Information processing device, information processing program, and information processing method

Abstract

To provide an apparatus that can estimate a flooded area with high accuracy, regardless of an image quality and a photographing condition of remote sensing data to be used.SOLUTION: An information processing apparatus 10 includes: an initial flooded area estimation unit 11 that estimates an initial flooded area 11A by comparing a first image #1 with a second image #2 which is taken at a date and time earlier than the first image #1, calculates an index value indicating a degree of flooding in a depression area 12A when the depression area 12A obtained by analyzing a topographic gradient for elevation information 30 indicating an elevation of a terrain includes at least a part of the initial flooded area 11A, determines that the depression area 12A is flooded when the index value is a threshold value or more, and fills the depression area 12A with a flooded area based on a determination result indicating flooding.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an information processing device, an information processing program, and an information processing method, and more particularly to information processing for estimating a flooded state of a house or a forest when a flood disaster occurs. [Background technology]

[0002] Ground sensors have traditionally been used to grasp flood damage during water disasters such as floods, heavy rains, and typhoons. Methods of grasping flood damage using ground sensors are useful for grasping the flooding situation at specific spots such as elevators or power plants. However, in situations where damage occurs over a wide area, methods of grasping flood damage using ground sensors are not suitable for obtaining information on the extent of the area, such as which areas have suffered the most damage.

[0003] A flood depth estimation method that utilizes remote sensing data has been proposed as a method for grasping flood damage over a wide area (see Non-Patent Document 1). In Non-Patent Document 1, SAR satellite images taken at two different times, before and after a disaster, are compared to detect changed areas, and the inundated area, which is the extent of the flooding, is estimated. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] “An attempt to rapidly extract flooded area and depth during heavy rain disasters using satellite SAR.” Kenichi Honda et al., Journal of Remote Sensing Society of Japan, Vol. 40 No. 3 (2020), pp. 158-162. Summary of the Invention [Problem to be solved by the invention]

[0005] In Non-Patent Document 1, flooded areas are calculated by comparing two SAR satellite images, a first image taken at a certain time and a second image taken at a time in the past relative to the first image. Generally, a location where there is a significant difference between the two images is considered to be a flooded area. In this case, there are cases where the difference occurs sparsely due to noise in the images and seasonal fluctuations. In this way, in the case of a flooded area detection method that relies on images, the image quality and imaging conditions affect the determination of the flooded area. Therefore, even if an area is actually flooded, there is a possibility that the area will be considered as a non-flooded area because there is no difference between the images of the area. This is an issue in terms of estimation accuracy.

[0006] The present disclosure aims to estimate flooded areas with high accuracy, regardless of the image quality and imaging conditions of the remote sensing data used. [Means for solving the problem]

[0007] The information processing device of the present disclosure includes: an estimation unit that estimates an initially flooded area that indicates a flooded area that exists in both the first image and the second image by comparing a first image with a second image that was taken at an earlier date and time than the first image; a flooded area filling unit which, when at least a portion of the initially flooded area is included in a depression area obtained by analyzing the terrain gradient for elevation information indicating the elevation of the terrain, calculates an index value indicating the degree of flooding of the depression area, and, when the index value is equal to or greater than a threshold value, determines that the depression area is flooded, and fills the depression area with a flooded area based on the determination result indicating flooding; Equipped with. Effect of the Invention

[0008] According to the information processing device of the present disclosure, flooded areas can be estimated with high accuracy regardless of the image quality or imaging conditions of the remote sensing data used. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 is a block diagram of an information processing device 101 according to a first embodiment. [Diagram 2] FIG. 1 is a diagram showing a hardware configuration of an information processing device 101 according to a first embodiment. [Diagram 3] FIG. 1 is a flowchart showing the operation of an information processing method according to the first embodiment. [Figure 4] FIG. 11 is a diagram of the first embodiment, showing a potential flooded depression 131A and an initially flooded area 11A. [Diagram 5] FIG. 11 is a block diagram of an information processing device 20 according to a modified example of the first embodiment. [Figure 6] FIG. 2 is a diagram of the first embodiment that supplements the hardware configuration of information processing devices 10 and 20. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the description of the embodiments and the drawings, the same elements and corresponding elements are given the same reference numerals. Descriptions of elements given the same reference numerals are omitted or simplified as appropriate. In the following embodiments, "unit" may be read as "circuit", "step", "procedure", "process" or "circuitry" as appropriate.

[0011] Embodiment 1 FIG. 1 is a functional configuration diagram of an information processing device 10. As shown in FIG. FIG. 2 shows the hardware configuration of the information processing device 101.

[0012] ***Configuration Description*** 1, the information processing device 101 includes an initial flooded area estimation unit 11, a depression detection unit 12, and a flooded area filling unit 13. The flooded area filling unit 13 includes a candidate detection unit 131, a flood determination unit 132, and a flooded depression filling unit 133. The initial flooded area estimation unit 11 is an estimation unit.

[0013] The information processing device 10 is a computer. The information processing device 10 includes a processor 510. The information processing device 10 includes multiple pieces of hardware in addition to the processor 510. The multiple pieces of hardware are a main memory device 520, an auxiliary memory device 530, an input interface 540, an output interface 550, and a communication interface 560. The processor 510 is connected to the other hardware via a signal line 570 and controls the other hardware.

[0014] The information processing device 10 includes, as functional elements, an initial flooded area estimation unit 11, a depression detection unit 12, and a flooded area filling unit 13. The functions of the initial flooded area estimation unit 11, depression detection unit 12, and flooded area filling unit 13 are realized by the information processing program 531.

[0015] The processor 510 is a device that executes an information processing program 531. The processor 510 executes the information processing program 531 to realize the functions of the initial flooded area estimation unit 11, the depression detection unit 12, and the flooded area filling unit 13. The processor 510 is an IC (Integrated Circuit) that performs arithmetic processing. Specific examples of the processor 510 are a CPU (Central Processing Unit), a DSP (Digital Signal Processor), and a GPU (Graphics Processing Unit).

[0016] The main memory 520 is a storage device. Specific examples of the main memory 520 include an SRAM (Static Random Access Memory) and a DRAM (Dynamic Random Access Memory). The main memory 520 holds the results of calculations by the processor 510.

[0017] The auxiliary storage device 530 is a storage device that stores data in a non-volatile manner. A specific example of the auxiliary storage device 530 is a hard disk drive (HDD). The auxiliary storage device 530 may also be a portable recording medium. Examples of portable recording media include a Secure Digital (SD) memory card, a NAND flash, a flexible disk, an optical disk, a compact disk, a Blu-ray (registered trademark) disk, and a digital versatile disk (DVD). The auxiliary storage device 530 stores an information processing program 531.

[0018] The input interface 540 is a port through which data is input from each device. The output interface 550 is connected to various devices. The output interface 550 is a port through which data is output by the processor 510 to various devices. The communication interface 560 is a communication port through which the processor communicates with other devices.

[0019] The processor 510 loads the information processing program 531 from the auxiliary storage device 530 to the main storage device 520. The processor 510 reads the loaded information processing program 531 from the main storage device 520 and executes it. In addition to the information processing program 531, an OS (Operating System) is also stored in the main storage device 520. The processor 510 executes the information processing program 531 while executing the OS. The information processing device 10 may include a plurality of processors that replace the processor 510. These plurality of processors share the execution of the information processing program 531. Each processor is a device that executes the information processing program 531, like the processor 510. Data, information, signal values, and variable values ​​used, processed, or output by the information processing program 531 are stored in the main storage device 520, the auxiliary storage device 530, or a register or cache memory in the processor 510.

[0020] The information processing program 531 is a program that causes a computer to execute each process, procedure, or step of the initial flooded area estimation unit 11, depression detection unit 12, flooded area filling unit 13, candidate detection unit 131, flooding judgment unit 132, and flooded depression filling unit 133, where the "part" is replaced with "process," "procedure," or "step."

[0021] The method is an information processing method performed by the information processing device 10, which is a computer, executing the information processing program 531. The information processing program 531 may be provided by being stored in a computer-readable recording medium, or may be provided as a program product.

[0022] ***Explanation of Operation*** The operation of the information processing device 10 will be described with reference to FIG. 3 is a flowchart illustrating the operation of the information processing device 10. The operation of the information processing device 10 corresponds to an information processing method. Also, the operation of the information processing device 10 corresponds to the processing of an information processing program.

[0023] <Step S1> In step S1, the initial flooded area estimation unit 11 estimates an initial flooded area 11A from the first image #1 and the second image #2. The initial flooded area estimation unit 11 estimates an initial flooded area 11A, which indicates an area that is present in both the first image #1 and the second image #2 and is flooded, by comparing the first image #1 with the second image #2 that was taken at an earlier date and time than the first image #1. This will be explained in detail below. The first image #1 and the second image #2 are remote sensing data captured by a photographing device mounted on an air vehicle. The air vehicle may be an aircraft, a UAV, or an artificial satellite. The initial flooded area estimation unit 11 receives the first image #1 and the second image #2 as input data. The first image #1 is remote sensing data acquired at a time T1 indicating a certain date and time. The second image #2 is remote sensing data acquired at a time T2 indicating a certain date and time older than the time T1. The second image #2 and the first image #1 include the same area. The second image #2 and the first image #1 are compared for the difference between the same area. The initial flooded area estimation unit 11 compares the first image #1 and the second image #2, and estimates the initial flooded area 11A from the comparison result. Here, the "initial" in "initial flooded area 11A" refers to the "flooded area" before it is input to the flooded area filling unit 13. In contrast to the "final flooded area 133A" after correction processing has been performed by the flooded area filling unit 13, the "initial" is added to indicate the area before correction processing has been performed. The initial flooded area estimation unit 11 outputs the initial flooded area 11A, which is the estimation result, to the candidate detection unit 131 of the flooded area filling unit 13. The initial flooded area estimation unit 11 can estimate the presence or absence of flooding from (1) optical images or (2) SAR images, for example, as follows.

[0024] (1) Optical image When estimating the initial flooded area 11A from an optical image, the initial flooded area estimation unit 11 can use NDWI (Normalized Difference water index), which is a water index that uses an image in the near-infrared band. NIR , ρ SWIR are the measured values ​​in the NIR (Near Inreared) and SWIR (Short Wave Infrared) bands at a certain point, respectively. In this case, the NDWI is expressed by the following formula (1). The initial flooded area estimation unit 1 can estimate the initial flooded area 11A by detecting the change in NDWI between the first image #1 and the second image #2. NDWI=[ρ NIR -ρ SWIR ] / [ρ NIR +ρ SWIR ] Formula (1) In recent years, methods for estimating flooded areas using visible bands instead of infrared bands have also been proposed. The initial flooded area estimation unit 11 can also estimate the initial flooded area 11A using a method that uses the visible band. (2)SAR images When estimating the initial flooded area 11A from the SAR image, the method of Non-Patent Document 1 compares SAR images before and after the occurrence of a flood disaster, and extracts areas where the backscattering intensity is reduced as flooded areas. The initial flooded area estimation unit 11 may use the method of Non-Patent Document 1.

[0025] The above-described methods of (1) optical images and (2) SAR images are examples of remote sensing data. Various remote sensing data can be input to the information processing device of this specification by combining sensors and measurement devices.

[0026] <Step S2> In step S2, depression detection unit 12 acquires altitude information 30 and detects depression region 12A from the acquired altitude information 30. Altitude information 30, which will be described later, is input to depression detection unit 12. Depression detection unit 12 analyzes altitude information 30 and detects depression region 12A within the analysis range.

[0027] <Altitude information 30> As elevation information 30, DEM (Digital Elevation Model) information created by remote sensing technology or surveying can be used. DEM is created by methods such as laser surveying or photogrammetry. DEM is open data that can be obtained by general users. An example of open data that can be obtained by general users is "Geospatial Information Authority of Japan: Basic Map Information https: / / fgd.gsi.go.jp / download / menu.php." The Geospatial Information Authority of Japan has released 5m mesh DEM5A. SRTM-3 (Shuttle Rador Topography Mission) is released worldwide, and DEM data with high vertical resolution is also available.

[0028] <Depression area 12A> The depression detection unit 12 regards depressions as spatially connected regions with no gradient. As a result, the depression detection unit 12 detects depression regions 12A from the elevation information 30. The depression detection unit 12 calculates a two-dimensional numerical gradient of the elevation information 30, and calculates coordinates where the absolute value of the gradient is equal to or less than a preset threshold value. Of the connected elements formed by the calculated coordinates, the depression detection unit 12 detects an area whose area is equal to or more than a first threshold value and less than a second threshold value as depression region 12A.

[0029] Alternatively, as another implementation example, depression detection unit 12 detects depression region 12A by the following process. Depression detection unit 12 calculates the flow direction of each pixel from the two-dimensional numerical gradient of elevation information 30, and calculates coordinates where the flow direction does not apply to any direction. Of the connected elements formed by the calculated coordinates, depression detection unit 12 detects an area whose area is equal to or greater than a first threshold and less than a second threshold as depression region 12A.

[0030] <Step S3> In step S3, the flooded area filling unit 13 calculates an index value indicating the degree of flooding of a depression area when at least a part of the initial flooded area 11A is included in a depression area obtained by analyzing the terrain gradient for the elevation information 30 indicating the elevation of the terrain. This depression area is a flooded depression candidate, as described below. Examples of the index value are the ratio R or the area A, as described below. When the index value is equal to or greater than a threshold value, the flooded area filling unit 13 determines that the depression area is flooded, and fills the depression area with a flooded area based on the determination result indicating flooding. This will be described in detail below. Flooded area filling unit 13 determines which depression areas are flooded from initial flooded area 11A and depression area 12A. Flooded area filling unit 13 calculates final flooded area 133A, which is a more accurate version of initial flooded area 11A, by filling initial flooded area 11A with depression areas determined to be flooded. If initial flooded area 11A exists at a certain rate or greater in depression area 12A detected by depression detection unit 12, flooded area filling unit 13 fills the entire corresponding depression area into the initial flooded area and outputs it as final flooded area 133A. The operation of the candidate detection unit 131, the flooding determination unit 132, and the flooded depression filling unit 133 included in the flooded area filling unit 13 will be described below.

[0031] <Candidate detection unit 131> The candidate detection unit 131 detects a depression area that includes even a small amount of the initially flooded area 11A as a flooded depression candidate 131A.

[0032] <Flood determination section 132> The flooding determination unit 132 determines whether the flooded depression candidate 131A is flooded or not, and outputs the determination result, that is, a flooding determination result 132A, to the flooded depression filling unit 133. The flooding determination result 132A indicates either "flooded" or "not flooded." The specific details are explained below. Fig. 4 shows the flooded depression candidate 131A and the initially flooded area 11A. In Fig. 4, the flooded depression candidate 131A includes at least a part of the initially flooded area 11A. The flooding determination unit 132 calculates the percentage or area of ​​the initially flooded area 11A included in the area of ​​the flooded depression candidate 131A. The flooding determination unit 132 can determine that the flooded depression candidate 131A is flooded by any of the following (1), (2), or (3). (1) When the calculated ratio is equal to or greater than the ratio threshold value THr, the flooding determination unit 132 determines that the floodable depression candidate 131A is flooded. If the ratio is R, then Ratio R = [area of ​​initial flooded area 11A] / [area of ​​flooded depression candidate 131A] In R ≥ THR The flooding determination unit 132 then determines that there is flooding. (2) If the calculated area is equal to or larger than the area threshold value THa, the flooding determining unit 132 determines that the “prospective flooded depression 131A is flooded.” The calculated area is the area of ​​the initially flooded area 11A within the area of ​​the flooded depression candidate 131A. If the area of ​​the initial flooded area 11A is area A, then A ≥ THa The flooding determination unit 132 then determines that there is flooding. (3) The flooding determining unit 132 determines that the potential flooded depression 131A is flooded when the calculated ratio R is equal to or greater than a threshold value THr and the calculated area A is equal to or greater than a threshold value THa. R ≥ THr, and A ≥ THa The flooding determination unit 132 then determines that there is flooding. When the candidate detection unit 131 determines that the candidate for flooded depression 131A does not meet any of the criteria (1), (2), or (3), the candidate detection unit 131 determines that the candidate for flooded depression 131A is “non-flooded.”

[0033] Furthermore, if the initial flooded area 11A is included in a proportion or area of ​​the flooded depression candidate 131A that is less than a certain percentage, it may be determined that the "flooded depression candidate 131A is not flooded." That is, the flooding determination unit 132 may determine that the "flooded depression candidate 131A is not flooded" based on any of the following (4), (5), or (6). Conversely, if the flooding determination unit 132 determines that any of the following (4), (5), or (6) does not apply, the flooded depression candidate 131A is determined to be "flooded." (4) If the calculated ratio R is less than the threshold value THr, the flooding determining unit 132 determines that the "prospective flooded depression 131A is not flooded." R <THr The flooding determination unit 132 then determines that the area is not flooded. (5) If the calculated area A is less than the area threshold THa, the flooding determination unit 132 determines that the “prospective flooded depression 131A is not flooded.” A <THa The flooding determination unit 132 then determines that the area is not flooded. (6) If the calculated ratio R is less than the threshold value THr and the calculated area A is less than the threshold value THa, the flooding determination unit 132 determines that the "potential flooded depression 131A is not flooded." R <THr、かつ、A<THa The flooding determination unit 132 then determines that the area is not flooded.

[0034] <Flood depression filling part 133> The flooded depression filling unit 133 fills in the flooded depression candidates, which are depression areas, with flooded areas based on the determination result of the flood determination unit 132. This will be described below. (1) Based on the flooding determination result 132A indicating “flooded,” the flooded depression filling unit 133 of the flooded area filling unit 13 fills the flooded depression candidate 131A with a flooded area by using a part of the initial flooded area 11A included in the flooded depression candidate 131A, which is a depression area, as a flooded area. The flooded depression filling unit 133 outputs this filling result as the final flooded area 133A. (2) Alternatively, the flooded area filling unit 13 may, based on the flooding determination result 132A indicating “flooding,” The flooded depression candidate 131A is filled with a flooded area by using the entirety of the flooded depression candidate 131A as a flooded area. The flooded depression filling unit 133 outputs this filling result as a final flooded area 133A. (3) Furthermore, when the index value is less than the threshold, the flooded area filling unit 13 judges the flooded depression candidate 131A to be "non-flooded," and based on the flooding judgment result 132A indicating "non-flooded," excludes a part of the initial flooded area 11A included in the flooded depression candidate 131A from the initial flooded area 11A. The flooded depression filling unit 133 outputs the initial flooded area 11A reflecting this filling result as the final flooded area 133A.

[0035] ***Explanation of the Effects of the First Embodiment*** As described above, the information processing device 10 can correct the sparse initial flooded area 11A that occurs depending on at least one of the image quality and imaging conditions of the input images, the first image #1 and the second image #2, and estimate the flooded area with high accuracy. In other words, the flooded area can be estimated with high accuracy regardless of the image quality and imaging conditions of the remote sensing data used.

[0036] In the information processing device 10 of the first embodiment, the depression area 12A detected by the depression detection unit 12 is used to perform the improvement process for the initial flooded area 11A, but the present invention is not limited to this example. For example, the information processing device 10 may acquire the depression area 12A from an external system such as a system or device different from the information processing device 10, and the flooded area filling unit 13 may use the acquired depression area 12A to calculate the final flooded area 133A. This configuration will be described below as a modified example.

[0037] <Modification> Fig. 5 shows a functional configuration diagram of information processing device 20, which is a modified example of information processing device 10. Fig. 5 corresponds to Fig. 1. The hardware configuration of information processing device 20 is similar to the hardware configuration of information processing device 10 in Fig. 2. Information processing device 20 has the same configuration as information processing device 10, except that it acquires depression areas from an external system and inputs them to flooded area filling unit 13.

[0038] For example, depression information published by a local government can be used for depression area 12A of the modified example. The depression information published by a local government may be obtained by manually detecting an area where the ground level is lower than the surrounding area from topographical information. Compared to a case where depression detection unit 12 of information processing device 10 automatically calculates depression area 12A from elevation information 30, manual detection may enable depression detection with high accuracy.

[0039] ***Description of the Effects of Modifications*** The information processing device 20 can estimate flooded areas with high accuracy, thereby improving the speed of analysis, without the need to use elevation information 30. Furthermore, the information processing device 20 can estimate flooded areas with even higher accuracy depending on the accuracy of the depression information used.

[0040] <Hardware configuration supplement> 2, the information processing devices 10 and 20 are described as having their functions realized by software. However, the functions of the information processing devices 10 and 20 may be realized by hardware. FIG. 6 shows a configuration in which the functions of the information processing devices 10 and 20 are realized by hardware. The information processing device 10 will be described below as an example. The electronic circuit 90 in FIG. 6 is a dedicated electronic circuit for realizing the functions of the initial flooded area estimation unit 11, the depression detection unit 12, and the flooded area filling unit 13 of the information processing device 10. The electronic circuit 90 is connected to a signal line 91. Specifically, the electronic circuit 90 is a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, a logic IC, a GA, an ASIC, or an FPGA. GA is an abbreviation for Gate Array. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field-Programmable Gate Array. The functions of the components of the information processing device 10 may be realized by one electronic circuit, or may be distributed and realized by multiple electronic circuits. In addition, some of the functions of the components of the information processing device 10 may be realized by electronic circuits, and the remaining functions may be realized by software.

[0041] Each of the processor 510 and the electronic circuit 90 is also called a processing circuitry or a circuitry. In the information processing device 10, the functions of the initial flooded area estimation unit 11, the depression detection unit 12, and the flooded area filling unit 13 may be realized by the circuitry.

[0042] The above describes the first embodiment. Of the multiple technical matters included in the first embodiment, one technical matter may be partially implemented. Alternatively, the technical matters included in the first embodiment may be partially combined and implemented. [Explanation of symbols]

[0043] 10, 20 information processing device, 11 initial flooded area estimation unit, 11A initial flooded area, 12 depression detection unit, 12A depression area, 13 flooded area filling unit, 131 candidate detection unit, 131A flooded depression candidate, 132 flooding judgment unit, 132A flooding judgment result, 133 flooded depression filling unit, 133A final flooded area, 30 elevation information, 510 processor, 520 main memory device, 530 auxiliary memory device, 540 input interface, 550 output interface, 560 communication interface, 570 signal line, 90 electronic circuit, 91 signal line.

Claims

1. an estimation unit that estimates an initially flooded area that is an area that exists in both the first image and the second image and indicates a flooded area by comparing a first image with a second image that was taken at an earlier date and time than the first image; a flooded area filling unit which, when at least a portion of the initially flooded area is included in a depression area obtained by analyzing the terrain gradient for elevation information indicating the elevation of the terrain, calculates an index value indicating the degree of flooding of the depression area, and, when the index value is equal to or greater than a threshold value, determines that the depression area is flooded, and fills the depression area with a flooded area based on the determination result indicating flooding; An information processing device comprising:

2. The flooded area filling portion is The information processing device according to claim 1 , wherein the depression region is filled by using a part of the initial flooded area included in the depression region as the flooded area.

3. The flooded area filling portion is The information processing apparatus according to claim 1 , wherein the depression area is filled by using the entire depression area as the flooded area.

4. The flooded area filling portion is An information processing device as described in any one of claims 1 to 3, wherein when the index value is less than a threshold value, the depression area is judged to be non-flooded, and a portion of the initial flooded area contained in the depression area is excluded from the initial flooded area based on the judgment result indicating non-flooded.

5. The information processing device further includes: The information processing apparatus according to claim 1 , further comprising a depression detection unit that acquires the altitude information and detects a depression region from the acquired altitude information.

6. The first image and the second image are 6. The information processing apparatus according to claim 1, wherein the data is remote sensing data photographed by an imaging device mounted on a flying object.

7. On the computer, an estimation process for estimating an initially flooded area that is an area that exists in both the first image and the second image and indicates a flooded area by comparing a first image with a second image that was taken at an earlier date and time than the first image; a flooded area filling process for, when at least a portion of the initially flooded area is included in a depression area obtained by analyzing the terrain gradient for elevation information indicating the elevation of the terrain, calculating an index value indicating the degree of flooding of the depression area, and judging the depression area to be flooded if the index value is equal to or greater than a threshold value, and filling the depression area with a flooded area based on the judgment result indicating flooding; An information processing program that executes the above.

8. The computer By comparing a first image with a second image taken at an earlier date and time than the first image, an initial flooded area indicating a flooded area that exists in both the first image and the second image is estimated; When at least a portion of the initially flooded area is included in a depression area obtained by analyzing the terrain gradient for elevation information indicating the elevation of the terrain, an index value indicating the degree of flooding of the depression area is calculated, and when the index value is equal to or greater than a threshold value, the depression area is determined to be flooded, and the depression area is filled with a flooded area based on the determination result indicating flooding. Information processing methods.

Images