excluding nodes not suitable for specifying the altitude value in order to specify a more probable bridge altitude value. That is, the device 31 further includes a node designating unit 33, a node position determining unit 35, and a node excluding unit 37 in the bridge elevation value specifying device 1 shown in FIG.

The node designating unit 33 refers to the first storage unit 6, and the third corresponding to the connection point between the adjacent first link and the second link extracted as the target link by the target link extraction unit 5. Specify the node.
The node position determination unit 35 refers to the node specification unit 33 and the second storage unit 8 to determine the position of the specified third node. That is, it is determined whether or not the third node specified by the node specifying unit 33 exists between the first gradient change point and the second gradient change point stored in the second storage unit 8. .
When the node exclusion unit 37 determines that the third node exists between the first gradient change point and the second gradient change point as a result of the determination by the node position determination unit 35, the third node Is excluded.

FIG. 6 is a block diagram showing a hardware configuration of the bridge elevation value specifying device 21.
The hardware configuration of the device 21 is such that various elements are coupled to the central controller 221 via the system bus 222 in the same manner as a general computer system.
The central controller 221 includes a general-purpose CPU, a memory controller, a bus controller, an interrupt controller, and a DMA (direct memory access) device. The system bus 222 also includes a data line, an address line, and a control line. A memory circuit including a RAM (Random Access Memory) 223 and a nonvolatile memory (ROM 224, CMOS-RAM 225, etc.) is connected to the system bus 222. Data stored in the RAM 223 is read or rewritten by the central controller 221 or other hardware elements. The data in the non-volatile memory is read-only, and the data is not lost when the device is turned off. The system program for controlling the hardware is stored in the hard disk device 227 and also stored in the RAM 223, and is read and used by the central control device 221 as appropriate via the disk drive control device 226. The hard disk device 227 has an area for storing a computer program for operating a general-purpose computer system as the bridge elevation value specifying device 21.
A predetermined area of the hard disk device 227 is allocated for a storage unit that stores the result of the altitude value specifying unit 11.
Other areas of the hard disk device 227 are allocated for the map data storage unit 3 and the altitude data storage unit 4.

Connected to the system bus 222 are a flexible drive control device 231 that reads and writes data from and to the flexible disk 232, and a CD / DVD control device 233 that reads data from the compact disk 234. In this example, a printer 238 is connected to the printer interface 237.
A keyboard / mouse control device 241 is connected to the system bus 222 to enable data input from the keyboard 242 and the mouse 243. A monitor 245 is connected to the system bus 222 via the monitor control device 244. The monitor 245 can be a CRT type, a liquid crystal type, a plasma display type, or the like.
An empty slot 251 is prepared in order to allow the addition of various elements (such as a modem).

  Programs (OS program and application program (including those of the present invention)) necessary for operating the bridge elevation value specifying device 21 comprising this computer system are installed in the system via various recording media. . For example, it is possible to install in the form of a non-write recording medium (CD-ROM, ROM card, etc.), a writable recording medium (FD, DVD, etc.), or a communication medium using the network N. Of course, these programs can be written in advance in the nonvolatile memories 224 and 225 and the hard disk device 227.

  As mentioned above, although embodiment of this invention has been described, you may implement combining 2 or more embodiment among these. Alternatively, one of these embodiments may be partially implemented. Furthermore, among these, two or more embodiments may be partially combined.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

1 21 31 Bridge Elevation Value Identification Device 3 Map Data Storage Unit 4 Elevation Data Storage Unit 5 Target Link Extraction Unit 7 Gradient Change Point Determination Unit 9 Altitude Value Calculation Unit 11 Altitude Value Specification Unit 23 Control Unit 33 Node Designation Unit 35 Node Position Determination Part 37 Node exclusion part

Claims (10)

A target link extraction unit that extracts a link including a bridge as a target link from the map data storage unit;
Referring to the elevation data storage unit, adjacent to the first gradient change point adjacent to the first node corresponding to one end point of the target link and the second node corresponding to the other end point of the target link A gradient change point determination unit for determining a second gradient change point;
An altitude value calculator for calculating the determined first altitude value of the first gradient change point and the second altitude value of the second gradient change point;
An altitude value specifying unit for specifying an altitude value on the bridge based on the calculated first altitude value and the second altitude value;
Elevation value identification device with bridge. A first elevation difference between the first elevation value and the elevation value of the first node, and a second elevation difference between the second elevation value and the elevation value of the second node are calculated. A control unit that activates the elevation value specifying unit when the first elevation difference and / or the second elevation difference is equal to or greater than a predetermined threshold;
The bridge elevation value specifying device according to claim 1, comprising: The target link extraction unit includes the bridge, and extracts a continuous first link and second link as a target link,
A node designating unit for designating a third node corresponding to a connection point between the first link and the second link;
A node position determination unit that determines whether or not the third node exists between the first gradient change point and the second gradient change point;
As a result of the determination, when the third node exists between the first gradient change point and the second gradient change point, a node exclusion unit that excludes the third node;
The bridge elevation value specifying device according to claim 1, comprising: A target link extraction step of extracting a link including a bridge as a target link from the map data storage unit;
Referring to the elevation data storage unit, adjacent to the first gradient change point adjacent to the first node corresponding to one end point of the target link and the second node corresponding to the other end point of the target link A gradient change point determining step for determining a second gradient change point;
An altitude value calculating step of calculating the determined first altitude value of the first gradient change point and the second altitude value of the second gradient change point;
An elevation value identifying step for identifying an elevation value on the bridge based on the calculated first elevation value and the second elevation value;
A method for identifying bridge elevation values. A first elevation difference between the first elevation value and the elevation value of the first node, and a second elevation difference between the second elevation value and the elevation value of the second node are calculated. A control step of operating the elevation value specifying step when the first elevation difference and / or the second elevation difference is greater than or equal to a predetermined threshold value,
The bridge elevation value specifying method according to claim 4, comprising: In the target link extraction step, the first and second links that include the bridge and are continuous are extracted as target links,
A node designating step of designating a third node corresponding to a connection point between the first link and the second link;
A node position determination step for determining whether or not the third node exists between the first gradient change point and the second gradient change point;
A node exclusion step of excluding the third node when the third node exists between the first gradient change point and the second gradient change point as a result of the determination;
The bridge elevation value specifying method according to claim 4, comprising: A computer program for specifying an elevation value of a bridge, comprising:
A target link extraction means for extracting a link including a bridge as a target link from the map data storage unit;
Referring to the elevation data storage unit, adjacent to the first gradient change point adjacent to the first node corresponding to one end point of the target link and the second node corresponding to the other end point of the target link A gradient change point determining means for determining a second gradient change point;
Altitude value calculating means for calculating the determined first altitude value of the first gradient change point and the second altitude value of the second gradient change point;
An altitude value specifying means for specifying an altitude value on the bridge based on the calculated first altitude value and the second altitude value;
As a computer program. Said computer further
A first elevation difference between the first elevation value and the elevation value of the first node, and a second elevation difference between the second elevation value and the elevation value of the second node are calculated. Control means for operating the elevation value specifying means when the first elevation difference and / or the second elevation difference is equal to or greater than a predetermined threshold value,
The computer program according to claim 7, which is caused to function as: Said computer further
The target link extracting means extracts the first and second links that include the bridge and are continuous as target links,
Node designating means for designating a third node corresponding to a connection point between the first link and the second link;
Node position determination means for determining whether or not the third node exists between the first gradient change point and the second gradient change point;
Node exclusion means for excluding the third node when the third node exists between the first gradient change point and the second gradient change point as a result of the determination;
The computer program according to claim 7 or 8, which is caused to function as:   The recording medium which records the computer program in any one of Claims 7-9.

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