JP2003186393A - Altitude value interpolation method and altitude data generated thereby and method for preparing contour map prepared by altitude data and contour map - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely interpolate an latitude value into a basic contour map represented by known contour lines. <P>SOLUTION: The method is composed of a first step for dividing the basic contour map 20 represented by the known contour lines 10 into a plurality of meshes 12 at a constant interval in which the central points thereof are the lattice points 13; a second step for calculating the distance from a specified interpolation point 14 and the altitude value in which the specified interpolation point 14 is selected from the plurality of lattice points 13, and four points of intersection 16 which define the least distance from the specified interpolation point 14 are obtained by searching the nearest and the next nearest contour lines 10, at the sides of high and low altitude values crossing over extension lines 15 drawn from the specified interpolation point 14 in 16 directions; and a third step for reading the altitude value of the specified interpolation point 14 from a graph, in which the steepest geographical section including the specified interpolation point 14 is represented by a linear graph or a higher order curve graph, on the basis of the altitude values of the four points of intersections 16 and the distance from the specified interpolation point 14. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of interpolating elevation values, elevation data thereof, a method of creating a contour map and a contour map thereof. That is, in a known basic contour map or basic contour map that connects points of equal altitude or depth at constant contour intervals, the altitude values are interpolated with high accuracy in a grid pattern between existing contour lines to improve reliability. To obtain high altitude data. Further, based on this elevation data, a detailed contour map or a contour map with excellent reproducibility of actual topography is obtained by incorporating a dense contour line in a known basic contour map or basic contour map.

[0002]

2. Description of the Related Art Conventionally, there is an algorithm (method) for interpolating elevation values in contour maps, and elevation data (DEM) created by this conventionally known algorithm is used to model and analyze various phenomena related to a target topography. It is effective for display, and provides a lot of basic data for application in various fields in the field of earth science and engineering. Also, based on this elevation data, contour line intervals 100m, 20m, 10
In the m, 5 m contour maps and other known basic contour maps, there is a conventional technique for further subdividing the basic contour lines and interpolating dense contour lines to obtain a more detailed contour map. In the creating process, as shown in FIGS. 12 to 15, first, an arbitrary grid point is selected from grid points arranged in a grid on the basic contour map and set as a target interpolation point p. This focused interpolation point p
Draw an extension line in the eight azimuth directions of 45 ° vertically and horizontally.
Then, among the intersections of the extension lines in the eight azimuth directions and the nearest contour lines, the intersection q ₁ forming the shortest distance is searched for.
Next, on the opposite side of the intersection q ₁ , an intersection q ₂ between the contour line having an elevation value different from the contour line where q ₁ exists and the extension line is searched.

[0003] After searching the two intersections, the distance to reach the contours from interest in interpolated point p, that is, the distance l ₁ between the p and the intersection q ₁
When, by prorating the distance l ₂ between p and q _2, q ₁ and q ₂
The altitude value of the target interpolation point p is calculated in proportion to the altitude of the existing contour line. Then, the elevation values are calculated for a plurality of target interpolation points p set in the existing contour map, and based on these elevation values, dense contour lines are interpolated between the contour lines at coarse intervals. There has also been a method of drawing contour lines from the target interpolation point p only in the four horizontal and vertical directions to interpolate contour lines.

[0004]

However, in the conventional interpolation method using the extension lines in the four or eight azimuth directions, when the basic contour lines are complicated or have a special shape. In some cases, the altitude value of the interpolation point p of interest may be inaccurate or may be erroneously recognized. For example, the interpolated point p (1) of interest shown in FIG. 12 has steep slopes on both sides, and the center is located on a slightly gentle ridge. From this focused interpolation point p (1) to 8
Draw an extension line (2) Q _{1 to} Q ₄ in the azimuth direction to draw contour lines in the neighborhood.
When searching for intersections (4) q ₁ and q ₂ with (3), extension lines (2)
Is a contour line (3) that intersects with C ₂ , but at different elevations
(3) C ₃ cannot be detected, and the interpolation point p (1) of interest is erroneously recognized as existing on a flat ground.

Further, in the above conventional method, the interpolation point p of interest is
The contour line (3) that intersects the extension line (2) from (1)
We are searching one by one, but we are searching for two contour lines (3) above and below.
There are also conventional methods of searching. The search method is shown in FIG.
As shown, the extension point drawn in the eight azimuth directions from the interpolation point p (1) of interest.
Of the long lines (2), the contour line closest to the interpolation point p (1) of interest
(3) C₂Extension line that forms the shortest distance with (2) Q₂Above, in Figure 13
As shown, set the intersection (4) with the contour line (3) to q₁, Q₂, Q₃,
q_FourTo set. And q₁-Q₂, P (1) -q ₂while,
p (1) -q₃While q₃-Q_FourEach distance between₁, L₂, L₃, L
_Four, And each intersection (4) q₁, Q₂, Q₃, Q_FourIs present
Line (3) C₁, C₂, C₃, C_FourInterpolation point of interest based on the elevation value of
The altitude value of p (1) is calculated. Thus,
Increase the reference data for calculating the high price
I was trying to increase the reliability of the altitude of p (1).

However, since four intersections (4) q _{1 to} q ₄ are searched for on the same extension line (2) Q ₂ , these 4
The topographical cross section formed by the _four intersections (4) q _{1 to} q ₄ may not always have the steepest slope. That is, in the example of FIG. 13, the extension line (2) Q ₂ cannot search the contour line (3) C ₄ and the graph connecting the _four intersections (4) q _{1 to} q ₄ is not the steepest slope line. , It was easy to cause an error in the elevation value of the interpolation point p (1) of interest. Even if the elevation value is calculated by searching the four intersections (4) in the terrain shown in FIG. 12, the contour lines (3) C ₃ and C ₄ are searched for in the extension line (2) in the eight azimuth directions. This is not a solution to the problem that the focused interpolation point p (1) is recognized as a flat ground.

Further, when the interpolation point p (1) of interest exists in a valley or ridge having a large bend, the conventional method may be erroneously recognized as existing in the flat ground. That is, as shown in FIG. 14, when the target interpolation point p (1) exists in a valley portion having a large bend, an extension line (2) drawn from the target interpolation point p (1) in eight directions.
Can detect the contour lines (3) C ₃ and C ₂ on the ridge side, but cannot detect the contour line (3) C ₄ on the valley bottom side, and misrecognize that the focused interpolation point p (1) exists on the flat ground. To be done. In addition, FIG.
As shown in, at the interpolation point p (1) of interest in the saddle or pass, in the case of searching for two intersections (4), the contour line (3) C ₂ can be searched, but the contour lines (3) with different elevation values Since C ₃ cannot be detected, the focused interpolation point p (1) is erroneously recognized as existing on the flat ground. Also, in the case of searching for four intersections (4), contour lines (3)
C ₂ and C ₁ can be searched, but C ₃ and C ₄ cannot be searched, and the reliability of the elevation value of the interpolation point p (1) of interest cannot be improved.

Due to the above-mentioned problems, when contour lines are interpolated in an actual contour map in the prior art, FIGS.
An unnatural contour map was created as shown in. The thick black line in the figure is an existing contour line having a contour interval of 10 m, and the black thin line is a contour interval 1 newly interpolated by a conventionally known technique.
It is a contour line of m. First, in FIG. 16, contour lines are interpolated by a conventional method on a terrain having steep slopes on both sides and a ridge with a gentle slope in the center, and contour lines having an unnatural slope are formed on the ridge portion. In addition, FIG. 17 is an example of a terrain having contour lines with sharp bends, and an unnatural contour map lacking smoothness was formed. Further, FIG. 18 is an example of a complicated terrain having a mountain top and a saddle portion surrounded by curved valleys, and unnatural contour lines are interpolated in the valley portion and the saddle portion.
In this way, if the contour lines are complicated and complicated, or if the terrain has a special shape, the conventional interpolation method interpolates the contour lines that are unnatural and lack smoothness, and Was poor in reproducibility.

The present invention is intended to solve the above problems and provides an interpolation method capable of highly accurately interpolating elevation values to a known contour map represented by contour lines. Is. And even if the terrain is complicated or special terrain with complicated contour lines, the elevation value is interpolated with high accuracy,
It obtains excellent elevation data (DEM) with a high degree of contribution to various fields such as earth science and engineering. In addition, based on the highly accurate elevation data obtained by this interpolation method, the known basic contour map is interpolated with highly accurate contour lines at close intervals, and the reproducibility of the terrain topography is high. The contour map is excellent in terms of quality and quality.

The contour map is one of the contour maps that connect points having the same value at regular intervals, and the contour map described in the present specification is a contour map in which undulations of terrain are constant. Not only the contour map that connects points with the same elevation at intervals, but also the contour map that shows points with the same depth at fixed contour intervals such as the sea and lake are included.

[0011]

To solve the above problems, the first invention is to divide a basic contour map represented by known contour lines into a plurality of meshes at regular intervals,
From the first step in which the center of each mesh is used as a grid point, and one of the grid points determined by the plurality of meshes obtained in the first step is selected as a focused interpolation point, The nearest contour group that intersects the extension line drawn in the azimuth direction is searched for two each on the high side and the low side of the elevation value, and four intersections that form the shortest distance to the interpolation point of interest are obtained, The second step of calculating the distance and the elevation value from the interpolation point of interest, and the steepest including the interpolation point of interest based on the elevation values of the four intersections obtained in the second step and the distance from the interpolation point of interest This is a method of interpolating the elevation value, which comprises a topographical cross-section represented by a straight line graph or a higher-order curve graph and a third step of reading the elevation value of the interpolation point of interest from the graph.

A second aspect of the invention is to divide a basic contour map represented by known contour lines into a plurality of meshes at regular intervals, and to make the center of each mesh a grid point.
One of the grid points determined by a plurality of meshes obtained in the process is selected as a focused interpolation point, and 1 is selected from this focused interpolation point.
The nearest contour line group that intersects the extension line drawn in 6 directions,
A second step in which two lines are searched for each of the high and low altitude values to obtain four intersections that form the shortest distance to the target interpolation point, and the distance from the target interpolation point and the altitude value are calculated. And, based on the elevation value of the four intersections obtained in the second step and the distance from the target interpolation point, the steepest terrain cross section including the target interpolation point is represented by a straight line graph or a higher-order curve graph. It is elevation data obtained by applying the third step of reading the elevation value of the interpolation point of interest from, and the second step and the third step to the grid points of all meshes.

A third aspect of the present invention is to divide a basic contour map represented by publicly known contour lines into a plurality of meshes at regular intervals, and to make the center of each mesh a grid point.
One of the grid points determined by a plurality of meshes obtained in the process is selected as a focused interpolation point, and 1 is selected from this focused interpolation point.
The nearest contour line group that intersects the extension line drawn in 6 directions,
A second step in which two lines are searched for each of the high and low altitude values to obtain four intersections that form the shortest distance to the target interpolation point, and the distance from the target interpolation point and the altitude value are calculated. And, based on the elevation value of the four intersections obtained in the second step and the distance from the target interpolation point, the steepest terrain cross section including the target interpolation point is represented by a straight line graph or a higher-order curve graph. Based on the elevation data obtained by applying the third step of reading the elevation value of the interpolation point of interest from above, and the second step and the third step to the grid points of all meshes, between the contour lines of the coarse intervals, It is a method of creating a contour map including a fourth step of interpolating the contour lines.

A fourth aspect of the present invention is to divide a basic contour map represented by known contour lines into a plurality of meshes at regular intervals, and to make the center of each mesh a grid point, and a first step.
One of the grid points determined by a plurality of meshes obtained in the process is selected as a focused interpolation point, and 1 is selected from this focused interpolation point.
The nearest contour line group that intersects the extension line drawn in 6 directions,
A second step in which two lines are searched for each of the high and low altitude values to obtain four intersections that form the shortest distance to the target interpolation point, and the distance from the target interpolation point and the altitude value are calculated. And, based on the elevation value of the four intersections obtained in the second step and the distance from the target interpolation point, the steepest terrain cross section including the target interpolation point is represented by a straight line graph or a higher-order curve graph. Based on the elevation data obtained by applying the third step of reading the elevation value of the interpolation point of interest from above, and the second step and the third step to the grid points of all meshes, between the contour lines of the coarse intervals, It is a contour map obtained by the 4th process of interpolating a contour line.

If the elevation values of the 16 intersections of the extension line to the 16 azimuth and the nearest contour line are not all equal, the interpolation point of interest is an inclined ground grid point,
The first intersection is the intersection that forms the shortest distance from the extension line from this inclined grid point to the 16th direction and the nearest contour line, and the distance from the inclined ground lattice point and the elevation value are calculated, and the extension from the first intersection to the 16th direction The intersection that forms the shortest distance from the contour line that intersects the line is defined as the second intersection, and the distance from the first intersection and the elevation value are calculated, and the first intersection is intersected with the extension line extending from the inclined ground grid point to 16 directions. The third intersection is searched for on a contour line whose altitude is different from the existing contour line, and the distance from the inclined ground grid point and the altitude value are calculated, and
It is possible to calculate the distance from the third intersection and the altitude value by setting the intersection having the shortest distance to the contour line intersecting the extension line to the azimuth as the fourth intersection.

If the elevation values of the 16 intersections of the extension line to the 16 azimuth and the nearest contour line are all the same, the interest interpolation point is an extension line to the 16 azimuth from the interest interpolation point. The first intersection is the intersection that forms the shortest distance with the nearest contour line, and the distance from the sloping ground grid point and the elevation value are calculated, and the intersection that forms the shortest distance with the contour line that intersects the extension line from the first intersection to the 16 bearings Is the second intersection, the distance from the first intersection and the elevation value are calculated, and the other nearest neighbor grid point for which the elevation value has been calculated is the inclined ground grid point, and the four intersections searched for at this inclined ground grid point Among them, the two intersections searched on the side where the altitude is different from the contour line where the first intersection exists are the third and fourth intersections, respectively, and the calculated distance and the elevation value are adopted, and the distance of the third intersection is focused. Add the distances between the interpolated points and the inclined ground grid points to obtain the third intersection It may be re-calculate the distance from the eye in the interpolation points.

[0017]

The present invention is constructed as described above,
In the method for interpolating elevation values according to the invention, first, in a first step, a basic contour map represented by known contour lines is divided into a plurality of meshes at regular intervals, and a grid point is formed at the center of each mesh. This basic contour map is provided by government agencies, companies, research institutes, etc.
A conventionally known appropriate one such as a 5 m contour map can be used. Next, in the second step, one is selected from the plurality of meshes obtained in the first step, the grid points of the mesh are defined as the target interpolation points, and extension lines are drawn in 16 azimuth directions from the target interpolation points. Draw each. The nearest contour group that intersects with the extension line of 16 directions is searched for two each on the high side and the low side, and four intersections that form the shortest distance from the interpolation point of interest are obtained. The straight line distance from the interpolation point of interest of the intersection is calculated, and the elevation value of the contour line where each intersection exists is used as the elevation value of the intersection.

Further, in the prior art, since an extension line is drawn only in four or eight directions and an intersection is searched for on a straight line, it is not possible to search a plurality of contour lines having different elevation values, or an interpolation point of interest is selected. Since the distance to the intersection may not always be the shortest distance, there was a problem in reliability as basic data for calculating the elevation value of the interpolation point of interest. However, in the present invention, since the extension line is drawn in the 16 azimuth directions from the interpolation point of interest, there is a high probability that it will intersect contour lines with different elevation values,
The distance from the interpolation point of interest to the intersection becomes the shortest distance or is as close as possible to the shortest distance, and the obtained altitude value has high reliability.

Then, in the third step, 4 obtained in the second step
A graph showing the relationship between the interpolation point of interest and the four intersections is created based on the elevation value and the distance of the four intersections. It has x
Plot four intersections with distance on the axis and elevation on the y-axis, apply a straight line or higher-order curve calculated based on the elevations and distances of these four intersections as an interpolation function, and plot the graph. create. This graph shows up and down total 4 including the interpolation point of interest.
The steep topographic cross section between the contour lines of the book is shown, and the elevation value corresponding to the position of the interpolation point of interest can be read from the graph of the steep topographic cross section. This graph may be a straight line graph, but if it is a high-order curve graph, the slope of the terrain can be reproduced more naturally and smoothly. For example, if a third-order Hermitian function based on the first-order difference method is applied, the reliability of the altitude value of the interpolation point of interest obtained from this function can be further enhanced.

Further, in the prior art, the search direction of the contour line from the interpolation point of interest is limited to 4 directions or 8 directions, and two or four intersections are searched for on a straight line across the interpolation point of interest. Was there. Therefore, the topographical cross section connecting the intersections does not always have the steepest slope, and an error is likely to occur in the calculated elevation value of the interpolation point of interest. However, in the present invention, an extension line is drawn in the 16 azimuth direction from the interpolation point of interest, and a contour line is searched for in any direction of the 16 azimuth directions. Therefore, the extension is performed at the shortest distance or at a position as close as possible to the shortest distance. You can search for intersections between lines and contour lines. Therefore, the graph of the terrain cross section connecting the four intersections shows the steepest slope, and the elevation value of the interpolation point of interest obtained from this graph becomes highly reliable.

The second invention is elevation data obtained by obtaining the elevation values of the grid points of all meshes by the elevation value interpolation method of the first invention. Interpolation of grid-like elevation values with high accuracy between contour lines of a known basic contour map to obtain elevation data that is academically superior and highly contributes to various fields in the field of earth science and engineering. You can

The third invention is a method of creating a contour map,
A fourth invention is a contour map created by this creating method. In both cases, as in the first and second inventions, when the basic contour map is divided into a plurality of meshes in the first step, four intersection points search in the second step and calculation of the distance from the target interpolation point and the elevation value are performed. In the third step, the preparation of the steepest terrain cross-section graph and the reading of the elevation value are applied to all the mesh grid points to obtain the elevation data. Next, in the fourth step, based on the elevation data, dense elevation lines are newly interpolated between known contour lines to create a contour map. This new contour line is interpolated by proportional distribution based on the elevation value of each grid point and the distance between adjacent grid points by, for example, a computer program. Of course, the contour lines can be interpolated not only by this proportional distribution method but also by other conventionally known methods. Since highly accurate elevation values are obtained for all grid points in the second and third steps, dense contour lines are naturally and smoothly interpolated with high accuracy in this fourth step. And the reproducibility of the actual terrain is high,
It is possible to create contour maps that are academically and quality superior.

Therefore, when a dense contour line is newly interpolated between existing basic contour lines to form a contour map, for example, a terrain with steep slopes on both sides and a gentle ridge in the center, and a valley with large bends Natural and smooth contour lines can be interpolated to obtain contour maps with high reproducibility of actual terrain even for special terrain and complex terrain such as terrain with ridges, ridges, ridges, and saddles. To be This method of creating a contour map can of course be applied to a contour map or the like.

Further, the second invention shown in the first invention to the fourth invention.
In the process, one of the procedures for searching the intersection from the focused interpolation point will be described in detail. First, the elevations of the 16 intersection points between the extension line extending from the focused interpolation point to 16 directions and the nearest contour line. When the values are not all equal, that is, when two contour lines with different altitudes are searched, the interpolation point of interest is the inclined ground grid point. Then, the intersection from the sloped grid point extending in 16 directions and the shortest distance to the nearest contour line is defined as the first intersection, and the distance from the sloped grid point to the first intersection and the altitude value are calculated. Next, an extension line is newly drawn from the first intersection in 16 directions, the intersection that forms the shortest distance from the contour line that intersects with this extension line is searched for, and the second intersection is determined. The distance from the first intersection to the second intersection And calculate the elevation value.

Further, the third intersection is searched for on a contour line which intersects with the extension line extending from the inclined ground grid point in 16 directions and has a different altitude from the contour line where the first intersection exists, and the third intersection point is searched from the inclined ground grid point. Calculate the distance to and altitude. Further, the intersection point forming the shortest distance from the contour line intersecting the extension line drawn from the third intersection point in 16 directions is searched for, and is set as the fourth intersection point, and the distance from the third intersection point to the fourth intersection point and the elevation value are calculated. .
Then, based on the altitude values and distances of the first to fourth intersections searched in this way, a graph of the steepest terrain cross section is created in the third step, and the altitude value of the interpolation point of interest is obtained.

Contrary to the above, when the elevation values at all 16 intersections of the extension line from the interpolation point of interest to the 16 azimuth and the nearest contour line are equal, that is, when contour lines with different elevation values are not found. It is unclear as it is whether the interpolation point of interest exists on a flat ground, or whether it is located on a ridge, valley, saddle, mountain pass, or mountain peak of complicated terrain. A search method for solving this problem will be described. First, as for the first intersection and the second intersection, the intersection that forms the shortest distance between the extension line to the 16 azimuths from the target interpolation point and the nearest contour line is the first intersection, and the target interpolation is performed, as in the normal search. Calculate the distance from the point to the first intersection and the elevation value. Then, the intersection point that forms the shortest distance with the contour line that intersects the extension line drawn in 16 directions from the first intersection point is
The intersection and the distance from the first intersection to the second intersection and the elevation value are calculated.

Next, unlike the usual case, the third and fourth intersections are searched for. First, apart from the relevant interpolation point, another grid point in the nearest neighborhood for which the elevation value has been calculated is found. Explore,
This is the inclined ground grid point. Of the four intersections that have been searched for at this inclined ground grid point, the first searched for at the interpolation point of interest.
It exists on the side where the elevation differs from the contour line where the intersection exists. 2
The three intersections are the third and fourth intersections, respectively. Since the distance and the altitude value at the third and fourth intersections have already been calculated, this value is also adopted this time. However, the distance from the target interpolation point of the third intersection is recalculated by adding the distance between the target interpolation point and the inclined ground grid point to the distance of the third intersection. Based on the elevation values and the distances of the four intersections calculated in this way, a graph of the steepest terrain cross section is created in the third step, and the elevation value of the interpolation point of interest is calculated. As described above, even if the interpolated point of interest existing at a special position is used, the positional relationship of the interpolated point of interest is correctly recognized by adopting the data of the neighboring inclined ground grid points, and the reliability is high. Elevation value can be calculated.

[0028]

The present invention will be described in detail below with reference to the drawings.
1 to 3 are first to third embodiments of the contour diagram of the present invention, which are the same as those used in the conventional example shown in FIGS. I am using a figure. Then, based on the elevation data (DEM) obtained by the interpolation method of the elevation value of the present invention, a contour line having a contour interval of 1 m is newly inserted between existing basic contour lines shown by thick black lines, as shown by black thin lines. It is inserted. Also,
The first embodiment shown in FIG. 1 is a contour map carried out on a terrain having steep slopes on both sides and a somewhat gentle ridge in the center,
The second embodiment shown in FIG. 2 is a contour map carried out on a terrain having severely curved contour lines, and the third embodiment shown in FIG. 3 is carried out on a complex terrain having peaks and saddles surrounded by curved valleys. It is the contour map which did.

Before describing the method of creating a contour map, the method of interpolating elevation values for obtaining elevation data will be described with reference to FIG.
The specific description will be made with reference to the schematic diagram of FIG. 7. First, in the first step, as shown in FIG. 4, a plurality of meshes (11) are drawn on the basic contour map (20) represented by contour lines (10) having a contour interval of 10 m at intervals of 10 m. 12), and a grid point (13) is provided at the center of each mesh (12).

Next, in the second step, the plurality of meshes are
One of the grid points (13) determined by (12) is selected as a target interpolation point P (14), and from this target interpolation point P (14),
As shown in FIG. 4, an extension line (15) Q _i (0 ≦ 0
i ≤ 15) respectively. Then, a neighboring contour line (10) that first intersects each extension line (15) is searched for.

In the example of the terrain of FIG. 5, extension lines of 16 directions
The contour line (10) where (15) first intersects is C ₂ and C ₃ , and it is possible to search for two contour lines (10) having different elevation values. In this case, the target interpolation point P (14) is the contour line (10) C ₂
Since it exists on the sloping ground between C _{3 and} C ₃ , P (14) is defined as the sloping ground grid point. Then, among the intersections of the extension lines (15) of 16 directions and the contour lines (10), as shown in FIG. 5, on the contour line (10) C ₂ side closest to the inclined ground grid point P (14), the intersection point (1
6) q ₁ and q ₂ are searched respectively, and the intersection points (16) q ₃ and q are located on the side of the contour line (10) C ₃ whose elevation value is different from that of the contour line (10) C _2.
Search ₄ each.

First, q ₂ is the shortest distance from the sloping ground grid point P (14) among a plurality of intersections (16) of the extension line (15) in 16 directions and the contour line (10) C ₂ as described above. First intersection of eggplant
(16) and q ₁ is an extension line to 16 directions subtracted from q _2.
Among the intersections (16) between (17) and the nearest contour line (10) C ₁ , the shortest distance is formed, which is the second intersection (16). If the contour line (10) C ₂ is different from the contour line (1)
0) If C ₁ does not exist, the tilted ground grid point P (14) and q ₂
An extension line (15) drawn between and the first contour line that intersects
The intersection (16) with (10) is defined as q ₁ .

On the other hand, q ₃ is a contour line (10) C in which q ₂ exists.
The contour line (10) C ₃ on the side opposite to ₂ and the inclined ground grid point P (1
Among multiple intersections (16) with the extension line (15) from 4),
It is the third intersection (16) forming the shortest distance. Also, q ₄ is an extension line (18) and a contour line (10) drawn from q _{3 in} 16 directions.
Of the plurality of intersections (16) with C ₄ , the _fourth distance is the shortest.
It is the intersection point (16). Also in this case, if the contour line (10) C
If there is no contour line (10) C ₄ whose altitude value is different from that of ₃ ,
Extension line (15) drawn between the inclined ground grid point P (14) and q ₃
And the intersection (16) with the first intersecting contour line (10) is q ₄
And

As described above, when the four intersections (16) q ₁ , q ₂ , q ₃ and q ₄ are searched for at the shortest distance from the inclined ground grid point P (14), the inclined ground grid point P (14) -intersection ( 16) the linear distance between q ₂ l _2, q ₂ linear distance between _{-q 1 l 1, P (14} ) -
linear distance between q ₃ l _3, q ₃ calculates the linear distance l ₄ between -q _4. Also, the contour lines at which each intersection (16) q _{1 to} q ₄ exists
(10) From the groups C _{1 to} C ₄ , the elevation values h _{1 to} h ₄ corresponding to the intersections (16) q _{1 to} q ₄ are read.

Next, in the third step, the product obtained in the second step was obtained.
Intersection (16) q₁, Q₂, Q₃, Q_FourAnd the interpolation point P (14) of interest
Create a graph showing the positional relationship. To do that,
Separation ₁~ L_Four, H on the y-axis₁~ H_FourTake the intersection (16)
q₁~ Q_FourPlot the coordinates of each₁~ L_FourAnd h₁~
h_FourInterpolate a straight line or higher-order curve calculated based on the value of
It is applied as a function to produce the graph shown in FIG. This
The shape of the graph of the intersection point (1
6) q₁~ Q_FourIt represents the steepest terrain section between. That
Then, from the graph of the above interpolation function,
Corresponding elevation value h_PAsk for.

In the present embodiment, a more natural and smooth topographic cross section graph can be drawn by applying a cubic Hermitian function by the first-order difference method as the interpolation function. Further, in the conventional technique, the topographical cross-section graph connecting the intersection points (4) does not necessarily have the steepest slope, but in the present invention,
Since it is a method to search _four intersections (16) q _{1 to} q 4 in the shortest distance in the azimuth direction, the topographic cross-section graph connecting each intersection (16) is closer to the actual topography and shows the steepest slope. It can be something. Therefore, the altitude value h _P of the interpolation point P (14) of interest obtained from such a graph is highly reliable.

Then, the four intersections of the second step as described above
(16) Search for q _{1 to} q ₄ , elevation values h _{1 to} h ₄ at each intersection (16)
Pay attention to the reading of the above, calculation of the distances l _{1 to} l ₄ , the preparation of the steepest topographic cross-section graph in the third step, and the reading of the elevation value h _P of the noted interpolation point P (14) from this graph. This is performed for the grid points (13) of all meshes (12) corresponding to the area, and the altitude values h _P of all the grid points (13) are recorded as the altitude data (DEM).

Here, as an exception to the second step, the intersection point (16) q when the target interpolation point P (14) exists at a special position
The search method of _{1 to} q ₄ will be described with reference to the interpolation point P (14) present in the valley portion where the bending is severe as shown in FIG. Also in this case, the extension line (1
5) is searched for an intersection (16) q ₂ that forms the shortest distance between the nearest contour line (10) C ₂ and the shortest distance between the extension line (17) drawn from q ₂ and the contour line (10) C ₁ The intersecting point (16) is q ₁ . Again, if there is not present different contours (10) C ₁ altitude value and if contour lines (10) C _2, extended line connecting interest in interpolation point P (14) the intersection of (16) q ₂ (15 ) And the first intersecting contour line (10) are q ₁ . Then, the distance l ₂ from the point of interest P (14) to the intersection (16) q ₂ and the distance l ₁ from q ₂ to q ₁ are calculated, and q
_From the contour line (10) C ₂ , C _{1 in which 2} , ₂ , q ₁ exist, q ₂ , q ₁
Read the altitude values h ₂ and h ₁ of.

Next, the intersection points (16) q ₃ and q ₄ are searched. However, in the case of the terrain as shown in FIG. 7, all the extension lines (15) drawn from the target interpolation point P (14) in 16 directions are contour lines (10) C.
_It intersects with ₂ and C ₁ , but does not intersect with the contour lines (10) C ₄ and C _3, and in the usual search method, there is a possibility that the focused interpolation point P (14) is erroneously recognized as existing on the flat ground. There is.

In order to solve this problem, the present invention uses
First, the focused interpolation point P (14) is defined as the reserved grid point P (14), and the nearest inclined ground grid point F (21) is searched from this reserved grid point P (14). This inclined ground grid point F (21) has already searched for the intersections (16) q ₃ and q ₄ with the contour lines (10) C ₃ and C _4, and the elevation values h ₃ and h _{4 of} q ₃ and q ₄ have already been searched. If, because it is already calculating the distance between the between the sloping grid point F (21) -q ₃ and q ₃ -q _2, employing the data as the data of the current pending grid points P (14).

However, the distance l ₃ is the distance between the reserved grid point P (14) and the slope ground grid point F (21) and the slope ground grid point F (2
1) and the intersection (16) q ₃ and the distance l ₄ is
The intersection (16) is the distance between q ₃ and q ₄ . By taking the distances l _{1 to} l ₄ thus obtained on the x-axis, the elevation values h _{1 to} h ₄ on the y-axis, and applying the cubic Hermitian function, the reserved grid point P (14) is obtained. It is possible to create a graph of the steepest terrain section including the altitude value h _P corresponding to the reserved grid point P (14) with high accuracy from this graph.

Further, in the prior art, as shown in FIGS. 12 to 15, even if the altitude value of the interpolation point p (1) of interest is inaccurate or erroneously recognized, the reliability of the altitude value is improved by the present invention. Can be raised and the problem can be solved. The process of calculating the elevation value will be described with reference to FIGS. 8 to 11. The positions of the basic contour map (20) and the interpolated point P (14) of interest used in these processes are the same as those in the conventional example of FIGS. It is the same.

First, as shown in FIG. 12, in the terrain having steep slopes on both sides and a slightly gentle ridge in the center, the contour lines (3) C ₃ and C ₄ cannot be searched conventionally, and the interpolation point p of interest is used.
(1) was erroneously recognized as existing on level ground. However, in the method of the present invention, as shown in FIG.
(10) Since C _{1 to} C ₄ can be searched, the point of interest P (14)
Is correctly recognized as existing on the ridge, and a highly reliable altitude value can be calculated.

Further, in FIG. 13, since the intersection (4) is searched for on a straight line across the interpolation point p (1) of interest, two intersections (4) or four intersections (4) are formed. Since the terrain cross section does not always have the steepest slope and the contour line (3) C ₄ cannot be searched, an error occurs in the elevation value of the interpolation point p (1) of interest. However, in the present invention, as shown in FIG. 9, intersections (16) q ₂ and q ₃ of the shortest distance are searched for in any direction in 16 directions from the interpolation point P (14) of interest, and each q Also when searching for ₁ and q ₄ , an extension line from the previous interpolation point P (14)
Separately from (15), extension lines (17) and (18) are newly drawn in 16 directions from q ₂ and q ₃ , respectively, and intersection points (16) q ₁ and q ₄ that form the shortest distance in any direction are obtained. It is something to explore. Therefore, the topographical cross-section graph drawn by the _four intersections (16) q _{1 to} q ₄ becomes the steepest slope or is as close as possible to the steepest slope, and therefore the elevation value h of the interpolation point P (14) of interest obtained from this graph. _P is
It is highly reliable.

Further, as shown in FIG. 14, the contour line (3) C ₄ cannot be conventionally detected at the interpolated point p (1) of interest present in a valley portion or a ridge having a large bend, which is a point on the flat ground. Was mistakenly recognized as. However, in the present invention, as shown in FIG. 10, the contour line (10) C ₄ can be detected via the target interpolation point P (14) and the neighboring slope ground grid point F (21), and the target interpolation point The point P (14) is surely recognized as existing on the valley or ridge, and a highly reliable altitude value is obtained.

Further, as shown in FIG. 15, the interpolated point p (1) of interest on the saddle part or the pass, etc. also has an intersection point on the conventional straight line.
In the method of searching (4), contour lines (3) C ₂ and C ₁ could be detected, but C ₃ and C ₄ could not be searched, and it was erroneously recognized as a point on the level ground. Also in this case, according to the method of the present invention, as shown in FIG. 11, intersections (16) on contour lines (10) C ₂ and C ₃ having different altitudes are arranged in arbitrary directions in 16 directions from the interpolation point P (14) of interest. )
While searching for q ₂ and q ₃ , this intersection (16) q ₂ and q ₃
Contour lines with different elevation values in any direction from 16 to 16
(10) to obtain a C _1, C ₄ on the intersection _{(16) q 1, q 4} . Therefore, four intersections (16) q _{1 to} q ₄ having different altitude values are obtained, and the interpolated point P (14) of interest is recognized to exist at the saddle or the summit, and a highly reliable altitude value is obtained. .

As described above, in order to create a contour map using the highly accurate altitude data obtained by the altitude value interpolating method proposed in the present invention, as the fourth step, the basic pattern given at the beginning is given. A dense contour line having a contour interval of 1 m is interpolated by a conventionally known method between existing contour lines (10) having a contour interval of 10 m in the contour map (20). Since highly accurate elevation data is used, more natural and smooth contour lines can be interpolated as compared with the conventional one, and an academically excellent detailed contour map can be obtained.

Then, in the contour map of the first embodiment carried out on the terrain having steep slopes on both sides and a slightly gentle ridge in the center shown in FIG. 1, the ridge is compared with the first conventional example shown in FIG. The unnatural inclination of the contour lines of the part was eliminated, and it was possible to obtain a contour map that was visually natural, smooth, and highly reproducible. In addition, in the contour map of the second embodiment executed on the terrain having the contour lines with sharp bends shown in FIG.
Natural and smooth contour lines could be interpolated as compared with the second conventional example shown in FIG. Further, in the contour map of the third embodiment carried out on the complex terrain having the peaks and saddles surrounded by the curved valleys shown in FIG. 3, the conventional example shown in FIG. 18 shows the valleys, peaks and saddles. The unnaturalness of contour lines was eliminated as shown in FIG. 3, and a product with high reproducibility and excellent contour map could be obtained.

Further, although the above-mentioned respective embodiments are carried out by the contour map showing the ups and downs of the land, it is also possible to carry out by the contour map showing the depth of the sea or lake at a constant contour line interval. The present invention can be applied not only to contour maps and contour maps, but also to known publicly known contour maps. As this contour map, for example, an isobar map showing the distribution of atmospheric pressure by isobars at regular intervals, an isothermal map showing the distribution of air temperature by isothermal lines at regular intervals, and the like, which represent the climate of the earth and liquids. ,
The present invention can be used for an isotherm diagram in which the temperature distribution of a gas or solid substance is represented by isotherms at regular intervals. In addition, the pressure, tension, and other physical stresses exerted on an object are tied with a constant equal value, which is also a kind of contour map. Between the contour lines of these contour maps, the elevation value interpolating method of the present invention enables highly accurate interpolation of the elevation values in a grid pattern. In addition, based on the elevation data obtained by this, dense contour lines can be interpolated with high accuracy between the contour lines of the contour map, and a detailed and reliable contour map can be obtained. You can get it.

[0050]

The present invention is configured as described above, and when the elevation data (DEM) is obtained by interpolating the elevation values in a grid pattern on a publicly known contour map, the 16 azimuth points from the interpolation point of interest are obtained. In any direction, four intersections that form the shortest distances from contour lines with different elevations are searched, and the elevation value of the interpolation point concerned is calculated based on the positional relationship and elevation value of these four intersections. , It is possible to obtain highly reliable altitude data. Therefore, it is possible to provide excellent elevation data for application in various fields in the earth science and engineering fields. Then, by using highly accurate elevation data, dense contour lines and / or contour lines are interpolated with high accuracy into a conventionally known contour map or contour map to obtain a contour map or contour map with high reproducibility of topographical relief. I can do things. The contour map or contour map thus obtained reproduces the terrain in detail and accurately, even if the terrain is complicated or special terrain with complicated undulations. It is possible to do, and it will be an academically and quality superior product.

[Brief description of drawings]

FIG. 1 is a first embodiment of the present invention, which has steep slopes on both sides,
A contour map of the terrain with a gentle ridge in the center.

FIG. 2 is a contour map of a terrain having contour lines with sharp bends according to the second embodiment of the present invention.

FIG. 3 is a contour map of a complex terrain having peaks and saddles surrounded by curved valleys according to a third embodiment of the present invention.

FIG. 4 is a conceptual diagram showing a state in which an extension line is drawn in 16 directions from a target interpolation point P.

FIG. 5 is a conceptual diagram showing a process of searching for four intersections between a target interpolation point P and a nearest contour line.

FIG. 6 is a steepest terrain cross-section graph created from the distances and elevation values of four intersections.

FIG. 7 is a conceptual diagram showing a process of searching for four intersections of reserved grid points P using adjacent inclined ground grid points F.

FIG. 8 is a conceptual diagram showing a search process of four intersections between a target interpolation point P having steep slopes on both sides and a center of which is located on a gradual ridge, and the nearest contour line.

FIG. 9 is a conceptual diagram showing a state in which four intersections with the nearest contour line are searched at the shortest distance from the target interpolation point P.

FIG. 10 is a conceptual diagram showing a contour line searching process at a target interpolation point P existing in a valley or a ridge having a large bend.

FIG. 11 is a conceptual diagram showing a contour line searching process at a target interpolation point P existing in a saddle part or a pass.

FIG. 12 is a conceptual diagram showing a contour line searching process by a conventional method in the same area as FIG.

FIG. 13 is a conceptual diagram showing a contour line searching process by a conventional method in the same area as FIG.

14 is a conceptual diagram showing a contour line searching process by a conventional method in the same area as FIG.

FIG. 15 is a conceptual diagram showing a process of searching for an intersection by the conventional method in the same area as FIG. 11.

FIG. 16 is a contour map created by the conventional method in the same area as FIG.

FIG. 17 is a contour map created by a conventional method in the same area as FIG.

FIG. 18 is a contour map created by a conventional method in the same area as FIG.

[Explanation of symbols]

10 contour lines 12 mesh 13 grid points 14 Interpolation points of interest 15 extension line 16 intersections 17 extension line 18 extension line 20 Basic contour map 21 inclined ground grid points

Claims (12)

[Claims] 1. A basic contour map represented by known contour lines,
Interpolation is performed by dividing the mesh into a plurality of meshes at regular intervals and selecting one from among the grid points determined by the meshes obtained in the first step and the first step in which the center of each mesh is the grid point. The nearest contour line group that intersects the extension line drawn in 16 directions from this point of interest interpolation point is searched for each of the high side and low side of the elevation value The second step of obtaining the four intersections forming the distance and calculating the distance and the elevation value from the target interpolation point, and the elevation value of the four intersections obtained in the second step and the distance from the target interpolation point In addition, the steepest landform cross section including the interpolation point of interest is represented by a straight line graph or a higher-order curve graph, and the elevation value is characterized by comprising a third step of reading the elevation value of the interpolation point of interest from this graph. Interpolation method. 2. A basic contour map represented by known contour lines,
Interpolation is performed by dividing the mesh into a plurality of meshes at regular intervals and selecting one from among the grid points determined by the meshes obtained in the first step and the first step in which the center of each mesh is the grid point. The nearest contour line group that intersects the extension line drawn in 16 directions from this point of interest interpolation point is searched for each of the high side and low side of the elevation value The second step of obtaining the four intersections forming the distance and calculating the distance and the elevation value from the target interpolation point, and the elevation value of the four intersections obtained in the second step and the distance from the target interpolation point In, the steepest terrain cross section including the interpolation point of interest is represented by a straight line graph or a higher-order curve graph, and the elevation value of the interpolation point of interest is read from this graph, and the second step and the third step. Elevation data characterized by being obtained by applying the grid points to all mesh points. 3. A basic contour map represented by known contour lines,
Interpolation is performed by dividing the mesh into a plurality of meshes at regular intervals and selecting one from among the grid points determined by the meshes obtained in the first step and the first step in which the center of each mesh is the grid point. The nearest contour line group that intersects the extension line drawn in 16 directions from this point of interest interpolation point is searched for each of the high side and low side of the elevation value The second step of obtaining the four intersections forming the distance and calculating the distance and the elevation value from the target interpolation point, and the elevation value of the four intersections obtained in the second step and the distance from the target interpolation point In, the steepest terrain cross section including the interpolation point of interest is represented by a straight line graph or a higher-order curve graph, and the elevation value of the interpolation point of interest is read from this graph, and the second step and the third step. Based on the elevation data obtained by applying the grid points to all the meshes, between the contour lines at the coarse intervals, How to create contour diagram, characterized in that comprising a fourth step interpolating a high line. 4. A basic contour map represented by known contour lines,
Interpolation is performed by dividing the mesh into a plurality of meshes at regular intervals and selecting one from among the grid points determined by the meshes obtained in the first step and the first step in which the center of each mesh is the grid point. The nearest contour line group that intersects the extension line drawn in 16 directions from this point of interest interpolation point is searched for each of the high side and low side of the elevation value The second step of obtaining the four intersections forming the distance and calculating the distance and the elevation value from the target interpolation point, and the elevation value of the four intersections obtained in the second step and the distance from the target interpolation point In, the steepest terrain cross section including the interpolation point of interest is represented by a straight line graph or a higher-order curve graph, and the elevation value of the interpolation point of interest is read from this graph, and the second step and the third step. Based on the elevation data obtained by applying the grid points to all the meshes, between the contour lines at the coarse intervals, Contour map obtained by the fourth step interpolating a high line. 5. The interpolated point of interest is an inclined ground grid point when the elevation values of the 16 intersections of the extension line to the 16 azimuth and the nearest contour line are not all equal, The first intersection is the intersection that forms the shortest distance from the extension line from this inclined grid point to the 16th direction and the nearest contour line, and the distance from the inclined ground lattice point and the elevation value are calculated, and the extension from the first intersection to the 16th direction The intersection that forms the shortest distance from the contour line that intersects the line is defined as the second intersection, and the distance from the first intersection and the elevation value are calculated, and the first intersection is intersected with the extension line extending from the inclined ground grid point to 16 directions. The third intersection is searched for on a contour line with a different altitude from the existing contour line, and the distance from the inclined grid point and the elevation value are calculated, and the contour line that intersects the extension line from the third intersection to 16 directions is the shortest. The intersection that forms the distance is the fourth intersection, and the third intersection The method of interpolating an elevation value according to claim 1, wherein the distance from the point and the elevation value are calculated. 6. The interpolated point of interest is an inclined ground grid point when the elevation values of the 16 intersections of the extension line to the 16 azimuth and the nearest contour line are not all equal, The first intersection is the intersection that forms the shortest distance from the extension line from this inclined grid point to the 16th direction and the nearest contour line, and the distance from the inclined ground lattice point and the elevation value are calculated, and the extension from the first intersection to the 16th direction The intersection that forms the shortest distance from the contour line that intersects the line is defined as the second intersection, and the distance from the first intersection and the elevation value are calculated, and the first intersection is intersected with the extension line extending from the inclined ground grid point to 16 directions. The third intersection is searched for on a contour line with a different altitude from the existing contour line, and the distance from the inclined grid point and the elevation value are calculated, and the contour line that intersects the extension line from the third intersection to 16 directions is the shortest. The intersection that forms the distance is the fourth intersection, and the third intersection The elevation data according to claim 2, wherein the distance from the point and the elevation value are calculated. 7. The interpolated point of interest is an inclined ground grid point when the elevation values of 16 intersections of the extension line to the 16 azimuth and the nearest contour line are not all equal, The first intersection is the intersection that forms the shortest distance from the extension line from this inclined grid point to the 16th direction and the nearest contour line, and the distance from the inclined ground lattice point and the elevation value are calculated, and the extension from the first intersection to the 16th direction The intersection that forms the shortest distance from the contour line that intersects the line is defined as the second intersection, and the distance from the first intersection and the elevation value are calculated, and the first intersection is intersected with the extension line extending from the inclined ground grid point to 16 directions. The third intersection is searched for on a contour line with a different altitude from the existing contour line, and the distance from the inclined grid point and the elevation value are calculated, and the contour line that intersects the extension line from the third intersection to 16 directions is the shortest. The intersection that forms the distance is the fourth intersection, and the third intersection The method for creating a contour map according to claim 3, wherein the distance from the point and the elevation value are calculated. 8. The interpolated point of interest is an inclined ground grid point when the elevation values of 16 intersections of the extension line to the 16 azimuth and the nearest contour line are not all equal, The first intersection is the intersection that forms the shortest distance from the extension line from this inclined grid point to the 16th direction and the nearest contour line, and the distance from the inclined ground lattice point and the elevation value are calculated, and the extension from the first intersection to the 16th direction The intersection that forms the shortest distance from the contour line that intersects the line is defined as the second intersection, and the distance from the first intersection and the elevation value are calculated, and the first intersection is intersected with the extension line extending from the inclined ground grid point to 16 directions. The third intersection is searched for on a contour line with a different altitude from the existing contour line, and the distance from the inclined grid point and the elevation value are calculated, and the contour line that intersects the extension line from the third intersection to 16 directions is the shortest. The intersection that forms the distance is the fourth intersection, and the third intersection The contour map according to claim 4, wherein the distance from the point and the altitude value are calculated. 9. The interpolated point of interest is an extended line from the interpolated point of interest to 16 azimuths when all the elevation values of 16 intersections of the extended line to the 16 azimuth and the nearest contour line are equal. The first intersection is the intersection that forms the shortest distance with the nearest contour line, and the distance from the inclined ground grid point and the elevation value are calculated, and 1 from the first intersection is calculated.
The second intersection is the intersection that forms the shortest distance with the contour line that intersects the extension lines to the six directions, and the distance from the first intersection and the elevation value are calculated, and the other neighboring grid points for which the elevation value has been calculated are sloped. 4 points that have already been searched at this sloping ground grid point
Of the two intersections, the two intersections searched on the side where the elevation is different from the contour line where the first intersection exists are the third and fourth intersections, respectively, and the calculated distance and elevation value are adopted, and the distance of the third intersection The method of interpolating an elevation value according to claim 1, wherein the distance between the target interpolation point and the inclined ground grid point is added to and the distance from the target interpolation point at the third intersection is recalculated. 10. The interpolation point of interest is an extension line from the interpolation point of interest to 16 orientations when the elevation values of all 16 intersections of the extension line to 16 orientations and the nearest contour line are equal. The first intersection is the intersection that forms the shortest distance with the nearest contour line, and the distance from the sloping ground grid point and the elevation value are calculated, and the intersection that forms the shortest distance with the contour line that intersects the extension line from the first intersection to the 16 bearings Is the second intersection, the distance from the first intersection and the elevation value are calculated, and the other nearest neighbor grid point for which the elevation value has been calculated is the inclined ground grid point, and the four intersections searched for at this inclined ground grid point Among them, the two intersections searched on the side where the altitude is different from the contour line where the first intersection exists are the third and fourth intersections, respectively, and the calculated distance and altitude value are adopted, and
3. The elevation data according to claim 2, wherein the distance between the interpolation point of interest and the inclined ground grid point is added to the distance of the intersection point to recalculate the distance from the interpolation point of interest of the third intersection point. 11. The interpolation point of interest is an extension line from the interpolation point of interest to 16 orientations when the elevation values of all 16 intersections of the extension line to 16 orientations and the nearest contour line are equal. The first intersection is the intersection that forms the shortest distance with the nearest contour line, and the distance from the sloping ground grid point and the elevation value are calculated, and the intersection that forms the shortest distance with the contour line that intersects the extension line from the first intersection to the 16 bearings Is the second intersection, the distance from the first intersection and the elevation value are calculated, and the other nearest neighbor grid point for which the elevation value has been calculated is the inclined ground grid point, and the four intersections searched for at this inclined ground grid point Among them, the two intersections searched on the side where the altitude is different from the contour line where the first intersection exists are the third and fourth intersections, respectively, and the calculated distance and altitude value are adopted, and
4. The method for creating a contour map according to claim 3, wherein the distance between the point of interest and the inclined ground grid point is added to the distance of the point of intersection to recalculate the distance from the point of interest of interpolation of the third point of intersection. 12. The interpolation point of interest is an extension line from the interpolation point of interest to 16 orientations when the elevation values of all 16 intersections between the extension line to 16 orientations and the nearest contour line are equal. The first intersection is the intersection that forms the shortest distance with the nearest contour line, and the distance from the sloping ground grid point and the elevation value are calculated, and the intersection that forms the shortest distance with the contour line that intersects the extension line from the first intersection to the 16 bearings Is the second intersection, the distance from the first intersection and the elevation value are calculated, and the other nearest neighbor grid point for which the elevation value has been calculated is the inclined ground grid point, and the four intersections searched for at this inclined ground grid point Among them, the two intersections searched on the side where the altitude is different from the contour line where the first intersection exists are the third and fourth intersections, respectively, and the calculated distance and altitude value are adopted, and
The contour map according to claim 4, wherein the distance from the target interpolation point of the third intersection is recalculated by adding the distance between the target interpolation point and the inclined ground grid point to the distance of the intersection.