WO2022173383A1

WO2022173383A1 - Method for determining height of crop covered soil surface from sea level through use of aerial photographs

Info

Publication number: WO2022173383A1
Application number: PCT/TH2022/000004
Authority: WO
Inventors: Khwantri SAENGPRACHATANARUG; Kanda SAIKAEW; Adulwit CHINAPAS; Mahisorn Wongphati
Original assignee: Saengprachatanarug Khwantri
Priority date: 2021-02-11
Filing date: 2022-02-01
Publication date: 2022-08-18

Abstract

The determination of the height of soil surface from the sea level which is covered by crops through the use of aerial photographs, is the use of aerial photographs of crop plots and DSM values to determine the mean difference of the lowest DSM values to represent the height of the soil surface covered by crops without the need for GCP. This is considered a useful method for obtaining soil height data for estimating yields in agricultural plots.

Description

TITLE OF INVENTION

METHOD FOR DETERMINING HEIGHT OF CROP COVERED SOIL SURFACE FROM SEA LEVEL THROUGH USE OF AERIAL PHOTOGRAPHS

TECHNICAL FIELD

5 Computer engineering and agricultural engineering, in relation to the method of determining the height of the crop covered soil surface from the sea level through the use of aerial photographs.

BACKGROUND ART

There are two types of aerial image-related elevation models: the digital surface model 0 (DSM), and the digital terrain model (DTM). The DTM is often found to be plagued with inaccuracy because photographs cannot distinguish the surface which is covered by crops. This problem has prevented an accurate estimation of the crop heights and therefore cannot accurately estimate crop yields. However, there are researches that solve the issue of inaccurate DTM by using GCP, or

Ground Control Point, which in aerial photographs, are constructed objects having a constant 5 height, and are robust in structure and stationary, such as houses, structures, or buildings. GCPs provide a more accurate picture of the DTM. However, most of the crops are not planted near buildings or structure, therefore, no GCP is readily available resulting in erroneous calculations of the DTM, as well as, taking a long time and imposing increased costs.

Pertaining to such issues, it has given rise to the idea of a DTM calculation method in0 which the object height of an image outside the crop plot (DSM) is taken to represent the height of the soil surface inside the plot. This method of determining the height of the crop covered soil surface from the sea level through the use of aerial photography is expected to improve the efficiency of predicting DTM faster and more accurately without the need of GCP. Additionally, it also saves cost and time in aerial photography as the use of GCP requires 2 rounds of photo5 shoots, before and after cropping, and taking the height values of the two images to find the differences, resulting in extra time and money. This is different from this invention which requires only one round of photo shoot after cropping has been conducted. The principle used for this invention is based on the centroid, which is the intersection of the straight lines that divide the shape into two equal parts according to the ‘moment’, or also known as the central tendency of all0 points within that shape. CHARACTERISTICS AND INTERTION OF THE INVENTION

The method for determining the height of the crop covered soil surface from the sea level through the use of aerial photographs consist of the following steps: a. Use the aerial photographs of the crop plots that the height of the soil surface needs to be determined and increase the area around the plots in the photo. b. Create the centroid of the plot. c. Create a frame to cover the area of the plot area that increased the area around the plot. Create a straight line through the centroid and then draw a number of perpendiculars to the straight line. This will result in the plot in the photograph to be divided into spaces. d. Determine the lowest DSM within each area of the plot. e. Determine the difference of the lowest DSM between within each area. f. Use the difference of all the lowest DSM values obtained from step e. and determine the mean. Establish the mean obtained to be the lowest DSM value at the point where the straight line is at 0 degrees. g. Then rotate the straight line in increments of 0.1 - 5 degrees, by making each rotation equally until it reaches 180 degrees. In each rotation, find the average difference of the DSM value that was determined according to steps e. - g. h. Select the position of the degree of rotation that yielded the least mean difference of the lowest DSM values. The plot area and the lowest DSM value in each plot is the rotational variance that produces the lowest mean difference of the DSM value, representing the height of the crop covered soil surface according to the split crop area.

The aim of this invention is to solve the issue of determining the height of the crop covered soil surface from the sea level through the use of computers and automatically displaying it. The method relies on the principles of aerial photography without the need for GCP by means of a method to determine the height of the crop covered soil surface from the sea level through the use of aerial photographs. It is a useful step in obtaining soil surface data to assess yields in agricultural plantations.

DISCLOSURE OF INVENTION

The methods for determining the height of the soil surface from the sea level covered by crops through the use of aerial photographs consist of the following steps: a. Take aerial photographs of the crop plots in which the height of the soil surface from the sea level needs to be determined. The photographs will contain information about the height of the object from the sea level, or DSM values at various points in the photo. The area around the plot in the photo is to be increased by increments of 0.1 - 5 meters by comparing it to the plant-to- photo ratio. The increase in the area around the plot in the photograph is to cover the surface area outside the plot (Figure 1). b. Create the centroid (1) of the plot with an increase in the area around the plot to use it as a pivot point (Figure 2). c. Create a frame to cover the plot area that increases the surrounding area. Then create a straight line (2) that cuts through the centroid (l) by determining the position where the line (2) crosses the centroid (1) at 0 degrees. Then create a number of perpendiculars (3) with the straight line (2), with the distance between each perpendicular line (3) having the same distance which is between 5 - 50 meters by comparing it to the ratio of the plot to that particular photograph. The straight line (2) and the perpendicular lines (3) will result in the plot area in the photograph to be divided into spaces (Figure 3). d. Determine the area within the plot between the straight lines (2) into 2 parts, namely, area 1 (a) and area 2 (b) (as shown in Figure 4). e. Determine the lowest DSM value in each plot area (Figure 5). Then, use the lowest DSM value that was obtained to find the minimum difference in DSM between area 1 (a) and area 2 (b) in each pair, which are the spaces between the same perpendicular lines (3). f. Take the difference of all the lowest DSM values obtained according to step e. and find the mean value. The mean difference of the lowest DSM values will be the mean difference of the lowest DSM value (DSM) at the point where the straight line (2) is at 0 degrees. g. Then turn the straight line (2) from its original position by equal increments until it completes 180 degrees. The appropriate increment for each rotation should be between 0.1 - 5 degrees. Such rotations will make all the perpendicular lines (3) move along with the movement. For each rotation, the mean difference of the lowest DSM should be determined in accordance with e. - g. Figure 6 shows an example of the straight line rotation (2) on the plot at different rotating positions. h. Select the position of the degree of rotation that results in the lowest mean difference of the lowest DSM values. The plot area and the lowest DSM values in each section that was the result of the rotation and produced the lowest mean difference of DSM values represents the height of the crop covered soil surface according to the split crop area.

The researchers determined the height of the crop cover from the sea level through the use of aerial photographs. The processing found that the lowest DSM difference or object height difference from lowest sea level between area 1 (a) and area 2 (b) in each pair, is the space between the same perpendicular (3) as shown in Table 1 («at a 150-degree rotation position). When comparing the mean difference of the minimum DSM value in each degree as shown in Table 2, it was found that at the rotation position of 150 degrees, the lowest mean difference was obtained from the lowest DSM value. The rotation position of 150 degrees point was thus chosen to be the height of the soil surface above sea level. The characteristic of splitting the plot area at the rotation position of 150 degrees is illustrated by the DSM grayscale feature as shown in Figure 7 b.

The mean absolute error is evaluated by means of finding the difference between the actual altitude and the predicted value and then determining the mean value. The actual height data was obtained from 3 sugar cane plots, each plot consisting of 180 points, thus yielding a total of 540 samples, resulting in the accuracy of this method (the difference between the DSM and the lowest DSM value) when compared to the results obtained from finding the difference between the DSM and DTM values. Table 3 illustrates that the error of the method according to this invention is low when compared to the results obtained from finding the difference between the DSM and DTM values.

Table 1. Shows the calculation of the lowest DSM differential between area 1 (a) and area 2 (b) in each pair, which are the spaces between the same perpendicular lines (3) («at the 150-degree rotation position). -

Pairs Lowest DSM value in Lowest DSM value inLowest DSM differential area 1(a) area 2(b) between (a) and (b)

1 154.06 2 154.12 155.76 1.64

3 154.43 156.36 1.93

4 154.43 156.81 2.38

5 155.04 157.26 2.22 6 154.93 157.46 2.53

7 154.73 157.29 2.56

8 154.39 155.73 1.37

9 154.69 154.81 0.12

10 155.16 Lowest DSM differential mean _ 1.84 _

Table 2. Displays the lowest DSM differential mean (DSM) calculation, from 0 to 180 degrees. No. of Degrees Lowest DSM differential mean

0 2.34

10 2.41 15 2.52

150 1.84

180 2.04 Table 3. Shows a comparison of the mean absolute error of the height of the soil surface from the sea level covered by crops through the use of aerial photographs according to this invention with the DSM DTM method. _

Sampling Actual Predicted Value (1) Predicted Value (2) Error Error

Points Height According to this According to the Value (1) Value (2) _ invention _ DSM-DTM method _

1 1.9 2.2 0.8 0.3 1.1

2 1.1 1.0 0.1 0.1 1.0

3 1.4 0.8 0.1 0.6 1.3 100 0.8 0.7 0.1 0.1 0.7

540 0.7 0.7 0.2 0 0.5 Mean absolute error _ 054 _ 0.98 _

From the above data, it can be seen that the method of determining the height of the soil surface from the sea level covered by crops through the use of aerial photographs based on this invention will help increase the efficiency of predicting the height of the soil surface from the sea level faster and more accurately without using GCP. Additionally, it will also help to save cost and time in using aerial photography.

Further, the method based on this invention was applied for crop height prediction to validate its accuracy compared with conventional software in the market. Crop heights were calculated using the DSM which represents the height of the crop canopy from the sea level minus with the height of the soil surface from the sea level based on this invention compared with the conventional DSM-DTM method without GPC assignment using commercial software (Pix4DMapper version 4.3.33, Switzerland). Actual average heights of sugarcane of 163 subplots with the size of 5x5 m from 6 different fields at the closed canopy stage were collected to calculate the accuracy of both methods as shown in figure 8. The results show that using the method based on this invention had a Mean absolute percentage error (MAPE) of 14_% and Root mean square error (RMSE) of 0.54 m, while the conventional methods had a MAPE of 94_% and RMSE of 2.99 m. Refer to these results, it can be seen that the method of determining the height of the soil surface from the sea level covered by crops through the use of aerial photographs based on this invention could be used for crop height prediction with much higher accuracy compared with the conventional methods when applied to closed-canopy field. Brief description of the drawing

Figure 1. a. Shows the crop plot characteristics in which the height of the soil surface from the sea level is to be determined b. Shows the increased crop plot area characteristics.

Figure 2. Shows the plot with the centroid (1)

Figure 3. Shows the creation of the frame, straight line (2), and the perpendicular line (3) on the photo of the plot. Figure 4. Shows how the plot is divided.

Figure 5. Shows an example of a plot with the lowest DSM value in each area (each space) Figure 6. Shows an example of the different rotation angles (2) of the straight line on the plot. Figure 7. Shows the crop plot (g) and the plot characteristics with the area divided into squares at the angle of rotation (2), resulting in the least mean difference of the lowest DSM value (b.)

Figure 8. Shows the comparison of the crop height prediction by using the height of the soil surface from the sea level covered by crops through the use of aerial photographs according to this invention (a) with those by using the DSM DTM method (b).

Best mode for Carrying out the invention

As mentioned in the Disclosure of Invention

Claims

1. The determination of the height of the land surface from the sea level which is covered by crops through the use of using aerial photographs, consist of the following steps; a. Take aerial photographs of the crop plots in which the height of the soil surface from the sea level needs to be determined. Increase the area around the plot in the photo so as to cover the surface area outside the targeted plot. b. Create the centroid (1) of the plot including the increased area around the plot. c. Build a frame to cover the plot and its increased area. Then create a straight line (2) that cuts through the centroid (1) and assigning the position where the line (2) intersects with the centroid (1) as 0 degrees. Next, create a number of perpendicular lines (3) to intersect with the straight line (2), with the distance between each perpendicular (3) equally spaced. The straight line (2) and the perpendiculars (3) will divide the plot into different sections. d. Define the area within the plot between the straight lines (2) into 2 parts, namely, area 1 (a) and area 2 (b). e. Determine the lowest DSM value in each plot area, then use it to determine the minimum difference in DSM between area 1 (a) and area 2 (b) in each pair, which is the space between the same perpendicular (3). f. Use the difference of all the lowest DSM values obtained in step e. to determine the mean. The mean difference of the lowest DSM values will be the point where the straight line (2) is at 0 degrees. g. Rotate the straight line (2) from its original position by equal incremental angles until it reaches 180 degrees. Each rotation of the straight line will cause the perpendicular line (3) to move accordingly. For each rotational angle, find the mean difference of the lowest DSM in accordance with steps e. - g. h. Select the angle of rotation that results in the lowest mean difference of the lowest DSM values. The plot area and the lowest DSM values in each space which resulted from the rotation will produce the lowest mean difference of the DSM values and will represent the height of the soil surface covered by crops according to the crop division zone.

2. The determination of the height of the soil surface from the sea level which is covered by crops through the use of aerial photographs according to the Rights to Claim item 1, where the photograph of the crop plots contains height information of an object from the sea level, or DSM, at various points in the photograph.

3. The determination of the height of the soil surface from the sea level which is covered by crops through the use of aerial photographs according to the Rights to Claim item 1 or 2, where the area around the crop plot in the photograph is increased by 0.1 - 5 m. by comparing the crop plot to that photograph.

4. The determination of the height of the soil surface from the sea level which is covered by crops through the use of aerial photographs according to the Rights to Claim items 1 -3, where the distance between each perpendicular line (3) is between 5 - 50 meters, when compared to the ratio of crops to that photograph.

5. The determination of the height of the soil surface from the sea level which is covered by crops through the use of aerial photographs according to the Rights to Claim items 1 -3, where the appropriate size for each rotation is between 0.1 -5 degrees.