WO2024262203A1 - Ground surface composite image creation method, ground surface composite image creation system, and ground surface composite image creation program - Google Patents

Abstract

[Problem] To provide a ground surface composite image creation method, a ground surface composite image creation system, and a ground surface composite image creation program that can make it possible to relatively easily understand a use state of a ground surface, such as vegetation, by using height information. [Solution] The present invention acquires an ortho-image of a target area and a digital surface model, and creates, on the basis of the digital surface model, a ground height image pertaining to the height of an object on the ground. Each pixel having a ground height equal to or greater than a prescribed threshold is extracted from the created ground height image. A grayscale image is created in which a grayscale value of each of the extracted pixels is set on the basis of the corresponding ground height or set to a constant value. The created grayscale image is superimposed on the ortho-image to create a composite image.

Description

Earth's surface composite image creation method, earth's surface composite image creation system, and earth's surface composite image creation program

The present invention relates to a method for creating a composite image of the earth's surface, a system for creating a composite image of the earth's surface, and a program for creating a composite image of the earth's surface.

In recent years, as symbolized by the increasing number of Globally Important Agricultural Heritage Sites and Japanese Agricultural Heritage Sites being certified, attention has been paid to the culture, landscape, biodiversity, and other functions of rural areas. For example, private homestead forests are one of the main elements that form the rural landscape, and also play a role in the surrounding environment, such as conserving biodiversity. For this reason, there is a need to quantitatively evaluate and understand the current state of rural areas, including private homestead forests.

Traditionally, in order to understand the use of the ground surface by vegetation and other factors, and the topography, it has been common to use manned aircraft or unmanned aerial vehicles (UAVs or drones) to continuously photograph the target area from different viewpoints in the sky, and then process the images using techniques such as Structure from Motion (SfM), or measure the target area from the sky with a Light Detection and Ranging (LiDAR) to obtain digital image data and measurement data, thereby obtaining ground surface images (orthoimages) and digital surface models (DSMs).

Also, methods have been proposed for detecting plants on the ground surface and grasping the utilization status of vegetation on the ground surface using the orthoimages and DSMs obtained in this way. For example, a method has been proposed in which a DSM image of a target area and a DSM image of a target object such as a plant are obtained, and then a target object is detected from the DSM using artificial intelligence (see, for example, Patent Document 1); a method has been proposed in which a slope map and a curvature map are obtained based on the DSM, and these are combined with an orthoimage to generate a composite image that is more three-dimensional and has higher visibility than an orthoimage (see, for example, Patent Document 2); a method has been proposed in which a distribution of a second type of plant is extracted from a DSM of a field having a first type of plant and a second type of plant according to the difference in plant height (see, for example, Patent Document 3); and a method has been proposed in which, for a target area including a forest, feature values are extracted from laser measurement data and aerial photographed images, and the pixel values of the color image at each pixel are determined based on the value of each feature value corresponding to each pixel, thereby visualizing differences in forest types in a color image (see, for example, Patent Document 4).

JP 2018-92628 A Patent No. 6700519 JP 2022-66907 A JP 2015-141118 A

However, the method described in Patent Document 1 uses only DSM image information and does not use orthoimages, which results in poor detection efficiency for target objects. The method described in Patent Document 2 generates a three-dimensional, highly visible composite image that is effective for grasping topography, but has the problem that it is difficult to grasp the utilization status of the ground surface, such as vegetation. The method described in Patent Document 3 is for farm fields with only two types of plants, and has the problem that it is difficult to grasp the utilization status of target areas other than farm fields, such as rural areas. The method described in Patent Document 4 allows for various settings for the feature amounts to be extracted, but has the problem that the procedures and formulas for determining the pixel values of the color image are complicated.

The present invention was made with a focus on these problems, and aims to provide a method for creating a composite image of the ground surface, a system for creating a composite image of the ground surface, and a program for creating a composite image of the ground surface that can relatively easily grasp the utilization status of the ground surface, such as vegetation, using height information.

In order to achieve the above object, the method for creating a composite image of the earth's surface according to the present invention is characterized by having an image acquisition step of acquiring an orthoimage of a target area and a digital surface model (DSM; Digital Surface Model), a ground height image creation step of creating a ground height image relating to the height of objects on the ground based on the digital surface model acquired in the image acquisition step, a pixel extraction step of extracting pixels having a ground height equal to or greater than a predetermined threshold from the ground height image created in the ground height image creation step, a grayscale image creation step of creating a grayscale image in which the grayscale value of each pixel extracted in the pixel extraction step is set based on the corresponding ground height or set to a constant value, and a composite image creation step of creating a composite image by superimposing the grayscale image created in the grayscale image creation step on the orthoimage.

The earth surface composite image creation system of the present invention is characterized by having an image acquisition means for acquiring an ortho-image and a digital surface model of a target area, a ground height image creation means for creating a ground height image relating to the height of objects on the ground based on the digital surface model acquired by the image acquisition means, a pixel extraction means for extracting pixels having a ground height equal to or greater than a predetermined threshold from the ground height image created by the ground height image creation means, a grayscale image creation means for creating a grayscale image in which the grayscale value of each pixel extracted by the pixel extraction means is set based on the corresponding ground height or set to a constant value, and a composite image creation means for creating a composite image by superimposing the grayscale image created by the grayscale image creation means on the ortho-image.

The earth's surface composite image creation program of the present invention is characterized by having a computer function as an image acquisition means for acquiring an ortho-image and a digital surface model of a target area, a ground height image creation means for creating a ground height image relating to the height of objects on the ground based on the digital surface model acquired by the image acquisition means, a pixel extraction means for extracting pixels having a ground height equal to or greater than a predetermined threshold from the ground height image created by the ground height image creation means, a grayscale image creation means for creating a grayscale image in which the grayscale value of each pixel extracted by the pixel extraction means is set based on the corresponding ground height or set to a constant value, and a composite image creation means for creating a composite image by superimposing the grayscale image created by the grayscale image creation means on the ortho-image.

The method, system, and program for creating a composite image of the earth's surface according to the present invention can easily obtain a composite image that reflects height information by setting the shading of the ortho-image of the target area based on the ground height, which indicates the height of objects on the ground. Furthermore, by using this composite image, it is possible to determine not only the appearance from the sky, but also differences in height, making it relatively easy to grasp the utilization status of the ground surface, such as vegetation. Furthermore, even if the resolution of the ortho-image is low, the accuracy of extracting vegetation, etc. can be improved. Note that ground height refers to the height from the ground of objects on the ground, such as buildings and trees.

The earth surface composite image creation method, earth surface composite image creation system, and earth surface composite image creation program of the present invention create a composite image that reflects height information in the shading of the orthoimage, and the composite image can be obtained as a three-channel image of red, green, and blue. For example, general image processing programs using machine learning and the like are developed on the premise of processing three-channel images of RGB, and images taken with a normal camera mounted on a UAV are also three-channel images. For this reason, the earth surface composite image creation method, earth surface composite image creation system, and earth surface composite image creation program of the present invention are highly versatile, as there is no need to convert a three-channel image into an image with four or more channels or to modify an image processing program for use with four or more channels.

The composite image created by the earth surface composite image creation method, earth surface composite image creation system, and earth surface composite image creation program of the present invention may be used as training data for machine learning together with the utilization status of the earth surface, such as vegetation, as understood from the composite image, in order to build a system for grasping the utilization status of the earth surface, such as vegetation. In addition, the utilization status of the earth surface, such as vegetation, may be grasped from the newly created composite image using a system thus constructed. In the earth surface composite image creation method, earth surface composite image creation system, and earth surface composite image creation program of the present invention, it is preferable that each pixel of the ground height image and the grayscale image correspond 1:1 to each pixel of the orthoimage, but this does not necessarily have to correspond 1:1 as long as the positions of the images are not shifted.

In the method for creating a composite ground surface image according to the present invention, the grayscale image creating step may set each grayscale value to a constant value so that each pixel extracted in the pixel extraction step becomes white. In the system for creating a composite ground surface image and the program for creating a composite ground surface image according to the present invention, the grayscale image creating means may set each grayscale value to a constant value so that each pixel extracted in the pixel extraction means becomes white. In this case, in the created composite image, parts above a certain threshold level above ground level become white, so that parts higher than the threshold level can be easily extracted. For this reason, for example, when a target area is a rural area, it is very difficult to distinguish between plants such as hedges that are lower than the house and a woodland that has grown higher than the house in an image taken from the sky, but in a composite image obtained by setting the certain threshold level higher than the height of the house, only the woodland can be easily extracted.

In the method for creating a composite earth surface image according to the present invention, the grayscale image creating step may set the grayscale value of each pixel extracted in the pixel extraction step to a value obtained by converting the corresponding height above ground with a predetermined monotonically increasing function or monotonically decreasing function. In the system for creating a composite earth surface image and the program for creating a composite earth surface image according to the present invention, the grayscale image creating means may set the grayscale value of each pixel extracted by the pixel extraction means to a value obtained by converting the corresponding height above ground with a predetermined monotonically increasing function or monotonically decreasing function. In this case, the ground height image is converted in tone according to the height above ground of each pixel and reflected in the grayscale of the composite image, making it easy to grasp height information from the created composite image. Therefore, the composite image makes it easy to extract differences in vegetation, etc. that are difficult to grasp just from the appearance from above.

In the ground surface synthetic image creation method of the present invention, the ground height image creation step may create a digital elevation model (DEM; Digital Elevation Model) based on the digital surface model, and create the ground height image from the difference between the digital surface model and the created digital elevation model. Alternatively, the image acquisition step may also acquire a digital elevation model of the target area, and the ground height image creation step may create the ground height image from the difference between the digital surface model and the digital elevation model acquired in the image acquisition step. In the ground surface synthetic image creation system and ground surface synthetic image creation program of the present invention, the ground height image creation means may create a digital elevation model based on the digital surface model, and create the ground height image from the difference between the digital surface model and the created digital elevation model. Alternatively, the image acquisition means may also acquire a digital elevation model of the target area, and the ground elevation image creation means may create the ground elevation image from the difference between the digital surface model and the digital elevation model acquired by the image acquisition means.

When using this digital elevation model, when creating a digital elevation model based on a digital surface model, for example, the digital surface model can be filtered to remove the heights of objects on the ground such as buildings and trees, thereby creating the digital elevation model. Furthermore, when acquiring a digital elevation model in the image acquisition step or image acquisition means, for example, a digital elevation model provided by the Geospatial Information Authority of Japan can be used. Furthermore, by using the digital elevation model, a ground height image can be easily created from the difference between the digital surface model (DSM) and the digital elevation model (DEM). The created ground height image is, for example, an image based on a digital height model (DHM; Digital Height Model).

In the earth surface synthetic image creation method according to the present invention, the image acquisition step may acquire three-dimensional point cloud data from image data of the target area photographed from the sky, and create the ortho-image and the digital surface model from the acquired three-dimensional point cloud data. In the earth surface synthetic image creation system and earth surface synthetic image creation program according to the present invention, the image acquisition means may acquire three-dimensional point cloud data from image data of the target area photographed from the sky, and create the ortho-image and the digital surface model from the acquired three-dimensional point cloud data. In this case, for example, three-dimensional point cloud data can be easily acquired by processing image data photographed continuously from different viewpoints in the sky by a UAV using Structure from Motion (SfM) or the like.

In the method for creating a synthetic earth surface image according to the present invention, the image acquisition step may create the ortho-image and the digital surface model based on an aerial photograph of the target area taken from the sky and measurement data obtained by measuring the target area from the sky with a LiDAR (Liquid Detection and Ranging). In the synthetic earth surface image creation system and the synthetic earth surface image creation program according to the present invention, the image acquisition means may create the ortho-image and the digital surface model based on an aerial photograph of the target area taken from the sky and measurement data obtained by measuring the target area from the sky with a LiDAR (Liquid Detection and Ranging). In this case, the ortho-image and the digital surface model can be created using the aerial photograph and measurement data obtained by the LiDAR (Liquid Detection and Ranging) without using a UAV.

The earth surface composite image creation method according to the present invention preferably includes a composite image display step for displaying the composite image created in the composite image creation step. The earth surface composite image creation system according to the present invention preferably includes a composite image display means for displaying the composite image created by the composite image creation means. The earth surface composite image creation program according to the present invention preferably causes the computer to further function as a composite image display means for displaying the composite image created by the composite image creation means. In this case, the utilization status of the earth surface, such as vegetation, can be grasped using the displayed composite image.

The ground surface composite image creation method, ground surface composite image creation system, and ground surface composite image creation program of the present invention are preferably used in areas with little elevation difference, such as rural areas, because they use height information to grasp the utilization status of the ground surface, such as vegetation. The ground surface composite image creation method, ground surface composite image creation system, and ground surface composite image creation program of the present invention can be used, for example, to grasp the distribution of trees and plantings in residential forests and parks, to grasp the distribution of artificial objects such as buildings and solar panels, to grasp fallen trees due to disasters, and to manage them. For this reason, they are suitable for use in environmental consulting, environmental information processing services, construction, aerial surveying, and the agriculture, forestry, and fisheries industries, etc.

The present invention provides a method for creating a composite image of the ground surface, a system for creating a composite image of the ground surface, and a program for creating a composite image of the ground surface that can relatively easily grasp the utilization status of the ground surface, such as vegetation, by using height information.

1 is a block diagram showing a configuration of a ground surface composite image creation system according to an embodiment of the present invention; 4 is a flowchart showing a processing procedure of the ground surface composite image creation system according to the embodiment of the present invention. (a) An ortho-image created by using a rural area as a target area of a system for creating a composite image of the earth's surface according to an embodiment of the present invention; (b) a grayscale image (1) created in the target area of (a); (c) a grayscale image (2) created in the target area of (a); and (d) a composite image created by superimposing the ortho-image (a) and the grayscale image (b).

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
1 to 3 show a ground surface composite image creating method, a ground surface composite image creating system, and a ground surface composite image creating program according to an embodiment of the present invention. The ground surface composite image creating method according to the embodiment of the present invention is a method preferably implemented by the ground surface composite image creating system according to an embodiment of the present invention, and can be executed by a computer using the ground surface composite image creating program.

As shown in FIG. 1, the earth surface composite image creation system 10 according to an embodiment of the present invention is made up of a computer, and has a storage means 11, an input means 12, a display means 13, and a main control unit 14. The storage means 11 is made up of a memory capable of storing various data. The input means 12 is made up of a keyboard, mouse, etc. that allow the user to input various data and information. The display means 13 is made up of a monitor (display). The main control unit 14 is made up of a CPU, and has calculation and control functions. The main control unit 14 is connected to the input means 12, storage means 11, and display means 13, and is configured to be able to control each of them.

The storage means 11 is configured to store digital aerial image data of the target area taken from the sky, previously acquired by a UAV, aerial photographs of the target area taken from the sky, and measurement data of the target area measured from the sky by a laser distance measuring device (LiDAR). The aerial image data taken by the UAV consists of multiple images taken continuously from different viewpoints in the sky. The storage means 11 is also configured to store three-dimensional point cloud data, orthoimages, digital surface models (DSM), ground height images, grayscale images, composite images, and the like, created by the main control unit 14. The storage means 11 may also be configured to store a digital elevation model (DEM) of the target area provided by the Geospatial Information Authority of Japan, etc., previously acquired via the Internet, etc.

The input means 12 is configured to input the set threshold value and to instruct the method of creating the grayscale image. The display means 13 is configured to be capable of displaying the aerial image data stored in the storage means 11, the orthoimage, the digital surface model, the digital elevation model, the ground height image, the grayscale image, the composite image, etc.

The main control unit 14 has an image acquisition means 21, a ground height image creation means 22, a pixel extraction means 23, a grayscale image creation means 24, a composite image creation means 25, and a composite image display means 26. The image acquisition means 21 is configured to acquire three-dimensional point cloud data by processing a plurality of aerial image data stored in the storage means 11 using Structure from Motion (SfM) and to create an orthoimage and a digital surface model of the target area from the three-dimensional point cloud data, or to create a digital surface model from LiDAR measurement data stored in the storage means 11. The image acquisition means 21 may also be configured to acquire a digital elevation model from the storage means 11. The created orthoimage is a three-channel image of RGB.

The ground height image creation means 22 is configured to create a ground height image relating to the height of an object on the ground based on the digital surface model acquired by the image acquisition means 21. The ground height image creation means 22 may, for example, create a digital elevation model based on the digital surface model, and create a ground height image from the difference between the digital surface model and the created digital elevation model. Alternatively, the ground height image creation means 22 may create a ground height image from the difference between the digital surface model and the digital elevation model acquired by the image acquisition means. In these cases, the created ground height image is an image based on the digital height model (DHM; Digital Height Model).

The pixel extraction means 23 is configured to extract pixels having a ground height equal to or greater than a predetermined threshold input by the input means 12 from the ground height image created by the ground height image creation means 22.

The shading image creation means 24 is configured to set the shading value of each pixel extracted by the pixel extraction means 23 from the ground height image created by the ground height image creation means 22 according to the following (1) and (2), and to create each shading image.
(1) The shading value of each pixel extracted by the pixel extracting means 23 is set to a constant value so that each pixel becomes white.
(2) The gray value of each pixel extracted by the pixel extracting means 23 is set to a value obtained by converting the corresponding ground height using a predetermined monotonically increasing or decreasing function.

The composite image creation means 25 is configured to create a composite image by superimposing the grayscale image (1) or the grayscale image (2) created by the grayscale image creation means 24 on the orthoimage created by the image acquisition means 21 based on the selection input by the input means 12. The composite image display means 26 is configured to display the composite image created by the composite image creation means 25 on the display means 13.

In the embodiment of the present invention, the earth's surface composite image creation system 10 is configured so that each pixel not extracted by the pixel extraction means 23 is colored black (pixel value is zero), and the shading value of the orthoimage created by the image acquisition means 21 becomes the shading value of the composite image as is. Note that when creating the shading image of (1), it is also possible to set each pixel extracted by the pixel extraction means 23 to be black, and each pixel not extracted by the pixel extraction means 23 to be white.

Next, the processing procedure and operation of the ground surface composite image generating system 10 according to the embodiment of the present invention will be described with reference to FIG.
As shown in Fig. 2, when using a UAV (drone), first, a target area is photographed continuously from different viewpoints in the sky, and the acquired multiple aerial image data are stored in the storage means 11 (step 31). Next, each aerial image data stored in the storage means 11 is processed by the image acquisition means 21 using SfM to create 3D point cloud data (step 32). Furthermore, the image acquisition means 21 creates an orthoimage (step 33) and a digital surface model (DSM image) (step 34) of the target area from the 3D point cloud data.

The ground height image creation means 22 uses the digital surface model and a digital elevation model (DEM image) (step 35) provided by a provider such as the Geospatial Information Authority of Japan and stored in the storage means 11 to obtain differential data (DSM-DEM) between the DSM image and the DEM image (step 36), and creates a ground height image (DHM) (step 37).

In addition, when aerial photographs and LiDAR measurement data are used without using a UAV (drone), the image acquisition means 21 orthorectifies the aerial photographs stored in the storage means 11 to create an orthoimage (step 33), and creates a digital surface model (DSM image) from the LiDAR measurement data stored in the storage means 11. The ground height image creation means 22 filters the digital surface model to remove the heights of objects on the ground such as buildings and trees, creates a digital elevation model (DEM image), obtains difference data (DSM-DEM) between the DSM image and the DEM image (step 36), and creates a ground height image (DHM) (step 37). Here, when creating the orthoimage, the aerial photograph may be orthorectified using the DEM image created by the ground height image creation means 22. An example of an aerial photograph of a rural area is shown in FIG. 3(a) as a target area.

A ground height threshold is set by referring to the orthoimage, the created DSM image, the DEM image, the ground height image, etc., and the threshold is input from the input means 12 (step 38). The pixel extraction means 23 extracts pixels from the ground height image that have a ground height equal to or greater than the input threshold (step 39).

The grayscale image creation means 24 sets the grayscale value of each pixel to a constant value so that each extracted pixel becomes white, and creates a grayscale image (1) according to the setting (step 40). Furthermore, the grayscale image creation means 24 uses a gradation conversion (contrast conversion) technique to set the grayscale value of each extracted pixel to a value obtained by converting the corresponding ground height with a predetermined monotonically increasing or decreasing function, and creates a grayscale image (2) according to the setting (step 41). At this time, each pixel not extracted by the pixel extraction means 23 is set to black (pixel value is zero) (binarization). Examples of the grayscale image (1) and the grayscale image (2) in the target area of Figure 3(a) are shown in Figures 3(b) and (c), respectively. In Figures 3(b) and (c), a threshold value is set to a ground height higher than plants such as hedges and houses and lower than a residential forest. Note that Figures 3(b) and (c) are images taken using aerial photographs and LiDAR measurement data.

When creating the grayscale image (2), a monotonically increasing function or a monotonically decreasing function for converting the ground height into a grayscale value may be preset, and the type of monotonically increasing function or monotonically decreasing function to be used may be specified from the input means 12. Furthermore, the monotonically increasing function and the monotonically decreasing function may be a linear function or a nonlinear function, or may be a combination of these.

By referring to the created grayscale image (1) and grayscale image (2), the user selects grayscale image (1) or grayscale image (2), and inputs the selection from input means 12 (step 42). The composite image creation means 25 creates a composite image by superimposing the grayscale image (1) or grayscale image (2) selected by input from input means 12 on the orthoimage (step 43). The composite image display means 26 sends the composite image created by the composite image creation means 25 to display means 13, and displays the composite image on display means 13 (step 44). This makes it possible to grasp the utilization status of the ground surface, such as vegetation, using the displayed composite image.

An example of a composite image of the target area of FIG. 3(a) is shown in FIG. 3(d). The composite image of FIG. 3(d) is obtained by superimposing the grayscale image of (1) on the ortho-image. In such a composite image created by superimposing the grayscale image of (1) on the ortho-image, the parts above a certain threshold are white, so that the parts higher than the threshold can be easily extracted. For example, when the target area is a rural area, it is very difficult to distinguish between hedges and other plantings that are lower than the houses and the residential forests that have grown higher than the houses in an image taken from the sky (for example, the image of FIG. 3(a)). However, in a composite image obtained by setting the certain threshold higher than the height of the houses, only the residential forests can be easily extracted. For example, the white parts can be easily extracted as the residential forests from the composite image of FIG. 3(d).

In addition, in the composite image created by superimposing the grayscale image (2) on the orthoimage, the range above ground level that is above a certain threshold is converted into gradations and reflected in the grayscale of the composite image, making it easy to grasp height information from the composite image. Therefore, even in the composite image created by superimposing the grayscale image (2) on the orthoimage, differences in vegetation, etc. that are difficult to grasp from the appearance alone from above can be easily extracted.

The earth surface composite image creation system 10 according to the embodiment of the present invention can easily obtain a composite image that reflects height information by setting the shading of the ortho-image of the target area based on the height above ground. Furthermore, by using this composite image, it is possible to determine not only the appearance from the sky, but also differences in height, making it relatively easy to grasp the utilization status of the earth surface, such as vegetation. Furthermore, even if the resolution of the ortho-image is low, the accuracy of extracting vegetation, etc. can be improved.

The earth surface composite image creation system 10 according to the embodiment of the present invention creates a composite image that reflects height information in the shading of the ortho-image, and can obtain the composite image as a three-channel image of RGB. This means that there is no need to convert a three-channel image into an image with four or more channels, or to modify an image processing program for use with four or more channels, making it highly versatile.

The composite image created by the ground surface composite image creation system 10 according to the embodiment of the present invention may be used as training data for machine learning together with data on the ground surface utilization status, such as vegetation, as understood from the composite image, in order to construct a ground surface utilization status estimation system for grasping the utilization status of the ground surface, such as vegetation. Furthermore, the ground surface utilization status, such as vegetation, may be grasped from the newly created composite image using the ground surface utilization status estimation system constructed in this manner.

　A synthetic image was created for a number of regions using the earth's surface synthetic image creation system 10 according to an embodiment of the present invention. Images obtained by dividing a synthetic image into multiple parts were divided into training data and test data, and machine learning was performed using the training data (teacher data; actual distribution of compound forests) to construct an estimation system for the distribution of compound forests. Next, the accuracy of compound forest extraction was evaluated for the constructed system using the test data. The Dice coefficient was used for the accuracy evaluation. As a comparative example, machine learning and accuracy evaluation were performed using images obtained by dividing only the orthoimage into multiple parts as training data and test data without using the earth's surface synthetic image creation system 10 according to an embodiment of the present invention.

As a result, the Dice coefficient in the comparative example where the compound grove was extracted using only the orthoimage was 0.64. In contrast, the Dice coefficient was 0.76 when the compound grove was extracted using the composite image made up of the grayscale image (1). The Dice coefficient was 0.80 when the compound grove was extracted using the composite image made up of the grayscale image (2). It should be noted that when creating the grayscale image (2), a linear transformation was used as the tone transformation. From these results, it can be said that the use of composite images can improve extraction accuracy.

The earth surface composite image creation program of the embodiment of the present invention may be provided from the outside via a communication line, for example, or may be provided in a form recorded on a computer-readable recording medium such as a CD (CD-ROM, CD-R, CD-RW, etc.), DVD (DVD-ROM, DVD-RAM, DVD-R, DVD-RW, DVD+R, DVD+RW, etc.), USB memory, etc. In these cases, the computer can read the earth surface composite image creation program from the communication line or recording medium, transfer it to the computer's internal storage device, and store it for use. The earth surface composite image creation program of the embodiment of the present invention may also be recorded in a storage device (recording medium) such as a magnetic disk, optical disk, or magneto-optical disk, and provided to the computer from the storage device via a communication line.

Here, a computer is a concept that includes hardware and an OS (operating system), and refers to hardware that operates under the control of the OS. Also, in cases where an OS is not required and the hardware is operated by an application program alone, the hardware itself corresponds to a computer. The hardware is equipped with at least a microprocessor such as a CPU, and a means for reading computer programs recorded on an internal storage device or recording medium.

The application program as the earth surface composite image creation program of the embodiment of the present invention includes program code that is executed by the computer as described above. In addition, some of the functions may be executed by the OS instead of the application program.

REFERENCE SIGNS LIST 10 Earth's surface composite image creation system 11 Storage means 12 Input means 13 Display means 14 Main control unit 21 Image acquisition means 22 Ground height image creation means 23 Pixel extraction means 24 Grayscale image creation means 25 Composite image creation means 26 Composite image display means

Claims (10)

an image acquisition step for acquiring an orthoimage and a digital surface model (DSM) of the area of interest;
a ground height image creation step of creating a ground height image relating to the height of an object on the ground based on the digital surface model acquired in the image acquisition step;
a pixel extraction step of extracting pixels having a ground height equal to or greater than a predetermined threshold from the ground height image created in the ground height image creation step;
a grayscale image creating step of creating a grayscale image in which the grayscale value of each pixel extracted in the pixel extracting step is set based on the corresponding ground height or set to a constant value;
a composite image creation step of creating a composite image by superimposing the grayscale image created in the grayscale image creation step on the orthoimage;
A method for creating a composite image of the earth's surface, comprising: The method for creating a composite earth surface image according to claim 1, characterized in that the grayscale image creation step sets each grayscale value to a constant value so that each pixel extracted in the pixel extraction step becomes white. The method for creating a synthetic earth surface image according to claim 1, characterized in that the grayscale image creation step sets the grayscale value of each pixel extracted in the pixel extraction step to a value obtained by converting the corresponding ground height using a predetermined monotonically increasing or decreasing function. The method for creating a synthetic ground surface image according to claim 1, characterized in that the ground height image creation step creates a digital elevation model (DEM; Digital Elevation Model) based on the digital surface model, and creates the ground height image from the difference between the digital surface model and the created digital elevation model. The image capturing step also captures a digital elevation model of the area of interest;
2. The method for generating a synthetic earth surface image according to claim 1, wherein the ground height image generating step generates the ground height image from a difference between the digital surface model and the digital elevation model acquired in the image acquiring step. The method for creating a synthetic earth surface image according to any one of claims 1 to 5, characterized in that the image acquisition step includes acquiring three-dimensional point cloud data from image data obtained by photographing the target area from the air, and creating the orthoimage and the digital surface model from the acquired three-dimensional point cloud data. The method for creating a synthetic earth surface image according to any one of claims 1 to 5, characterized in that the image acquisition step creates the orthoimage and the digital surface model based on an aerial photograph taken of the target area from above and measurement data obtained by measuring the target area from above using a laser distance measuring device (LiDAR). The method for creating a composite image of the earth's surface according to any one of claims 1 to 5, further comprising a composite image display step for displaying the composite image created in the composite image creation step. image acquisition means for acquiring an orthoimage and a digital surface model of a target area;
a ground height image generating means for generating a ground height image relating to the height of an object on the ground based on the digital surface model acquired by the image acquiring means;
a pixel extraction means for extracting pixels having a ground height equal to or greater than a predetermined threshold from the ground height image created by the ground height image creation means;
a grayscale image creating means for creating a grayscale image in which the grayscale value of each pixel extracted by the pixel extracting means is set based on the corresponding ground height or set to a constant value;
a composite image creation means for creating a composite image by superimposing the grayscale image created by the grayscale image creation means on the orthoimage;
A ground surface synthetic image creation system comprising: Computer,
image acquisition means for acquiring an orthoimage and a digital surface model of a target area;
a ground height image creation means for creating a ground height image relating to the height of an object on the ground based on the digital surface model acquired by the image acquisition means;
a pixel extraction means for extracting pixels having a ground height equal to or greater than a predetermined threshold from the ground height image created by the ground height image creation means;
a grayscale image creating means for creating a grayscale image in which the grayscale value of each pixel extracted by the pixel extracting means is set based on the corresponding ground height or set to a constant value;
a composite image creation means for creating a composite image by superimposing the grayscale image created by the grayscale image creation means on the orthoimage;
A ground surface composite image creation program that functions as follows.

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