Unmanned aerial vehicle and water depth measuring method of the unmanned aerial vehicle

Abstract

The embodiment provides a kind of unmanned plane and the water depth measurement method of unmanned plane, the unmanned plane includes: winch (winch), is attached to the lower part of unmanned plane, and built-in motor is provided with rotating force;Winch type size measuring tape, marked with scale, and move up and down by the shaft of motor;Water sample collection container, is connected at the lower end of winch type size measuring tape;Buoy, between winch and water sample collection container, when water sample collection container sinks below water surface, on water surface;Camera, for identifying the scale of winch type size measuring tape;And payload, winch and camera are provided with, and control winch and camera.

Description

Technical Field

[0001] This embodiment relates to a drone for measuring water depth in a saltwater pool and a method for measuring water depth using the drone. Background Technology

[0002] Recently, due to the explosive growth of electric vehicles worldwide, the use of lithium, a core material for batteries, is increasing significantly. Lithium is extracted either as a mineral or clay, or as a salt solution through evaporation and concentration.

[0003] Currently, when extracting lithium from brine by evaporation and concentration, people manually collect water samples directly from the brine pool and measure the water depth using a ruler. Furthermore, the evaporation rate of the brine is determined by measuring changes in water depth.

[0004] Because people have to manually collect water samples directly from the saltwater pools and measure the water depth with a ruler, it is difficult to simultaneously collect water samples and measure water depth, which are necessary for the management of a large salt lake area. Summary of the Invention

[0005] (a) Technical problems to be solved This embodiment provides a drone capable of simultaneously performing water sample collection and water depth measurement required for the management of a wide-area salt lake, as well as a water depth measurement method for the drone.

[0006] In addition, this embodiment can also provide a drone capable of measuring water depth in relatively shallow salt lakes in a robust manner in response to malfunctions, and a water depth measurement method for the drone.

[0007] (II) Technical Solution According to one aspect, this embodiment provides a drone, comprising: a winch attached to the lower part of the drone and having a built-in motor to provide rotational force; a winch-type dimensional measuring tape marked with graduations and moving up and down via the motor shaft; a water sample collection container connected to the lower end of the winch-type dimensional measuring tape; a buoy located between the winch and the water sample collection container, positioned on the water surface when the water sample collection container is submerged below the water surface; a camera for identifying the graduations on the winch-type dimensional measuring tape; and a payload, equipped with the winch and the camera, and controlling the winch and the camera.

[0008] According to another aspect, this embodiment provides a method for measuring water depth using a drone. The method utilizes a drone to measure the water depth of a saltwater pool. The drone includes a winch-type measuring tape with graduations, a water sample collection container connected to the lower end of the winch-type measuring tape, and a camera for identifying the graduations on the winch-type measuring tape. The method includes the following steps: using an image of a specific saltwater pool captured by the camera, identifying the graduations on the buoy using an OCR algorithm; calculating the tilt angle of the winch-type measuring tape; and calculating the final water depth based on the identified graduations, the tilt angle of the winch-type measuring tape, and the height of the water sample collection container.

[0009] (III) Beneficial Effects According to the UAV and the water depth measurement method of the UAV in this embodiment, it is possible to simultaneously collect water samples and measure water depth required for the management of a wide-area salt lake.

[0010] According to the UAV and the water depth measurement method of the UAV in this embodiment, water depth can be measured in relatively shallow salt lakes with robust fault response. Attached Figure Description

[0011] Figure 1 This is a structural diagram of a commercial plant (CP) used to produce lithium brine.

[0012] Figure 2 This is a perspective view of a drone according to one embodiment.

[0013] Figure 3 yes Figure 2 A diagram showing the operational status of the drone.

[0014] Figure 4 It is to utilize Figure 3 The mirror was used to take the picture of the scale.

[0015] Figure 5 This is an explanation Figure 2 A diagram showing the effective load of the winch entrance / exit structure and its positional relationship with the camera.

[0016] Figure 6 yes Figure 2 A structural diagram of a buoy.

[0017] Figure 7 yes Figure 2 A plan view of the markings formed on the buoy.

[0018] Figure 8 yes Figure 2 Internal structure diagram of the drone.

[0019] Figure 9 Show Figure 2 The process of using drones to measure water depth.

[0020] Figure 10 This is a flowchart of a method for measuring water depth using a drone according to another embodiment. Detailed Implementation

[0021] Hereinafter, some embodiments of the present disclosure will be described in detail with reference to the exemplary accompanying drawings. When assigning reference numerals to components in the various drawings, the same components will, as far as possible, have the same reference numerals even if shown in different drawings. In describing this embodiment, detailed descriptions of related well-known structures or functions may be omitted if it is determined that such detailed descriptions might obscure the essence of the technical concept. When using terms such as "comprising," "having," or "formed as" in this specification, other parts may be added unless "only" is used. Unless otherwise clearly stated, singular expressions for components include plural meanings.

[0022] In addition, when describing the components of this disclosure, terms such as first, second, A, B, (a), (b) may be used. These terms are used only to distinguish one component from another, and the nature, order, sequence, or number of the corresponding components are not limited by these terms.

[0023] When describing the positional relationship between components, if two or more components are described as "connected," "combined," or "connected," it should be understood that the two or more components can be directly "connected," "combined," or "connected," but it can also be that other components are "interspersed" between the two or more components to "connect," "combined," or "connect." Here, other components can be included in at least one of the two or more components that are "connected," "combined," or "connected" to each other.

[0024] When describing the time-series relationships of components, operating methods, or manufacturing methods, for example, when using words such as "after," "following," "next," or "before" to describe the time sequence or process sequence, discontinuous situations may also be included unless "immediately" or "directly" is used.

[0025] On the other hand, when referring to the numerical value of a component or its corresponding information (e.g., level, etc.), even if not explicitly stated otherwise, the numerical value or its corresponding information should be interpreted as including the range of errors that may be caused by various factors (e.g., process factors, internal or external shocks, noise, etc.).

[0026] Hereinafter, each embodiment will be described in detail with reference to the accompanying drawings.

[0027] In order to extract lithium in specific overseas regions, such as brine in Argentina, it is necessary to maintain the target concentration in each brine pool. These brine pools are places where lithium is extracted from brine by evaporation and concentration. As part of the management of maintaining the concentration, water sampling and water depth measurement are carried out in each brine pool.

[0028] Figure 1 This is a structural diagram of a commercial plant (CP) used to produce lithium brine.

[0029] like Figure 1 As shown, the area of ​​the brine pool for a specific overseas region, such as Argentina (CP), is approximately 1.5 times the area of ​​Yeouido, South Korea (290 Ha). Due to such a vast work area, manual labor would require a significant amount of time, and operators would inevitably have to enter the brine to take water samples and measure water depth.

[0030] Drones can fly in a straight line, allowing them to operate over a wide area without requiring direct immersion in saltwater. The saltwater pool is approximately 60cm deep, while most commercial underwater ultrasonic sensors are designed for depths measured in meters (m). Therefore, solutions for measuring relatively shallow water depths like 60cm are relatively few. Lithium-ion brine is a highly concentrated solution, more than 10 times the concentration of seawater. Direct contact between electronic devices and the brine poses a risk of malfunction and corrosion.

[0031] The following is for reference Figures 2 to 9 This paper describes in detail a drone capable of simultaneously performing water sampling and depth measurement required for salt lake management over a wide area, and measuring water depth in relatively shallow salt lakes in a robust manner to handle malfunctions.

[0032] Figure 2 This is a perspective view of a drone according to one embodiment.

[0033] Reference Figure 2 According to one embodiment, the drone 100 can fly using an electric motor 110 and a propeller 120. The electric motor 110 converts electricity into electrical energy and uses it to rotate the propeller 120. This rotational motion pushes the air and generates an upward force propelling the drone 100. The propeller 120 uses this rotational motion to help move the air, and the drone 100 is able to fly using this principle.

[0034] According to one embodiment, a drone 100 includes: a winch 130 attached to the lower part of the drone 100 and having a built-in motor 132 to provide rotational force; a winch-type dimensional measuring tape 140 marked with graduations 142 and movable up and down via a shaft 134 of the motor 132; a water sample collection container 150 connected to the lower end of the winch-type dimensional measuring tape 140; a buoy 160 located between the winch 130 and the water sample collection container 150, positioned on the water surface when the water sample collection container 150 is submerged below the water surface; a camera 170 for recognizing the graduations 142 of the winch-type dimensional measuring tape 140; and a payload 180 equipped with the winch 130 and the camera 170, and controlling the winch 130 and the camera 170.

[0035] There can be two or more water sample collection containers 150. When there are two or more water sample collection containers 150, there are also two or more winches 130. Each winch 130 can be connected to one water sample collection container 150 through a winch-type dimensional measuring tape 140.

[0036] That is, considering the corrosiveness of brine, without designing electronic devices or complex structures for the water sample collection container 150, one winch 130 drives one water sample collection container 150, and the number of water sample collection containers 150 corresponds one-to-one with the number of brine pools where water samples can be collected.

[0037] At this point, the water sample collection container 150 and the buoy 160 can be made of waterproof structures and materials capable of withstanding the corrosive effects of high-concentration salt water. For example, the water sample collection container 150 and the buoy 160 can be made of materials coated with highly chemically resistant PTFE (Teflon), or of plastics (polypropylene, PVC, etc.) with excellent corrosion resistance to certain high-concentration salt water, or of stainless steel with robust waterproof performance, such as IP67 or higher, but are not limited to these.

[0038] The UAV 100 has a built-in battery (not shown) that allows it to fly or perform water sampling and depth measurements. The battery can be a disposable battery or a rechargeable battery.

[0039] Figure 3 yes Figure 2 A diagram showing the operational status of the drone.

[0040] Reference Figure 3As the water sample collection container 150, which is connected to the shaft 134 of the motor 132 of the winch 130 and moves up and down via the winch 130, sinks below the water surface, the buoy 160 located above the water sample collection container 150 floats on the water surface. The distance between the water sample collection container 150 located at the bottom of the salt lake and the buoy 160 located on the water surface is measured by the winch 140 and the camera 170 in the payload 180.

[0041] Specifically, after the drone 100 moves to the airspace above the target pool and hovers, the payload 180 controls the winch 130 to lower the water sample collection container 150 to the bottom of the pool where the precipitate 14 is located. During the descent, the buoy 160 is positioned on the surface 10 of the lithium brine 12.

[0042] The camera 170 inside the payload 180 captures images. After the winch 130 raises the water sample collection container 150, the drone 100 returns upon completion of the operation. The winch-type dimensional measuring tape 140 has a concave structure made of stainless steel. The motor 132 is controlled by torque measurement inside the winch 130, ensuring that the winch-type dimensional measuring tape 140 always remains straight.

[0043] Figure 4 It is to utilize Figure 3 The mirror was used to take the picture of the scale.

[0044] Reference Figure 4 The drone 100 also includes a reflector 190 positioned above the buoy 160 to illuminate the scale 142 of the winch-type dimensional measuring tape 140, thereby improving the visibility of the scale 142. A camera 170 can capture images of the reflector 190. The reflector 190 can be attached to the upper end of the buoy 160.

[0045] The reflector 190 is tilted at an angle above the buoy 160 to the scale 142 of the winch-type dimensional measuring tape 140. The vertical direction of the reflector 190 is oriented towards the camera 170, and the camera 170, mounted on the payload 180, can move toward the reflector 190. Conversely, the camera 170 can be fixed, and the reflector 190 can rotate toward the camera 170.

[0046] Because the distance between the drone 100 and the water surface 10 is greater than the distance between the winch 130 and the camera 170, the scale 142 may not be visible. To solve this problem, a reflector 190 is mounted on the buoy 160 so that the camera 170 can capture the scale.

[0047] Figure 5 This is an explanation Figure 2A diagram showing the effective load of the winch entrance / exit structure and its positional relationship with the camera.

[0048] Reference Figure 5 The winch 130 and camera 170 are set in the payload 180, and the winch-type dimensional measuring tape 140 moves up and down through the shaft 134 of the motor 132 of the winch 130.

[0049] The payload 180 has a measuring tape inlet / outlet 182, and the winch-type measuring tape 140, which is wound on the shaft 134 of the motor 132 in the winch 130, can be set to the outside through the measuring tape inlet / outlet 182.

[0050] like Figure 5 As shown, the payload 180 is provided with a measuring tape inlet / outlet 182, which can prevent the winch-type measuring tape 140 from bending and position the scale 142 on the side of the camera 170.

[0051] Figure 6 yes Figure 2 A structural diagram of a buoy.

[0052] Reference Figure 6 The buoy 160 may include a roller 164 disposed within a through hole 162 and having a hole 166 through which a winch-type measuring tape 140 passes. That is, the roller 164 is disposed within the through hole 162, and the winch-type measuring tape 140 passes through the hole 166 to connect to the water sample collection container 150.

[0053] To prevent the winch-type measuring tape 140 from being bent by the float 160, the winch-type measuring tape 140 is made to pass through the hole 166 of the roller 164.

[0054] like Figure 5 and Figure 6 As shown, the winch-type measuring tape 140 passes through the inlet / outlet 182 of the effective load 180 and the hole 166 of the roller 164, which prevents bending and keeps the scale 142 on the side of the camera 170.

[0055] Figure 7 yes Figure 2 A plan view of the markings formed on the buoy.

[0056] Reference Figure 7 The upper part of the buoy 160 has a mark 168 for identifying the tilt of the winch-type dimensional measuring tape 140, and the camera 170 is able to identify the mark 168. The mark 168 may be, for example, an Aruco mark with a specific shape, but is not limited thereto.

[0057] The upper camera 170 captures the Aruco marker 168 and measures its position relative to the vertical lower position of the drone 100, thereby calculating the angle of tilt of the winch-type dimensional measuring tape 140 relative to the vertical direction.

[0058] Figure 8 yes Figure 2 Internal structure diagram of the drone.

[0059] Reference Figure 8 The winch 130 can control the motor 132 by measuring the torque of the motor shaft 134, so that the winch-type dimensional measuring tape 140 always remains straight.

[0060] The drone 100 stores GPS information 102, mission data 104 and status data 106. It can use this data to be assigned work commands, or it can have its own built-in work commands and modify them periodically or irregularly.

[0061] Payload 180 can receive and transmit data with UAV 100. Payload 180 may include system management unit 183. System management unit 183 is responsible for data transmission and reception of UAV 100, winch 130 commands, database 183a management, etc.

[0062] The payload 180 includes: a winch control unit 184 for controlling the winch; a sensor module 186 for controlling the camera 170; and an algorithm unit 188 for extracting the angle of the measuring tape based on the recognition of Aruco marks and extracting the size of the measuring tape based on an OCR algorithm, thereby calculating the water depth.

[0063] The winch control unit 184 receives commands from the system management unit 183, controls the position of the winch 130, and identifies defects such as rope entanglement. The algorithm unit 188 calculates the water depth based on image data received from the database 183a.

[0064] like Figure 8 As shown, considering the possibility of communication interruption with the operating system that issues the instructions, the system management unit 183 and the algorithm unit 188 can be built into the onboard computer so that tasks can be automatically executed internally and emergency responses can be handled.

[0065] The algorithm unit 188 can use the image captured by the camera 170 of a specific saltwater pool to identify the scale 142 where the buoy 160 is located, and calculate the tilt angle of the winch-type size measuring tape 140. It can also calculate the final water depth by reflecting the identified scale 142, the tilt angle of the winch-type size measuring tape 140, and the height of the water sample collection container 150.

[0066] Figure 9 Show Figure 2 The process of using drones to measure water depth.

[0067] Reference Figure 9 After receiving multiple images 188a of a saltwater pool from the database 183a, the algorithm unit 188 performs size extraction 188c and calculates the tilt angle 188f of the winch-type size measuring tape 140.

[0068] Size extraction 188c can identify the scale 142 where the buoy 160 is located using OCR algorithm 188b. The tilt angle of the winch-type size measuring tape 140 is determined by identifying the Aruco marker 162 188d and extracting the position of the buoy 160 188e, and the current tilt angle of the winch-type size measuring tape 140 is calculated using the position difference of the Aruco marker 162 between the image of the winch-type size measuring tape 140 during vertical descent and the captured image. The final water depth 188g is calculated by reflecting the extracted scale, the tilt angle of the tape, and the height of the water sample collection container 150.

[0069] According to the above embodiment, the drone 100 can simultaneously perform water sampling and water depth measurement required for salt lake management over a wide area.

[0070] Furthermore, the drone 100 according to the above embodiment can measure water depth in relatively shallow salt lakes in a robust manner in response to malfunctions.

[0071] Figure 10 This is a flowchart of a method for measuring water depth using a drone according to another embodiment.

[0072] Reference Figure 10 According to another embodiment, the water depth measurement method 200 of the UAV is a method of measuring the water depth of a saltwater pool using a UAV 100. The UAV 100 includes: a winch-type size measuring tape 140 marked with a scale 142, a water sample collection container 150 connected to the lower end of the winch-type size measuring tape 140, a buoy 160 located on the water surface when the water sample collection container 150 is submerged below the water surface, and a camera 170 for identifying the scale 142 of the winch-type size measuring tape 140.

[0073] According to another embodiment, the water depth measurement method 200 using a drone includes: a step of identifying the scale of a buoy 160 using an image captured by a camera 170 of a specific saltwater pool (S210); a step of calculating the tilt angle of a winch-type dimensional measuring tape 140 (S220); and a step of calculating the final water depth based on the identified scale, the tilt angle of the winch-type dimensional measuring tape, and the height of the water sample collection container 150 (S230).

[0074] In the step of identifying the scale (S210), the image captured by the camera 170 of a specific saltwater pool can be used to identify the scale where the buoy 160 is located through an OCR algorithm.

[0075] As mentioned above Figure 3 and Figure 4 The drone 100 also includes a reflector 190, which is positioned above the buoy 160 to illuminate the scale 142 of the winch-type dimensional measuring tape 140, thereby improving the visibility of the scale 142 of the winch-type dimensional measuring tape 140. The camera 170 can capture images of the reflector 190.

[0076] In the step of identifying the scale (S210), the scale where the buoy 160 is located can be identified by using the image captured by the camera 170 through the reflector 190 of a specific saltwater pool.

[0077] As mentioned above Figure 7 The drone 100 may also include a buoy 160 which is located on the water surface 10 when the water sample collection container 150 is submerged below the water surface 10, and a mark 168, such as an Aruco mark, is formed on the upper part of the buoy 160 for identifying the tilt of the winch-type dimensional measuring tape 140.

[0078] As mentioned above Figure 9 In the step of calculating the tilt angle (S220), the tilt angle of the current winch-type dimensional measuring tape can be calculated by the position difference of the Aruco mark between the image of the winch-type dimensional measuring tape 140 when it is vertically descending and the captured image.

[0079] The drone 100 may also include a winch 130 attached to the lower part of the drone 100, with a built-in motor 132 providing rotational force, which moves the winch-type dimensional measuring tape 140 up and down via the shaft 134 of the motor 132.

[0080] The winch 130 can control the motor 132 by measuring the torque of the motor shaft 134, so that the winch-type dimensional measuring tape 140 always remains straight.

[0081] According to another embodiment, the underwater depth measurement method 200 of the UAV can be performed by all the components and actions of the aforementioned UAV 100.

[0082] According to the UAV water depth measurement method 200 of the other embodiment described above, water sampling and water depth measurement required for salt lake management can be performed simultaneously over a wide area.

[0083] Furthermore, the water depth measurement method 200 for unmanned aerial vehicles according to another embodiment described above can measure water depth in relatively shallow salt lakes in a robust manner in response to malfunctions.

[0084] The above description of the UAV 100 and its water depth measurement method (200) with reference to the accompanying drawings is provided, but the invention is not limited thereto. For example, although the payload 180 is described as a component of the UAV 100, the payload 180 can be a separate device and can be fastened to the lower end of the UAV 100. In this case, the payload 180 may include the winch 130, the winch-type dimensional measuring tape 140, the water sample collection container 150, the buoy 160, and the camera 170 described above.

[0085] That is, a payload 180 containing the above-mentioned components can be installed on a commercial drone 100, and the above-mentioned drone water depth measurement method 200 can be executed.

[0086] The above description is merely illustrative of the technical concept of this disclosure. Those skilled in the art to which this disclosure pertains can make various modifications and variations without departing from the essential characteristics of this technical concept. Furthermore, these embodiments are not intended to limit the technical concept of this disclosure, but rather to illustrate it; therefore, the scope of this technical concept is not limited by these embodiments. The scope of protection of this disclosure should be interpreted according to the claims, and all technical concepts within the equivalent scope should be interpreted as being included within the scope of the rights of this disclosure.

[0087] Cross-references to related applications This patent application claims priority to Patent Application No. 10-2023-0182823, filed in Korea on December 15, 2023, pursuant to Section 119(a) of the United States Patent and Trademark Office (35 USC § 119(a)), the entire contents of which are incorporated herein by reference. Furthermore, for the same reason, if this patent application also claims priority to any country outside the United States, the entire contents of that country are incorporated herein by reference.

Claims

1. An unmanned aerial vehicle (UAV), comprising: A winch is attached to the lower part of the drone and has a built-in motor to provide rotational force; A winch-type measuring tape, marked with graduations, moves up and down via the shaft of the motor; A water sample collection container is attached to the lower end of the winch-type dimensional measuring tape. A buoy is located between the winch and the water sample collection container, and is positioned on the water surface when the water sample collection container is submerged below the water surface. A camera is used to identify the graduations on the winch-type dimensional measuring tape; as well as The payload includes the winch and the camera, and controls the winch and the camera.

2. The drone according to claim 1, further comprising: A reflector, positioned above the buoy, illuminates the scale of the winch-type dimensional measuring tape, thereby improving the visibility of the scale. The camera captures images of the reflector.

3. The UAV according to claim 1, wherein, The buoy includes a roller disposed within a through hole and has a hole through which the winch-type measuring tape passes.

4. The UAV according to claim 1, wherein, The upper part of the buoy has Aruco markings for identifying the tilt of the winch-type dimensional measuring tape. The camera recognizes the Aruco tag.

5. The UAV according to claim 2, wherein, The winch controls the motor by measuring the torque of the motor shaft, ensuring that the winch-type dimensional measuring tape always remains in a straight line.

6. The UAV according to claim 1, wherein, The payload includes: A winch control unit for controlling the winch; A sensor module for controlling the camera; and The algorithm department extracts the angle of the winch-type measuring tape based on the recognition of Aruco markers, and extracts the dimensions of the winch-type measuring tape based on the OCR algorithm, thereby calculating the water depth.

7. The UAV according to claim 6, wherein, The algorithm unit uses the image captured by the camera on a specific saltwater pool, identifies the scale where the buoy is located through an OCR algorithm, calculates the tilt angle of the winch-type size measuring tape, and calculates the final water depth by reflecting the identified scale, the tilt angle of the winch-type size measuring tape, and the height of the water sample collection container.

8. A method for measuring water depth using an unmanned aerial vehicle (UAV), the method utilizing the UAV to measure the water depth of a saltwater pool, the UAV comprising a winch-type measuring tape with graduations, a water sample collection container connected to the lower end of the winch-type measuring tape, a buoy positioned on the water surface when the water sample collection container is submerged below the water surface, and a camera for identifying the graduations of the winch-type measuring tape. The method includes the following steps: Using images captured by the camera on a specific saltwater pool, the scale markings of the buoy are identified. Calculate the tilt angle of the winch-type dimensional measuring tape; as well as The final water depth is calculated by reflecting the identified scale, the tilt angle of the winch-type dimensional measuring tape, and the height of the water sample collection container.

9. The method for measuring water depth using a UAV according to claim 8, wherein, In the step of identifying the scale, the image of a specific saltwater pool captured by the camera is used to identify the scale where the buoy is located through an OCR algorithm.

10. The method for measuring water depth using a UAV according to claim 8, wherein, The drone further includes: A reflector, positioned above the buoy, illuminates the scale of the winch-type dimensional measuring tape, thereby improving the visibility of the scale. The camera captures an image of the reflector. In the step of identifying the scale, the camera uses the mirror to capture an image of the specific saltwater pool to identify the scale on which the buoy is located.

11. The method for measuring water depth using a UAV according to claim 8, wherein, The drone further includes a buoy that is positioned on the water surface when the water sample collection container is submerged, and has an Aruco mark formed on its upper part for identifying the tilt of the winch-type dimensional measuring tape. In the step of calculating the tilt angle, the current tilt angle of the winch-type dimensional measuring tape is calculated by the position difference of the Aruco marker between the image of the winch-type dimensional measuring tape when it is vertically descending and the captured image.

12. The method for measuring water depth using a UAV according to claim 8, wherein, The drone further includes a winch attached to the lower part of the drone and containing a motor to provide rotational force. The winch-type dimensional measuring tape is moved up and down via the motor's shaft. The winch controls the motor by measuring the torque of the motor shaft, ensuring that the winch-type dimensional measuring tape always remains in a straight line.

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