WO2016102721A1

WO2016102721A1 - Method and system for spatial localisation using luminous markers for any environment

Info

Publication number: WO2016102721A1
Application number: PCT/ES2015/000182
Authority: WO
Inventors: Eugenio VILLAR BONEL; PATRICIA Mª MARTINEZ MEDIAVILLA; Francisco José ALCALÁ GALÁN; Pablo Pedro SÁNCHEZ ESPESO; Victor FERNÁNDEZ SOLORZANO
Original assignee: Universidad De Cantabria
Priority date: 2014-12-23
Filing date: 2015-12-16
Publication date: 2016-06-30
Also published as: ES2543038A1; ES2543038B2

Abstract

The invention relates to a method and system for spatial localisation of an object (10) in a three-dimensional environment (11), comprising at least one luminous marker, comprising a stereo camera (12) for capturing a first image frame in a current moment and a second image frame in a previous moment, an angle-measuring device (13) for obtaining an angle of rotation of the object (10), a signal processor (14) with access to a memory (15) that stores, inter alia, a radius of the at least one marker detected in a real-time moment and in a previous moment n-1, said signal processor being configured to calculate coordinates (x-., y) of the object (10) in a moment in time i as follows: if the angle of rotation in the real-time moment and in the previous moment are different, (Xn, Yn )=(Xn-1, Yn-1 ); if the two image frames are the same, (Xn, Yn )=(Xn-1, Yn-1 ); in another case: if the radii are the same and there are a number of markers, (Xn, Yn) are calculated by means of triangulation using both image frames; if the radii are different and there are a number of markers, (Xn, Yn ) are calculated by means of triangulation using a single image frame; if the radii are different and there is a single marker, (Xn, Yn) are calculated by means of stereo geometry; if the radii are the same and there is a single marker, (Xn, Yn) are calculated using image coordinates of the marker in the current moment and in the previous moment.

Description

Method o w System ds Spatial location by Marc dores Lümiriosos for Cis lgguier atmosphere

PURPOSE OF THE WINTER

The present invention belongs to the fields of electronics and telecommunications. Specifically, the present invention applies to the industry area! that collects the techniques of detection of reference points for the location and positioning of a target (a person, animal or an object) in controlled environments.

More particularly, the present invention relates to a method and system for obtaining, from the use of light markers, the position and orientation of an object or subject, applicable to any type of environment, interior or exterior.

BACKGROUND OF THE INVENTION

In recent years, there is a growing interest in those systems or products related to the location of objects in three dimensions (3D). The sectors that cover this technology are very wide, such as reboot, medicine or video games, among others.

Specifically, object tracking is closely related to augmented reality, where knowledge of the individual's position is essential. This technology mixes virtual elements with real images, allowing the user to expand their information from the real world or interact with it. Virtual reality, however, replaces physical reality with computer data. Augmented reality systems can use a transparent optical display (for example, Google Glass) or an image mixing screen (for example, using a smart mobile phone, ^' smartphcne ^{') as a} visuaiizadón device. in English). In addition to knowing the position of the individual with precision, they can be based on the use of cameras, optical sensors, accelerometers, gyroscopes, GPS, etc. In the case that vision systems are used, it is necessary to perform a preprocessing of the region of interest where the individual is located, using image algorithms that allow to detect corners, edges or reference markers; for later, with this data obtain the real 3D coordinates of the environment. These systems require the use of a CPU and RAM with sufficient capacity to computation, to be able to process the images of the cameras in real time! and with the least possible latericia.

When only one reference marker can be displayed, the use of stereo cameras and epipole geometry must be used. The characterization of a point in three-dimensional space requires knowledge of its coordinates (y, y, z) within the environment where it is located, with respect to a reference position. The most common technique is based on the use of two or more calibrated cameras, which provide a left and right image of the same scene. To obtain the 3D coordinates of the point and object to be characterized, stereo correspondences are applied (look for the same point in both images) and projective or epipolar geometry is calculated (it describes the relationship between the image planes of the cameras and the point).

In the case of having more than one marker or pattern available, other techniques can be applied to locate the object on the stage. Through triangulation, knowing the real distance between markers, it is possible with only two markers and a single camera to obtain the parameters to achieve the depth of the objective and position it in the environment. This practice simplifies the computational cost, by not having to analyze two images and their correspondences; but it requires greater precision when it comes to detecting markers. Despite this, some authors ("Optics! Tracking using projective invariant marker pattern proprietors",. Van Liere et al., Proceedings of the IEEE Virtual Roality Conference 2003, 2003) consider that, in order to better track the object, it is necessary that the object has four or more markers and that stereo vision is also used; to achieve a more precise but more efficient system.

One of the problems that have been found in other studies (US 7,231, 063 32, "Fudicial Detection System", L. Waimark et ai.) When using markers, is the luminosity of the environment where they will be feared the images. The points to be detected may be lost in the scene due to lack of light. This limits the applications that use this system indoors or with controlled brightness. In addition, the use of contrast enhancement algorithms and / or the use of specific markers stored in a database is necessary, which substantially increases the computation time of these systems. In addition to considerably limiting the distance between printed markers and ye! user of the system, unless its size is large enough to be captured by the image sensor. In some cases (VVO 201 3/120041 A1, "ethod and apparatus fctr 3D spatiai lecalizaiion and tracking of objects using active optics! lighting and sensing ") have proposed this type of light sources with variable illuminance or pulsed light, so it can cause synchronization failures. Even so, the use of light markers can pose problems, specifically in environments where there are sources of light with an Iuminance much greater than the marker itself (in the worst case, sunlight) or sources that emit radiation in the same direction; in those situations, the image sensor is not able to differentiate one light source from another, so it will force such and as it happened before, to use this technology in luminous environments without large sources of light in it.

The idea of detecting and positioning markers serves to characterize the objects or individuals in it. that way they are located in space. In the article "Wide area optical tracking ín unconsfrained indoor environments" (by A. Mossei et ai., 23rd Snternacionai Conference on Artificial ealíty and Teiexistence (iCAT), 2013) it is proposed to incorporate infrared light markers in a tape located on the head of the Username. To do this, two independent cameras co-operate on the stage, which require a synchronization process to perform the shooting simultaneously, located at a distance equal to the length of the wall of the room where it is to be tested. The algorithm used to estimate the position is kissed in the search for stereo correspondences. One of the disadvantages that it presents is that it cannot be implemented for augmented or simulated reality systems, because the cameras do not show what the user sees, in addition to being restricted to indoor environments with limited dimensions.

Other studies such as "Tracking of user position and orientation by stereo measurement of infrared markers and orientation sensing" (by M. Maeda, et al., Proceeding of te 8th. International Symposlum on Wearable Computers ÍJS C 4), 2004) raise the use gives infrared markers located on the wall of a room, to locate the user. Specifically, they propose the use of two types of markers: active and passive. The active markers are formed by a set of three infrared LEDs and a signal emitter, which sends data of its real position to a signal decoder that the user carries, so that once it is detected they know their absolute position. Passive markers are only an infrared light source, from which they obtain the relative position of the user. In addition to relying on the reception of signals from active markers, they calculate the relative distance to the marker from stereo vision. He Use of this technique, even here! which occurred in the cases explained above, is limited to interior spaces.

There are other methods, which do not require direct vision of one or more cameras with the reference markers, for location and user tracking systems. Radio frequency techniques consist of measuring distances, of static or mobile objects, from the emission of electromagnetic pulses that are reflected in a receiver. These electromagnetic waves will be reflected when there are significant changes in the atomic density between the environment and the object, so they work particularly well in cases of conductive materials (metals). They are able to detect objects at a greater distance than other systems based on light or sound, however they are quite sensitive to interference or noise. It is also difficult to measure objects that are between each other at different distances to the emitter, because the pulse frequency will vary (slower the farther and vice versa). Even so, there are experimental studies such as "RADAR: an in- struction RF-based user location and tracking system" (by P. Bahl et al., Proceedings of IEEE INFOCOM 2000, Tel-Aviv, 2000) that demonstrate its use to estimate The location of the user with a high level of precision. This technique is not appropriate in augmented reality applications.

Another example of existing solutions is LIDAR systems, which calculate the distance over the time it takes for a light pulse to be reflected on an object or surface, using a device with a pulsed laser as a light emitter and a photodetector as a signal receiver. reflected. The advantage of these systems is the precision they achieve over long distances (using lasers with a wavelength> 1000 nm) and the possibility of mapping large areas, by sweeping light pulses. Its drawbacks are the need to perform the analysis and processing of each point, as well as the difficulty of automatically reconstructing three-dimensional images.

The objective technical problem that arises is thus to provide a system for the detection of the position and orientation of an individual or object in any type of environment, interior or exterior, with whatever their lighting conditions. DESCRIPTION OF THE ÉNVENCÜÓN

The present invention serves to solve the aforementioned problems, solving the problems presented by the solutions mentioned in the state of the art, providing a system that, from; Using one or more reference luminous markers and a single stereo camera, it allows locating space objects or individuals in a scenario under any environmental condition and with greater distances between the user and the marker. The system relies primarily on the use of light markers to calculate relative positions of! object / individual, a stereo camera to visualize those markers on the stage image and an electronic device for measuring angles, such as a gyroscope or electronic compass, to provide turning angles of the target user (object, person or animal) .

The present invention makes it possible to detect reference luminous markers in any type of environment, regardless of the light sources that determine the environmental conditions.

One aspect of the invention relates to a method for positioning or locating an objective by using reference markers in any 3D environment that, from a first image frame at an instant of current time and a second image frame in a previous time instant captured by a stereo camera, images in which at least one marker is detected, obtains the coordinates (χ _Λ , and _n ) of the objective at the current time instant n, for which it performs the following steps:

- obtain an angle of rotation of the target at the current time instant and at the previous time instant;

- if the angle of rotation at the current time instant and the angle of rotation at e! The previous instant of time is different, calculate the coordinates (x _n¡ and _n ) of the target at the current instant n equating them to the coordinates {x _r . ~ yn-i) of the target at the previous instant n-1

- If the first image frame and the second image frame are equal, calculate the coordinates (x _n> yr.) Of! target instantly acts! equalizing them to the coordinates ( ^χ , ΐ, ν, .. ·; of the objective in the previous instant; - if not, otherwise, it obtains the image coordinates of, at least one detected marker, and its radius, to compare ios radios in the current time instant n and in the previous time instant n-1 and: - if the radii are equal and there are a plurality of markers, the coordinates (x _n . and _n ) of the objective at the present time are obtained by triangulation using the first image frame and the second image frame;

- if the radios are different and there is also more than one marker, the coordinates (x _n , and _f ,) of the objective at the current moment are obtained by triangulation but using a single image frame, the one captured at the current moment;

^■ if the radios are different and there is a single marker detected, the coordinates {x _r „and _n ) of the target at the current moment are obtained by the stereo geometry algorithm known in the prior art;

- if the radii are equal and there is a unique marker detected, the coordinates (x _r , y _n ) of the target at the present time are obtained through an algorithm reminiscent of stereo geometry but using the image coordinates of the marker in e! instant time acts! and in the previous instant of time, instead of a left and right image of the same instant of time

Another aspect of the invention relates to a system for locating an objective, which can be an object or an individual, from at least one reference marker in a 3D space or environment, comprising the following means;

a stereo camera to capture image frames in which one or more markers are detected;

- an angle measuring device to obtain the angle of rotation of the target at each instant of time;

- a signal processor, with access to a storage device (a memory), configured to perform the steps of the method described above to obtain at its output the coordinates (x _< and _r ) of the target calculated at the instant of current time, using, according to each case indicated above, the data obtained at the previous time stored in memory.

As a retentive marker, a light source is used, identifiable in the environment of use.

In a possible field of application, the invention described can be used for Simulated Reality applications. For this, glasses are incorporated into the system Virtual reality. Both the stereo camera and the glasses can be part of a helmet or holding equipment that is placed on the user's head and connecting the camera with the glasses. The system can additionally incorporate an accelerometer, which measures the displacement made in a finite time, which would reduce the cumulative errors.

The present invention has a series of differentiating characteristics with respect to the existing solutions discussed in the prior art which have technical advantages as follows:

- With respect to US 7,231, 083 62. the present invention solves the problem of computation time of existing systems such as that described in US 7,231, 063 B2 _< because contrast enhancement algorithms and / or specific saved markers are required on a data base _s because in the present invention light markers are used that work in the visible or infrared spectrum, such as light emitting diodes (LEDs)

- With respect to WO 2013/120041 A1, one of the differences of the present invention is that it uses fixed light sources and comes to solve the problem that occurs in environments where there are light sources with an intensity much greater than the marker itself . To solve this problem, the present invention uses an element that prevents the light conditions of an environment from affecting significantly as is the use of a background after the source of iuz.

BRIEF DESCRIPTION OF THE FIGURES

Next, a series of drawings that help to better understand the invention and that expressly relate to an embodiment of said invention which is presented as a non-limiting example thereof is described very briefly.

FIGURE 1 .- Shows a schematic block diagram of the spatial location system of individuals or objects, according to a preferred embodiment of the invention.

FIGURE 2. ^» Shows a simplified representation of a type of light marker, which can be used by the system of Figure 1. FIGURE 3.- Shows an environment of use of the markers of Figure 2 and in which the system of Figure 1 is applicable, according to a possible embodiment.

FIGURES 4Ά-4Β.- They show a scheme of the markers and parameters used by the system to locate individuals or objects that move vertically in it and when only one marker is detected.

FIGURES 5A-5B - They show a scheme of the markers and parameters that the system uses to locate in the environment individuals or objects that move vertically and when more than one marker is detected.

FIGURE 6A.- It shows a scheme of the markers and parameters that the system uses to locate individuals or objects that move orizontally in the environment and when only a single marker is detected.

FIGURE 8B - Shows a scheme of the markers and parameters used by the system to locate in the environment individuals or objects that move horizontally and when more than one marker is detected.

FIGURE 7.- It shows a scheme of the operation of the method, it is merely an example of data flow.

PREFERRED EMBODIMENT OF THE INVENTION

Next, possible embodiments of the obtaining system are proposed, based on the use of one or more luminous markers, from the position and orientation of a user, in different possible environments, which can be indoors or outdoors, within A controlled scenario.

Figure 1 shows a schematic diagram of the system block architecture for locating in e! space ios objects or individuals that constitute an objective (10) in a three-dimensional environment (1 1) under any environmental condition defined by a number m¾1 of light sources (f, fLg, ft _: ¾ fL ™), having one or more light markers (20) as coughs shown in Figures 2-3, 4A-4B, 5A-5B and 6A-8B E! The system comprises a stereo camera {12} to detect the luminous markers (20) and an electronic angle measuring device (13), for example, a gyroscope or electronic compass, with which the rotation angles of the objective are obtained ( 10). In addition, the system comprises a digital signal processor (14) that calculates the position coordinates in the space of each luminous marker (20) in time and stores them in a memory or storage device (15). AND! Digital signal processor (14) uses the stored coordinates and the output parameters obtained from the stereo camera (12) and the angle measuring device (13) to determine at its output (18) the position of the target user (10) .

A type of reference marker (20) of those used is shown in Figure 2, which is a luminous marker and comprises two main elements: a light source (21) and a contrast surface (22). The preferred light source (21) is an LED emitting in e! visible range: 400-700 nm. This type of source is a point light source that achieves ranges greater than 50 m for powers greater than 1 W. In addition, an LED can be considered a non-hazardous product due to the optical powers in which it works since in the worst of the cases the exposure time is very low (aversion reaction time ^ -250 ms). Even so, the system can use luminous markers (20) with other types of light sources (21), because the device detecting the luminous marker (20), that is, the stereo camera (12) used as light receiver detects both light sources {21} that work in the visible and infrared spectrum. The image sensor of the stereo camera (12) has a spectral curve that, for the wavelength of the LED used, indicates a spectral response with a value greater than 0.005 A / VV. Filament bulbs are another example of light sources (21), although they are diffuse sources with emitted optical powers below the range with an LED. Another possible light source (21) can be a laser diode, although it is a collimated source capable of focusing the light on a very small point and, for most cases, all those optical powers greater than 1 mW can be Dangerous, The last type of light source (21) that can be used is an infrared LED, although due to the scope it presents, the drawback is that the user is not able to perceive it and could cause eye damage. On the other hand, the contrast surface (22) is of a color - for example, black - and dimensions that allow distinguishing between the light marker (20) and any external light source. The contrast screen or surface (22) allows you to apply the method proposed here in environments with little or a lot of light, and at great distances. The shape of the contrast surface (22) can be any, for example, square as in Figure 2. The dimensions of the contrast surface (22) depend on the surrounding light conditions (1 1), the luminous flux of The light source (21) and the maximum distance between the objective (10) and the light markers (20). The template or contrast surface (22) is located on the outside of the light source (21), specifically at the rear, the light source (21) being left in view of the user. In the case that the environment or the background behind the light source (21) is dark enough, it is not necessary to add the contrast surface (22). The system supports the use of other types of luminous markers (20), such as white printed markers with a black border, although these cannot be used in any type of environment.

Figure 3 shows a possible system application scenario, in which the distribution of the markers (20). However, the markers (20) can be located at different distances from each other, which the system must know in advance. The height between each luminous marker (20) and the ground is not preset, but it is recommended that it be that which allows direct vision between the stereo camera (12) and the igloo light sources. _: , fLa, fL & ..,. _; fLm} of the luminous markers (20). In the case of outdoor environments, the markers (20) are placed on vertical supports to achieve the necessary height. In the case of indoor environments, the luminous markers (20) can also be placed on vertical supports or subjects on the surrounding walls or objects. The relationship between the number rn of markers (20) and the distance between them (di, c) depends on the opening angle (2φ) of the stereo camera (12), the emission angle (2Θ) of the source of light (21), for example the LED, of the luminous marker (20) and of the minimum distance (L) that must be between the target (10), user of the system, and the light sources (fL-¡, ft. _2l fL.3 ...... fl. _F r}, i.e., the LEDs, so that at least one pair of sources can be displayed; as reflected in the following in the md equation

The scenario where the method is applied does not present any predefined characteristics with respect to distribution, plant, obstacles, so that the system adapts to it. The type of environment, as explained above, can be indoor or outdoor. The only restriction is that having the maximum dimensions of the environment, being limited by ei reach the light sources _(fL;, fL ₂ fL¾ FLM) chosen. Said scope is measured in function of 3a intensity and luminous flux of the light sources (fLi, fL _2l fL _R „) and of the sensitivity of the image sensor of the stereo camera (12).

From the images captured by the stereo camera (12) and the image coordinates of the light markers (20) calculated in a previous capture, as described below, by the digital signal processor (14) of the system , this system allows ioealizar in the image specific reference points by means of an algorithm of detection of luminous markers (20), as eS described below. The method to be described is not unique, other variants can be used, returning as output parameters the image coordinates (u.v) and the diameter of the luminous markers (20) detected. In the image coordinates (u, v) in 2 dimensions, the first coordinate or denotes the coordinate along a horizontal axis and the second coordinate v denotes the coordinate along a vertical axis, on the 2D piano of the image where movements are detected . The detection of light markers (20) is divided into the following steps:

Image conversion to grayscale to significantly reduce the size of the image, as this goes from having three channels, red, green and blue, to only one black and white. That is, each pixel in the image reduces its value from 3 bytes to 1 byte.

Noise removal filtering to eliminate erroneous pixels and noise from images captured by cameras. The type of filter depends on how clear the images are desired and the delay time that can be introduced into the system.

Localization of neighboring pixels with strong contrasts, analyzing the image by windows and looking for those regions where the contrasts between neighboring pixels are greater, This algorithm makes sense because the light sources (21) have pixel variances in the image around 255 and the black template (22) has values around Q.

Obtaining the coordinates of the Suminous markers (20), once the regions that can correspond to light sources (21) are located, verifying that they really are. The first thing that is checked is the shape of the light sources (21), which approximates a circle or ellipse, and the image coordinates (u _s v) of its central point as well as its radius are obtained. In addition, these regions have to be checked against each other, verifying that they are all in very similar rows of pixels and that they have intensity values similar, since it is assumed that íddas are sources of uz (21) with the same illuminance.

- Final verification, comparing the coordinates of the luminous markers (20) calculated with those obtained is a previous capture.Once obtained the regions that have been verified correspond to luminous markers (20), a final check is made. , comparing the positions of the current markers with those of a previous moment, taking into account that in the case of consecutive moments, the coordinates do not change very significantly from one site to another.

To locate in the Image of an environment (1 1) the reference points that give the location of the target user (10), it is necessary to know the following information:

a) the image (u, v) and radius coordinates of each marker (20) detected by the marker obtaining algorithm described above from the image captured by the stereo camera (12);

b) the value in degrees ^δ , of the rotation of the target user, returned by the angle measuring device (1 3), at the time of capture by the stereo camera (12) of each image; and c) the data stored in memory (5) such as: previous position actual distance between markers, focal length of the cameras, camera opening angle, distance between cameras {'baseline', in English), image frame ( trame ', in English) anterior, anterior radius of the markers, anterior position vectors of the markers and anterior angle of rotation.

Considering the particular case of a continuous, unobstructed, square-shaped environment (1 1), for example, as the scenario depicted in Figure 3, the position of the target user (10) depends on the turns and the type of movements that perform - vertical: up or down, horizontal: left or right-; or if it does not make any movement.

The methods for calculating the position described below are summarized in Figure 7, they are used in different ways, illustrated in Figures 4A-4B, 5A-5B and 6A-6B, depending on the kind of displacement has registered and the number of markers detected, being valid for any type of marker, both luminous and printed. As Figure 7 shows, the first thing is to check e! value, in degrees, returned by the angle measuring device (13) to determine if there is a significant turn, which occurs if the angle obtained at the instant acting ^δ (η) is different from that of the previous instant ⁵ (n -one ); however, if ^δ ( ^η ) - ^δ (η ~ 1) indicates that the target user (10) has not turned. If there is rotation, the user coordinates are the same even though the images captured by the stereo camera (12) change. When the angle of rotation, obtained by the angle measuring device {13), is constant over time, the image frame captured at the current moment is compared, frarne n), with the immediately previous frame (n ~ 1) and if they coincide, it is interpreted as having been no movement of the user. In the case that there is no displacement, the method returns the same user coordinates as in the previous moment (x „-i, y-,); otherwise, the position is calculated with all the information, a) -c), mentioned above. In this way, redundant and unnecessary operations are avoided. When position change is detected, the marker detection algorithm is applied. By knowing the values of the radii of the markers detected in the current instant, r (n) and those of the previous instant r (n ~ 1), the type of displacement of! target user (10):

* If those radii are different, r (n ~ 1) ≠ r n), the offset is up or down. To know the position of the objective (10) it is necessary to know the distance between it and the markers, that is, to know the displacement made vertically.

~ If those radii are the same, r (n-1) ~ r {n), displacement is to the right or left. In order to know the position of the objective (10) it is necessary to know how much it has moved horlzontalrnente.

Once the type of movement performed by the objective (10) has been identified, it can be located in the environment (1 1) according to the following methods, which depend on the type of movement and the number m of markers (20) detected.

Figures A-48 show the case in which it has been determined that there is a vertical movement of the lens (10) and when only a single marker (20) is detected in the binocular image (40) captured by the stereo camera (12), In this case, a triangulation algorithm cannot be used, because the pixels cannot be related to a real distance; Therefore, the stereo vision technique must be used and the following parameters are needed:

binocular disparity { ^'disparity:, ai} English stereo vision given by the UL and U coordinates, rectified and distortion respectively marker dei (2Q) obtained from the two image components, left (41) and right (42), captured by the stereo camera {12);

ios baseline B and focal length ength f focal values of the stereo camera (12); Y

and! angle of rotation (δ) of the target user (10).

In order to transform the image coordinates to depth, the project geometry is calculated at the present time n according to the equation: baseline ^x focaljenght

^' * · ~ Mura ado r ^ j shoot it ty

Once the distance L _msft - has been _calculated . _SC i _C ¡- {n} between the objective (10) and the marker (20), you can get your position on stage. As it has moved vertically, the only one that has apparently changed is its coordinate and, but it is necessary to take into account the angle of the year ^δ to obtain the absolute coordinates. The coordinates (x.-. And „) in the current instant are equal to the coordinates in the previous instant (χ _: · .- ..> ¾. · ¾) plus the um of the displacement made ^'

If r (n-1) r (n) ½ .... 4- sin (o} - i ^: "?« &Rs' s á ¡í ,, ..,

„..¡Os (5)" I ^i-: ?? Sff> - íJ .:? -...

If r (n-1)> rn) · - sin ($) - * ~ m ares dor ^^ and »_ t eos (or ^" ) * I ¾4 _: - _: > V: ^: ·>, .., .

Figures 5A-5B show the case in which it has been determined that there is a vertical movement of the lens (10) and two or more markers (20, 20 ^' , 20 ") are detected in the image (50) captured by the stereo camera {12) In this case, triangulation can be applied, since more than one marker is available, of the actual distance (d / m) between markers (2C _S 20 ', 20 "), of the angle of rotation (δ ), the aperture angle (2 <p) of the camera (12) and the number of pixels (AxB) of the image (50). Knowing the horizontal or image coordinates of the markers (20, 20 ^' , 20 "), it is calculated, in pixels, the distance in pixels q between them, q = uj-ui, which in the real world is equal ad / m meters, m being the number of markers. Therefore, the actual meters of distance L ^^ a ^) between the objective (10) and one of the markers, marker (20), at the present time n is:

In Figures 4A-4B and 5A-5B, the angle Φ is shown which refers to half of the opening angle (2cp) of the chamber (12),

Known the distance to the marker and the distance that was at the previous moment n ~ 1, the meters traveled are calculated as the difference between the two, From that value and the user's previous position, coordinates of the target (10) in the previous moment {x _? . _? , and „.i), its new coordinates { _n , and _n ) can be calculated at the current moment:

I If r (n ~ 1) <r (n) _{x ^} - _¾, 4,

I If r {n-1)> r (n) _{Xn mx} ^ _

^L ^ a c.ííí; a¾ ..., '\ -. ·? «<·. > i | w _f . _s . «f _íj \ ^ _ΐ ^■

In this case, stereo vision can also be used to obtain depth at the markers. But it is necessary to apply stereo correspondences, that is, to relate the markers of the left image with their equivalents of the right image. Once the correspondences have been obtained, projective geometry can be applied, as in the case of a single marker to obtain the real distance to each marker.

Figures 6A-6B show the case in which it has been determined that there is a horizontal movement of the target (10).

Figure 6A refers to the case in which only a single marker (20) is detected in the image (61, 62). An algorithm that can be reminded of stereo geometry is applied, but in this case two images of the same are not used moment taken from two different angles, but two images of contiguous instants and the same perspective will be used: the image captured at the current moment (61) and the one captured at an immediately previous instant 62). Also, there are the horizontal coordinates of the marker in e! current moment (u „) and those obtained from the previous frarne (υ, - ,. ι), as well as the previous distance between the marker and the user (Lmarcador) and the focaí distance (foealjength) of the camera (12) , to calculate the horizontal displacement (D) performed by the target user {10) according to the following expression:

Once the displacement D is known, in meters, that the target user has made (10), its real coordinates can be obtained, which depend on its position in the previous instant n-1 and on the type of displacement, left or right, performed :

Figure 6B refers to the case in which more than one marker (20, 20 ^' _. 20 ") is detected in the image. A technique similar to that of triangulation explained in the case of a vertical user movement with a plurality is used. of detected markers, but in this case two images {83, 84) captured by the same image sensor are used consecutively in time, having the current image (63) and the image captured in the previous instant (64). Knowing the real distance between markers and the pixels between them, px pies in the current moment and pqxies in the previous instant n-1, it can be extrapolated to the length that has been moved by the user. of the distance between markers (d / m), the angle of rotation ( ^s ) and the image coordinates (u _n .f) of the markers (20, 20 ', 20 ") in the previous image (64).

As in the case of a single marker, once the offset D is known, the actual coordinates of the target user (10) can be obtained:

In this case, the previous case of a single marker detected can also be applied to obtain the displacement (D) performed by the target user (10). Fs, from the coordinates of the same marker in two contiguous images, disregarding the rest of the markers detected, and with the previous distance between the marker and the user, calculate the displacement D.

Claims

1. Method for the spatial location of a target (10) using at least one luminous marker (20) identifiable in the reference use environment, which in a moment of time í calculates coordinates (x _¡( y,) of the target (10), characterized in that it comprises:

- capturing through a stereo camera (12) a first image frame at an instant of current time and a second image frame at an earlier time, detecting at least one marker (20) in the first and second image frame;

- obtaining a radius at a current time instant and a radius at the previous time instant of the at least one marker (20) detected in the first image frame and second image frame;

- obtaining an angle of rotation of the objective (10) by means of an angle measuring device (13) at the current time instant and at the previous time instant;

- if the angle of rotation at the current time instant and the angle of rotation at the previous time instant are different, calculate the coordinates (x _n , yv,) of the target (10) at the current time equal to the coordinates ( x _n .¾, and _R. <) of the objective (10) in the previous instant;

- If the first image frame and the second image frame are the same, calculate the coordinates (x.-. y-) of the target (10) at the current time Equal to the coordinates {:: · -. and, vi} of the objective (10) in the previous instant;

- if not, compare the radios at the instant of current time and at the previous time of the at least one, marker (20) detected and:

- if the radii are equal and there is more than one marker (20, 20 ', 20 ") detected, the coordinates (x, -. and„) of the target (10) at the present time are obtained by triangulation using the first frame of image and the second image frame;

- if the radios are different and there is more than one marker (20, 20 ', 20 ") detected, the coordinates (,. and _n ) of the target (10) at the present time are obtained by triangulation using a single image frame which is the first image frame;

- if the radii are different and there is a single marker (20) detected, the coordinates (x, .. and, -,) of the target (10) at the present time are obtained by stereo geometry;

^■ if the radii are equal and there is a single marker (20) detected, the target coordinates (Xn, y-) (10) at the current time are obtained by calculating image coordinates of the marker (20) at the current time instant in the first image frame and image coordinates of the marker (20) obtained at the previous time in the second image frame.

2. The method of spatial location, according to claim 1, characterized in that it uses a luminous marker (20) comprising a light pattern (21) and a coniarial surface (22).

3. Spatial location method, according to claim 2, characterized in that it uses a luminous marker (20) comprising a light source (21) which is an LED.

4. Spatial location method, according to claim 1, characterized in that, if the radii are equal and there is more than one marker (20, 2Q \ 20 ") detected, obtain the coordinates (x _fl! And„) of the objective (10) at the present moment comprises:

- for each marker (. 20, 20 '20 "), obtained in the first image frame ia a horizontal coordinates u _n image at the current time instant and the second frame image gives a horizontal coordinates u obtain _n -i image at the previous time instant:

~ measure a displacement expression:

where p is a number of pixels in the current instant nyq is a number of pixels in the previous instant n-1, m is a total number of markers, d / m is a real distance between markers (20, 20 ', 20 ") and ⁵ is the angle of rotation of the target (10) obtained;

- calculate the coordinates (x _n , yv.) of the objective (10) at the current time using the equation:

Yes Us i ^ ¾ ·;

5. The method of spatial location, according to claim 1, will ensure that, if the radii are equal and there is a single marker (20) detected, obtain the coordinates (A,, and -.) Of the objective (10) in The current moment includes: - for e! marker (20) obtain horizontal coordinates or image _n in the first image frame at the current time instant and in the second image frame obtain horizontal image _n- i coordinates in the previous time instant; ^■■ measure a displacement D sion:

where the camera (12) has a focal length of distance iength and the smoker _iV i is a distance between the marker (20) and the target (10) measured at the previous time, ~ calculate the coordinates {x «. and _rt ) of the objective (10) at the current time using the equation:

6. The method of spatial location, according to claim 1, characterized in that, if the radii, which are the radius at the current instant r (n) and the radius at the previous instant r {n-1), are different and there is more than one marker {20, 20 ^r , 20 ") detected, obtaining the coordinates (x _r , and _n ) of the target (10) at the present time comprises:

~ obtain in the first image frame first horizontal coordinates or image of a primary marker (20. 20 ', 20 ") and second horizontal coordinates of image of a second marker (20')

- measure a marker distance * between the target (10) and the first marker (20) at the current time

where the camera (12) has an opening angle 2φ, AxB is a number of two-dimensional image pixels! at the present time, m is a total number of markers, d / m is a real distance between the markers (20, 20 ^' ) and ^ñ is the turning angle of the target (10) obtained; - get a distance Lmarcadasv; measured at the previous time between the objective (10) and the first marker (20);

- calculate the coordinates (x.-, y _n ) of the objective (10) at the current moment rrt equation:

If r (n-1) <r (n) _{¾ ^} ^SK x - sm (S) * v ... _; -t osí ^ Ó ^ *

If r (n-1)> r (n) _¾ ^■ ::: < _v: ··· ¾ | ¾ | íl ^: i * <5 £ · ^ i

- v .. _; - cos (<¾

7. Spatial location method according to claim 1, characterized in that, if the radios, which are the radius at the current instant r {n) and the radius at the previous instant r (n-1), are different and there is a single marker (20) detected, obtaining the coordinates (x „, y _n ) of the target (10) at the current time comprises:

^■ obtain rectified marker coordinates (20) and SJR respectively in a left image component (41) and a right image component (42) captured by the stereo camera (12), a binocular disparity

- measure a marker distance at the current time, between the target (10) and the marker (20) by means of the expiration

where the stereo camera (12) has a binocular disparity equal to ui. - u, a reference distance B and a focal distance f;

^■■ get a distance

measured at the previous time between the objective (10) and the marker (20);

- calculate the coordinates (x, - ,, y ₍₁ ) of the target (10) at the current time using the equation, where ⁵ is the angle of rotation of the target (10) obtained at the current time:

8. ^~ Spatial location system of a target (10) in a three-dimensional environment (1 1) comprising at least one reference light marker (20) and yn digital signal processor (14) to calculate coordinates (x¡, and,} of the objective (10) in an instant of time i, characterized in that it comprises:

- a stereo camera (12) for capturing a first image frame at an instant of current time and a second image frame at an earlier time;

- an angle measuring device (1 3) to obtain an angle of rotation of the target (10) at the current time instant and the previous time instant;

- the signal processor (14) with access to a memory {15) that stores a radio in an instant of current time and in a radie in the previous time of the at least one, marker (20) detected in the first image frame and second image frame; The serial processor (14) configured to:

- if the angle of rotation at the current time instant and the angle of rotation at the previous time instant are different, calculate the coordinates (x _r¡ , and _f; ) of the target (10) at the current time Equal to the coordinates (x _n -i, ri) of the objective (10) in the previous instant;

- if the first frame image and the second image frame are equal, calculate the coordinates and _n) of the target (1 0) in ei current time equating to the coordinates (x _{f, -} i, _v:) of the target (10 ) in the previous instant;

- if not, compare the radios at the current time instant and at the previous time instant of the at least one, marker (20) detected and:

- if the radii are equal and there is more than one marker (20, 2G \ 20 ") detected, calculate the coordinates (χ. ·. and _n ) of the target (10) at the current moment by triangulation using the first image frame and the second image frame;

- if the radios are different and there is more than one marker (20, 20 ', 20 ") detected, calculate the coordinates { _n , and _n ) of the target (10) at the current moment by triangulation using a single image frame that it is the first image frame; - if the radios are different and there is a single marker (20) detected, calculate the coordinates (x _n , y _n ) of the objective (10) at the current moment using stereo geometry;

- if the radii are equal and there is a cynical marker {20} detected, calculate the coordinates ( ^χ _Πι and _n ) of the target (10) at the current moment using image coordinates of the marker (20) at the instant time in the first image frame and image coordinates of the marker (20) obtained in e! instant of previous time in! to second image frame.

9. - Spatial location system according to claim 8, characterized by the luminous marker (20) comprising a light source (21) which is an LED

10, - Spatial location system according to any of claims 8-9, characterized in that the luminous marker (20) includes a contrast surface (22)

1 1 - Spatial location system according to any of claims 8-10, characterized in that the environment (1) is interior.

12. Spatial location system according to any of claims 8-10, characterized in that the environment (1 1) is external.