Method and apparatus for detecting the location of an object on a virtual surface

Abstract

 A method and a system for detecting the location of an object on a virtual surface, the system comprising a data bus communicatively coupled to a memory and a controller, the system being further comprising: at least two light emitters (101); a linear light detector (105), comprising a plurality of optical detectors; a shadow edges detector for detecting recesses in the lightness curve detected by the linear light detector circuit and for detecting the location of edges based on the detected recesses the shadow edges; an object's center coordinates calculation circuit, wherein: the at least two light emitters (101) are positioned at one side of a shooting target (102) on a virtual straight horizontal line being parallel to the shooting target; the linear light detector (105) is placed at the opposite side of the shooting target (102) with respect to the light emitters (101) and parallel to the light emitters (101); the shooting target (102), the light emitters (101) and the linear light detector (105) are positioned such that overlapping of the shadows on the linear light detector is avoided.

Description

[0001] The present invention relates to a method and apparatus for detecting the location of an object on a virtual surface. In particular the present invention relates to detecting of a location of a bullet on a shooting target.

[0002] Modern shooting ranges use electronic systems for detecting a location of a bullet on a shooting target in order to conveniently count scores and obviate the need of a shooter going to the target in order to check the score or the need of pulling the shooting target card to the shooter by means of an electric motor and a rail or similar pulley system.

[0003] For example, one such device is disclosed in U.S. Pat. No. 3,614,102. This automated target range system discloses a carriage that is mounted on an overhead track that extends longitudinally away from the shooter. The target carriage is pulled along the track by a steel puller cable, takeup pulley and drive motor arrangement. The steel puller cable is also an electrical conductor which provides power to the target turning device.

[0004] Another prior art publication US 5967522 A entitled "Automated range target carrier system" discloses an automated indoor pistol range target carrier has an overhead power rail along which a target-supporting, -lighting and -rotating carriage travels toward and away from the firing line. The carriage supports, rotates, repositions and lights the target and is controlled by and feeds back information as to the target's position to a central controller. Portions of the power rail are electrically insulated one from the other and function as bus bars to carry d.c. current used to operate motors and circuits in the trolley without using electrical cables. Electrical pickups in the form of wheeled trolleys wipe the bus bars to supply power to motors and lights to operate the various target carrier systems. All system components are located within the carriage which may easily be removed from the rail for service without requiring the disconnection of any power cords or cables.

[0005] Yet another prior art publication WO 1995007471 A1 entitled "Method and apparatus for detecting the presence and location of an object in a field" discloses an optical system and method for detecting the presence and location of at least one stationary or moving object in a field. The optical system has at least one light source to generate a beam, which beam is scanned by at least one first reflecting surface to generate a plurality of beams. The beams are overlapped across the field by at least one second reflecting surface and their intensity is measured by at least one detection means.

[0006] A further prior art publication US 4949972 A entitled "Target scoring and display system" discloses an automatic target shooting system for determining projectile location relative to a target, calculating a score based upon the location and displaying a replica of the target with an indication of the location of the projectile relative to the target and the score. A target support structure defines a target area with criss-crossing X-Y-type coordinate light beams extending thereacross between light emitter devices and light receiving devices which generate output signals indicative of the location of a projectile during passage through the target area. The output signals are utilized by a computer device to identify the location of the projectile relative to the target and score the shot in accordance with the location.

[0007] In this solution there are detectors and emitters of light facing each other wherein one emitter corresponds to one detector. An opaque object covers the emitters light and the detectors directly provide coordinates of a shadow and therefore also the object (a location of each detector is known a'priori). An orthogonal setup of two such sets of detectors and emitters of light allows for determining position of an object in two axes.

[0008] The aim of the development of the present invention is an improved and cost effective method and apparatus for detecting the location of an object on a virtual surface.

[0009] The object of the present invention is a method for detecting the location of an object on a virtual surface using a system according to the present invention, the method being comprises the steps of: determining which optical detectors of the linear light detector detect shadow; determining a single axis coordinate of those optical detectors of the linear light detector that detect edges of the shadows; computing coefficients of lines virtually drawn from each light emitter edges to respective shadow edges created by that light emitter; calculating coordinates X, Y of points of intersection of the virtually drawn lines; grouping the intersection points in pairs whereas each pair comprises one intersection point to the left of the center of the object and one intersection point to the right of the object wherein all intersections possibilities are covered; for each pair of points determining an equation of a virtual straight line crossing such both points of such pair of points thereby arriving at X, Y coordinates of a point located in the middle between said pair of points on said straight line; and calculating an average result for the obtained coordinates of a middle points.

[0010] Preferably, the shooting target, the light emitters and the linear light detector are positioned such that overlapping of the shadows on the sensor is avoided.

[0011] Preferably, it further includes the step of providing the linear light detector with a scan area extender for extending area of detection of light.

[0012] Preferably, the light emitters are symmetrically spaced with respect to the center of the shooting target.

[0013] Preferably, the shooting target is approximately three times smaller than the scan area of the linear light detector as well as the light emitters are positioned approximately at a distance from the center of the shooting target of three times the diameter of the shooting target.

[0014] Preferably, the object is an air gun bullet.

[0015] Preferably, the light emitters are such that they generate maximum readings at 90 to 95% of saturation level of the optical detector of the linear light detector.

[0016] Another object of the present invention is a system for detecting the location of an object on a virtual surface, the system comprising a data bus communicatively coupled to a memory and a controller, the system being further comprising: at least two light emitters that are appropriately supplied with power and controlled by the controller; a linear light detector, comprising a plurality of optical detectors, which is appropriately supplied with power and controlled by the controller; a shadow edges detector for detecting recesses in the lightness curve detected by the linear light detector circuit and for detecting the location of edges based on the detected recesses the shadow edges; an object's center coordinates calculation circuit, configured to execute the steps of the method according to the present invention; wherein: the at least two light emitters are positioned at one side of a shooting target on a virtual straight horizontal line being parallel to the shooting target; the linear light detector is placed at the opposite side of the shooting target with respect to the light emitters and parallel to the light emitters; the shooting target, the light emitters and the linear light detector are positioned such that overlapping of the shadows on the linear light detector is avoided.

[0017] Preferably, it further comprises a display or a transmitter of data allowing for outputting the determined data.

[0018] Preferably, the light emitter is smaller than the diameter of the object.

[0019] Another object of the present invention is a shooting target frame characterized in that it comprises the system according to the present invention

[0020] Another object of the present invention is a computer program comprising program code means for performing all the steps of the computer-implemented method according to the present invention when said program is run on a computer.

[0021] Another object of the present invention is a computer readable medium storing computer-executable instructions performing all the steps of the computer-implemented method according to the present invention when executed on a computer.

[0022] These and other objects of the invention presented herein are accomplished by providing a method and apparatus for detecting the location of an object on a virtual surface. Further details and features of the present invention, its nature and various advantages will become more apparent from the following detailed description of the preferred embodiments shown in a drawing, in which:

Fig. 1 presents general principles of the present invention;

Fig. 2 presents an exemplary curve detected by a linear light detector;

FIG. 3 presents a method according to the present invention;

FIG. 4A and Fig. 4B present shadow edges lines; and

FIG. 5 presents a system according to the present invention.

NOTATION AND NOMENCLATURE

[0023] Some portions of the detailed description which follows are presented in terms of data processing procedures, steps or other symbolic representations of operations on data bits that can be performed on computer memory. Therefore, a computer executes such logical steps thus requiring physical manipulations of physical quantities.

[0024] Usually these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. For reasons of common usage, these signals are referred to as bits, packets, messages, values, elements, symbols, characters, terms, numbers, or the like.

[0025] Additionally, all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Terms such as "processing" or "creating" or "transferring" or "executing" or "determining" or "detecting" or "obtaining" or "selecting" or "calculating" or "generating" or the like, refer to the action and processes of a computer system that manipulates and transforms data represented as physical (electronic) quantities within the computer's registers and memories into other data similarly represented as physical quantities within the memories or registers or other such information storage.

[0026] The method according to the present invention is an optical method and detects a location wherein a bullet (or an object in general) crosses an optical barrier (a virtual surface). The method allows for very accurate measurements.

[0027] Fig. 1 presents general principles of the present invention. There are at least two light emitters 101 arranged at one side of the setup (in this example at the top). The point light emitters (as small as possible, for sure smaller than a projectile) have omnidirectional light characteristics.

[0028] The omni-directional emitter is preferably a smallest possible emitter that emits light omnidirectionally. In practice it is sufficient that the emitter is smaller that a bullet. For example in case of an air gun bullet caliber 4,5 mm the light emitter must not be greater than 3mm. The light emitters may be LED (light emitting diode), preferably emitting infrared but visible light is also possible.

[0029] At the opposite side of the light emitters (in the example at the bottom) there is located a linear light detector 105 comprising typically thousands of optical detectors. Such linear light detector may be a detector used in scanners. A specific example of such linear light detector is TCD1706DG sensor from Toshiba that may be further extended with optics extending area of detection. In case of use of an extender a mapping must be known between locations in the scan area and locations in the physical linear light detector (105).

[0030] An optical extender will typically be necessary as cost-effective and affordable linear light detectors are usually smaller than the scan area that needs to be covered. For example the TCD1706DG linear light detector is equipped with 7400 optical detectors located linearly over 34.8 mm (raster of 4.7um). It is often used in scanners of A4 paper sheets i.e. approximately 220 mm scan area. In order to facilitate that, there is located in front of the linear light detector, optics for projecting the scan area onto the linear light detector being typically narrower than the scan area.

[0031] For an exemplary shooting target sheet of 170x170 mm the assumed LED distance from the center of the shooting target sheet results in that the linear light detector has to cover the scan area of approximately 440 mm. In order to facilitate that a projecting optics will typically be applied. Such projecting optics will work as lens and will comprise one or more lens.

[0032] It is important to apply a proper distance between the light emitters and the linear light detector and a proper distance between individual light emitters. The greater the distance between the light emitters and the linear light detector, the smaller linear light detector may be used (shorter detection area). It is very important to place the shooting target area far enough from sensor to avoid overlapping of the shadows on the sensor. All dimensions are relative to size of shooting target area.

[0033] For example in case of a shooting target sheet of 170 mm x 170 mm and four light emitters each having a diameter of 3mm and located on a straight horizontal line parallel to the shooting target and spaced from the center of the shooting target sheet by 500 mm the LEDs are symmetrically spaced by 66.666 mm between each other. The two inner light emitters being spaced by 33.333 mm from the vertical axis of the shooting target sheet while the remaining two light emitters are spaced by 100 mm from the vertical axis of the shooting target sheet. The linear light detector is positioned on a straight line parallel to the straight line on which the emitters are positioned. The linear light detector is positioned on a straight line, parallel to the shooting target, being spaced by 200 mm from the center of the shooting target sheet in a direction opposite vertically to the direction where the light emitters are located.

[0034] The linear light detector covers the scan area of 440 mm onto which the light is projected by the light emitter. In Fig. 1 the light emitters are not evenly spaced, nevertheless in a preferred embodiment the light emitters are symmetrically positioned. The distance between the light emitters may by variable but it is more convenient to apply equal distances.

[0035] The shooting target sheet is therefore approximately three times smaller than the scan area as well as the light emitters are positioned approximately at a distance from the center of the shooting target sheet of three times the diameter of the shooting target sheet.

[0036] Such dimensions have been applied in order to guarantee that the shadows generated by the a bullet will not overlap at the line of the linear light detector. Owing to this there is obtained a reading shown in Fig. 2.

[0037] If the light emitters were too close to each other and the line of the linear light detector was too close to the center of the shooting target sheet, the cast shadows would overlap, which would first of all increase the difficulty of analysis of the readings.

[0038] The length of the scan area depends on the distance of the light emitters from the horizontal axis of the center of the shooting target sheet and the size of the shooting target sheet. A suitably thick paper sheet will be a typical material however other materials are possible for a shooting target. The exemplary area of 170 mm x 170 mm is the observed shooting target are while the shooting target total are may be greater and has no significance for the method according to the present invention.

[0039] If a center of a bullet (or object in general) is located in a right-top corner of the shooting target (coordinates 85, -85 mm relative to the center of the shooting target) then the location of the leftmost light emitter determines where the shadow will be cast. From triangles similarity it follows that it will be 212 mm from the vertical axis of the center of the shooting target. Therefore, the preferred scan area is 2 * 220 mm i.e. 440 mm. The additional length is present due to diameter of the bullet and the fact that the edge of a shadow will be located further that the center of the shadow.

[0040] In case there is not any object obscuring the light emitted by the light emitters 101, the linear light detector will detect light intensity of which defines a curve being similar to an inverse parabola. This effect will occur as far as the intensity of the light emitters has been appropriately chosen. In particular, all light emitters should emit light with the same intensity. Intensity of the light emitters should be chosen in such a way as to obtain maximum readings from light emitter about 90..95% of saturation level of the light detector (and analog to digital converter range).

[0041] If an opaque object 103 (or substantially opaque) is present between the emitters 101 and the linear light detector 105, the linear light detector still detects the same curve, which this time however comprises recesses that represent shadows. The lightness does not fall to zero because each optical sensor is also lit by at least one other light emitter at the location where the shadow 104 occurs.

[0042] There are as many recesses in the curve as there are light emitters, for example four light emitters will generate four recesses in the curve detected by the linear light detector 105.

[0043] By knowing the location of light emitters and the location of the linear light detector one may calculate, based on shadows, where the object that creates shadows is located.

[0044] In Fig. 1 there are drawn two lines starting at each light emitter that determine edges of the shadow. A line crossing the midpoint of the opaque object may be calculated based on the edges of the shadow.

[0045] One may also calculate coordinates of the midpoint of the opaque object based on the lines defining the edges of shadows.

[0046] Fig. 2 presents an exemplary curve detected by a linear light detector. The curve 201 includes four recesses 202 created due to use of four light emitters 101. As already explained, the minimum number of light emitters is two. The greater number of light emitters is advantageous, because it allows for averaging the results thereby reducing error of location determination.

[0047] It is worth noting that the present invention is such that a single linear light detector and at least two inexpensive LEDs are sufficient to determine X and Y coordinates.

[0048] There is eliminated an error of positioning two or more detection circuits versus each other and there are no more detection circuits.

[0049] FIG. 3 presents a method according to the present invention. The first step is to determine which optical detectors of the linear light detector detect shadow 301. It is assumed that one of the X and Y coordinates is constant because the light detector is linear. For example when the Y coordinate is constant only the X coordinates need to be determined.

[0050] Next, at step 302, there is determined single axis coordinate (for example X coordinate in case the Y coordinate of the linear light detector is constant) of those detectors of the linear light detector that detect edges of the shadows. In case of four light emitters there will be eight edges.

[0051] Subsequently, at step 303, is necessary to compute coefficients of lines virtually drawn from each light emitter edges to respective shadow edges created by that light emitter. This is achieved by mean of a simple function y = a * x + b. The edges of a light emitter are reversed versus the edges of shadows. For example, in case of two light emitters a line starting at the left edge of a left emitter will connect to a left edge of the right shadow and a line starting at the right edge of a left emitter will connect to a right edge of the right shadow. Similarly, a line starting at the left edge of a right emitter will connect to a left edge of the left shadow and a line starting at the right edge of a right emitter will connect to a right edge of the left shadow.

[0052] At step 304 there are calculated coordinates X, Y of points of intersection of the virtual lines determined at step 303 and step 305 the intersection points are grouped in pairs. Each pair comprises one intersection point to the left of the center of the object and one intersection point to the right of the object and all intersection possibilities are covered. Taking Fig. 4B example the first pair comprises a point of intersection of lines 401a - 401 b and 402a - 402b, the second pair comprises a point of intersection of lines 401 a - 401 c and 402a - 402c, the third pair comprises a point of intersection of lines 401a - 401d and 402a - 402d, the fourth pair comprises a point of intersection of lines 401b - 401 c and 402b - 402c, the fifth pair comprises a point of intersection of lines 401 b - 401 d and 402b - 402d, while the sixth pair comprises a point of intersection of lines 401c - 401 d and 402c - 402d. Thus, there is determined an equation of a virtual straight line crossing both points such pair of points thereby arriving at X, Y coordinates of a point located in the middle between said pair of points on said straight line.

[0053] Finally, at step 306, there is calculated an average result for the obtained coordinates of a middle point(s). For two light emitters there is obtained one result, for three light emitters there are obtained three results, for four light emitters there are obtained 6 results. In general the results number for N light emitters equals (N*(N-1))/2.

[0054] Based on this average result there may be determined a single location on the observed shooting target.

[0055] In case of four light emitters there will be four left lines and four right lines as shown in Fig. 4A. There are four pairs of edges 401 a-402a to 401 d-402d. The center of the opaque object is located in a center of a circle inscribed between the eight lines, the lines being all tangent to the circle.

[0056] Since a case of a circle is discussed, one needs to assume that the opaque object, location of which is to be determined, is spherical or cylindrical (or otherwise an object having a circular cross-section). This assumption is fulfilled in case of sports or military ammunition.

[0057] The accuracy of location determination in case of the present invention, may be as high as 0,05 mm using the aforementioned linear light detector. This is by far the most accurate system taking into account the cost effectiveness of the location system.

[0058] FIG. 5 presents a system according to the present invention. The system may be realized using dedicated components or custom made FPGA or ASIC circuits. The system comprises a data bus 501 communicatively coupled to a memory 504. Additionally, other components of the system are communicatively coupled to the system bus 501 so that they may be managed by a controller 506.

[0059] The system comprises at least two light emitters 508 that are appropriately supplied with power and controlled by the controller 506. Similarly, the system comprises a linear light detector 507, which is appropriately supplied with power and controlled by the controller 506. Typically, the light emitters and the linear light detector are switched on when the system operates and are switched off when the system shuts down.

[0060] An additional component of the system according to the present invention is a shadow edges detector 502. As already explained the task of this circuit is to detect the recesses in the lightness curve detected by the linear light detector circuit 507. Based on the detected recesses the shadow edges detector 502 detects the location of edges.

[0061] A further circuit of the system according to the present invention is an object's center coordinates calculation circuit 503, which is configured to execute the steps of the method presented in Fig. 3.

[0062] Lastly, the system comprises a display or a transmitter of data 505 which allows for data output, in particular for providing the determined data to a user.

[0063] It is to be noted that such system may be configured for and fixed on a frame that may be offered as a complete product. A shooting target paper sheet will typically be situated right behind such frame comprising the system according to the present invention.

[0064] The above-described method allows for computing a position of a projectile on a target surface. The scoring depends on the rules of a given sport event and is external to the described method.

[0065] It can be easily recognized, by one skilled in the art, that the aforementioned method for detecting the location of an object on a virtual surface may be performed and/or controlled by one or more computer programs. Such computer programs are typically executed by utilizing the computing resources in a computing device such as personal computers, personal digital assistants, cellular telephones, receivers and decoders of digital television or the like. Applications are stored on a non-transitory medium. An example of a non-transitory medium is a non-volatile memory, for example a flash memory or volatile memory, for example RAM. The computer instructions are executed by a processor. These memories are exemplary recording media for storing computer programs comprising computer-executable instructions performing all the steps of the computer-implemented method according the technical concept presented herein.

[0066] While the invention presented herein has been depicted, described, and has been defined with reference to particular preferred embodiments, such references and examples of implementation in the foregoing specification do not imply any limitation on the invention. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader scope of the technical concept. The presented preferred embodiments are exemplary only, and are not exhaustive of the scope of the technical concept presented herein.

[0067] Accordingly, the scope of protection is not limited to the preferred embodiments described in the specification, but is only limited by the claims that follow.

Claims

1. Method for detecting the location of an object (103) on a virtual surface using a system as claimed in claim 8, the method being characterized in that it comprises the steps of:

• determining which optical detectors of the linear light detector detect shadow (301);

• determining (302) a single axis coordinate of those optical detectors of the linear light detector (105) that detect edges of the shadows;

• computing (303) coefficients of lines virtually drawn from each light emitter (101) edges to respective shadow edges created by that light emitter (101);

• calculating (304) coordinates X, Y of points of intersection of the virtually drawn lines;

• grouping the intersection points in pairs whereas each pair comprises one intersection point to the left of the center of the object (103) and one intersection point to the right of the object (103) wherein all intersections possibilities are covered;

• for each pair of points determining an equation of a virtual straight line crossing such both points of such pair of points thereby arriving at X, Y coordinates of a point located in the middle between said pair of points on said straight line;

• calculating (306) an average result for the obtained coordinates of a middle points.

2. The method according to claim 1 characterized in that the shooting target, the light emitters (101) and the linear light detector (105) are positioned such that overlapping of the shadows on the sensor is avoided.

3. The method according to claim 1 characterized in it further includes the step of providing the linear light detector (105) with a scan area extender for extending area of detection of light.

4. The method according to claim 1 characterized in that the light emitters (101) are symmetrically spaced with respect to the center of the shooting target.

5. The method according to claim 1 characterized in that the shooting target is approximately three times smaller than the scan area of the linear light detector (105) as well as the light emitters (101) are positioned approximately at a distance from the center of the shooting target of three times the diameter of the shooting target.

6. The method according to claim 1 characterized in that the object is an air gun bullet.

7. The method according to claim 1 characterized in that the light emitters (101) are such that they generate maximum readings at 90 to 95% of saturation level of the optical detector of the linear light detector (105).

8. System for detecting the location of an object (103) on a virtual surface, the system comprising a data bus (501) communicatively coupled to a memory (504) and a controller (506), the system being characterized in that it further comprises:

• at least two light emitters (508) that are appropriately supplied with power and controlled by the controller (506);

• a linear light detector (507), comprising a plurality of optical detectors, which is appropriately supplied with power and controlled by the controller (506);

• a shadow edges detector (502) for detecting recesses in the lightness curve detected by the linear light detector circuit (507) and for detecting the location of edges based on the detected recesses the shadow edges;

• an object's center coordinates calculation circuit (503), configured to execute the steps of the method according to claim 1;

• wherein:

• the at least two light emitters (101) are positioned at one side of a shooting target on a virtual straight horizontal line being parallel to the shooting target;

• the linear light detector (105) is placed at the opposite side of the shooting target with respect to the light emitters and parallel to the light emitters (101);

• the shooting target, the light emitters (101) and the linear light detector (105) are positioned such that overlapping of the shadows on the linear light detector is avoided.

9. The system according to claim 1 characterized in that it further comprises a display or a transmitter of data (505) allowing for outputting the determined data.

10. The system according to claim 1 characterized in that the light emitter (101) is smaller than the diameter of the object (103).

11. A shooting target frame characterized in that it comprises the system according to claim 9.

12. A computer program comprising program code means for performing all the steps of the computer-implemented method according to any of claim 1 when said program is run on a computer.

13. A computer readable medium storing computer-executable instructions performing all the steps of the computer-implemented method according to any of claims 1 when executed on a computer.

Amended claims

Amended claims in accordance with Rule 137(2) EPC.

1. Method for detecting the location of an object (103) on a virtual surface using a system comprising

• a data bus (501) communicatively coupled to a memory (504);

• a controller (506);

• at least two light emitters (508) that are appropriately supplied with power and controlled by the controller (506);

• a linear light detector (507), comprising a plurality of optical detectors, which is appropriately supplied with power and controlled by the controller (506);

• a shadow edges detector (502) for detecting recesses in the lightness curve detected by the linear light detector circuit (507) and for detecting the location of edges based on the detected recesses the shadow edges;

• an object's center coordinates calculation circuit (503);

• wherein:

• the at least two light emitters (101) are positioned at one side of a shooting target on a virtual straight horizontal line being parallel to the shooting target;

• the linear light detector (105) is placed at the opposite side of the shooting target with respect to the light emitters and parallel to the light emitters (101);

• the shooting target, the light emitters (101) and the linear light detector (105) are positioned such that overlapping of the shadows on the linear light detector is avoided.

the method being characterized in that it comprises the steps of:

• determining which optical detectors of the linear light detector detect shadow (301);

• determining (302) a single axis coordinate of those optical detectors of the linear light detector (105) that detect edges of the shadows;

• computing (303) coefficients of lines virtually drawn from each light emitter (101) edges to respective shadow edges created by that light emitter (101);

• calculating (304) coordinates X, Y of points of intersection of the virtually drawn lines;

• grouping the intersection points in pairs whereas each pair comprises one intersection point to the left of the center of the object (103) and one inter-section point to the right of the object (103) wherein all intersections possibilities are covered;

• for each pair of points determining an equation of a virtual straight line crossing such both points of such pair of points thereby arriving at X, Y coordinates of a point located in the middle between said pair of points on said straight line;

• calculating (306) an average result for the obtained coordinates of a middle points.

2. The method according to claim 1 characterized in that the shooting target, the light emitters (101) and the linear light detector (105) are positioned such that overlapping of the shadows on the sensor is avoided.

3. The method according to claim 1 characterized in it further includes the step of providing the linear light detector (105) with a scan area extender for extending area of detection of light.

4. The method according to claim 1 characterized in that the light emitters (101) are symmetrically spaced with respect to the center of the shooting target.

5. The method according to claim 1 characterized in that the shooting target is approximately three times smaller than the scan area of the linear light detector (105) as well as the light emitters (101) are positioned approximately at a distance from the center of the shooting target of three times the diameter of the shooting target.

6. The method according to claim 1 characterized in that the object is an air gun bullet.

7. The method according to claim 1 characterized in that the light emitters (101) are such that they generate maximum readings at 90 to 95% of saturation level of the optical detector of the linear light detector (105).

8. System for detecting the location of an object (103) on a virtual surface, the system comprising a data bus (501) communicatively coupled to a memory (504) and a controller (506), the system being characterized in that it further comprises:

• at least two light emitters (508) that are appropriately supplied with power and controlled by the controller (506);

• a linear light detector (507), comprising a plurality of optical detectors, which is appropriately supplied with power and controlled by the controller (506);

• a shadow edges detector (502) for detecting recesses in the lightness curve detected by the linear light detector circuit (507) and for detecting the location of edges based on the detected recesses the shadow edges;

• an object's center coordinates calculation circuit (503), configured to execute the steps of the method according to claim 1;

• wherein:

• the at least two light emitters (101) are positioned at one side of a shooting target on a virtual straight horizontal line being parallel to the shooting target;

• the linear light detector (105) is placed at the opposite side of the shooting target with respect to the light emitters and parallel to the light emitters (101);

• the shooting target, the light emitters (101) and the linear light detector (105) are positioned such that overlapping of the shadows on the linear light detector is avoided.

9. The system according to claim 8 characterized in that it further comprises a display or a transmitter of data (505) allowing for outputting the determined data.

10. The system according to claim 8 characterized in that the light emitter (101) is smaller than the diameter of the object (103).

11. A shooting target frame characterized in that it comprises the system according to claim 9.

12. A computer program comprising program code means for performing all the steps of the computer-implemented method according to any of claim 1 when said program is run on a computer.

13. A computer readable medium storing computer-executable instructions performing all the steps of the computer-implemented method according to any of claims 1 when executed on a computer.

Drawing