Altitude change amount calculation system

Abstract

To provide an altitude change amount calculation system capable of obtaining a further reliable altitude change amount while referring to an altitude value related to a peripheral mesh.SOLUTION: An altitude change amount calculation system of the present invention is a system that uses a first topographical model and a second topographical model obtained at different points in time in the same target region to determine an "altitude change amount" based on altitude values pertaining to a first mesh constituting the first topographical model and altitude values pertaining to a second mesh constituting the second topographical model. The altitude change amount calculation system includes second mesh extracting means, intermediate altitude value setting means, intermediate altitude difference calculating means, corrected altitude value setting means, and altitude difference calculating means. An altitude difference calculated by the altitude difference calculating means is used as an altitude change amount between two points in time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technology for calculating the amount of change in elevation value between two time periods (hereinafter simply referred to as "elevation change"), and more specifically to an elevation change calculation system that can calculate the amount of elevation change while taking into account the planar deviation that occurs when measuring at two time periods. [Background technology]

[0002] The topography that forms the earth's surface is constantly changing, albeit minutely, due to crustal movement. The rate of change is usually extremely slow, but major earthquakes and other events can cause rapid topography change, and in some cases, large-scale soil movement. Furthermore, when landslides begin to occur due to heavy rain or earthquakes, the earth's surface also begins to change accordingly, and ultimately the landslide can move large masses of soil, causing extensive damage to the surrounding area.

[0003] Japan has repeatedly suffered devastating damage from natural disasters, but by tracking and understanding changes in topography, it may be possible to prevent such disasters or mitigate the damage. Furthermore, once a disaster occurs, comparing the topography before and after the disaster makes it possible to identify the damaged areas, estimate the causes of the disaster, and determine the possibility of secondary disasters, which is ultimately a very effective means of emergency response and recovery. In this way, understanding changes by comparing topography at different times, such as the past and present, is often extremely useful.

[0004] Comparing the topography of two periods can be used to detect changes in land use as well as changes in topography. For example, in July 2021, a landslide occurred in the Izuyama district of Atami City, which prompted a nationwide survey to understand the shape of embankments. In this case, too, comparing the topography of two periods is effective. In other words, if an area was a valley in the past but is now flat, it can be assumed that the area is an embankment.

[0005] However, it is not so easy to understand changes by comparing topography measured at two different times. For example, it is possible to create a topographic model such as a DEM (Digital Elevation Model) or DSM (Digital Surface Model) based on the results of aerial photogrammetry or airborne laser measurement, and then compare this topographic model between the two periods to understand changes. In this case, if there is no difference in the accuracy of the planar positions measured at both times, it is possible to understand changes in elevation values ​​with a fairly accurate accuracy.

[0006] However, the performance of measuring equipment differs between the past and present, and therefore the measurement accuracy of planar position also differs. In such cases, it is known that a so-called "positional deviation" occurs between the mesh that constitutes the DEM obtained from the past measurement (hereinafter referred to as the "previous mesh" for convenience) and the mesh that constitutes the DEM obtained from the current measurement (hereinafter referred to as the "current mesh" for convenience).

[0007] When there is a misalignment of meshes between two time periods, this misalignment must be taken into account in order to accurately grasp the amount of elevation change. Therefore, various techniques have been proposed to calculate the change in elevation value between two time periods after adjusting for the misalignment. For example, Patent Document 1 proposes a technique that assumes that the misalignment of meshes between two time periods is determined by the inclination direction of the slope, and then aligns the orientation of the meshes between the two time periods before comparing the elevation values. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2023-75394 Summary of the Invention [Problem to be solved by the invention]

[0009] As mentioned above, the technology disclosed in Patent Document 1 is based on the premise that the misalignment of meshes between two time periods is determined by the inclination direction of the slope. However, mesh misalignment is not limited to the inclination direction of the slope, and is thought to be caused by a combination of various factors. As mentioned above, misalignment can occur when the measurement accuracy of the planar position between the two time periods differs. In addition, since DEM and the like are essentially a forced alignment of discrete point cloud data, unique misalignment can occur for each mesh regardless of the slope inclination. Furthermore, Patent Document 1 does not disclose a method for resolving misalignment caused by such factors.

[0010] The object of the present invention is to solve the conventional problems, that is, to provide an elevation change calculation system that can more accurately determine the amount of change in elevation value while referring to the elevation values ​​of surrounding meshes. [Means for solving the problem]

[0011] The present invention focuses on the fact that the elevation value at a displaced location is calculated based on the elevation values ​​of surrounding meshes, and that this elevation value is used to correct the elevation value of the mesh in question, and is an invention based on an idea that has not been seen before.

[0012] The elevation change calculation system of the present invention uses a first terrain model and a second terrain model obtained at different times for the same target area, and calculates an "elevation change" based on the elevation values ​​of the first mesh that constitutes the first terrain model and the elevation values ​​of the second mesh that constitutes the second terrain model, and is equipped with a second mesh extraction means, an intermediate elevation value setting means, an intermediate elevation difference calculation means, a corrected elevation value setting means, and an elevation difference calculation means. The second mesh extraction means, when one first mesh from among a plurality of first meshes is selected as a "mesh of interest," extracts a second mesh from among the plurality of second meshes that is located in the same position as the mesh of interest as a "corresponding mesh," and extracts a plurality of second meshes surrounding the corresponding mesh as "surrounding meshes." The intermediate elevation value setting means is a means for setting two or more "surrounding intermediate elevation values" so that the elevation differences are equally spaced within the range between the elevation value of the corresponding mesh and the elevation values ​​of the surrounding meshes, and the intermediate elevation difference calculation means is a means for calculating the absolute value of the difference between the elevation value of the target mesh and the surrounding intermediate elevation value as the "intermediate elevation difference." The corrected elevation value setting means is a means for setting the surrounding intermediate elevation value corresponding to the intermediate elevation difference that is the smallest of the two or more intermediate elevation differences of the surrounding meshes as the "corrected elevation value." The elevation difference calculation means is a means for calculating the elevation difference between the corrected elevation value set by the corrected elevation value setting means and the elevation value of the target mesh. The elevation difference calculated by the elevation difference calculation means is then used as the amount of elevation change between the two periods.

[0013] The elevation change calculation system of the present invention may further include an intermediate elevation value determination means. When an intermediate elevation difference exceeds a predetermined threshold, the intermediate elevation value determination means determines the surrounding intermediate elevation value related to that intermediate elevation difference as an "inappropriate surrounding intermediate elevation value." In this case, the second mesh extraction means first extracts second meshes adjacent to the corresponding mesh as surrounding meshes, and if the surrounding mesh is determined to have an inappropriate surrounding intermediate elevation value by the intermediate elevation value determination means, further extracts second meshes adjacent to the surrounding mesh as surrounding meshes.

[0014] The elevation change calculation system of the present invention may further include a range-of-interest setting means for setting a "range of interest" based on the mesh of interest. In this case, the mesh extraction means extracts a second mesh included in the range of interest set by the range-of-interest setting means as a comparison mesh.

[0015] The elevation change calculation system of the present invention can also set the surrounding intermediate elevation value by dividing the surrounding intermediate elevation value and the elevation value related to the target mesh by a predetermined number of divisions. In this case, the number of divisions can also be set based on the value obtained by dividing the separation distance between the corresponding mesh and the surrounding mesh by a predetermined unit distance. [Effects of the Invention]

[0016] The altitude change calculation system of the present invention has the following advantages. (1) By comparing elevation values ​​at two different times while taking into account the positional shift of the mesh, a more accurate amount of elevation change can be obtained. (2) As a result, it is possible to estimate the shape of the embankment more accurately and to take effective measures in advance. (3) It also leads to more accurate tracking of topographical changes, which also allows for effective measures to be taken in advance. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a block diagram showing the main configuration of an altitude change calculation system according to the present invention; [Figure 2] (a) is a model diagram showing a schematic representation of multiple second meshes that make up a second terrain model, (b) is a model diagram showing a schematic representation of multiple first meshes that make up a first terrain model, and (c) is a model diagram showing a schematic representation of the situation in which the second meshes are aligned with the first mesh. [Figure 3] (a) is a model diagram that shows a schematic representation of a mesh of interest selected from the first terrain model, and (b) is a model diagram that shows a schematic representation of the corresponding mesh and surrounding meshes extracted from the second terrain model. [Figure 4] FIG. 10 is a model diagram schematically showing surrounding meshes extracted according to a range of interest. [Figure 5] FIG. 10 is a model diagram showing a schematic diagram of newly extracted surrounding meshes around the first extracted surrounding meshes. [Figure 6] FIG. 2 is a flowchart showing the main processing flow of the altitude change calculation system of the present invention. [Figure 7] 10 is a flowchart showing a process performed by an intermediate elevation value determining means to determine a minimum intermediate elevation difference. DETAILED DESCRIPTION OF THE INVENTION

[0018] An example of an embodiment of the altitude change calculation system of the present invention will be described with reference to the drawings. The present invention is capable of grasping the amount of change in altitude value (hereinafter simply referred to as "altitude change") by comparing the topography of two different periods. For convenience, one of the two periods will be referred to as the "first period" and the other as the "second period." Note that the newer of the two periods can be referred to as the first period and the older as the second period, or the older of the two periods can be referred to as the first period and the newer as the second period. Below, an example will be described in which the newer of the two periods is referred to as the first period and the older as the second period.

[0019] 1 is a block diagram showing the main components of an elevation change calculation system 100 of the present invention. As shown in this figure, the elevation change calculation system 100 of the present invention comprises second mesh extraction means 101, intermediate elevation value setting means 102, intermediate elevation difference calculation means 103, corrected elevation value setting means 104, and elevation difference calculation means 105, and can also comprise intermediate elevation value determination means 106, focus range setting means 107, focus mesh selection means 108, map creation means 109, first terrain model storage means 110, second terrain model storage means 111, etc.

[0020] Each of the means constituting the altitude change calculation system 100 (particularly the second mesh extraction means 101 to the map creation means 109) can be manufactured as a dedicated means, or a general-purpose computer device can be used. That is, the computer device executes calculation processing according to a predetermined program, thereby performing processing specific to each means. This computer device is equipped with a processor such as a CPU, memories such as ROM and RAM, and some also include input means such as a mouse and keyboard, and a display, and can be configured, for example, as a personal computer (PC) or a server.

[0021] The first terrain model storage means 110 and the second terrain model storage means 111 can be configured as a storage device of a general-purpose computer (for example, a personal computer) or as a database server. When configured as a database server, they can be placed on a local network (LAN: Local Area Network) or as a cloud server that stores data via the Internet.

[0022] Hereinafter, each of the main elements constituting the altitude change calculation system 100 of the present invention will be described in detail.

[0023] (First terrain model storage means and second terrain model storage means) The first terrain model storage means 110 stores a three-dimensional model of the terrain at a first time (hereinafter referred to as the "first terrain model"), and the second terrain model storage means 111 stores a three-dimensional model of the terrain at a second time (hereinafter referred to as the "second terrain model"). The first terrain model and the second terrain model are so-called three-dimensional terrain models such as DEM or DSM created based on point cloud data obtained by aerial photogrammetry or airborne laser measurement. Of course, the first terrain model and the second terrain model include the area for which the amount of elevation change is to be determined (hereinafter referred to as the "target area").

[0024] Typically, a 3D terrain model is composed of small areas (hereafter referred to as "meshes") that divide the target planar area. These meshes are formed, for example, by dividing the area into orthogonal grids, and each mesh has a representative point, to which height information (elevation value) is assigned. Since point clouds obtained by measurement are often random data (data that are irregularly arranged on a plane), geometric calculations are often used to assign elevation values ​​to the representative points of the mesh. Examples of calculation methods include the TIN (Triangulated Irregular Network) method, which calculates height using an irregular triangulation network formed from random data, the Nearest Neighbor method, which uses the nearest measurement point, as well as the Inverse Distance Weighting (IDW), Kriging method, and averaging method.

[0025] FIG. 2(a) is a model diagram showing multiple meshes (hereinafter referred to as "second meshes") constituting a second terrain model, and FIG. 2(b) is a model diagram showing multiple meshes (hereinafter referred to as "first meshes") constituting a first terrain model. As shown in this figure, 3D terrain models from different time periods may have different mesh sizes and may have different positions of the grid lines dividing the meshes. When comparing 3D terrain models from two time periods, as in the present invention, the mesh sizes and grid positions of the two time periods are often matched, and the 3D terrain model with the smaller mesh is typically used. For example, in FIG. 2(c), the second mesh constituting the second terrain model is larger than the first mesh constituting the first terrain model, so the second mesh is reconfigured to have the same size and layout as the first mesh. In this case, the newly configured second mesh should inherit the elevation values ​​of the original second mesh in the same location.

[0026] (Means for selecting meshes of interest) The mesh-of-interest selection means 108 is a means for selecting one of the multiple first meshes that make up the first terrain model as a “mesh of interest.” This mesh-of-interest selection means 108 can be configured to select all of the first meshes included in the target area as meshes of interest, and can, for example, select the first mesh in the upper left corner, the first mesh to the right, and the first mesh below.

[0027] (Second mesh extraction means) The second mesh extraction means 101 is a means for extracting a "corresponding mesh" and "surrounding meshes" from the plurality of second meshes that make up the second terrain model. Of these, the corresponding mesh is the second mesh that is located in the same position as the mesh of interest in the first terrain model, while the surrounding meshes are the plurality of second meshes that are located around the corresponding mesh. Therefore, when the mesh of interest selection means 108 selects a mesh of interest as shown in Figure 3(a), the second mesh extraction means 101 extracts a corresponding mesh from the second terrain model as shown in Figure 3(b), and then extracts the surrounding meshes based on the corresponding mesh.

[0028] As shown in FIG. 3(b), the second mesh extraction means 101 can extract second meshes adjacent to a corresponding mesh as peripheral meshes (M01 to M08 in the figure). Alternatively, the second mesh extraction means 101 can be configured to extract peripheral meshes based on a range set by the interest range setting means 107 (hereinafter referred to as the "interest range"). For example, when an operator inputs a desired interest range using a keyboard, pointing device, or the like, the interest range setting means 107 sets the interest range (circular in the figure) for the second terrain model as shown in FIG. 4, and the second mesh extraction means 101 extracts peripheral meshes according to the interest range. Note that in this figure, second meshes that are partially included in the interest range are extracted as peripheral meshes, but second meshes that are entirely included in the interest range can also be configured to be extracted as peripheral meshes.

[0029] (Means for setting intermediate elevation values) The intermediate elevation value setting means 102 is a means for setting two or more elevation values ​​(hereinafter referred to as "surrounding intermediate elevation values") for the surrounding meshes based on the elevation value of the corresponding mesh and the elevation values ​​of the surrounding meshes. More specifically, the intermediate elevation value setting means 102 sets two or more surrounding intermediate elevation values ​​within the range between the elevation value of the corresponding mesh and the elevation values ​​of the surrounding meshes, and sets surrounding intermediate elevation values ​​for all surrounding meshes. For example, in the case where eight surrounding meshes (M01 to M08) are extracted around the corresponding mesh as shown in Figure 3(b), two or more surrounding intermediate elevation values ​​are set for each of the eight surrounding meshes.

[0030] The surrounding intermediate elevation values ​​can be set by dividing the elevation value of the corresponding mesh and the elevation values ​​of the surrounding meshes by a predetermined number (hereinafter referred to as the "number of divisions"). For example, if the elevation value of the corresponding mesh is "110.50m", the elevation value of the surrounding mesh is "110.00m", and the number of divisions is "10", the surrounding intermediate elevation values ​​will be set as "110.05", "110.10", "110.15", ... "110.40", "110.45", i.e., 9 surrounding intermediate elevation values ​​will be set.

[0031] Furthermore, the number of divisions can be set to any desired number, such as 5 or 10, or can be set based on a "separation distance" and a "unit distance." Here, the separation distance is the distance between the centers of the corresponding mesh and the surrounding mesh, and the unit distance is a predetermined length. When setting the number of divisions based on the separation distance and the unit distance, it is advisable to set it based on the value obtained by dividing the separation distance by the unit distance. For example, if the unit distance is 10 cm and the separation distance is 1.0 m, the number of divisions can be set as "1.0 m ÷ 0.1 m = 10."

[0032] (Means for calculating intermediate elevation difference) The intermediate elevation difference calculation means 103 is a means for calculating the absolute value of the difference between the elevation value of the corresponding mesh and the surrounding intermediate elevation value (hereinafter referred to as "intermediate elevation difference"). The intermediate elevation difference calculation means 103 calculates the intermediate elevation difference for all surrounding intermediate elevation values ​​set by the intermediate elevation value setting means 102. For example, in a case where eight surrounding meshes (M01 to M08) are extracted around the corresponding mesh as shown in FIG. 3(b), and nine surrounding intermediate elevation values ​​are set for each of the surrounding meshes, an intermediate elevation difference of "8 x 9 = 72" is calculated.

[0033] (Means for setting corrected altitude value) The corrected elevation value setting means 104 selects the minimum intermediate elevation difference (hereinafter simply referred to as the "minimum intermediate elevation difference") from among the multiple (72 in the above example) intermediate elevation differences related to the corresponding mesh, and sets the surrounding intermediate elevation value (hereinafter referred to as the "corresponding intermediate elevation value") related to that minimum intermediate elevation difference as the "corrected elevation value." If a "positional shift" occurs between the first mesh and the second mesh, i.e., if the mesh of interest (first terrain model) is considered to be located in a different position from the corresponding mesh in the second terrain model, the position of the corresponding intermediate elevation value that is closest to the elevation value of the mesh of interest can be considered to be the original position of the mesh of interest in the second terrain model. Therefore, the elevation value of the corresponding mesh is corrected to the corresponding intermediate elevation value, i.e., a new corrected elevation value is set as the elevation value of the corresponding mesh.

[0034] However, there are cases where the minimum intermediate elevation difference selected by the corrected elevation value setting means 104 is not sufficiently small, i.e., the corresponding intermediate elevation value is not close to the elevation value of the mesh of interest. Therefore, instead of immediately setting the corresponding intermediate elevation value as the corrected elevation value, it is possible to select a new minimum intermediate elevation difference and then set the corrected elevation value. In this case, it is preferable for the intermediate elevation value determination means 106 to make a determination on the first minimum intermediate elevation difference. This intermediate elevation value determination means 106 compares the minimum intermediate elevation difference with a predetermined threshold value (hereinafter referred to as the "difference threshold"), and if the minimum intermediate elevation difference exceeds the difference threshold, determines that the minimum intermediate elevation difference is inappropriate, and sets the surrounding intermediate elevation value (i.e., the corresponding intermediate elevation value) related to that minimum intermediate elevation difference as an "inappropriate surrounding intermediate elevation value."

[0035] If the intermediate elevation value determination means 106 determines that a corresponding intermediate elevation value is an inappropriate surrounding intermediate elevation value, the corresponding intermediate elevation value may not be set as a corrected elevation value. In this case, the second mesh extraction means 101 extracts multiple (16 in the figure) second meshes adjacent to the surrounding meshes (M01 to M08) extracted the first time as new surrounding meshes (M09 to M24), as shown in Figure 5. Then, the intermediate elevation value setting means 102 sets N surrounding intermediate elevation values ​​for each of the 16 surrounding meshes, and the intermediate elevation difference calculation means 103 calculates 16 x N intermediate elevation differences. Then, the corrected elevation value setting means 104 again selects the smallest intermediate elevation difference and sets the corresponding intermediate elevation value as the corrected elevation value.

[0036] (Elevation difference calculation means) The elevation difference calculation means 105 is a means for calculating the difference between the corrected elevation value and the elevation value of a mesh of interest (hereinafter referred to as "elevation difference"). The elevation difference calculated by the elevation difference calculation means 105 is then set as the "elevation change amount" for that mesh of interest. Once all first meshes included in the target area have been selected as meshes of interest, that is, once the elevation change amounts have been obtained for all first meshes included in the target area, an "elevation change map" can also be created by the map creation means 109. This elevation change map shows the elevation change amount for each mesh, and is a map in which each mesh is assigned a display color according to the elevation change amount. It is preferable to set the display colors assigned to the meshes in stages after dividing the elevation change amount into multiple ranges.

[0037] (Processing flow) The main processing of the altitude change calculation system 100 of the present invention will be described in detail below with reference to Fig. 6. Fig. 6 is a flow chart showing the flow of the main processing of the altitude change calculation system 100 of the present invention. In this figure, the action to be performed is shown in the center column, what is necessary for that action is shown in the left column, and what results from that action is shown in the right column.

[0038] To grasp the elevation change amount using the elevation change amount calculation system 100 of the present invention, first, the target mesh selection means 108 selects a "target mesh" for the first terrain model read out from the first terrain model storage means 110 (Step 201 in Fig. 6). Next, the second mesh extraction means 101 extracts a "corresponding mesh" and "surrounding meshes" using the second terrain model read out from the second terrain model storage means 111 (Step 202 in Fig. 6).

[0039] Once the corresponding mesh and surrounding meshes are extracted, the intermediate elevation value setting means 102 sets two or more "surrounding intermediate elevation values" for each of the 16 surrounding meshes (Step 203 in FIG. 6), and the intermediate elevation difference calculation means 103 calculates an "intermediate elevation difference" for each surrounding intermediate elevation value (Step 204 in FIG. 6). Then, the corrected elevation value setting means 104 selects the "smallest intermediate elevation difference" from the multiple intermediate elevation differences and also selects a "corresponding surrounding intermediate elevation value" (Step 205 in FIG. 6).

[0040] As mentioned above, the minimum intermediate elevation difference selected by the corrected elevation value setting means 104 may not be sufficiently small, i.e., the corresponding surrounding intermediate elevation value may not approximate the elevation value of the target mesh. In this case, as shown in FIG. 7, the intermediate elevation value determination means 106 may perform a first determination of the minimum intermediate elevation difference (Step 209 in FIG. 7). That is, if the intermediate elevation value determination means 106 determines the corresponding surrounding intermediate elevation value to be an "inappropriate surrounding intermediate elevation value" (No in Step 209), a new surrounding mesh is extracted around the first extracted surrounding mesh (Step 202), a surrounding intermediate elevation value is set (Step 203), an intermediate elevation difference is calculated (Step 204), and a corresponding intermediate elevation value is selected (Step 205). On the other hand, if the minimum intermediate elevation difference is below the difference threshold (Yes in Step 209), the corresponding intermediate elevation value is selected without extracting a new surrounding mesh, and the process proceeds to the subsequent steps.

[0041] When the corresponding intermediate elevation value is selected, the corrected elevation value setting means 104 sets the corresponding intermediate elevation value as the "corrected elevation value" (Step 206 in FIG. 6), and the elevation difference calculation means 105 calculates the "elevation difference" (Step 207 in FIG. 6). When the series of processes described up to this point (Steps 201 to 207) are executed for all first meshes included in the target area (Step 208 in FIG. 6), the map creation means 109 creates an "elevation change map." [Industrial Applicability]

[0042] The elevation change calculation system of the present invention can be used in a variety of cases to grasp elevation changes, such as estimating topographical changes such as the shape of embankments, tracking the amount of displacement of slopes, or detecting the subsidence of structures such as bridges, dams, and office buildings.The present invention can prevent serious accidents such as the collapse of embankments and landslides, and considering that it can detect abnormalities in construction infrastructure such as bridges in advance, it can be said that the present invention is not only applicable to industry but is also an invention that is expected to make a great contribution to society. [Explanation of symbols]

[0043] 100 Altitude change calculation system of the present invention 101 (Elevation change calculation system) second mesh extraction means 102 (Elevation change calculation system) intermediate elevation value setting means 103 (Elevation change calculation system) intermediate elevation difference calculation means 104 (Altitude change calculation system) Corrected altitude value setting means 105 (Elevation change calculation system) Elevation difference calculation means 106 (Elevation change calculation system) intermediate elevation value determination means 107 (Altitude change calculation system) focus range setting means 108 (Elevation change calculation system) method of selecting meshes of interest 109 Map creation method (of the altitude change calculation system) 110 (of the elevation change calculation system) first terrain model storage means 111 (of the elevation change calculation system) second terrain model storage means

Claims

1. A system for calculating an amount of elevation change based on an elevation value of a first mesh constituting the first terrain model and an elevation value of a second mesh constituting the second terrain model, the system using a first terrain model and a second terrain model obtained at different times in the same target area, the system comprising: a second mesh extraction means for extracting, when one of the plurality of first meshes is selected as a "mesh of interest," a second mesh of the plurality of second meshes that is located at the same position as the mesh of interest as a "corresponding mesh," and extracting a plurality of second meshes located around the corresponding mesh as "peripheral meshes"; an intermediate elevation value setting means for setting two or more "surrounding intermediate elevation values" so that the elevation differences are equal to each other within the range between the elevation value of the corresponding mesh and the elevation value of the surrounding mesh; an intermediate elevation difference calculation means for calculating an absolute value of the difference between the elevation value of the mesh of interest and the surrounding intermediate elevation value as an "intermediate elevation difference"; a corrected elevation value setting means for setting the peripheral intermediate elevation value relating to the intermediate elevation difference that shows the smallest value from among two or more intermediate elevation differences relating to each of the peripheral meshes as a "corrected elevation value"; an elevation difference calculation means for calculating an elevation difference between the corrected elevation value set by the corrected elevation value setting means and an elevation value related to the target mesh, The altitude difference calculated by the altitude difference calculation means is set as the altitude change amount. An altitude change calculation system characterized by:

2. and an intermediate elevation value determining means for determining, when the intermediate elevation difference indicating the minimum value exceeds a predetermined threshold, the surrounding intermediate elevation value relating to the intermediate elevation difference as an "inappropriate surrounding intermediate elevation value," the second mesh extraction means first extracts the second mesh adjacent to the corresponding mesh as the surrounding mesh, and when the surrounding mesh is determined to have an inappropriate surrounding intermediate elevation value by the intermediate elevation value determination means, further extracts the second mesh adjacent to the surrounding mesh as the surrounding mesh; 2. The altitude change calculation system according to claim 1.

3. Further provided is a focus range setting means for setting a "focus range" based on the focus mesh, the second mesh extraction means extracts the second mesh included in the range of interest set by the range of interest setting means as the peripheral mesh; 2. The altitude change calculation system according to claim 1.

4. the intermediate elevation value setting means sets the surrounding intermediate elevation value by proportionally dividing the surrounding intermediate elevation value and the elevation value related to the target mesh by a predetermined number of divisions; 2. The altitude change calculation system according to claim 1.

5. The number of divisions is set based on a value obtained by dividing the separation distance between the corresponding mesh and the surrounding mesh by a predetermined unit distance.

5. The altitude change calculation system according to claim 4.

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