JPWO2020044628A1 - Field photography system and field photography method - Google Patents

Abstract

The field photographing system includes a flying object, a plurality of imaging units, a chart, and a parallax correction unit (11c). The plurality of imaging units are held by the flying object, and during the flight of the flying object, the fields in which the crops are grown are photographed from the sky to acquire field images having different wavelength bands. The parallax correction unit is a pixel position indicating the same point caused by parallax between each field image based on each chart image obtained by photographing a chart from the sky by a plurality of imaging units during the flight of the flying object. Correct the deviation. The chart above is located in or around the field.

Description

The present invention relates to a field photography system and a field photography method for photographing a field from the sky.

Conventionally, a system for measuring a plant growth index has been proposed. For example, in the system of Patent Document 1, the reflected light measuring unit measures the light intensity of the reflected light of the measurement target having a plurality of leaves at the first wavelength and the second wavelength, and the sun angle acquisition unit measures the sunlight. The angle of incidence on the sun is acquired as the sun angle, and the direction of the sun with respect to the measurement direction of the reflected light measuring unit is acquired as the sun direction by the sun direction acquisition unit. Then, the growth index calculation unit acquires each light intensity of the reflected light at each of the first and second wavelengths measured by the reflected light measurement unit, the sun angle acquired by the sun angle acquisition unit, and the sun direction acquisition unit. Based on the direction of the sun, a growth index showing the degree of growth in the measurement target is obtained. In Patent Document 1, for example, NDVI (Normalized Difference Vegetation Index) is required as the above-mentioned growth index.

Here, the reflected light measuring unit is a so-called multispectral camera including a visible imaging unit that generates a visible light image and an infrared imaging unit that generates an infrared light image. Each of the visible imaging unit and the infrared imaging unit includes a bandpass filter, a lens (imaging optical system), and a sensor.

WO2016 / 181743 (see claim 5, paragraphs [0021] to [0077], FIG. 5, etc.)

In recent years, a multispectral camera is mounted on an unmanned aerial vehicle (also called a drone), and the drone is flown to take a picture of the field from the sky to acquire visible and infrared images and measure NDVI. ing. The above-mentioned field refers to a paddy field or field in which crops are grown. However, when the multispectral camera is mounted on the drone and the visible image and the infrared image are acquired in this way, the NDVI value fluctuates due to the following causes.

(A) Changes in the internal state of the camera Due to vibrations and temperature changes during flight of the drone, for example, the relative orientation and focal length of each optical axis of the visible imaging unit and the infrared imaging unit change. In this case, a shift (also referred to as parallax) occurs at a position indicating the same point between the visible image and the infrared image. Therefore, if the NDVI value is calculated using the pixel values at the same coordinate position in the visible image and the infrared image, the NDVI value is calculated using the pixel values corresponding to different points in the field. , It becomes impossible to obtain an accurate NDVI value for any point in the field.

(B) Changes in the external state of the camera The mounting directions of the visible imaging unit and the infrared imaging unit shift due to vibration during flight of the drone and variations in gimbal control. Also in this case, since parallax occurs between the visible image and the infrared image, it becomes impossible to obtain an accurate NDVI value at an arbitrary point in the field as in the above (A).

In particular, when each optical system included in the visible imaging unit and the infrared imaging unit is contaminated due to, for example, adhesion of dust, the pixel values of the visible image and the infrared image acquired by the visible imaging unit and the infrared imaging unit are increased. Noise is included. Therefore, the fluctuation of the NDVI value due to the above (A) and (B) becomes larger.

Therefore, when a multispectral camera is mounted on a drone and flew, the influence of parallax between the visible image and the infrared image is reduced so that the fluctuation of the NDVI value due to the above-mentioned causes can be prevented. It is desirable to perform parallax correction (calibration) for this purpose. In this regard, Patent Document 1 described above does not study parallax correction when a multispectral camera is mounted on a drone and is flown. Further, even when parallax correction is performed, it is desirable to perform parallax correction at the same time as photographing the field from the viewpoint of improving processing efficiency, and it is desirable to construct a system capable of realizing such parallax correction.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to mount a plurality of imaging units for acquiring images having different wavelength bands on a flying object and to photograph a field from the sky in a system. A field photographing system and a field that can reduce the influence of parallax between images acquired by a plurality of imaging units and can perform parallax correction for reducing the influence of the parallax at the same time as shooting the field. The purpose is to provide a shooting method.

The field photographing system according to one aspect of the present invention captures a flying object and a field held by the flying object and grows crops from the sky during the flight of the flying object, and acquires field images having different wavelength bands. Based on the plurality of imaging units, the charts captured by the plurality of imaging units, and the chart images obtained by photographing the chart from the sky by the plurality of imaging units during the flight of the flying object. The chart is located in or around the field, including a misalignment correction unit that corrects misalignment of pixels indicating the same location caused by misalignment between the field images.

In the field photographing method according to another aspect of the present invention, a field image in which crops are grown is photographed from the sky during the flight of the flying object by a plurality of imaging units held by the flying object, and field images having different wavelength bands are obtained. And the chart located in the field or around the field are photographed from the sky by the plurality of imaging units during the flight of the flying object to acquire each chart image. The chart image acquisition step and the misalignment correction step of correcting the positional deviation of the pixels indicating the same point caused by the misalignment between the field images based on the chart images are included.

According to the above-mentioned field photographing system and field photographing method, a plurality of imaging units held by the flying object photograph the field from the sky, so that field images having different wavelength bands are acquired. The parallax correction unit corrects the positional deviation of the pixels indicating the same point caused by the parallax between the field images based on each chart image obtained by photographing the chart by a plurality of imaging units. As a result, even if parallax occurs between each field image due to vibration of the flying object or the like, it is possible to obtain each field image in which the position shift of the pixels due to the parallax is corrected, and the influence of the parallax is reduced. It becomes possible. Further, since the above chart is located in or around the field, the plurality of imaging units can shoot the chart from the sky at the same time as shooting the field from the sky. As a result, the parallax correction unit can perform the parallax correction for reducing the influence of the above-mentioned parallax at the same time as the image of the field, and the processing efficiency can be improved.

It is explanatory drawing which shows typically the whole structure of the field photography system which concerns on one Embodiment of this invention. It is explanatory drawing which shows typically the detailed structure of the image pickup apparatus included in the said field photography system. It is a block diagram which shows the schematic structure of the terminal apparatus included in the said field photography system. It is a top view of the chart included in the said field photography system. It is a top view which shows the other structure of the said chart. It is explanatory drawing which shows the state which attached the chart to the transport vehicle. It is explanatory drawing which shows the state which attached the chart to the helmet. It is explanatory drawing which shows typically the missing part in the field which is substituted as a chart. It is explanatory drawing which shows typically the reflection spot of the sunlight reflected on the water surface in a field, which is substituted as a chart. It is a block diagram which shows the detailed structure of the flying object included in the said field photography system. It is a flowchart which shows the flow of the process by the field photography method carried out by the said field photography system. It is a flowchart which shows the flow of the parallax correction processing in the said field photography system. It is explanatory drawing which shows typically the chart image extracted from a plurality of photographed images. It is explanatory drawing which shows the projective transformation schematically.

An embodiment of the present invention will be described below with reference to the drawings.

[Structure of field photography system]
FIG. 1 is an explanatory diagram schematically showing the overall configuration of the field photographing system 1 of the present embodiment. The field photographing system 1 is a system for photographing a field FD in which a crop PL is grown, and includes a flying object 10, an imaging device 20, a terminal device 30, and a chart C. The aircraft body 10 and the terminal device 30 are communicably connected via a communication line NW. The communication line NW is composed of a network (whether wired or wireless) such as a LAN (Local Area Network) or an Internet line. The image pickup device 20 may be provided with the communication function of the flying object 10, and the image pickup device 20 and the terminal device 30 may be communicably connected via the communication line NW.

(Imaging device)
The image pickup device 20 is composed of, for example, a multispectral camera, and is held by the flying object 10. FIG. 2 schematically shows a detailed configuration of the image pickup apparatus 20. The image pickup apparatus 20 includes a first image pickup unit 21 and a second image pickup unit 22. The first imaging unit 21 is a visible imaging unit that captures a field FD and acquires an image (visible image) in the wavelength band of visible light. The second imaging unit 22 is a near-infrared imaging unit that photographs a field FD and acquires an image (near-infrared image) in the wavelength band of near-infrared light. Since the image pickup device 20 includes the first image pickup unit 21 and the second image pickup unit 22, the field FD is photographed from the sky during the flight of the flying object 10 to acquire field images having different wavelength bands. Can be done.

The first imaging unit 21 includes a first bandpass filter 21a, a first imaging optical system 21b, a first image sensor (optical sensor) 21c, a first digital signal processor (not shown), and the like. Have. The first bandpass filter 21a is an optical filter that transmits light in a relatively narrow band having a wavelength of 650 nm as a center wavelength, for example. The first imaging optical system 21b is composed of at least one lens, and first forms an optical image of visible light of a measurement target (crops PL or field FD) transmitted through the first bandpass filter 21a. An image is formed on the surface. The first image sensor 21c is composed of, for example, a VGA type (640 pixels × 480 pixels) CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, and the light receiving surface is the first imaging surface. It detects light in a relatively narrow band with a wavelength of 650 nm contained in the sunlight reflected by the measurement target as the center wavelength, and converts the optical image of the visible light to be measured into an electrical signal. do. The first digital signal processor performs image processing on the output of the first image sensor 21c to form a visible image. The image data Rv of the visible image is output to the control unit 11 (see FIG. 10) of the flying object 10. In the present embodiment, the transmission wavelength band of the first bandpass filter 21a is a red (R) wavelength band, but other wavelength bands such as blue (B) or green (G) may be used. good.

The second imaging unit 22 includes a second bandpass filter 22a, a second imaging optical system 22b, a second image sensor (optical sensor) 22c, a second digital signal processor (not shown), and the like. Have. The second bandpass filter 22a is an optical filter that transmits light in a relatively narrow band having a predetermined wavelength of 750 nm or more (for example, a wavelength of 800 nm) as a central wavelength. The second imaging optical system 22b is composed of at least one lens, and forms an optical image of near-infrared light to be measured that has passed through the second bandpass filter 22a on the second imaging surface. do. The second image sensor 22c is composed of, for example, a VGA type CCD sensor or a CMOS sensor, is arranged so that the light receiving surface coincides with the second imaging surface, and is included in the sunlight reflected by the measurement target. It detects light in a relatively narrow band with a wavelength of 800 nm as the central wavelength, and converts the optical image of the near-infrared light to be measured into an electrical signal. The second digital signal processor performs image processing on the output of the second image sensor 22c to form a near-infrared image. The image data Ri of the near-infrared image is output to the control unit 11 of the flying object 10.

(Terminal device)
FIG. 3 is a block diagram showing a schematic configuration of the terminal device 30. The terminal device 30 is composed of, for example, a PC (personal computer), and has an input unit 31, a display unit 32, a storage unit 33, a communication unit 34, and a control unit 35. The terminal device 30 may be composed of a multifunctional mobile terminal (for example, a smartphone or a tablet terminal).

The input unit 31 is operated by the user and is provided to accept the input of information by the user. Specifically, such an input unit 31 is composed of an operation unit such as a keyboard, a mouse, and a touch pad. The display unit 32 is a display that displays various types of information, and is composed of, for example, a liquid crystal display device.

The storage unit 33 is composed of, for example, a hard disk, and stores various information in addition to a program for operating the control unit 35. For example, the calculation formula (distortion correction information) for correcting the distortion of the visible image and the near-infrared image acquired by the imaging device 20 (first imaging unit 21, second imaging unit 22) is the imaging device 20. It is obtained in advance according to the design of the first imaging optical system 21b and the second imaging optical system 22b. Such distortion correction information is stored in advance in the storage unit 33, and when the distortion correction processing is performed inside the flying object 10, it is provided to the flying object 10 via the communication line NW. The distortion correction described above and the parallax correction described later may be performed by the control unit 35 of the terminal device 30.

The communication unit 34 is an interface for communicating with the flying object 10, and includes a transmission circuit, a reception circuit, a modulation circuit, a demodulation circuit, an antenna, and the like, and is communicably connected to the communication line NW. ing. The control unit 35 is composed of, for example, a CPU (Central Processing Unit), operates according to an operation program stored in the storage unit 33, controls the operation of each unit of the terminal device 30, and is necessary. Arithmetic processing is performed accordingly.

(chart)
The chart C is located in the field FD or around the field FD, and is used when performing parallax correction described later. For example, the chart C is attached to an object OB located in or around the field FD, thereby being located in or around the field FD. FIG. 1 shows an example in which a takeoff / landing platform 40 located around a field FD is used as the object OB and the chart C is attached to the takeoff / landing platform 40. The takeoff and landing platform 40 is a seat (table) installed on the ground for the purpose of preventing the surrounding sand from being rolled up when the flying object 10 takes off and landing. Such a chart C is photographed from the sky by the first imaging unit 21 and the second imaging unit 22 described above during the flight of the flying object 10.

FIG. 4 is a plan view of the chart C. The chart C has a pattern including at least one circular portion C ₁ (for example, a black circle). In order to distinguish between a pattern that naturally exists in or around the field FD (not intentionally generated) and a chart C for parallax correction, the chart C is a pattern that includes _{a plurality of circular portions C 1.} it is desirably, three or more and is more preferably a pattern including a circular portion C _1, reflectance from this, in addition to the circular part C ₁ different circular portion C ₂ (for example, black and sheets of background It is desirable that the pattern includes a circular portion (a circular portion colored with a color different from the color). Further, as shown in FIG. 5, the chart C may have a checkerboard pattern. The overall shape of the chart C is preferably a square, but may be another shape such as a rectangle.

Here, the object OB to which the chart C is attached is not limited to the above-mentioned takeoff and landing platform 40. As shown in FIG. 6, as the object OB, a transport vehicle 41 that transports the flying object 10 may be used, and the chart C may be attached to the transport vehicle 41 (for example, a ceiling or a bonnet). Further, as shown in FIG. 7, as the object OB, a helmet 42 worn by a pilot who remotely controls the flight of the flying object 10 is used, and a chart C (for example, one circular portion C ₁ ) is placed on the upper part of the helmet 42. It may be attached.

In addition, as the object OB, for example, an incident light sensor installed on the ground (around the field FD) may be used, and a chart C may be attached to the incident light sensor. The incident light sensor is provided to correct the image data Rv of the visible image and the image data Ri of the near-infrared image acquired by the image pickup apparatus 20 according to the weather (sunny, cloudy). It corresponds to the solar measuring unit of Patent Document 1. Further, a generator (located around the field FD) for charging the battery 17 (see FIG. 10) mounted on the air vehicle 10, a field server such as a thermometer and a water level gauge installed in the field FD, and an RTK. -GPS (Real Time Kinematic --Global Positioning System) base station (located in or around the field FD), agricultural machinery such as tractors and combines (located around the field FD), irrigation equipment such as water gates (field FD) (Positioned in or around the field FD) or the like may be used as the object OB, and the chart C may be attached to these objects OB.

Further, as shown in FIG. 8, the missing portion N of the crop PL located in the field FD may be substituted as the chart C. Here, the deficient portion N of the crop PL refers to a portion (region) in which the crop PL is not grown from the beginning in the field FD. For example, when the crop PL is rice, rice is not planted from the beginning. Refers to the part. In FIG. 8, the shaded portion indicated by the hatched portion indicates the region where the crop PL grows in the field FD, and the white-painted portion without the hatched portion corresponds to the missing stock portion N. Further, as shown in FIG. 9, the reflection spot S of sunlight reflected on the water surface when the inside of the field FD is immersed in water may be substituted as the chart C.

(Flying body)
The flying object 10 shown in FIG. 1 is composed of, for example, an unmanned aerial vehicle (drone) capable of autonomous flight. The aircraft body 10 may be composed of a balloon, an airship, an airplane, a helicopter, or the like, in addition to the above-mentioned unmanned aerial vehicle. The flight of the aircraft body 10 is remotely controlled by a ground pilot (operator) operating the operation unit 50 (see FIG. 10). By flying the flying object 10 along the field FD, a plurality of regions T constituting the field FD are photographed from the sky by the imaging device 20, and an image (for example, a visible image or an infrared image) is obtained for each region T. Can be obtained. Therefore, it is possible to finally acquire an image of the entire field FD by pasting together the images of each region T. By raising the altitude of the flying object 10 and photographing the entire field FD at once, it is possible to acquire one image of the entire field FD without pasting the images of each region T.

FIG. 10 is a block diagram showing a detailed configuration of the flying object 10. The aircraft body 10 includes a control unit 11, a communication unit 12, a warning unit 13, a position information acquisition unit 14, an image storage unit 15, a flight drive unit 16, and a battery 17. The flight drive unit 16 has, for example, a propeller, a motor, and the like, and drives the motor to rotate the propeller to fly the flying object 10. The flight control of the flying object 10 is performed by the control unit 11. At this time, the control unit 11 controls the flight drive unit 16 based on the operation of the operation unit 50 by the pilot on the ground. The battery 17 is a battery that supplies electric power for driving to each part of the flying object 10.

The control unit 11 is composed of, for example, a CPU, and includes an overall control unit 11a, a distortion correction unit 11b, a parallax correction unit 11c, a growth index calculation unit 11d, and an image composition unit 11e. That is, the CPU functions as an overall control unit 11a, a distortion correction unit 11b, a parallax correction unit 11c, a growth index calculation unit 11d, and an image composition unit 11e. The overall control unit 11a controls the operation of each unit of the flying object 10 according to an operation program stored in a program storage unit (not shown). The details of the distortion correction unit 11b, the parallax correction unit 11c, the growth index calculation unit 11d, and the image composition unit 11e will be described together in the operation description described later.

The communication unit 12 is an interface for communicating with the terminal device 30, includes a transmission circuit, a reception circuit, a modulation circuit, a demodulation circuit, an antenna, and the like, and is communicably connected to the communication line NW. ing.

The warning unit 13 controls when the amount of change in the pixel value position shift due to parallax exceeds the threshold value in a predetermined period (for example, one day or one week) calculated by the parallax correction unit 11c of the control unit 11. A warning is issued based on the control of the unit 11 (for example, the overall control unit 11a). Such a warning unit 13 transmits a display unit 13a (for example, a liquid crystal display device or a simple light source) for displaying a warning, an audio output unit 13b (for example, a speaker) for emitting a warning sound, and warning information to the outside. It can be configured by at least one of communication units (for example, communication unit 12).

The position information acquisition unit 14 is composed of, for example, GPS, and acquires the position information (latitude X, longitude Y, height Z) of the flying object 10 (imaging device 20). As a result, the control unit 11 (for example, the overall control unit 11a) controls the flight drive unit 16 based on the above position information, and moves the flying object 10 to a predetermined height position above the predetermined region T of the field FD. Can be flown.

The image storage unit 15 is composed of, for example, a non-volatile memory, and stores the image data of the visible image and the near-infrared image acquired by the first image pickup unit 21 and the second image pickup unit 22 of the image pickup apparatus 20. At the same time, the growth index obtained by the growth index calculation unit 11d (particularly, the image data of the NDVI image obtained based on the pixel value after the parallax correction) is stored.

[Processing in the field photography system]
Next, a field photography method using the field photography system 1 having the above configuration will be described. FIG. 11 is a flowchart showing the flow of processing by the field photography method of the present embodiment. Here, it is assumed that the chart C is attached to the takeoff and landing platform 40 located around the field FD.

First, the flying object 10 is flown, and the field FD is photographed and the chart C is photographed (S1; photographing step). More specifically, the pilot takes off the aircraft 10 from the takeoff / landing platform 40 by operating the operation unit 50. Then, during the flight of the flying object 10, the field FD is photographed from the sky by the first imaging unit 21 and the second imaging unit 22 held by the flying object 10, and field images having different wavelength bands are acquired (S1). -1; Field image acquisition process). That is, the first imaging unit 21 acquires a visible image of the field FD as one field image, and the second imaging unit 22 acquires a near-infrared image of the field FD as the other field image. The acquired image data Rv of the visible image and the near-infrared image data Ri are input from the first imaging unit 21 and the second imaging unit 22 to the control unit 11 of the flying object 10, respectively.

Further, during the flight of the flying object 10, the chart C attached to the takeoff and landing platform 40 is photographed from the sky by the first imaging unit 21 and the second imaging unit 22, and each chart image is acquired (S1-2). ; Chart image acquisition process). That is, the first imaging unit 21 acquires the visible image of the chart C as one chart image, and the second imaging unit 22 acquires the near-infrared image of the chart C as the other chart image. Here, in the above-mentioned "in flight of the flying object 10", the flying object 10 is ascending from the takeoff / landing platform 40 to reach a predetermined altitude above the field, and the flying object 10 is in the field. It is assumed that the flight body 10 is descending from a predetermined altitude in the sky to landing on the takeoff / landing platform 40. The image data of each chart image acquired by the first imaging unit 21 and the second imaging unit 22 is input to the control unit 11 of the flying object 10, respectively.

In the present embodiment, the first imaging unit 21 and the second imaging unit 22 simultaneously perform the field image acquisition step of S1-1 and the chart image acquisition step of S1-2. That is, the first imaging unit 21 and the second imaging unit 22 photograph the field FD from the sky and at the same time photograph the chart C. As a result, a field image (a field image also serving as a chart image) in which the chart C is reflected can be obtained for each of the visible and the near infrared.

Next, the distortion correction unit 11b of the control unit 11 has the first image pickup unit 21 and the distortion correction unit 11b based on the distortion correction information (calculation formula for correcting the distortion) provided from the terminal device 30 via the communication unit 12. The image data of each image (each field image, each chart image) output from the second imaging unit 22 is corrected. As a result, distortions such as barrel type and pincushion type in each image are corrected, and the next parallax correction can be appropriately performed using each image in the state where the distortion is corrected.

Subsequently, the parallax correction unit 11c of the control unit 11 between the field images based on the chart images obtained by photographing the chart C from the sky by the first imaging unit 21 and the second imaging unit 22. , Parallax correction (calibration) is performed to correct the positional deviation of the pixels indicating the same point caused by parallax (S3; parallax correction step). The details of the parallax correction in S3 will be described later.

After the parallax correction in S3, the overall control unit 11a determines whether or not the amount of change in the amount of change in the position deviation in the predetermined period exceeds the threshold value (S4). For example, when the visible image and the near-infrared image are superposed, the overall control unit 11a has elapsed a predetermined period (for example, one day or one week) of the length of the straight line connecting the positions indicating the same points. The difference before and after the operation is defined as the above-mentioned "change amount of positional deviation", and it is determined whether or not this change amount exceeds the threshold value. Then, when the amount of change exceeds the threshold value, the warning unit 13 issues a warning based on the control of the overall control unit 11a (S5; warning step). In this warning step, at least one of warning display by the display unit 13a, output of the warning sound by the voice output unit 13b, and transmission of the warning information to the outside by the communication unit 12 is performed. On the other hand, when the amount of change is equal to or less than the threshold value, the process directly shifts to S6.

Next, the growth index calculation unit 11d of the control unit 11 calculates the growth index of the crop PL based on each field image after the parallax correction unit 11c corrects the positional deviation (S6; growth index calculation step). .. In this embodiment, NDVI is used as the above-mentioned growth index. NDVI is an index showing the distribution status and activity of vegetation, and is the image data Rv of one field image (visible image) and the other field image (visible image) in which the above-mentioned positional deviation due to distortion and parallax is corrected as described above. Using the image data Ri of the near infrared image), it is represented by NDVI = {(Ri-Rv) / (Ri + Rv)}. NDVI indicates a normalized value between -1 and 1, and the larger the positive number, the darker the vegetation. When the NDVI is calculated for each pixel of each field image, an NDVI image showing the distribution of each pixel of the NDVI is obtained.

The growth index calculation unit 11d may calculate the following values as the growth index instead of NDVI. Examples of indexes other than NDVI include RVI (Ratio Vegetation Index; RVI = Ri / Rv), DVI (Difference Vegetation Index; DVI = Ri-Rv), TVI (Transformed Vegetation Index, TVI). = NDVI ^0.5 +0.5), or IPVI (Infrared Percentage Vegetation Index, IPVI = Ri / (Ri + Rv) = (NDVI + 1) / 2) and the like.

Further, the growth index calculation unit 11d may calculate the vegetation coverage rate as a growth index instead of NDVI. The vegetation coverage ratio indicates the ratio of the crop PL covering the ground surface of the field FD. For example, the growth index calculation unit 11d performs binarization processing on the near-infrared image after correcting the above-mentioned positional deviation due to distortion and parallax to form a binarized image of white and black, and this binarization. The planting coverage ratio can be calculated by calculating the ratio occupied by the white portion in the image. In the binarized image, the white part corresponds to the crop PL and the black part corresponds to the soil.

Next, the image synthesizing unit 11e of the control unit 11 may obtain a plurality of NDVI images for each field FD, or when a plurality of NDVI images are obtained for each region T included in each field FD. The NDVI images are combined to generate one NDVI image as a whole (S7; image composition step). The term "composite" here refers to joining a plurality of NDVI images side by side. If the number of obtained NDVI images is originally one, image composition is not required, so the process of S7 is skipped and the process is terminated.

[Details of parallax correction]
Next, the details of the parallax correction in S3 will be described. FIG. 12 is a flowchart showing a flow of parallax correction processing. First, the parallax correction unit 11c is shown on the chart C from a plurality of captured images acquired at different timings when the flying object 10 is moving in the sky by the first imaging unit 21 and the second imaging unit 22. An image including an image is extracted as the chart image described above (S11). For example, the parallax correction unit 11c includes an image of the chart C in which at least one (preferably four) images corresponding to _{the circular portion C 1 of the chart C are present in the image from the plurality of captured images.} Extract as a chart image. Then, such chart image extraction is performed on a plurality of captured images acquired by the first imaging unit 21 and the second imaging unit 22, respectively.

FIG. 13 schematically shows a chart image extracted by the parallax correction unit 11c from the plurality of captured images. Here, the first imaging unit 21 acquires the chart image CR-1 at time t1, the chart image CR-2 at time t2, the chart image CR-3 at time t3, and the second. When the chart image Ci-1 is acquired at time t1, the chart image Ci-2 is acquired at time t2, and the chart image Ci-3 is acquired at time t3, the imaging unit 22 arranges them in chronological order. Shown. CR is a chart image in the visible wavelength band, and Ci is a chart image in the near infrared wavelength band. In FIG. 13, in each chart image, an image corresponding to _{the circular portion C 1} of the chart C is indicated _{by C 1'.}

Next, the parallax correction unit 11c extracts the region CA of the chart C from each of the extracted chart images (S12). For example, the disparity correction portion 11c is within the extracted chart image 'calculates the position of the (coordinate), an image C _1' image C ₁ corresponding to the circular portion C ₁ and calculates the number of. Then, the image C ₁ 'if there four are parallax correction unit 11c extracted image C ₁ adjacent in the chart image' the distance between the image C ₁ 'is within a predetermined range, and, 'If a shape surrounding the has a square shape, its 4 Tsunozo C _1' 4 Tsunozo C ₁ extracts a region surrounding the as area CA of the chart C. Further, for example, in the extracted chart image in the image C ₁ 'if it is one that is, the image C _1' to extract a region of a predetermined size of square surrounding the area CA of the chart C.

Next, the parallax correction unit 11c is included in one chart image (for example, a visible image) based on each chart image captured and acquired at the same time by the first imaging unit 21 and the second imaging unit 22. A projection matrix for converting the position coordinates of the reference point P to the position coordinates of the corresponding point Q (indicating the same point in the field FD) corresponding to the other chart image (for example, a near-infrared image) is calculated (S13). Here, the reference point P and the corresponding point Q described above are, for example, the center positions of the region CA of the chart C obtained in S12 in each chart image. The center position is, for example 'if there are four, four image C _1' image C ₁ of the chart image mean value between the positions of the (x-coordinate and by adding the y-coordinate 4 divided by the coordinate position) it can be, 'If there is one, its image C _1' image C ₁ of the chart image may be a position of.

Here, a method of calculating the projection matrix will be described. Generally, projecting one plane onto another using a projective matrix is called homography (projection transformation). As one of the projective transformations, the affine transformation represented by the following equation is generally known (see, for example, http://zellij.hatenablog.com/entry/20120523/p1). Hereinafter, the projective transformation is assumed to be an affine transformation.

As shown in FIG. 14, the coordinates of an arbitrary point O on the xy plane are (x, y), and the point O is the xy'plane by a projection matrix (corresponding to a matrix of 3 rows and 3 columns of the equation 1). Let the coordinates of the point O'projected above be (x', y'). A projective transformation is a transformation that combines a linear transformation and a translation, and the linear transformation described above includes differential scaling, skew, and rotation. In the above projection matrix, the coefficient t _x and t _y, refers to coefficients for parallel movement (translation), the remaining coefficients a, b, c and d refer to coefficients for linear transformation.

To calculate the projection matrix is to calculate the six parameters of the coefficients a, b, c, d, t _x and t _{y in the projection matrix.} Since there are six unknown parameters (coefficients), if six equations can be established, all six unknown parameters can be obtained (that is, the projection matrix can be calculated). At this time, if the position coordinates of one point before and after the projective transformation are known, two equations can be established for x and y by substituting them into the equation 1. Therefore, six equations can be established by substituting the position coordinates before and after the projective transformation for the three points into the equation 1, and all six parameters can be obtained by solving them simultaneously.

Therefore, in the present embodiment, the parallax correction unit 11c inputs the position coordinates of the three points into the equation 1 as follows, and calculates the projection matrix. First, the coordinates (x1, y1) of the reference point P on the xy plane of the chart image CR-1 acquired at time t1 correspond to the correspondence on the x'y'plane of the chart image Ci-1 acquired at the same time. The coordinates (x1', y1') of the point Q are input to the equation 1. Similarly, the coordinates (x2, y2) of the reference point P on the xy plane of the chart image CR-2 acquired at time t2 and the coordinates (x2, y2) of the chart image Ci-2 acquired at the same time on the x'y'plane. Enter the coordinates (x2', y2') of the corresponding point Q in the equation 1. Further, the coordinates (x3, y3) of the reference point P on the xy plane of the chart image CR-2 acquired at time t3 correspond to the correspondence on the x'y'plane of the chart image Ci-3 acquired at the same time. Enter the coordinates (x3', y3') of the point Q in the equation 1. The projection matrix can be calculated by solving the six equations obtained by these methods at the same time. Since the flying object 10 is moving in the sky, the coordinates of the reference point P at time t1 (x1, y1), the coordinates of the reference point P at time t2 (x2, y2), and the reference point at time t3. The coordinates of P (x3, y3) are different from each other. Similarly, the coordinates of the corresponding point Q at time t1 (x1', y1'), the coordinates of the corresponding point Q at time t2 (x2', y2'), and the coordinates of the corresponding point Q at time t3 (x3', y3). ') Are different from each other.

Here, the projection matrix is calculated by formulating six equations by substituting the position coordinates of the three reference points P and the corresponding points Q into the equation 1, but it seems that linear conversion is not necessary, for example. In the case of a projective transformation (in the case of a projection transformation with only parallel movement), the position coordinates of one reference point P and the corresponding point Q are numbered, with all the coefficients a, b, c, and d of the projection matrix set to 0. By substituting into one equation, it is possible to obtain the _{coefficients t x} and t _{y and determine the projection matrix.}

It is also possible to formulate eight or more equations by substituting the position coordinates of the four or more reference points P and the corresponding points Q into the equation of equation 1. In this case, create a plurality of groups in which 6 equations are arbitrarily selected from 8 or more equations, obtain the coefficients of the projection matrix for each group, and finally use the least squares method from the coefficients obtained in each group. Factors may be determined. In this case, each coefficient, that is, the projection matrix can be obtained with high accuracy.

When the parallax correction unit 11c calculates the projection matrix as described above, the parallax correction unit 11c converts the position coordinates of all the points included in one field image (for example, a visible image) by the projection matrix obtained in S13 (S14). As a result, the misalignment of the pixels indicating the same point caused by the parallax between the one field image and the other field image (for example, a near infrared image) is corrected. That is, each pixel of one field image is associated with a pixel representing the same point in the field FD in the other field image.

〔effect〕
As described above, in the present embodiment, in the field image acquisition step, the field FD is photographed from the sky by the first imaging unit 21 and the second imaging unit 22 during the flight of the flying object 10 to obtain the wavelength band. Different field images (visible image, near infrared image) are acquired (S1-1). Further, in the chart image acquisition step, during the flight of the flying object 10, the chart C is photographed from the sky by the first imaging unit 21 and the second imaging unit 22, and each chart image is acquired (S1-2). Then, in the parallax correction step, the parallax correction unit 11c corrects the positional deviation of the pixels indicating the same point caused by the parallax between the field images based on each chart image (S3). As a result, even if a parallax occurs between the field images due to the vibration of the flying object 10, it is possible to obtain each field image in which the position deviation of the pixels due to the parallax is corrected, and the influence of the above parallax can be obtained. It is possible to reduce it.

Further, since the chart C is located in the field FD or around the field FD, the first imaging unit 21 and the second imaging unit 22 simultaneously perform the chart C at the same time as the field FD during the flight of the flying object 10. It becomes possible to shoot. As a result, the parallax correction unit 11c can perform parallax correction based on the chart image at the same time as the image of the field FD. Therefore, for example, the efficiency of the processing can be improved as compared with the case where the parallax correction is performed at a timing different from the photographing of the field FD. That is, the first imaging unit 21 and the second imaging unit 22 simultaneously perform the field image acquisition step (S1-1) and the chart image acquisition step (S1-2) to improve the processing efficiency. be able to. Further, since the field image and the chart image can be obtained at the same time by one shooting (because one shot image can serve as both the field image and the chart image), an increase in shooting man-hours can be avoided.

In addition, the flight of the above-mentioned flying object 10 includes ascending and descending of the flying object 10. Therefore, not only while the flying object 10 is flying over the field FD at a predetermined altitude, but also while the flying object 10 is ascending or descending, the first imaging unit 21 and the second imaging unit 22 respectively. Since the chart image can be acquired, the parallax correction unit 11c can perform the parallax correction even while the flying object 10 is ascending or descending.

Further, when the object OB is located in the field FD or around the field FD, the chart C can be positioned by using the object OB by attaching the chart C to the object OB. That is, in this case, the object OB can be effectively used in the installation of the chart C.

In particular, when the takeoff and landing platform 40 of the flying object 10, the transport vehicle 41 for carrying the flying object 10, and the helmet 42 worn by the pilot who remotely controls the flight of the flying object 10 are used to photograph the field FD. Is absolutely necessary. Therefore, by attaching the chart C to any of these objects OB (takeoff / landing platform 40, transport vehicle 41, helmet 42), it is not necessary to newly search for a place to install the chart C or to provide the chart C separately. It can be quickly installed on the object OB to quickly start photographing the field.

The chart C may be directly attached to the head of the pilot who remotely controls the flight of the flying object 10 without using the helmet 42. From this, it can be said that the chart C may be attached to the head of the pilot who remotely controls the flight of the flying object 10, regardless of whether or not the pilot is wearing the helmet 42.

The above-mentioned incident light sensor, generator, and RTK-GPS base station may be required when photographing the field FD using the flying object 10 (for example, when the weather fluctuates drastically, the field FD may be required. When it is vast and the battery 17 needs to be charged during shooting, or when it is necessary to communicate with the above base station in order to acquire the position information by the position information acquisition unit 14). Further, the above-mentioned field server, agricultural machine, and irrigation equipment are indispensable for the management of the field FD, and are always present in the field FD or around the field FD. Therefore, the chart C may be attached to these object OBs, and even in that case, the chart C may be quickly installed on the object OB while effectively utilizing the object OB, and the field FD photography may be started quickly. Can be done.

Further, when the chart C has a _{pattern including at least one circular portion C 1} or a lattice pattern, the chart C is photographed by the first imaging unit 21 and the second imaging unit 22 from the sky above the field FD. Then, when each chart image is acquired, an image of chart C ( _{including, for example, image C 1} ') clearly appears in each chart image. As a result, the parallax correction unit 11c can reliably obtain the position of the image of the chart C based on the pixel value, and can accurately and surely acquire the position information, and the above-mentioned parallax correction based on each chart image can be performed. It is possible to perform with high accuracy.

Further, the missing portion N of the crop PL located in the field FD and the sunlight reflection spot S reflected on the water surface in the field FD simultaneously display the field FD by the first imaging unit 21 and the second imaging unit 22. When photographed, it appears in each photographed image as a position indicating the same point in the field FD. Therefore, even if the missing portion N or the reflection spot S of sunlight is utilized as the chart C, the first imaging unit 21 and the second imaging unit 22 acquire each chart image, and the parallax correction unit 11c Can perform parallax correction based on each chart image. Therefore, in performing the parallax correction, it is not necessary to attach the chart C to the object OB in the field FD or around the field FD. Further, even when such an object OB does not exist, the parallax correction can be performed by utilizing (effectively utilizing) the missing stock portion N or the reflection spot S of sunlight as the chart C.

Further, in the disparity correction step, the disparity correction unit 11c is included in one of the chart images based on the chart images taken and acquired at the same time by the first imaging unit 21 and the second imaging unit 22. By calculating a projection matrix that converts the position coordinates of the reference point P into the position coordinates of the corresponding corresponding points Q in the other chart image, and by converting the position coordinates of all the points included in one field image by the projection matrix. , Correct the parallax (S13, S14). As a result, even if the internal state or external state of the first image pickup unit 21 and the second image pickup unit 22 changes due to vibration during flight of the flying object 10 (for example, optical axis deviation, mounting direction). It is possible to associate each pixel of one field image (visible image) with a pixel representing the same point in the field FD in the other field image (near infrared image).

Further, the parallax correction unit 11c is a chart from a plurality of captured images acquired at different timings when the flying object 10 is moving in the sky in each of the first imaging unit 21 and the second imaging unit 22. After extracting the image including the image of C as a chart image, the center position of the image of chart C is obtained from the extracted chart image, and the center position of the image of chart C in one of the chart images taken at the same time is used as a reference. The projection matrix is calculated with the center position of the image of the chart C in the other chart image taken at the same time as the point P as the corresponding point Q (S11 to S13). In this way, in each chart image taken at the same time, by calculating the projection matrix with the center position of the image on the chart C as the reference point P and the corresponding point Q, respectively, the projection matrix required for parallax correction can be appropriately obtained. Can be obtained.

Further, in the growth index calculation step, the growth index calculation unit 11d calculates the growth index (for example, NDVI value) of the crop PL based on each field image after the parallax correction unit 11c corrects the positional deviation (S6). ). Even when the first imaging unit 21 and the second imaging unit 22 are mounted on the flying object 10 and flown for the purpose of acquiring the NDVI value as in the present embodiment, the parallax correction unit 11c described above causes parallax. Since the influence can be reduced, it is possible to effectively prevent the fluctuation of the NDVI value due to parallax. Therefore, the growth index calculation unit 11d can acquire an accurate NDVI value at an arbitrary point in the field FD, and can avoid deterioration of the image quality of the NDVI image. Further, even when each of the optical systems included in the first imaging unit 21 and the second imaging unit 22 becomes dirty due to the adhesion of dust and the pixel values of the field images contain noise, as in the present embodiment. By correcting the misalignment of the pixels due to the parallax, it is possible to suppress the fluctuation of the NDVI value due to the noise at any point in the field FD as compared with the case where such correction is not performed. ..

Further, in the warning step, the warning unit 13 issues a warning when the amount of change in the positional deviation in a predetermined period exceeds the threshold value (S5). In S4, when the amount of change in the position shift exceeds the threshold value, the change in the position shift is not caused by the vibration of the flying object 10, but rather by the first imaging unit 21 and the second imaging unit 22. Most likely due to a failure. Therefore, the warning in S5 promptly prompts the user to take necessary measures such as inspection and repair, and enables the user to quickly take action against the failure. In particular, the warning unit 13 includes at least one of the display unit 13a, the audio output unit 13b, and the communication unit 12, and in S5, at least one of the warning display, the output of the warning sound, and the transmission of the warning information is performed. It is possible to reliably notify the user that an abnormality such as a failure has occurred and prompt the user to take necessary measures such as inspection.

〔others〕
In parallax correction (calibration), it is automatically determined whether or not there are three or more images with different chart positions, and if the number of images with different chart positions is less than three, a warning is given and the number of images is increased. If there are three or more sheets, a notification to the effect that they are appropriate may be given.

If the image for calibration is not found at the end of the shooting of the day, a warning may be given.

The field photographing system has a calibration mode, in which the flying object 10 may be automatically flown by a predetermined route in the calibration mode, or may be provided with a program for executing such an automatic flight.

The field photography system and the field photography method of the present embodiment described above can be expressed as follows.

The field photographing system of the present embodiment is held by the flying object and the flying object, and during the flight of the flying object, a plurality of fields in which crops are grown are photographed from the sky and field images having different wavelength bands are acquired. Based on the imaging unit, the charts taken by the plurality of imaging units, and the chart images obtained by photographing the chart from the sky by the plurality of imaging units during the flight of the flying object, each of the above. The chart includes a misalignment correction unit that corrects a misalignment of pixels indicating the same point caused by misalignment between field images, and the chart is located in or around the field.

In the field imaging system, the chart may be attached to an object located in or around the field.

In the field imaging system, the object may be the takeoff and landing platform of the flying object.

In the above-mentioned field photographing system, the object may be a transport vehicle for carrying the flying object.

In the field imaging system described above, the chart may be mounted on the head of a pilot who remotely controls the flight of the flying object.

In the above-mentioned field photographing system, the chart may have a pattern including at least one circular portion, or a lattice pattern.

In the above-mentioned field photographing system, the chart may be a missing portion of the crop located in the field or a reflection spot of sunlight reflected on the water surface in the field.

In the above-mentioned field photographing system, the parallax correction unit sets the position coordinates of the reference point included in one chart image to the other based on the chart images acquired by being photographed at the same time by the plurality of imaging units. The position deviation is corrected by calculating the projection matrix to be converted to the position coordinates of the corresponding points in the chart image of the above and converting the position coordinates of all the points included in one field image by the projection matrix. May be good.

In the above-mentioned field photographing system, the parallax correction unit is an image of the chart from a plurality of captured images acquired at different timings when the flying object is moving in the sky in each of the plurality of imaging units. After extracting the image containing the above as the chart image, the center position of the image of the chart is obtained from the extracted chart image, and the center position of the one chart image taken at the same time is set as the reference point. The projection matrix may be calculated with the center position of the other chart image taken at the same time as the corresponding point.

The field photographing system may further include a growth index calculation unit that calculates a growth index of the crop based on each field image after the position deviation is corrected by the parallax correction unit.

The field photographing system may further include a warning unit that issues a warning when the amount of change in the positional deviation exceeds a threshold value in a predetermined period.

In the above-mentioned field photographing system, the warning unit may include at least one of a display unit that displays a warning, a voice output unit that emits a warning sound, and a communication unit that transmits warning information to the outside.

In the field photographing method of the present embodiment, a field in which crops are grown is photographed from the sky during the flight of the flying object by a plurality of imaging units held by the flying object, and field images having different wavelength bands are acquired. The image acquisition step and the chart image acquisition step of acquiring each chart image by photographing the chart located in the field or around the field from the sky by the plurality of imaging units during the flight of the flying object. And, based on each of the chart images, a misalignment correction step of correcting the positional deviation of the pixels indicating the same point caused by the disparity between the field images is included.

In the above field photographing method, it is desirable that the field image acquisition step and the chart image acquisition step are simultaneously performed by the plurality of imaging units.

In the above-mentioned field photographing method, the flight of the flying object may include ascending and descending of the flying object.

In the above-mentioned field photographing method, in the difference correction step, the position coordinates of the reference point included in one chart image are set to the other based on the chart images acquired by being photographed at the same time by the plurality of imaging units. Even if the positional deviation is corrected by calculating the projection matrix to be converted into the position coordinates of the corresponding points in the chart image of the above and converting the position coordinates of all the points included in one field image by the projection matrix. good.

In the above-mentioned field photographing method, in the difference correction step, the image of the chart is obtained from a plurality of captured images acquired at different timings when the flying object is moving in the sky in each of the plurality of imaging units. After extracting the image containing the above as the chart image, the center position of the image of the chart is obtained from the extracted chart image, and the center position of the one chart image taken at the same time is set as the reference point. The projection matrix may be calculated with the center position of the other chart image taken at the same time as the corresponding point.

The above-mentioned field photographing method may further include a growth index calculation step of calculating the growth index of the crop based on each field image after the positional deviation is corrected by the parallax correction step.

The above-mentioned field photographing method may further include a warning step of issuing a warning when the amount of change in the positional deviation in a predetermined period exceeds a threshold value.

In the above-mentioned field photographing method, at least one of the warning display, the output of the warning sound, and the transmission of the warning information to the outside may be performed in the warning step.

Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to this, and can be extended or modified within a range that does not deviate from the gist of the invention.

The present invention can be used in a system in which a field is photographed from the sky by a plurality of imaging units held by a flying object, field images having different wavelength bands are acquired, and a growth index is calculated based on the acquired field images. be.

1 Field photography system 10 Flying object 11c Parallax correction unit 11d Growth index calculation unit 12 Communication unit (warning unit)
13 Warning section 13a Display section 13b Audio output section 21 First imaging section 22 Second imaging section 40 Takeoff and landing platform 41 Transport vehicle 42 Helmet C chart C ₁ Circular section C ₂ Circular section FD Field P Reference point Q Corresponding point OB Object N Missing part S Reflection spot

Claims (20)

With the flying object,
A plurality of imaging units held by the flying object, and during the flight of the flying object, a plurality of imaging units that capture a field in which crops are grown from the sky and acquire field images having different wavelength bands.
The charts taken by the plurality of imaging units and
Based on the chart images obtained by photographing the chart from the sky by the plurality of imaging units during the flight of the flying object, the position shift of the pixels indicating the same point caused by parallax between the field images. Including a parallax correction unit that corrects
The chart is a field imaging system located in or around the field. The field photographing system according to claim 1, wherein the chart is attached to an object located in or around the field. The field photographing system according to claim 2, wherein the object is a takeoff and landing platform of the flying object. The field photographing system according to claim 2, wherein the object is a transport vehicle for transporting the flying object. The field photographing system according to claim 1, wherein the chart is attached to the head of a pilot who remotely controls the flight of the flying object. The field photographing system according to any one of claims 1 to 5, wherein the chart has a pattern including at least one circular portion or a lattice pattern. The field photographing system according to claim 1, wherein the chart is a missing portion of the crop located in the field or a reflection spot of sunlight reflected on the water surface in the field. The parallax correction unit corresponds to the position coordinates of the reference point included in one chart image in the other chart image based on the chart images captured and acquired at the same time by the plurality of imaging units. Any of claims 1 to 7, wherein the projection matrix to be converted into the position coordinates of the points is calculated, and the position coordinates of all the points included in one field image are converted by the projection matrix to correct the position deviation. Field photography system described in Crab. The parallax correction unit obtains an image including an image of the chart from a plurality of captured images acquired at different timings when the flying object is moving in the sky in each of the plurality of imaging units. After extracting as an image, the center position of the image of the chart is obtained from the extracted chart image, and the center position of the one chart image taken at the same time is set as the reference point, and the image is taken at the same time. The field photographing system according to claim 8, wherein the projection matrix is calculated with the center position of the other chart image as the corresponding point. The field photographing system according to any one of claims 1 to 9, further comprising a growth index calculation unit that calculates a growth index of the crop based on each field image after the position deviation is corrected by the parallax correction unit. .. The field photographing system according to any one of claims 1 to 10, further comprising a warning unit that issues a warning when the amount of change in the positional deviation exceeds a threshold value in a predetermined period. The field photographing system according to claim 11, wherein the warning unit includes at least one of a display unit that displays a warning, an audio output unit that emits a warning sound, and a communication unit that transmits warning information to the outside. A field image acquisition step of capturing a field in which crops are grown from the sky and acquiring field images having different wavelength bands during the flight of the flying object by a plurality of imaging units held by the flying object.
A chart image acquisition step of photographing a chart located in the field or around the field from the sky by the plurality of imaging units during the flight of the flying object to acquire each chart image.
A field photographing method including a parallax correction step of correcting a misalignment of pixels indicating the same point caused by parallax between the field images based on the chart images. The field photographing method according to claim 13, wherein the field image acquisition step and the chart image acquisition step are simultaneously performed by the plurality of imaging units. The field photographing method according to claim 13 or 14, wherein the flight of the flying object includes ascending and descending of the flying object. In the disparity correction step, the position coordinates of the reference points included in one chart image correspond to each other in the other chart image based on the chart images captured and acquired at the same time by the plurality of imaging units. Any of claims 13 to 15, which corrects the positional deviation by calculating the projection matrix to be converted into the position coordinates of the above and converting the position coordinates of all the points included in one field image by the projection matrix. The field photography method described in. In the disparity correction step, the chart includes an image including the image of the chart from a plurality of captured images acquired at different timings when the flying object is moving in the sky in each of the plurality of imaging units. After extracting as an image, the center position of the image of the chart is obtained from the extracted chart image, and the center position of the one chart image taken at the same time is set as the reference point, and the image is taken at the same time. The field photographing method according to claim 16, wherein the projection matrix is calculated with the center position of the other chart image as the corresponding point. The field photographing method according to any one of claims 13 to 17, further comprising a growth index calculation step of calculating a growth index of the crop based on each field image after the positional deviation is corrected by the parallax correction step. .. The field photographing method according to any one of claims 13 to 18, further comprising a warning step of issuing a warning when the amount of change in the positional deviation exceeds a threshold value in a predetermined period. The field photographing method according to claim 19, wherein in the warning step, at least one of a warning display, a warning sound output, and a warning information transmission to the outside is performed.

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