WO2017178779A1

WO2017178779A1 - Calibrating an indoor and outdoor position measurement system

Info

Publication number: WO2017178779A1
Application number: PCT/GB2017/000049
Authority: WO
Inventors: Florin STROIESCU; Alan Clarke; Sean O'connor; Valerui Emanuel IONITA
Original assignee: Statsports Group Limited
Priority date: 2016-04-11
Filing date: 2017-03-30
Publication date: 2017-10-19

Abstract

A beacon for use in a system for measuring the position of one or more object in an area of interest. The beacon has a signal generator, a transceiver for transmitting and receiving a signal from one or more additional beacons and a calibration module which determines the distance between the beacon, a second beacon and a third beacon, calculates the angle between the beacons and determines whether the calculated angle matches a predetermined angle. The beacon has a user interface located on the beacon or upon an external device which indicates whether the angle matches the predetermined angle and indicates the direction in which the beacon is to be moved in order that the angle matches. The present invention provides a reliable means by which the position measurement system may be set up and calibrated in order to improve its accuracy and reliability.

Description

Calibrating an Indoor and Outdoor Position Measurement System

Introduction The present invention relates to the calibration of a position measurement system for real time measurement of the position of one or more object and in particular to the calibration of systems for measurement of the position and movement of individuals participating in an activity such as a team sport. Background to the Invention

There are many situations where the real time precise measurement of the position of objects or persons is needed, such as in team and individual sports, inventory location, construction sites, security, surveying, and many others. In team sports, for example, the position and movement of individual players in the context of the team and the opposing team can provide valuable information on player and team performance. Other data such as player speed, distance covered, acceleration and player position is also very valuable. Obtaining this data requires the creation of highly accurate and reliable systems for measuring player position and movement.

There are a number of known systems and methods for position measurement for example.

Global Positioning System (GPS) is a space-based navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. However, such systems may not be used indoors. There are a number of mapping and surveying techniques for wireless signals such as Skyhook4, Wifarer 5, Google6. However, these are expensive, have limited precision, and need to be reconfigured whenever the local wireless router's network changes. The Decawave7 system uses wireless sensors networks in ultra-wide-band radio frequency range. In this case, there is a need to maintain the network mesh at all times.

The process of calculating a current position by Dead Reckoning uses a previously determined position or fix and calculates the current position using information on speed and direction of travel such as would be provided using accelerometers and

gyroscopes. These techniques lack precision.

Optical techniques such as the use of Light Emitting Diodes are also known. The Bytelight, system is a retail solution which works by locating shoppers and offering up timely info on the back of an awareness of their proximity to the beacon; such systems require a perfect line of sight for their successful operation.

Another system for use indoors uses local beacons that have been precisely placed and which need to have very high precision clocks to provide the required level of positional accuracy. In some cases, expensive time-of-flight based devices, using extremely precise timing circuits are used. However, these are hard to accurately deploy and calibrate.

Summary of the Invention

It is an object of the present invention to provide a reliable means by which the position measurement system may be set up and calibrated in order to improve its accuracy and reliability. In accordance with a first aspect of the invention there is provided a beacon for use in a system for measuring the position of one or more object in an area of interest, the beacon comprising:

A signal generator for generating a signal;

A transceiver for transmitting said signal and receiving a signal from one or more additional beacons;

A calibration module which;

Determines the distance between the beacon, a second beacon

and a third beacon;

calculates the angle between the beacons; and

determines whether the calculated angle matches a predetermined angle;

Wherein the beacon has a user interface which indicates whether the angle matches the predetermined angle and indicates the direction in which the beacon is to be moved in order that the angle matches.

Preferably, the user interface is a visual interface.

More preferably, the user interface is a screen which displays a graphical user interface.

Preferably, the user interface further comprises an audio interface.

Preferably, the graphical user interface is displayed on a screen located upon the beacon.

Optionally, the graphical user interface is displayed on a screen located upon a computing device such as a smart phone, portable media player, tablet or laptop computer. Preferably, the calibration module comprises a processor which determines whether the calculated angle matches by calculating the locus of points between the beacon and the second beacon which creates the predetermined angle with respect to the line between the second beacon and the third beacon and determines whether the point where the beacon has been positioned is on the locus of points for the predetermined angle.

Preferably, the predetermined angle is 90°. Preferably, the calibration module applies Pythagoras's theorem where the

predetermined angle is 90°.

Preferably the positioning beacon is independent of data communication equipment and/or data beacons.

Preferably, the signal is a radio frequency signal.

More preferably, the signal is an ultrawideband signal. In accordance with a second aspect of the invention there is provided a method for calibrating the position of at least three beacons in a system for measuring the position of one or more object in an area of interest, the method comprising the steps of:

Determining a first distance between a second beacon and a third beacon;

Determining a second distance between the beacon and the second beacon calculating the angle between the beacons; and

determining whether the calculated angle matches a predetermined angle

indicating whether the predetermined angle matches the calculated angle and indicating the direction in which the beacon is to be moved in order that the calculated angle matches a predetermined angle. Preferably, the step of indicating whether the predetermined angle matches the calculated angle is provided by a user interface Preferably, the user interface is a visual interface.

More preferably, the user interface is a screen which displays a graphical user interface. Preferably, the user interface is an audio interface.

Preferably, the step of determining whether the calculated angle matches a

predetermined angle comprises:

calculating the locus of points between the beacon and the second beacon which creates the predetermined angle with respect to a line between the second beacon and the third beacon and determining whether the point where the second beacon has been positioned is on the locus of points for the predetermined angle.

predetermined angle is 90°.

Brief Description of the Drawings

The present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a beacon in accordance with the present invention showing a user interface; Figure 2 is a diagram which illustrates the calibration of the position of a third beacon in accordance with the present invention;

Figure 3 is a diagram which illustrates the calibration of the position of a fourth beacon in accordance with the present invention;

Figure 4 is a diagram which illustrates the second stage of the calibration of the position of a fourth beacon in accordance with the present invention;

Figure 5 is a schematic diagram of in a position measurement system.;

Figure 6 is a schematic diagram which shows the architecture ofa position

measurement system;

Figure 7 is a schematic diagram which shows the architecture of a position

measurement system;

Figure 8 is a schematic diagram which shows the architecture of a position

measurement system; Figure 9 is a diagram which shows a position measurement system;

Figure 10 is a diagram which shows a position measurement system;

Figure 11 is a system pulse diagram; Figure 12 is a diagram showing an object position calculation

Figure 13 illustrates the calculation of portable tag position using the intersection of parabolas; and

Figure 14 illustrates the parabola determined by distance "m" (or the inferred delay) as a geometric place where "m" is constant; Figure 5 is a schematic diagram which shows a position measurement system in which the fixed beacons may function as primary and secondary beacons;

Figure 16 is a schematic diagram which shows the system of figure 14 with beacon A configured to function as the primary beacon and beacons B and C configured to act as the secondary beacons;

Figure 17 is a schematic diagram which shows the system of figure 14 with beacon C configured to function as the primary beacon and beacons D and A configured to act as the secondary beacons;

Figure 18 is a schematic diagram which shows the system of figure 11 with beacon D configured to function as the primary beacon and beacons B and C configured to act as the secondary beacons; and Figure 19 is a schematic diagram which shows the system of figure 1 with beacon B configured to function as the primary beacon and beacons D and A configured to act as the secondary beacons.

Detailed Description of the Drawings The present invention relates to the installation of beacons at or near an area of interest where the measurement of the position of one or more portable tags is to be made. In this embodiment of the invention the beacon has a software module which assists with the position of the beacon with respect to two other beacons. It will be appreciated that all of the beacons may be provided with the software and user interface. In order to assist the fast installation of the beacons, the beacons have an installation procedure designed inside. In this procedure, the distance between each pair of beacons is measured, and assists the installation operator to correctly position each of the beacons.

Figure 1 is a schematic diagram of a beacon in accordance with the present invention showing the user interface which assists a user in accurately deploying the beacon.

The beacon 101 has a screen 102 which displays a graphical user interface comprising an illustration of, in this example, a sports pitch 103.

The graphical user interface on the screen 102 gives an indication of the beacon position on the pitch 104 and shows an arrow 105 which indicates the direction in which it is necessary to move the beacon in order to reach the optimum position. The arrow 105 changes length and direction as the beacon is moved around the required position, and it is reduced to a circle when the exact position is reached.

In other embodiments of the present invention, the screen may be the screen of a computing device and the graphical user interface may be part of a software application which is downloadable upon the portable computing device. Examples of such devices include mobile devices such as mobile phones, portable media players, tablet computers and lap top computers. Figure 2 depicts the installation of the third beacon C after the positioning of two beacons A and B, along one side of the monitored pitch. The user interface on the screen of beacon C indicates the direction in which the beacon should be moved in order to match the predetermined angle between the three beacons.

In this example of the invention, the angle between the beacons is 90° which means that the straight lines connecting the three beacons form a right angled triangle and Pythagoras's theorem is used to define the correct position on the beacon by verifying that the position of the beacon matches a set of points which coincide with the values given by the equation: c = (a² + fe²) (1)

In cases where the position of the beacon does not match values given by the equation, the screen shown in figure 1 shows the operator in which direction the beacon is to be moved in order to achieve a match. The positioning is directed on a single axis in this case, parallel with axis a, as the operator is free to choose the width of the pitch.

Figures 3 and 4 depict the installation of the fourth beacon, that will need to verify twice equation (1). The positioning is on two axes, in two separate steps. Figure 3 shows the first stage, where the operator is directed to move the beacon parallel with axis a, in order to verify the Pythagoras equation for corners A, B and D. Figure 4 shows the second stage, where the operator is directed to move the beacon parallel with axis b, in order to verify the Pythagoras equation for corners A, C and D. More than four beacons can be installed in order to cover more complex or larger pitches, the rotating beacon apparatus and technique permitting easy installation, fast deployment and reliable measurements of the position of the portable tags. Preferably for complex installation, separate positioning and data beacons are provided. The positioning beacons can be independent of data communication equipment, and the data beacons are linked to communication networks providing real time data from the monitored portable tags. An unlimited number of portable tags can coexist in the pitch area, each recording its own coordinates and other physical data.

In order to assist in the understanding of the present invention examples of position measurement systems with which the present invention may be used are provided.

The example of figure 5 is shown deployed for use on a sports pitch having area A, the area of interest. In this example, the system comprises a primary beacon 1 positioned near the side of area A, a secondary beacon 2 positioned on the same side of area A as the primary beacon 1 and a secondary beacon 3 positioned on the opposite side of area A from primary beacon 1 and secondary beacon 2. In this example, secondary beacons 2, 3 are spaced from primary beacon 1 in such way that straight lines connecting their position would form a right angled triangle. Other locations for the beacons may be used insofar as a direct line of sight is maintained between the beacons.

Portable tags or wearable receivers 4 are shown within the area of interest A. In this example, a portable tag has been attached to three separate players. During a game, the players may move around the area of interest A and the portable tags 4 receive signals transmitted from the primary beacon 1 and the secondary beacons 2, 3. In this and other embodiments, on the data channel, the portable tags are able to transmit, back to the primary beacon and/or secondary beacons, information such as own position, kinematics data, and /or any other physical measurements data. In the context of a sports pitch where players may be in close contact in front of and around one another, and whilst the degree to which a line-of-sight is maintained may be sufficient to allow the system to operate successfully, switching beacon function as in the present invention provides a solution to this problem.

Distance and position measurement signals from the signal generator are sent over a dedicated radio channel or data channel integrated in the time referenced primary pulses and echo pulses.

Where a dedicated radio channel is used it may employ a standard protocol (802.15.4, ZigBee, WiFi radio modem) for data transmission. This may include positioning data feedback and other metrics relating to player movement and health such as player speed, acceleration, deceleration, temperature and heart rate.

In other embodiments of the invention more radio channels may be used and, the time- of-flight integrated data channel may use another radio channel and/or protocol.

Figure 5 allows the calculation of the position of a number of objects in an area of interest where the object is fitted with a portable tag 4.

In order to calculate the position of each of the portable tags 4, the primary beacon 1 is positioned at a first fixed position at the side of the sports pitch A. As described in more detail with reference to figure 6 the primary beacon 1 has a signal generator, a transceiver for sending the signal to the secondary beacons 2, 3 and to the portable tags 4 and a data receiver.

The secondary beacons 2, 3 are located at separate fixed locations at the side of the pitch. As described in more detail with reference to figure 7, the secondary beacons each comprise a signal generator, a second transceiver for sending and receiving the signal to the portable tags 4 and to the primary beacon 1. The secondary beacons 2, 3 further comprise data transceivers which receive and transmits data relating to the operation of the secondary beacon. As described in more detail with reference to figure 8, the portable tags 4 comprise a transceiver operating for receiving and sending a signals from the primary beacon 1 and/or the secondary beacons 2, 3 and a data transceiver which receives and transmits data relating to the operation of the portable tag. The primary beacon, is connected to a computer that processes data received from the other components of the system over the secondary channel, which is unrelated to tag position. The distance between one of the portable tags 4 and the primary and secondary beacons is calculated by measuring the time it takes for a signal round trip from the portable tag to primary and secondary beacons using a Time-of-Flight calculation. The data channel is used to transmit the internal delay 33 and which corrects the Time of Flight value and provides a more accurate calculation of the position of the portable tag. The secondary beacons can be connected to computer if data transmission needs to be enlarged. Figure 6 is a schematic diagram which shows the architecture of the primary beacon used in the example of figure 5.

Figure 6 shows a microcontroller 5 which controls the functionality of the primary beacon and is connected to a host computer via the microcontroller interface 6. The first signal generator comprises a high frequency oscillator 7 which, oscillates continuously and which is switched by the fast switch 8 to produce time referenced trains of pulses which are transmitted to the secondary beacons and the portable tags through the antenna 9. The time-of-flight receiver 10 records accurately the time when the pulses are sent from the primary beacon 1 , and the time when the response time-of-flight pulses sent from the secondary beacons and/or the portable tags are received using antenna 11. The timing errors of the fast switch 8 are corrected using the pulse time delay information in the time-of-flight receiver. The data, including positioning data from the secondary beacons, and from the wearable receivers in the field are communicated via data transceiver 12 and antenna 13. Figure 7 is a schematic diagram which shows the architecture of an example of a secondary beacon.

The microcontroller 14 controls the functionality of the secondary beacon. The microcontroller may communicate with a host computer via the microcontroller interface 16. Index reference 15 uniquely identifies the secondary beacon in the system so as to distinguish between individual secondary beacons. The system has a high frequency oscillator 17, oscillating continuously, which is switched by the fast switch 8 to send to the other components of the system time reference (trains of) pulses through the antenna 19. The time-of-flight receiver 20 records accurately the time when the pulses received from the primary beacon are received, and the time when the response time- of-flight pulses are sent using antenna 21.

The inherent timing errors of the fast switch 18 are masked by using the reference in the time-of-flight receiver. The data, including timing information for the pulses received and sent are communicated via data transceiver 22 and antenna 23.

Figure 8 is a schematic diagram which shows the architecture functionality of an example of the wearable device or portable tag in accordance with the present invention. The microcontroller 24 uses the index reference 25 for uniquely identifying the device to the system. The time-of-flight receiver 26 records accurately the difference in time between the pulses received from the main and the secondary beacons. These pulses are received using antenna 27. The data, including information comprising of own position, kinematics data, and /or any other physical measurements data are communicated via data transceiver 28 and antenna 29.

In the above example, the core components of the system are consistent across the primary beacon, the secondary beacons and the portable tags and comprises a circuit that is able to precisely measure the interval between several events, and then report it back to the local microcontroller. This is the time-of-flight receiver, based on a time to digital converter {TDC). The converter is able to measure the delay between two or more pulses.

Time-of-flight may be measured as the time that the signal travels between a primary beacon to the secondary beacon, and then back.

In figure 9, the intersection between line 30 and the vectors represents the primary beacon events. The intersection between line 31 and the vectors represents the secondary beacon events. The primary beacon transmits a pulse which is transmitted to the second beacon in the time interval 32, the secondary beacon sends back an echo with an un-avoidable time delay 33, which takes to transmit to the primary beacon the interval 34, equal with the interval 32 if the beacons are stationary. By measuring the round-trip time 35, and knowing the delay 33, the effective time of flight and the distance between the beacons can be computed.

In order to avoid measurement errors, the primary beacon measures the round trip (32)+(33)+(34) = (35) as the delay between the sending of the pulse, and the receiving of the echo, measured as well with the time- flight-receiver. The time-of-flight receiver has a Start input, triggered by the emerging pulse, and a Stop input triggered by the reception of the echo pulse. In this way the time-of-flight is accurately measured, without the intervention of the microcontroller, which is too slow to give accurate results for such fast processes.

The time delay 33 cannot be easily controlled, and with standard microcontroller techniques jitter of over 20 ns, or even 100 ns are expected. These delays can easily produce calculated errors between 3 and 15 m, or even bigger when other perturbing factors are considered. In order to compensate for this arbitrary delay, the time-of-flight receiver on the secondary beacon measures the effective delay between the emergent primary beacon to secondary beacon pulse reception, and the echoed pulse from the secondary beacon to the primary beacon. This measured delay is then transmitted over the data channel back to the primary beacon, which has now the means to calculate the effective time-of-flight of the pulse.

The calculated distance is:

D = (T(35) - T(33))*c/2 where:

D is the distance between the beacons;

T(35) is the time measured for the round trip;

T(33) is the time transmitted back, via the data channel, to the primary beacon; c is the speed of light in air (for terrestrial measurements, 299,705,000 m/s). Figure 10 is a diagram which shows a compensated time of flight measurement which relates to clock errors. Another perturbing factor is the fact that the frequency of the clocks of the time-of-flight receivers can differ or drift. This can be compensated by sending two pulses from the primary beacon, and comparing the delay between these pulses measured on the primary beacon and measured on the secondary beacon. In figure 10, the intersection between line 30 and the vectors represents the primary beacon events. The intersection between line 31 and the vectors represents the secondary beacon events.

Considering that the distance between the beacons is the same as in the case of figure 9, the delay 32 is the same. In the ideal case, the delay 36 measured between the two pulses sent from the primary beacon, and the delay 37 measured between the reception of the two pulses on the secondary beacon shall be equal. However, the drift or difference in frequency between the two beacons can account for different values measured. In this case, sending back on the data channel the value of the time delay 37 can be used for correcting the time delay 33, this improving the precision of the time-of- flight measurement. Applying the described techniques, the distance between the beacons can be accurately calculated as:

D = (T(35) - T(33)*T(36)/T(37)) * c I 2 where:

D is the distance between the beacons;

T(35) is the time measured for the round trip;

T(32) is the time transmitted back, via the data channel to the primary beacon;

T(36) and T(37) are the delays between the primary beacon reference pulses, measured by the primary beacon, and respectively measured by the secondary beacon; c is the speed of light in air (for terrestrial measurements, 299,705,000 m/s). The wearable receivers are receiving the pulses from all the beacons, measuring the delay between the main beacon pulse, and the secondary beacons pulses. The pulses diagram for the whole system is depicted in figure 11. For simplicity reasons, only the standard time-of-flight technique is depicted here, but corrections as for clock frequency errors may be included.

The intersection between line 30 and the vectors represents the primary beacon events. The intersection between line 31 and the vectors represents the first secondary beacon events. The intersection between line 39 and the vectors represents the second secondary primary events. The intersection between line 40 and the vectors represents one of the wearable devices events (the wearable device is not transmitting on the timing channel).

The interval 41 is the first secondary beacon round trip, while the interval 42 is the delay in the first secondary beacon. Using 41 and 42 the distance between the primary beacon and the first secondary beacon can be calculated, as shown above.

The interval 43 is the second secondary beacon round trip, while the interval 44 is the delay in the second secondary beacon. Using 43 and 44 the distance between the primary beacon and the second secondary beacon can be calculated, as shown above.

The interval 45 is the delay between the reception of the primary beacon pulse received by the wearable device, and the reception of the first secondary beacon pulse. The interval 46 is the delay between the reception of the first secondary beacon pulse received by the wearable device, and the reception of the second secondary beacon pulse. These intervals are used to calculate the position of the portable tag in relative to the beacons. Any number of portable tags can be included in the system and each can calculate its own position using the primary beacon pulses, secondary beacon echo and delay signals. Arranging the beacons in a perpendicular manner as shown in figure 12 allows for the calculation of the position of each of the wearable devices relative to the primary beacon from the positioning data transmitted to the tag. Using 4 beacons, the position of the wearable device can be calculated with arbitrary positioning of the beacons. Figure 8 depicts a geometric representation that applies to the calculation of the position of the receiver.

In figure 12, A is the position of the primary beacon, considered to be the origin of the coordinates system, B and C are positions of the secondary beacons, and E is the position of the wearable receiver. The position of the wearable receiver (x,y) is the solution of the equations system shown below

The solution of the above equations system is the intersection of two parabolas in the pitch area, and it is calculated on each of the portable tags in the area. Figure 13 is the representation of the intersection of the two parabolas. Determining the position of the tags. The parabola "p" is determined by the delay "m", representing the geometric place of all the points that have the common distance difference between the primary beacon A and the secondary beacon C. The parabola "q" is determined by the delay "d", representing the geometric place of all the points that have the common distance difference between the primary beacon A and the secondary beacon B. The common distance difference translates, in terms of time- of-flight, in constant delay between the two receiving signals.

Figure 14 depicts the parabola determined by the common distance difference "m" (or the inferred delay) as a geometric place where "m" is constant.

A pre-calculated lookup table is created containing the delays in each of the divisions of the pitch (as example 10x10 cm for a pitch of 100x100m) is recorded in each of the portable tags and used with a fast converging halving algorithm to efficiently determine the relative position of the portable tag compared to the position of the primary and secondary beacons. A scaling method was designed, so the pre-calculated table can be scaled independently on each of the axes corresponding to the distance measured between the primary and secondary beacons. More, a single lookup table is sufficient for both axes.

Figure 15 a four beacons system that enhances the reliability and the precision of the system by allowing each beacon in the system to switch from having primary beacon functionality to secondary beacon functionality. Figure 15 shows an area of interest which in this example is a sports pitch with beacons A, B, C and D positioned at the corners of the pitch.

In this system, the role of primary beacon is taken alternatively by each of the beacons from the corner of the pitch, secondary beacons being the beacons from the adjacent corners. The role of the primary beacon is rotated or switched in time between the beacons in the system. In this way, four groups of (x,y) coordinates can be calculated for the position of each portable tag. The position of the tag is calculated using an average of the coordinate values, so as to increase the reliability of the position measurement.

In addition, measuring the position of the tag from multiple primary beacon positions is useful where a temporary obstruction obscures the line of between one or more of the beacons and the portable tag. , tin effect, movement of the primary beacon function between beacons in the system rotates the coordinates system from which the portable tag's position is measured in every cycle of the measurement. In one embodiment, ten full cycles are performed per second, but any frequency is possible depending upon the processing power of the system components.

Figure 16 depicts the configuration of the system when beacon A is primary, and beacons B and C are secondary. As example, this way the first set of coordinates x and y of the tag are computed.

Figure 7 depicts the configuration of the system when beacon C is primary, and beacons A and D are secondary. As the same example as in figure 16, this way coordinates x and b-y of the tag are computed, and the second set of coordinates x and y are computed.

Figure 18 depicts the configuration of the system when beacon D is primary, and beacons B and C are secondary. As the same example as in figure 16, this way coordinates a-x and b-y of the tag are computed, and the third set of coordinates x and y are computed.

Figure 19 depicts the configuration of the system when beacon B is primary, and beacons A and D are secondary. As the same example as in figure 16, this way coordinates a-x and y of the tag are computed, the fourth set of coordinates x and y are computed. Averaging over the four sets of coordinates obtained this way increases the precision of the measurement. This arrangement and design of the beacons and portable tags takes eight round trips of signal/echo to perform, having an increased reliability and precision. However, if the data channel is used over the same frequency, this procedure congests the

transmission and computing time, and two redundant parabolas are created for each beacon pair.

A system may be adopted which uses a simplified measurement sequence which uses less bandwidth. In this example of the invention, in which the beacons create a single delay measurement for each beacon pair, so only four round trips are necessary, creating a single delay measurement and a single parabola for each beacon pair. This arrangement and design of the beacons and portable tags is is less accurate than the eight round trips arrangement, but much more stable than the three beacons system descripted at the start of this patent application.

The precise arrangement of the beacons in a rectangle makes the measuring process simpler and less prone to errors.

The principle of switching the functionality of the beacons may be extended to operate in areas of interest in which the beacons are positioned in a shape other than a right angled parallelogram and the number of beacons may be any number greater than four. For example, the beacons may define a pentagonal or hexagonal shape with five or six beacons respectively at the vertices. In another example, eight beacons may be used and positioned at the vertices of a hexagon. In these examples, the system can operate by calculating the position of the portable tag using adjacent beacons, which will be at 108° for the pentagonal shape and 120° for the hexagonal shape. Alternatively, four beacons which form a right angled

parallelogram can be selected to calculate the portable tag position.

The present invention provides an improved calibration system that greatly assists the operator in quickly and accurately deploying the beacons which form the positioning measurement system. Improvements and modifications may be incorporated herein without deviating from the scope of the invention.

Claims

1. A beacon for use in a system for measuring the position of one or more object in an area of interest, the beacon comprising:

a signal generator for generating a signal;

a calibration module which

Determines the distance between the beacon, a second beacon

and a third beacon;

calculates the angle between the beacons; and

determines whether the calculated angle matches a predetermined angle; . Wherein the beacon has a user interface which indicates whether the angle matches the predetermined angle and indicates the direction in which the beacon is to be moved in order that the angle matches.

2. A beacon as claimed in claim 1 wherein, the user interface is a visual interface.

3. A beacon as claimed in claim 1 or claim 2 wherein, the user interface is a screen which displays a graphical user interface.

4. A beacon as claimed in claim 3 wherein, the graphical user interface is displayed on a screen located upon the beacon.

5. A beacon as claimed in claim 3 wherein, the graphical user interface is displayed on a screen located upon a computing device such as a smart phone, portable media player, tablet or laptop computer.

6. A beacon as claimed in any preceding claim wherein, the user interface further comprises an audio interface.

7. A beacon as claimed in any preceding claim wherein, the calibration module comprises a processor which determines whether the calculated angle matches by calculating the locus of points between the beacon and the second beacon which creates the predetermined angle with respect to the line between the second beacon and the third beacon and determines whether the point where the beacon has been positioned is on the locus of points for the predetermined angle.

8. A beacon as claimed in any preceding claim wherein, the predetermined angle is 90°.

9. A beacon as claimed in claim 8 wherein, the calibration module applies

Pythagoras's theorem where the predetermined angle is 90°.

10. A beacon as claimed in any preceding claim wherein the positioning beacon is independent of data communication equipment and/or data beacons.

1 1. A method for calibrating the position of at least three beacons in a system for measuring the position of one or more object in an area of interest, the method comprising the steps of:

Determining a first distance between a second beacon and a third beacon;

Determining a second distance between the beacon and the second beacon calculating the angle between the beacons and

determining whether the calculated angle matches a predetermined angle

indicating whether the predetermined angle matches the calculated angle and indicating the direction in which the beacon is to be moved in order that the calculated angle matches a predetermined angle.

12. A method as claimed in claim 11 wherein, the step of indicating whether the predetermined angle matches the calculated angle is provided by a user interface

13. A method as claimed in claim8 or claim 11 wherein, the user interface is a visual interface.

14. A method as claimed in claims 1 1 to 13 wherein, the user interface is a screen which displays a graphical user interface.

15. A method as claimed in claim 14 wherein, the graphical user interface is displayed on a screen located upon the beacon.

16. A method as claimed in claim 14 wherein, the graphical user interface is displayed on a screen located upon a portable computing device such as a smart phone, tablet or laptop computer.

17. A method as claimed in claims 1 1 to 16 wherein, the user interface further comprises an audio interface.

18. A method as claimed in claims 11 to 17 wherein, the step of determining whether the calculated angle matches a predetermined angle comprises:

19. A method as claimed in claim 11 to 18 wherein, the predetermined angle is 90°.

20. A method as claimed in claims 11 to 19 wherein, the calibration module applies Pythagoras's theorem where the predetermined angle is 90°.

21. A method as claimed in claims 1 1 to 20 wherein the positioning beacon is independent of data communication equipment and/or data beacons.