Vision-based system and method for the relative positioning of an object with respect to a target surface and a navigation system for navigating said object

Abstract

The present invention relates to a vision-based system and method for relative positioning with respect to a target surface, characterised in that it comprises: at least three reference markers (1) located on the target surface on the vertices of an equilateral triangle (2) seen from an overhead view of said target surface; at least one image forming device located on the object; processing means configured to receive and process the captured images (4) and configured to either detect the reference markers (1) in the received image (4), or identify the centroid (5) of a triangle (7) formed by the reference markers (1) in the received image (4), or circumscribe the reference markers (1) by means of a circumscribed ellipse (6), or determine the relative position with respect to the target surface by means of the relationship between the circumscribed ellipse (6) and the position of the reference markers (1).

Description

[0001]DESCRIPTION System and method for relative positioning of an object with respect to a target surface based on vision and navigation system for said object Field of the invention The invention relates to a system and method for estimating the position of an object relative to a target surface. The method could be used as part of vehicle navigation systems, such as aircraft, to achieve accurate positioning and / or provide redundancy to traditional positioning systems in complex environments, for example, with a denied Global Satellite System (GNSS). Background of the invention Vision-based navigation (VBN) refers to the use of data acquired optically, by cameras,for navigation purposes. The three main steps in vision-based navigation (VBN) are typically: a) Capture an image of a portion of the environment surrounding an object. This image will contain the information needed to generate a position measurement. b) Extract and process information from the captured image to generate the position measurement. This step typically uses computer vision techniques such as pattern recognition, object detection and identification, or motion estimation with visual odometry. c) Filter the measurements to calculate an optimal position estimate. Landing on unpaved runways is known to make such an operation more demanding than usual. In these cases, instrument approaches with very high frequency omnidirectional range (VOR), distance measuring equipment (DME), and even less so,Instrument Landing Systems (ILS). At airports, Ground Augmentation Systems (ILS / GBAS) that enable assisted landings are currently the primary way to facilitate the piloting task during this phase. Thanks to these systems, aircraft deviations from the ideal approach can be calculated and used in guidance laws. However, these systems are expensive and their availability is limited to airports that have deployed the necessary infrastructure. Furthermore, in the case of unpaved runways, relying solely on the Global Positioning System (GPS) poses some problems. Familiar vision-based systems usually have limited range, and the aircraft must be close to the target to achieve precise localization. In addition, a vision-based system can be affected by lighting conditions such as glare and shadows,which make it difficult to see some features on unpaved runways. In certain environments, such as feature-free terrain, snow, and deserts, vision-based methods cannot be used because there are no distinctive visual features in the environment. Summary of the Invention The objective of the invention is to estimate the position of the object, for example, an aircraft, with respect to a target surface. To this end, the system object of the invention allows the relative position of said object to be estimated in spherical coordinates, providing angles and a distance, which positions the object three-dimensionally. More specifically, the system and method object of the invention allows the distance, elevation, and azimuth of the object to be provided with respect to a pattern located on the target surface. According to the above,The subject of the present invention is a system for estimating the relative position of an object with respect to a target surface based on vision, comprising: ^ At least three reference markers configured to be located on the target surface such that they are located at the vertices of an equilateral triangle seen from a top-down view of said target surface, where the three vertices have a centroid. The centroid of said triangle corresponds to the origin of the reference system to be used for relative positioning. Seen from a top-down view, the three reference markers could be circumscribed by a circle called a circumscribed circle. ^ At least one imaging device, configured to be located on the object, the object being capable of spatially locating the reference markers,and for capturing images of the target surface including the reference markers, the imaging device having a focal length. ^ A processing means configured to receive and process images captured by the at least one imaging device and configured to: o detect the reference markers in the received image, o identify the centroid of a triangle formed by the reference markers in the received image, o circumscribe the reference markers in the received image by a circumscribed ellipse centered at the centroid of the triangle and passing through the vertices of the triangle, or determine the relative position of the object with respect to the target surface according to its spherical geometric coordinates distance,elevation and azimuth by means of the geometric relationship in the received image between the semi-axes and the angle of the major semi-axis of the circumscribed ellipse and the position of the reference markers and the radius of its circumscribed circle. Accordingly, the processing means has the input data provided by the three reference markers which constitute two-dimensional coordinates in pixels in the image taken by the imaging device. According to the claimed invention, the equilateral triangle formed by the three reference markers can be circumscribed by a circle. When said triangle is viewed in perspective, that is, from an object, for example, an aircraft approaching a landing strip, the triangle is no longer equilateral. The circumscribed circle is then perceived as an ellipse,whose parameters can be analytically determined on the image taken. This ellipse is called the circumscribed Steiner ellipse, which is the only ellipse that passes through the three vertices and has its center at the centroid of the triangle. According to the above, the objective of the claimed invention is to obtain the estimate of the relative position of an object. The invention therefore solves the estimation of the relative 3D position of an object by means of the image capture device and the objects observed in the captured image. Furthermore, the installation of reference markers on the target surface, for example, on the target terrain, could allow the creation of a low-cost and easily transportable landing system. Several types of objects could benefit from the system of the invention: airplanes, helicopters, drones, reusable first-stage rockets, unmanned vehicles,A specific application of the system and method object of the invention could be a landing aid on unpaved runways, thus reducing the pilot's workload. Other applications could be relative positioning during in-flight refueling maneuvers, landing on small or mobile helidecks, landing guidance for the retropropulsive vertical landing of a reusable rocket stage, as a landing aid for multicopters, etc. Another application in which vision-based landing (VBL) is very helpful is when the landing surface is in motion, for example, on the decks of ships or aircraft carriers, since a few centimeters of difference can endanger and compromise the mission. The invention is capable of determining the relative position in 3D in these scenarios where landing aids are often not available. Furthermore,The ability to land accurately on unpaved terrain and in GPS-deprived environments would facilitate the logistics of humanitarian missions. The claimed system could reduce crew fatigue and training costs, thus providing more efficient operations, for example, in-flight refueling. The determination of the number of reference markers takes into account the combination of the following two aspects: o Use the smallest possible number of markers. o Allow detection of the object's 3D position. Placing three reference markers as if they were the vertices of an equilateral triangle is sufficient to solve the 3D positioning analytically,provided that the hypothesis that the object is located within a 120° azimuth sector is met, since there are three possible solutions in azimuth and it is necessary to resolve the ambiguity. This hypothesis is usually applicable to many of the described scenarios. The system object of the invention provides accurate results even with a basic camera as an image capture device. The present invention includes the method for converting the 2D pixel coordinates of the three reference points in the captured image into a relative 3D position with respect to the centroid of the triangle formed by the reference points. Therefore, the method determines the relative 3D position with respect to the centroid of the equilateral triangle formed by the reference points, from the 2D pixel coordinates of said reference points. In this way, the reference markers facilitate the image processing task. Therefore,The claimed system and method comprise a solution that provides results that are both accurate and quick to calculate. The claimed system has the following advantages: • It is capable of using images from one or more imaging devices, for example, cameras, installed on the object to estimate its 3D position, infrared sensors, etc. • It is a potentially certifiable system under aeronautical regulations. This is due to the deterministic nature of the method. • Initially, it is intended to be used as an external navigation aid system, in addition to certified sensor architectures, for example, ADIRUS (Air Data Inertial Reference Unit) and GPS on civil platforms. • It is compatible with current Flight Management System protocols to be able to integrate into different avionics architectures. • It is lightweight. • It has low power consumption. • It is low cost. • It allows real-time processing, i.e.,The algorithm has a low processing time. • It is reliable and complete. • Easy to install and maintain. • The markers can be detected from a great distance. As previously mentioned, this positioning system has been applied to develop a solution that allows an aircraft to land accurately without the need for complex infrastructure and at a low cost. This innovative landing system allows for specific applications such as landing on unpaved runways, as already mentioned. Additionally,The claimed relative positioning system could also be used as part of an object's navigation systems to achieve precise positioning and / or provide estimation redundancy in addition to traditional positioning sensors. Another object of the invention is a navigation system comprising a vision-based relative positioning system of an object with respect to a target surface as explained above. Another object of the present invention is a method for estimating the position of an object with respect to a target surface, comprising the following steps: ^ providing at least three reference markers located on the target surface such that they are located at the vertices of an equilateral triangle seen from a zenith view, where the equilateral triangle has a centroid and a circumscribed circle,^ providing at least one imaging device positioned on the object for capturing images of the target surface including the reference markers, the imaging device having a focal length, ^ providing processing means for receiving and processing captured images received from the at least one imaging device that: o detects the reference markers in the received image, o identifies the centroid of the triangle formed by the reference markers in the received image, o circumscribes the reference markers in the received image by a circumscribed ellipse centered at the centroid of the triangle and passing through the vertices of the triangle, o determines the position of the object relative to the target surface according to its spherical geometric coordinates: distance, elevation and azimuth,by the geometric relationship in the received image between the semi-axes and the angle of the major semi-axis of the circumscribed ellipse and the position of the reference markers and the radius of its circumscribed circle. Description of the figures To complete the description and provide a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate preferred embodiments of the invention. The drawings comprise the following figures. Figure 1 shows a schematic representation of three reference markers located at the vertices of an equilateral triangle having a centroid, the three vertices being circumscribed by a circle. Figure 2 shows an image captured from an aircraft of a runway and its surroundings,showing three reference markers located on the runway, viewed from a top-down view. Figure 3 shows an image captured from an aircraft of the runway in Figure 2 and its surroundings, showing three reference markers located on the runway, viewed from an aircraft approaching the runway. Figure 4 shows a schematic representation of three reference markers located at the vertices of an isosceles triangle; the three vertices are circumscribed by an ellipse. Figure 5 shows the three-dimensional polar coordinates that position an object: distance, elevation, and azimuth. Figure 6 is a schematic representation of a camera,the camera image plane and the observed object in 3D space. Detailed description of the invention Figure 1 shows a schematic representation of three reference markers (1) located at the vertices of an equilateral triangle (2) having a centroid (5). The three vertices are circumscribed by a circle (3). The three reference markers (1) are located on the target surface. The target surface may be a runway, as shown in Figures 2 and 3. Alternatively,The decks of ships or aircraft carriers can also be a target surface. Figure 2 shows an image of a runway (8) and its surroundings captured from an aircraft (10). The three reference markers (1) are located on the runway (8) and are seen from a top-down view. The three reference markers (1) form an equilateral triangle (2) seen from said top-down view. The captured images (4) of Figures 2 and 3 are taken from at least one image capture device located on an aircraft (10). It is clear from the captured images (4) of Figures 2 and 3 that, seen from above, i.e. from above, it is an equilateral triangle (2). There would be a circumscribed circle (3) passing through the vertices of the equilateral triangle (2). However, seen in perspective, as in Figure 3, the equilateral triangle (2) would no longer be equilateral. In that case,the circumscribed circle (3) would become a circumscribed ellipse (6) as seen in figure 4. According to the above, the processing means are configured to receive and process the captured images (4) received from the at least one imaging device and configured to: o detect the reference markers (1) in the received image (4), o identify the centroid (5) of the triangle (7) formed by the reference markers (1) in the received image (4), o circumscribe in the received image (4) the reference markers (1) by means of a circumscribed ellipse (6) centered at the centroid (5) of the triangle (7) and passing through the vertices of the triangle (7), o determine the relative position of the object with respect to the target surface according to its spherical geometric coordinates: distance, elevation and azimuth,through the geometric relationship in the received image (4) between the semi-axes and the angle of the major semi-axis of the circumscribed ellipse (6) and the position of the reference markers (1) and the radius of its circumscribed circle (3). These spherical geometric coordinates are represented in figure 5 with respect to the aircraft object (10). The spherical geometric coordinates are the distance, the elevation and the azimuth. The parameters that define the circumscribed ellipse (6), the Steiner ellipse, have an analytical solution. It is the only ellipse that passes through the vertices of a triangle and has as its center the centroid of the triangle (7). The Steiner circumscribed ellipse (6) is also the ellipse with the smallest area that passes through the vertices. The parameters of the circumscribed ellipse (6) are known. With them, as explained above,a relative position estimate can be made analytically. Visual position estimation is the process of estimating the position of the object based on data provided, for example, by a camera (9). The semi-major axis of the circumscribed ellipse (6) measures the same for any azimuth considering a constant distance to the object. The semi-minor axis of the circumscribed ellipse (6) varies its dimensions depending on the elevation of the object above the target for the same distance. The distance is the distance from the camera to the center of the ellipse. Knowing the focal length of the camera and the actual measurements of the pattern and those perceived in the image (4) it is possible to calculate the distance at which I am seeing that point. In the embodiment example in Figure 6,the x - y - z imaging device frame is a three-dimensional frame with the origin as the center of projection and has its z axis pointing in the target direction. The image frame (4) u - v is a two-dimensional frame with the u and v axes parallel to the x and y axes of the imaging device frame, respectively. It is possible to relate the three-dimensional coordinates (x, y, z) to the image coordinates (u, v) as follows: ^ ^ ^ ^ ^ or, Where f is the focal length of the imaging device, uov is the major size of the semi-axes of the circumscribed ellipse (6) in the received image (4), xoy are the actual radii of the circumscribed circle (3) size, and z is the distance from the imaging device to the reference markers (1). f is a constant for a specific camera model and, for the above equations, its dimensions are in pixels. A parameter of the reference marker (1) will be selected to input into the equation both its actual dimension (x) and its length measured on the image (4) (u). This parameter is the major semi-axis of the circumscribed ellipse (6). Therefore, in an exemplary embodiment for estimating the distance of the object with respect to the reference markers (1), the processing means are configured to calculate the geometric relationship using the following equation: where f is the focal length of the imaging device, v is the size of the semi-major axis of the circumscribed ellipse (6) in the received image (4), y is the actual radius of the size of the circumscribed circle (3) and z the distance of the object to the reference markers (1). In another embodiment for estimating the elevation of the object with respect to the reference markers (1) the processing means is configured to calculate the geometric relationship by means of the arcsine of the relationship between the semi-minor axis and the semi-major axis of the circumscribed ellipse (6). In another embodiment for estimating the azimuth of the object with respect to the reference markers (1) the processing means is configured to calculate the angle between the semi-major axis of the circumscribed ellipse (6) and one of the sides of the triangle (7) formed by the reference markers (1) in the image (4) received from a zenith view to the target surface.The semi-major axis of the circumscribed ellipse provides information on the object's azimuth. Said semi-major axis is perpendicular to the vector that joins the object with the origin projected on the plane, but only if we see it from a top-down view. When the image is deformed by being in another view, this is no longer true. In one embodiment, the processing means are configured to undo this deformation and try to replicate the top-down view. Said angle can be calculated in various ways. In one embodiment, the processing means are configured to calculate the Steiner inellipse of the triangle (7) of the reference markers (1) and apply Marden's theorem to calculate the angle between the semi-major axis of said Steiner inellipse and one of the sides of the triangle (7), the base for example, which coincides with the angle of the semi-major axis of the circumscribed ellipse (6) and the base of the triangle (7).More specifically, starting from the basis of Marden's Theorem: Suppose the three complex zeros of a third degree polynomial p(z) are z1, z2 and z3 and suppose that these three points of the complex plane are not collinear. Then there exists a unique ellipse inscribed in the triangle with vertices z1, z2, z3 and tangent to the sides at their midpoints: the Steiner inellipse. The foci of such an ellipse are precisely the zeros of the derived polynomial p' (z). The Steiner inellipse is an inellipse tangent to the sides of the triangle at their midpoints and has the maximum area of ​​any inellipse. It is also the image of the Steiner circumellipse in the homothety with homothetic center G and similarity ratio 1 / 2. The meaning of this is that the axis of symmetry of the Steiner inellipse will have the same direction as the Steiner circumellipse. The foci of any ellipse are on the major axis and, taking advantage of Marden's theorem, obtaining its coordinates is facilitated.Finally, to obtain the angle between the major axis of the ellipse and the axis of one side of the triangle, for example, the base of the triangle, the foci of the Steiner inellipse are subtracted and the angle of the resulting complex number is calculated. This is the angle that defines the azimuth of the object. In one embodiment, the system comprises a fourth reference marker (1) located on one of the sides of the equilateral triangle (2) to uniquely determine the azimuth. In this way, the ambiguity in the determination of the azimuth is resolved, since, according to the calculation methods, it is possible to obtain three azimuth solutions if three reference points are used. One of the first aspects that must be resolved is to determine what the reference markers should be like: what type, what size, how many, etc. In one embodiment, the three reference markers (1) are passive cooperative objectives.Passive cooperative targets, as opposed to active cooperative targets, are simpler, that is, less mechanically complicated. Active cooperative targets actively illuminate the scene, have flashing targets, or some other active mechanism. An example of such active fiducial markers (1) could be infrared lights. More specifically, the three fiducial markers (1) could be circles, as shown in Figures 2 and 3. More specifically, the circles could be white circles. The advantages of using white circles as passive cooperative targets are as follows: o Cooperative targets are an optical navigation aid. The target to be searched for is known in advance. Therefore, algorithms can adapt to them, resulting in high efficiency and accuracy. o Circles are detected robustly and are, for the most part, insensitive to translations and rotations.o White circles are not a common geometric figure that can appear in aerial images. o It is desired that the reference marker (1) be seen from the greatest possible distance. A smooth circle, without elements inside it, fulfills this characteristic. In one embodiment, the centers of the circles form the vertices of the triangles (3, 7). In one embodiment, the pattern is a recursive pattern, for example, within the three circles there would be three more circles and so on. This is because, as the object approaches the target, the object may already have the three outer circles out of its field of vision. In another embodiment, the passive cooperative targets are painted with a paint containing titanium dioxide. Thus, the white circles are painted with titanium dioxide. In another embodiment, the passive cooperative targets are part of a cover that is placed on the target surface.Thus, the cover comprising, for example, the white circles, is spread over the ground. The circles can be sewn to the cover, painted, glued, etc. According to the above, in an exemplary embodiment, to determine the 3D position of an aircraft (10), the white circles of the reference marker (1) must be detected. In particular, the centers of the circles are the sought parameters. To obtain them, computer vision techniques are used. Then, it is expected that, if the threshold that discriminates whether a pixel is white or black is correctly chosen, the white circles will appear in a binarized image. Once the centers have been obtained at this point, it is necessary to calculate the circumscribed ellipse (6) that passes through the vertices of the triangle (7). In an exemplary embodiment, the imaging device is located in an aircraft (10), preferably, it is installed on a longitudinal axis of the aircraft (10).In one embodiment, the target surface is a runway (8) and the reference markers (1) are located at the start of the runway (8) on its longitudinal axis as shown in Figures 2 and 3. The imaging device may be a camera. There are several types of cameras (9) that use structured light technologies. However, for vision-based landing (VBL) the selection preferably narrows down to monocular and stereoscopic cameras (9). The selection of the camera (9) will influence the design of the reference markers (1). Preferably, the choice is to use a monocular camera (9). In one embodiment, the camera (9) is a grayscale camera. If the installed camera (9) were to capture color images, an intermediate step in the computer vision process would be to convert the RGB image into a grayscale intensity image.Therefore, the best option is to install a grayscale camera (9) in the aircraft (10). This is because: o When loaded into memory, a grayscale image takes up one third of the space required for an RGB image. o As a grayscale image has one third of the data, it requires less computing power to process and can reduce computing time. o A grayscale image is conceptually simpler than an RGB image, so the development of an image processing algorithm can be simpler when working with grayscale. In order to meet the exact definition of estimating the position of the object, for example, an aircraft (10), the orientation of the aircraft (10) must also be obtained. The system object of the invention makes it possible to obtain the orientation of the aircraft, for example, in the form of roll, pitch and yaw angles. - Roll: the angle could be obtained by trigonometry.- Pitch: the center of the circumscribed ellipse (6) will appear higher in the captured image (4) as the pitch of the aircraft (10) increases. The angle is obtained by trigonometry. - Yaw: as the aircraft (10) yaws, the center of the circumscribed ellipse (6) moves to the left or right in the captured image (4). The angle is obtained by trigonometry. Another object of the invention is a navigation system comprising a system for relative positioning of an object with respect to a target surface based on vision as explained above.

Claims

CLAIMS 1.- System for relative positioning of an object with respect to a target surface based on vision, characterized in that it comprises: ^ at least three reference markers (1) configured to be located on the target surface such that they are located at the vertices of an equilateral triangle (2) seen from a zenith view of said target surface, where the equilateral triangle (2) has a centroid (5) and a circumscribed circle (3), ^ at least one imaging device configured to be located on the object and to capture images (4) of the target surface that include the reference markers (1), where the imaging device has a focal length, ^ a processing means configured to receive and process the images (4) captured by the at least one imaging device and configured to: o detect the reference markers (1) in the received image (4),or identifying the centroid (5) of a triangle (7) formed by the reference markers (1) in the received image (4), or circumscribing the reference markers (1) in the received image (4) by means of a circumscribed ellipse (6) centered at the centroid (5) of the triangle (7) and passing through the vertices of the triangle (7), or determining the relative position of the object with respect to the target surface according to its spherical geometric coordinates: distance, elevation and azimuth, by means of the geometric relationship in the received image (4) between the semi-axes and the angle of the major semi-axis of the circumscribed ellipse (6) and the position of the reference markers (1) and the radius of its circumscribed circle (3). 2.- System for relative positioning of an object with respect to a target surface based on vision, according to claim 1, characterized in that in order to estimate the distance, of the object with respect to the reference markers (1), the processing means is configured to calculate the geometric relationship using the equation: ^ ^ ^ ^ ^ where f is the focal length of the imaging device, v is the size of the semi-major axis of the circumscribed ellipse (6) in the received image (4), y is the radius of the size of the circumscribed circle (3) on the target surface and z the distance of the object to the reference markers (1).

3. - Relative positioning system of an object with respect to a target surface based on vision, according to any one of the preceding claims, characterized in that for the calculation of the elevation of the object with respect to the target surface the processing means is configured to calculate the arcsine of the relationship between the semi-minor axis and the semi-major axis of the circumscribed ellipse (6). 4.- Relative positioning system of an object with respect to a target surface based on vision, according to any one of the preceding claims, characterized in that for calculating the azimuth of the object with respect to the target surface the processing means is configured to calculate the angle between the major semi-axis of the circumscribed ellipse (6) and one of the sides of the triangle (7) formed by the reference markers (1) in the image (4) received in a zenithal view of the target surface. 5.- Relative positioning system of an object with respect to a target surface based on vision, according to claim 4, characterized in that in order to calculate the angle between the major semi-axis of the circumscribed ellipse (6) and the side of the triangle (7) formed by the reference markers (1), the processing means is configured to calculate the Steiner inellipse of the triangle (7) of the reference markers (1) and apply Marden's theorem to calculate the angle between the major semi-axis of the Steiner inellipse and the side of the triangle (7) that coincides with the angle of the major semi-axis of the circumscribed ellipse (6) and the side of the triangle (7). because it comprises a fourth reference marker (1) located on one of the sides of the equilateral triangle (2) for the univocal determination of the azimuth.

7. - System for relative positioning of an object with respect to a target surface based on vision, according to any one of the preceding claims, characterized in that the three reference markers (1) are passive cooperative objectives.

8. - System for relative positioning of an object with respect to a target surface based on vision, according to claim 7, characterized in that the three reference markers (1) are circles.

9. - System for relative positioning of an object with respect to a target surface based on vision, according to claim 8, characterized in that the centers of the circles form the vertices of the triangles (3, 7). 10.- A vision-based relative positioning system for an object relative to a target surface according to claim 8 or 9, characterized in that the circles are white circles.

11. A vision-based relative positioning system for an object relative to a target surface according to any one of the preceding claims 7 to 10, characterized in that the passive cooperative targets are painted with a paint comprising titanium dioxide.

12. A vision-based relative positioning system for an object relative to a target surface according to any one of the preceding claims 7 to 11, characterized in that the passive cooperative targets form part of a sleeve configured to be positioned on the target surface. 13.- Relative positioning system of an object with respect to a target surface based on vision, according to any one of the preceding claims, characterized in that the object is an aircraft (10) and the imaging device is configured to be installed on a longitudinal axis of the aircraft (10).

14. A vision-based relative positioning system for an object relative to a target surface according to claim 13, characterized in that the target surface is a runway (8) and the reference markers (1) are configured to be located at the start of the runway (8) on its longitudinal axis.

15. A navigation system, characterized in that it comprises a vision-based relative positioning system for an object relative to a target surface according to any one of the preceding claims.

16. A method for vision-based relative positioning of an object relative to a target surface, characterized in that it comprises the following steps: providing at least three reference markers (1) located on the target surface such that they are located at the vertices of an equilateral triangle (2) seen from a zenith view,where the equilateral triangle (2) has a centroid (5) and a circumscribed circle (3), ^ providing at least one imaging device located on the object for capturing images (4) of the target surface including the reference markers (1), where the imaging device has a focal length, ^ providing processing means that receives and processes the captured images (4) received from the at least one imaging device that: o detects the reference markers (1) in the received image (4), o identifies the centroid (5) of the triangle (7) formed by the reference markers (1) in the received image (4), or circumscribes in the received image (4) the reference markers (1) by a circumscribed ellipse (6) centered at the centroid (5) of the triangle (7) and passing through the vertices of the triangle (7),or determine the position of the object relative to the target surface according to its spherical geometric coordinates: distance, elevation and azimuth, by means of the geometric relationship in the received image (4) between the semi-axes and the angle of the major semi-axis of the circumscribed ellipse (6) and the position of, the reference markers (1) and the radius of its circumscribed circle (3).

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