Ground evaluation method

Abstract

To accurately evaluate a degree of irregularity in the ground.SOLUTION: A ground evaluation method includes: calculation of a first Laplacian as an index of irregularity in the ground in a certain region from altitude data for each section when the certain region is divided into a first mesh size; calculation of second Laplacian as an index of irregularity in the ground in the certain region from altitude data for each section when the certain region is divided into a second mesh size differing from the first mesh size; and evaluation of a degree of irregularity in the ground in the certain region by using a computer on the basis of the first Laplacian and the second Laplacian.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a ground evaluation method. [Background technology]

[0002] In recent years, many human and property damages have been caused by concentrated heavy rains in urban areas, and the need for flood risk assessment has increased. In response to this, local governments and the like have created and published their own flood hazard maps. Meanwhile, companies with bases (factories, branches, etc.) scattered throughout the country may compare risk levels to determine priorities when taking flood prevention measures, but since conditions such as damage estimates differ for each local government, it is necessary to investigate the risk levels individually, which is time-consuming. Therefore, a method has been proposed to assess risk levels in different regions using the same index. For example, Non-Patent Document 1 discloses a method for assessing the risk level of flooding by using the Laplacian, which is often used as an index of topographical unevenness, in order to simply assess the risk level of flooding (inland flooding and outside flooding) that the land inherently has using the same index nationwide. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Obayashi Corporation Technical Research Institute Report No. 79 2015 "Study on simplified risk assessment of urban flood damage using GIS data" Summary of the Invention [Problem to be solved by the invention]

[0004] In the risk assessment method of Patent Document 1, the unevenness of the ground is calculated using elevation data obtained by dividing the area to be assessed into meshes of a given size (each side is 250 m long), but in this case, it was difficult to accurately grasp depressions of different scales. For example, when the average elevation data obtained by dividing the area to be assessed into a relatively large scale of 250 m is used, it was difficult to reflect in the assessment of unevenness areas areas where the elevation difference changes locally in a narrow area of ​​about 50 m. In other words, it was difficult to accurately assess the unevenness of the ground, and there was a possibility of a discrepancy between the unevenness assessment and the actual flood risk.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to accurately evaluate the unevenness of the ground. [Means for solving the problem]

[0006] A main invention for achieving the above object includes: calculating a first Laplacian, which is an index of ground unevenness in a certain area, from elevation data for each section when the certain area is divided into a first mesh size; calculating a second Laplacian, which is an index of ground unevenness in the certain area, from elevation data for each section when the certain area is divided into a second mesh size different from the first mesh size; and evaluating the ground unevenness in the certain area using a computer based on the first Laplacian and the second Laplacian. If the first Laplacian and the second Laplacian overlapping in a certain portion of the certain region are both positive values, the certain portion is evaluated as a depression. The ground evaluation method is characterized by:

[0007] Other features of the present invention will become apparent from the following detailed description of the present invention and the accompanying drawings. Effect of the Invention

[0008] According to the present invention, the unevenness of the ground can be accurately evaluated. [Brief description of the drawings]

[0009] [Figure 1] FIG. 13 is a diagram illustrating a method for calculating the Laplacian. [Diagram 2] FIG. 13 is a diagram illustrating an example in which the Laplacian is calculated for a certain region with a mesh size of 250 m. [Diagram 3] FIG. 13 is a diagram illustrating an example of a case where the Laplacian is calculated for a certain region with a mesh size of 50 m. [Figure 4] 1 is a diagram for explaining an area EA that is a target of unevenness evaluation. FIG. [Diagram 5] Fig. 5A is a diagram showing elevation data for each of the 3×4 meshes that make up area M250. Fig. 5B is a diagram showing the Laplacian L calculated for each mesh based on the elevation data in Fig. 5A. [Figure 6] This is a diagram showing the unevenness of the ground when the area EA is divided into a mesh size of 250 m. [Figure 7] Fig. 7A is a diagram showing elevation data for each of the 5 vertical × 4 horizontal meshes that make up area M100. Fig. 7B is a diagram showing the Laplacian L calculated for each mesh based on the elevation data in Fig. 7A. [Figure 8] This is a diagram showing the unevenness of the ground when the area EA is divided into a mesh size of 100 m. [Figure 9] Fig. 9A is a diagram showing elevation data for each of the 6 vertical × 6 horizontal meshes that make up area M50. Fig. 9B is a diagram showing the Laplacian L calculated for each mesh based on the elevation data in Fig. 9A. [Figure 10] This is a diagram showing the unevenness of the ground when the area EA is divided into a mesh size of 50 m. [Figure 11] This figure shows the unevenness of the ground when the Laplacian obtained when the area EA is divided into a mesh size of 250 m is combined with the Laplacian obtained when the area is divided into a mesh size of 100 m. [Figure 12]This figure shows the unevenness of the ground when the Laplacian obtained when the area EA is divided into a mesh size of 250 m, the Laplacian when it is divided into a mesh size of 100 m, and the Laplacian when it is divided into a mesh size of 50 m are combined. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A ground evaluation method comprising: calculating a first Laplacian, which is an index of ground unevenness in a certain area, from elevation data for each division when the certain area is divided into a first mesh size; calculating a second Laplacian, which is an index of ground unevenness in the certain area, from elevation data for each division when the certain area is divided into a second mesh size different from the first mesh size; and evaluating the ground unevenness in the certain area using a computer based on the first Laplacian and the second Laplacian.

[0011] According to this ground evaluation method, the ground unevenness is evaluated based on the first and second Laplacians calculated from elevation data of different mesh sizes, so that the effects of local depressions and wide-area depressions in the ground are easily reflected. Furthermore, if the first and second Laplacians are calculated using nationally uniform elevation data, regional variation is unlikely to occur, and unevenness evaluation can be performed using the same index. This allows the ground unevenness to be accurately evaluated.

[0012] In such a ground evaluation method, it is desirable that the length of one side of the first mesh size is at least twice the length of one side of the second mesh size.

[0013] According to this ground evaluation method, by dividing the area to be evaluated into meshes with sides that differ in length by at least twice, it becomes easier to deal with depressions of different scales, such as depressions that form over a wide area or localized depressions, and the unevenness of the ground can be evaluated more accurately.

[0014] In such a ground evaluation method, it is preferable that the first mesh size and the second mesh size are each changeable.

[0015] According to this ground evaluation method, a more accurate evaluation of unevenness can be performed by calculating the Laplacian by selecting an appropriate mesh size according to the scale of unevenness in each terrain, such as densely populated urban areas or mountainous areas along mountains.

[0016] In such a ground evaluation method, it is desirable to calculate a third Laplacian, which is an index of the ground unevenness of the certain area, from elevation data for each division when the certain area is divided into a third mesh size different from the first mesh size and the second mesh size, and to evaluate the degree of ground concavity of the certain area using a computer based on the first Laplacian, the second Laplacian, and the third Laplacian.

[0017] According to this ground evaluation method, by using three types of Laplacians with different mesh sizes, unevenness at different scales can be more easily reflected, and therefore a more accurate evaluation can be performed compared to the case where the unevenness of the ground is evaluated based on two types of Laplacians, the first Laplacian and the second Laplacian.

[0018] In such a ground evaluation method, it is desirable to calculate n types of Laplacians that each represent an index of the ground unevenness of the certain area from elevation data for each division when the certain area is divided into n types of mesh sizes, and to evaluate the degree of ground concavity of the certain area using a computer based on two or more of the n types of Laplacians.

[0019] According to this ground evaluation method, by calculating multiple Laplacians with different mesh sizes, it is possible to easily respond to unevenness of different scales, so by calculating multiple types (n types) of Laplacians and evaluating the ground unevenness based on two or more Laplacians from among them, it becomes easier to perform an accurate evaluation that corresponds to the actual ground unevenness.

[0020] In such a ground evaluation method, it is desirable that the length of one side of the mesh size is 5 m or more.

[0021] According to this ground evaluation method, if the mesh size is 5m or more, the Laplacian can be calculated based on highly uniform and stable data published by the Ministry of Land, Infrastructure, Transport and Tourism, etc. Furthermore, by setting the mesh size to 5m or more, the data is less likely to become complicated compared to when the mesh is too fine, and it is easier to suppress the occurrence of noise, making it easier to accurately evaluate the unevenness of the ground.

[0022] In such a ground evaluation method, it is desirable to evaluate the risk of flood damage in the certain area based on the evaluation result of the unevenness of the ground in the certain area.

[0023] According to such a ground evaluation method, the area where meshes evaluated as depressions overlap is likely to have a lower ground elevation than the surrounding area, and is therefore highly likely to be flooded in the future due to heavy rain, etc. Therefore, by taking into consideration the evaluation results of the unevenness of the ground using multiple Laplacians (e.g., the first Laplacian and the second Laplacian), it is possible to objectively evaluate the risk of future flooding, etc.

[0024] === Implementation form === In general, damage caused by flooding is likely to occur in areas where the elevation of the ground is lower than that of the surrounding areas. In other words, in areas where the ground is a depression (depression), there is a risk that once flooding begins, the flooding will progress at a rapid rate. Therefore, in this embodiment, the Laplacian is used as an index for determining the unevenness of the terrain to evaluate the unevenness of the ground in a certain area and determine the flood risk of the area. <Evaluation of ground unevenness using Laplacian> First, the basic principle of ground unevenness evaluation using the Laplacian will be explained. Conventionally, the Laplacian has often been used as an index of topographical unevenness, and by calculating the Laplacian based on elevation data of a certain area (ground), it is possible to quantify and express the fluctuation of unevenness in that area (ground).

[0025] FIG. 1 is a diagram for explaining a method for calculating the Laplacian. When calculating the Laplacian, first, the area to be evaluated is divided into meshes of a predetermined size, and the elevation data of the terrain is obtained for each mesh. In FIG. 1, a certain area E is divided into nine meshes R1 to R9 (3 vertical × 3 horizontal). The elevation data for each mesh (R1 to R9) can be, for example, the elevation data published nationwide by the Ministry of Land, Infrastructure, Transport and Tourism (Geospatial Information Authority of Japan, Basic Map Information: https: / / fgd.gsi.go.jp / download / menu.php).

[0026] In Figure 1, among the 3x3 meshes, if the elevation of the central mesh R5 is u(m,m), the Laplacian L(m,n) can be calculated by the following formula (1) using the elevations (m-1,n), u(m+1,n), u(m,n-1), and u(m,n+1) of the four meshes (R4, R6, R2, R8) surrounding R5.

[0027]

number

[0028] If the Laplacian L(m,n) calculated by formula (1) is a positive value (L>0), it indicates concave terrain, if it is zero (L=0), it indicates flat terrain, and if it is a negative value (L<0), it indicates convex terrain. Also, the larger the absolute value of Laplacian L(m,n), the greater the unevenness compared to the surrounding ground. Therefore, by calculating Laplacian L(m,n) for each region, it is possible to evaluate the unevenness of that region.

[0029] On the other hand, when performing unevenness evaluation using such Laplacian, unevenness evaluation may differ depending on the mesh size (mesh interval) even for the same region. Figure 2 is a diagram for explaining an example of a case where the Laplacian is calculated for a certain region with a mesh size of 250 m. Similarly, Figure 3 is a diagram for explaining an example of a case where the Laplacian is calculated for a certain region with a mesh size of 50 m.

[0030] FIG. 2 shows the relationship between the actual ground unevenness and the calculated Laplacian when the Laplacian is calculated with a relatively large mesh size (250 m). For the sake of simplicity, FIG. 2 only shows the variation in unevenness in the horizontal direction (east-west direction). The ground to be evaluated has an uneven shape as shown in FIG. 2A. Specifically, when three regions divided by a mesh size of 250 m are designated as X0, X1, and X2, there is a large depression A in the entire region X1 and in part of X2. In addition, in region X1, the depression A has a local depression B, which is a locally depressed portion, and a flat portion C, which is a flat portion corresponding to the bottom of the depression A.

[0031] When the Laplacian L is calculated for such an uneven ground using a 250m mesh, as shown in FIG. 2B, the Laplacian L is positive (L>0) in the area X1, and is zero or less (L≦0) in the areas X0 and X2. That is, the area X1 is evaluated as being a depression. As described above, the depression A is provided over a wide area in the area X1, so the evaluation that the area X1 is a depression is generally correct. However, when viewed locally, the elevation difference between the local depression B and the flat area C is not reflected in the evaluation, and the unevenness of the ground cannot be accurately evaluated. This is because the Laplacian L is calculated based on the average elevation data of the area divided into meshes of a predetermined size, and therefore even if an elevation difference (unevenness) occurs within the same mesh, the elevation difference is not detected.

[0032] Next, Fig. 3 shows the relationship between the actual ground unevenness and the calculated Laplacian when the Laplacian is calculated for area X1 of the same ground as in Fig. 2 using a smaller mesh size (50 m) than in Fig. 2. That is, the relationship between the unevenness and the Laplacian in areas X11 to X15 (50 m intervals) obtained by dividing area X1 (250 m intervals) in Fig. 2 into five meshes is shown (see Fig. 3A).

[0033] When the Laplacian L is calculated in the 50m mesh, as shown in FIG. 3B, the Laplacian L is positive (L>0) in the regions X11 and X12, and is zero or less (L≦0) in the regions X13 to X15. That is, the regions X11 and X12 are evaluated as depressions. In this case, the local depression B that is locally depressed in the region X12 is evaluated as a depression. On the other hand, the flat portion C formed in the regions X13 to X15 is evaluated as a convex or flat land, even though it is a part of the depression A (depression), and it is not reflected that it is a depression as a whole. This is because the Laplacian L is calculated based on the difference in elevation between adjacent meshes, and therefore the part with a small difference in elevation between adjacent meshes, such as the flat portion C, is not judged to be a depression. Therefore, in this case as well, the unevenness of the ground cannot be accurately evaluated.

[0034] <Roughness evaluation using multiple Laplacians> The evaluation of ground unevenness in this embodiment will be specifically described below. As described in Fig. 2 and Fig. 3, when evaluating the unevenness of the ground using the Laplacian, depending on how the mesh size is set, there is a risk that the unevenness cannot be accurately evaluated. In other words, there is a risk that the risk of flooding cannot be accurately determined. Therefore, in this embodiment, multiple types of Laplacians are calculated while changing the mesh size for a certain area, and the unevenness of the ground is evaluated based on the multiple types of Laplacians calculated.

[0035] FIG. 4 is a diagram illustrating an area EA that is the subject of unevenness evaluation in this embodiment. Area EA is an area of ​​a certain size that is cut out from an actually existing region, and is the area surrounded by the outermost frame line in FIG. 4. Within area EA, multiple flooded areas P are arranged, which are indicated by hatching. These flooded areas P indicate parts of area EA where flood damage occurred in the past. The following description focuses on flooded areas P1, P2, and P3 out of the multiple flooded areas P.

[0036] In this embodiment, the Laplacian is calculated for each of three mesh sizes: 250 m, 100 m, and 50 m. First, within the area EA, a range for calculating the Laplacian is set for each mesh size. For example, when calculating the Laplacian for a 250 m mesh, an area M250 surrounded by a long dashed line is set so that the flooded areas P1 and P2 are located near the center. The area M250 is an area divided into 3 vertical × 4 horizontal meshes at 250 m intervals (see FIG. 6 described later).

[0037] Similarly, when calculating the Laplacian using a 100m mesh, an area M100 surrounded by a thick solid line is set so that flooded areas P1 and P2 are located near the center. Area M100 is an area divided into 5 vertical x 4 horizontal meshes at 100m intervals (see Figure 8, described below). When calculating the Laplacian using a 50m mesh, an area M50 surrounded by short dashed lines is set so that flooded areas P1 and P2 are located near the center. Area M50 is an area divided into 6 vertical x 6 horizontal meshes at 50m intervals (see Figure 10, described below).

[0038] Next, for the set regions M250, M100, and M50, the Laplacian L is calculated according to the method explained in FIG. 1 and formula (1), and the unevenness of the ground is evaluated.

[0039] Fig. 5A is a diagram showing elevation data for each of the 3×4 meshes that make up the area M250. The elevation data can be obtained, for example, from the above-mentioned base map information of the Geospatial Information Authority of Japan. Fig. 5B is a diagram showing the Laplacian L calculated for each mesh based on the elevation data in Fig. 5A. In this way, the Laplacian L, which is an index of ground unevenness, is obtained for each mesh that divides the area M250.

[0040] FIG. 6 is a diagram showing the unevenness of the ground when the area EA is divided into meshes of 250 m size. In FIG. 6, the meshes are colored in five stages according to the magnitude of Laplacian L obtained in FIG. 5B, to visualize the parts of the area EA where the ground is low (parts with large concaves). In FIG. 6, Laplacian L is also calculated for the area outside the area M250, and the meshes are colored based on the result. In FIG. 6, the meshes where the value of Laplacian L is zero or negative in FIG. 5B (i.e., meshes where the ground is evaluated as flat or convex) are uncolored with Laplacian L set to "zero or less" uniformly. The same applies to the following FIG. 8 and FIG. 10.

[0041] In Figure 6, the Laplacian L of the mesh in which the floodable areas P1-P3 are located is less than zero. In other words, the ground in the parts in which the floodable areas P1-P3 are located is evaluated as being flat or convex. In other words, when the area EA is divided into mesh sizes of 250m and the Laplacian L is calculated, none of the floodable areas P1-P3 are evaluated as being depressions with a high risk of flooding. In this case, it is difficult to predict the risk of flooding in the floodable areas P1-P3.

[0042] Similarly, Laplacian L is calculated for each mesh in region M100 to evaluate the unevenness of the ground. Fig. 7A shows elevation data for each 5×4 mesh that constitutes region M100. Fig. 7B shows Laplacian L calculated for each mesh based on the elevation data in Fig. 7A. Fig. 8 shows the unevenness of the ground when region EA is divided into meshes with a size of 100 m.

[0043] In FIG. 8, the mesh in which flooded area P2 is located has the largest Laplacian L value, and flooded area P2 is evaluated as a large depression. The mesh in which part of flooded area P3 (the part on the right) is located also has a relatively large Laplacian L value, and is evaluated as a depression. On the other hand, the Laplacian L of the mesh in which flooded area P1 is located is below zero, and flooded area P1 is not evaluated as a depression. In other words, if the area EA is divided into meshes with a size of 100 m and Laplacian L is calculated, flooded areas P2 and P3 are evaluated as depressions with a high risk of flooding, but flooded area P1 is not evaluated as a depression, and it is difficult to predict the risk of flooding in flooded area P1.

[0044] Furthermore, for the area M50, the Laplacian L is calculated for each mesh in the same manner, and the unevenness of the ground is evaluated. Fig. 9A is a diagram showing the elevation data of each of the 6×6 meshes that make up the area M50. Fig. 9B is a diagram showing the Laplacian L calculated for each mesh based on the elevation data in Fig. 9A. Fig. 10 is a diagram showing the unevenness of the ground when the area EA is divided into meshes with a size of 50 m.

[0045] In Figure 10, the value of Laplacian L of the mesh in which flooded areas P1 and P2 are located is large, and flooded areas P1 and P2 are evaluated as depressions. On the other hand, the Laplacian L of the mesh in which flooded area P3 is located is below zero, and flooded area P3 is not evaluated as a depression. In other words, if the area EA is divided into mesh sizes of 50m and Laplacian L is calculated, flooded areas P1 and P2 are evaluated as depressions with a high risk of flooding, but flooded area P3 is not evaluated as a depression, making it difficult to predict the risk of flooding in flooded area P3.

[0046] As shown in Figures 6 to 10, when dividing a certain area into mesh sizes of a predetermined size, calculating the Laplacian, and evaluating the unevenness of the ground in the certain area based on the calculated Laplacian, it may not be possible to perform an accurate evaluation.

[0047] In contrast, by combining multiple types of Laplacians calculated for different mesh sizes, it is possible to more accurately evaluate the unevenness of the ground. Figure 11 shows the unevenness of the ground when combining the Laplacian (first Laplacian) obtained when the area EA is divided into a mesh size of 250 m and the Laplacian (second Laplacian) obtained when the area is divided into a mesh size of 100 m.

[0048] FIG. 11 is obtained by combining (adding) the data of Laplacian L (first Laplacian) in the mesh size of 250 m used in creating FIG. 6 and the data of Laplacian L (second Laplacian) in the mesh size of 100 m used in creating FIG. 8 using a known information processing device such as a computer. As a result, in FIG. 11, the flooded areas P2 and P3 are evaluated as depressions. Therefore, it can be seen that the evaluation of the unevenness is more accurate than when the evaluation of the unevenness is performed based only on the Laplacian (first Laplacian) in the mesh size of 250 m. In this way, by evaluating the concavity and convexity of the ground based on multiple Laplacians calculated from the elevation data of meshes of different sizes, the influence of local depressions and wide-area depressions in the ground can be easily reflected, and a more accurate evaluation of the unevenness of the ground can be performed. In addition, by using the nationally unified elevation data published by the Geospatial Information Authority of Japan, etc., it is possible to perform the evaluation of the unevenness of the ground using the same index without causing regional variations.

[0049] Furthermore, if two different Laplacians L (the first and second Laplacians) that overlap in a certain part of the area EA are both positive values ​​(depression evaluation), there is a high possibility that the part is actually a depression. Therefore, by evaluating the unevenness of the ground using multiple different Laplacians, it becomes easier to predict the risk of flooding.

[0050] Fig. 12 is a diagram showing the unevenness of the ground when the Laplacian (first Laplacian) obtained when the area EA is divided into a mesh size of 250 m, the Laplacian (second Laplacian) when the area is divided into a mesh size of 100 m, and the Laplacian (third Laplacian) when the area is divided into a mesh size of 50 m are combined. Fig. 12 was obtained by further combining (adding up) the data of Laplacian L (third Laplacian) for the 50 m mesh size used in creating Fig. 10 with Fig. 11.

[0051] In Figure 12, flooded areas P1 to P3 are all evaluated as depressions. For example, flooded area P1, which was not evaluated as a depression in Figure 11, is evaluated as a depression in Figure 12. Furthermore, in Figure 12, almost all of the parts of area EA where flooded areas P other than flooded areas P1 to P3 are located are evaluated as depressions. In other words, all of the parts of area EA with a high risk of flooding (areas where flooding has actually occurred) are evaluated as depressions.

[0052] In this way, in FIG. 12, in addition to the data of the first and second Laplacians, the data of the third Laplacian is further combined to evaluate the unevenness of the ground based on three types of Laplacians. In this case, local depressions that could not be extracted by the first Laplacian with a large mesh size (250 m) are easily extracted by the third Laplacian with a small mesh size (50 m). Conversely, depressions covering a wide area that could not be extracted by the third Laplacian with a small mesh size are easily extracted by the first Laplacian with a large mesh size. In other words, by using three or more types of Laplacians, depressions of different scales are more easily reflected. Therefore, a more accurate evaluation can be performed compared to the case where the unevenness of the ground is evaluated based on two types of Laplacians (the first Laplacian and the second Laplacian) as in FIG. 11.

[0053] Furthermore, a Laplacian (for example, a fourth Laplacian, not shown) obtained when the area EA is divided into mesh sizes different from the first to third Laplacians may be combined, and the unevenness of the ground may be evaluated based on four or more types of Laplacians. The more types of mesh sizes there are, the higher the possibility that depressions of different scales will be extracted, making it easier to improve the accuracy of the unevenness evaluation. However, care must be taken because increasing the number of types of Laplacians used for the unevenness evaluation too much (i.e., increasing the size of the mesh dividing the area too much) may cause noise and deteriorate the accuracy of the unevenness evaluation.

[0054] Alternatively, n types (n=2, 3, 4...) of Laplacians may be calculated by dividing the area EA into n different mesh sizes, and the unevenness of the ground may be evaluated based on two or more of the n types of Laplacians. As described above, by calculating multiple Laplacians with different mesh sizes, it is possible to easily deal with depressions of different scales (to easily extract depressions), so it is desirable to select a Laplacian with an appropriate mesh size according to the unevenness of the terrain to be evaluated and perform the unevenness evaluation. In this way, an accurate evaluation according to the unevenness of the actual terrain can be performed.

[0055] In addition, when dividing the area EA into different mesh sizes and calculating a plurality of types of Laplacians, it is desirable that the size of one mesh is more than twice the size of the other mesh. In other words, when dividing the area EA into two types of meshes, the first mesh and the second mesh, it is desirable that the length of one side of the first mesh is more than twice the length of one side of the second mesh. In this embodiment, three types of Laplacians are calculated by dividing the area EA into three types of mesh sizes, 250 m, 100 m, and 50 m (see Figs. 5 to 10), and the length of one side of one mesh is more than twice the length of one side of the other mesh. In this way, by adjusting the size of the mesh, it becomes easier to respond to the actual unevenness of the terrain to be evaluated. For example, it becomes easier to respond to depressions of different scales, such as a depression (depression A) formed over a wide range as described in Fig. 2 and a local depression (local depression B) as described in Fig. 3. Therefore, a more accurate unevenness evaluation can be performed.

[0056] In this embodiment, the Laplacian is calculated based on three different mesh sizes, 250 m, 100 m, and 50 m, but the mesh size can be changed as appropriate depending on the actual terrain. For example, in densely populated urban areas on plains, local unevenness may be formed in a narrow area, so it may be better to calculate the Laplacian by dividing the area into mesh sizes as small as possible. On the other hand, in mountainous areas along the mountains, unevenness may be formed on a large scale, so it may be better to divide the area into mesh sizes as large as possible and calculate the Laplacian. In this way, by selecting a mesh size appropriate to the terrain and calculating the Laplacian, it is possible to perform a more accurate unevenness evaluation.

[0057] However, the minimum mesh size in this embodiment is 5m. In other words, the length of one side of the mesh when dividing the area is 5m or more. Since the elevation data of the Geospatial Information Authority of Japan described above is displayed at 5m intervals, if the mesh is 5m or more, the Laplacian can be calculated based on the highly uniform and stable data published by the Geospatial Information Authority of Japan. In addition, if the evaluation target area is divided into very fine mesh sizes such as 1m, the data becomes complicated and there is a high possibility of noise generation, which may make it difficult to accurately evaluate the unevenness of the ground. Therefore, when performing the unevenness evaluation of the ground in this embodiment, it is desirable to set the mesh size to 5m or more.

[0058] In addition, in this embodiment, the possibility of flood damage in the ground can be evaluated based on the evaluation result of the ground unevenness using the Laplacian as described above. In Fig. 11 and Fig. 12, the area EA is divided into two or three mesh sizes, and the ground unevenness is evaluated by calculating the Laplacian for each divided mesh. At this time, the area where the areas divided into a plurality of mesh sizes overlap and are evaluated as a depression is likely to actually have a low altitude. For example, in a certain part of Fig. 12, when the area is evaluated as a depression in all of the first to third Laplacians, it is shown that the altitude is lower than the surrounding area when viewed at each mesh interval of 250 m, 100 m, and 50 m. In this case, in the overlapping part evaluated as a depression, the colored meshes overlap and are displayed in a dark color (in Fig. 12, meshes displayed with hatching or diagonal lines are displayed overlapping each other), so that the depression part is easy to visually recognize.

[0059] In other words, the area where meshes evaluated as depressions overlap is likely to have a lower ground elevation than the surrounding area, and there is a high probability of flooding due to heavy rains in the future. According to the above formula (1), the larger the Laplacian value of a mesh, the greater the possibility of a larger difference in elevation from the surrounding area, and therefore there is a risk of flooding in the area where such meshes overlap. Thus, for example, by using a computer to extract areas where meshes with large Laplacian values ​​overlap or areas where the magnitude of the overlapping Laplacian is greater than a predetermined value, it is possible to predict ground prone to flooding. In this way, in this embodiment, the risk of flooding in the future can be objectively evaluated based on the unevenness evaluation of the ground.

[0060] ===Other embodiments=== The above-mentioned embodiment is for facilitating understanding of the present invention, and is not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit of the present invention, and it goes without saying that the present invention includes equivalents. In particular, the following embodiments are also included in the present invention.

[0061] In the above-described embodiment, basic map information from the Geospatial Information Authority of Japan was used as the elevation data for calculating the Laplacian, but other elevation data may be used as long as it is standardized nationwide and has a certain degree of reliability. [Explanation of symbols]

[0062] A: concave portion, B: local concave portion, C: flat portion, X0~1 area, X11~15 area EA area, P flooded area, P1 flooded area, P2 flooded area, P3 flooded area, M250 area (mesh size 250m), M100 area (mesh size 100m), M50 area (mesh size 50m)

Claims

1. Calculating a first Laplacian, which is an index of ground unevenness in a certain area, from elevation data for each section obtained by dividing the certain area into a first mesh size; Calculating a second Laplacian, which is an index of ground unevenness of the certain area, from elevation data for each section obtained by dividing the certain area into a second mesh size different from the first mesh size; evaluating the unevenness of the ground in the certain area using a computer based on the first Laplacian and the second Laplacian; having A ground evaluation method, characterized in that if the first Laplacian and the second Laplacian that overlap in a certain part of the certain area are both positive values, the certain part is evaluated as a depression.

2. Calculating a first Laplacian, which is an index of ground unevenness in a certain area, from elevation data for each section obtained by dividing the certain area into a first mesh size; Calculating a second Laplacian, which is an index of ground unevenness of the certain area, from elevation data for each section obtained by dividing the certain area into a second mesh size different from the first mesh size; evaluating the unevenness of the ground in the certain area using a computer based on the first Laplacian and the second Laplacian; having A ground evaluation method, characterized in that the mesh of the first mesh size and the mesh of the second mesh size are meshes of different sizes and intersect with each other.

3. The ground evaluation method according to claim 1 or 2, A ground evaluation method, characterized in that the first mesh size and the second mesh size are each changeable.

4. The ground evaluation method according to any one of claims 1 to 3, A third Laplacian, which is an index of ground unevenness of the certain area, is calculated from elevation data for each division when the certain area is divided into a third mesh size different from the first mesh size and the second mesh size; A ground evaluation method, comprising: evaluating a degree of depression of the ground in the certain area using a computer based on the first Laplacian, the second Laplacian, and the third Laplacian.

5. The ground evaluation method according to any one of claims 1 to 4, The certain area is divided into n different mesh sizes, and n different Laplacians each representing an index of ground unevenness of the certain area are calculated from the elevation data for each division. A ground evaluation method, comprising: evaluating the degree of depression of the ground in the certain area using a computer based on two or more of the n types of Laplacians.

6. The ground evaluation method according to any one of claims 1 to 5, A ground evaluation method, characterized in that the length of one side of the mesh size is 5 m or more.

7. The ground evaluation method according to any one of claims 1 to 5, A ground evaluation method, comprising: evaluating the risk of flooding in a certain area based on an evaluation result of the unevenness of the ground in the certain area.

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