WO2018229030A1

WO2018229030A1 - Method for calculating a position and possibly mapping of a space-related variable by means of acoustic signals and corresponding apparatus for implementing the method

Info

Publication number: WO2018229030A1
Application number: PCT/EP2018/065453
Authority: WO
Inventors: Paolo GUIDORZI
Original assignee: Alma Mater Studiorum - Universita' Di Bologna
Priority date: 2017-06-14
Filing date: 2018-06-12
Publication date: 2018-12-20
Also published as: IT201700066160A1

Abstract

Method for calculating a position and possible mapping of a space-related variable by means of acoustic signals, comprising the following steps: providing at least three position emitters (A, B, C, D) with known relative position at a three-dimensional measuring space and at least one acoustic receiver (R) located at a not known distance (D1, D2, D3, D4) from each of said position emitters (A, B, C, D); making each position emitter (A, B, C, D) emit a position acoustic signal (X1, X2, X3, X4); acquiring by means of the acoustic receiver (R) a received acoustic signal (J) comprising contributions associated with the individual position acoustic signals (X1, X2, X3, X4); obtaining a position identification signal (H1, H2, H3, H4) for every position acoustic signal (X1, X2, X3, X4); obtaining, from the position identification signals (H1, H2, H3, H4), the time of flight (T1, T2, T3, T4); calculating the distances (D1, D2, D3, D4) starting from the times of flight (T1, T2, T3, T4); calculating the position (P) of the acoustic receiver (R) in the three- dimensional measuring space starting from said distances (D1, D2, D3, D4).

Description

Title: Method for calculating a position and possibly mapping of a space- related variable by means of acoustic signals and corresponding apparatus for implementing the method

DESCRIPTION Field of the invention

The present invention relates to a method for calculating a position and possible mapping of a space-related variable by means of acoustic signals and an apparatus for implementing the above-mentioned method.

The invention may be employed in applications wherein it is necessary to measure and save the exact positioning in the three-dimensional space of an object. In particular, it may be employed to create a three-dimensional planimetry, for example of a room, a building or an archaeological site.

Furthermore, the invention can be employed in applications wherein it is necessary to obtain the value of a physical quantity varying with position and to obtain a mapping of the value in the space. In particular, it can be used in the field of acoustics to obtain the acoustic field in a specific environment or the acoustic properties of a material.

Prior art

In the technical field of the present invention, as it is known, complex position detection systems of a three-dimensional space are employed, which use optical devices such as laser or cameras.

The systems using radio waves are also known in the field, such as the GPS system (global positioning system) which uses a dedicated network of artificial satellites transmitting radio signals to a receiver, which provides geographical coordinates of the receiver itself by applying trilateration calculations.

Even though they are advantageous under many aspects and substantially meet nowadays needs of this field, the position detection systems known in the art are quite expensive and have low accuracy level in some cases, for example the GPS system. Furthermore, the GPS system frequently does not work properly if used indoor or generally in areas implying the presence of obstacles, which do not allow the radio waves to pass between the satellites and the receiver.

Furthermore, the known systems do not allow further processing of the position data, for example in terms of obtaining a mapping of a variable related to the measurement of the position.

The technical problem underlying the present invention is thus to conceive a method for calculating the position in a three-dimensional space, which allows to overcome the drawbacks of the prior art and is particularly easy and cost-effective to implement, and to ensure an exact measurement even indoor.

Summary of the invention

The solution idea underlying the present invention is to conceive a system comprising emitters of acoustic signals discriminable from each other (for example decoded from a different pseudo-random sequence) and a receiver of such signals that, after processing the received signals, allows to calculate the 3D position of the receiver itself and possibly to associate the value of a physical quantity to the position.

Based on such solution idea, the above-mentioned technical problem is solved by a method for calculating a position and possible mapping of a space-related variable by means of acoustic signals, comprising the following steps: providing at least three position acoustic emitters with known relative position at a three-dimensional measuring space; - providing at least one acoustic receiver located at a not known distance from each of said position acoustic emitters into the three-dimensional measuring space; making each position acoustic emitter emit a position acoustic signal, the position acoustic signals being discriminable from each other; - acquiring a received acoustic signal by means of the acoustic receiver, the received acoustic signal comprising contributions associated with the individual position acoustic signals; obtaining a position identification signal for each position acoustic signal starting from the received acoustic signal; obtaining the time of flight that each position acoustic signal spent to travel the distance between the position acoustic emitter and the acoustic receiver by means of analysis of said position identification signals; calculating the distances starting from the times of flight; calculating the position of the acoustic receiver in the three- dimensional measuring space starting from said distances. Advantageously the method according to the invention can further comprise the following steps: providing, also the three-dimensional measuring space, a test acoustic emitter; making the test acoustic emitter emit a test acoustic signal discriminable from the position acoustic signals; the received acoustic signal comprising a contribution associated even with the test acoustic signal; obtaining a test identification signal related to the test acoustic signal starting from said received acoustic signal; obtaining the value of a physical quantity different from the time of flight that the test acoustic signal spent to reach the acoustic receiver, such as the level of sound pressure of the test acoustic signal, starting from the test identification signal.

The physical quantity is calculated starting from the test identification signal, preferably obtained by a test acoustic emitter different from the other emitters used for calculating the distance. Optionally, it is possible to use one of the position acoustic emitters as a test acoustic emitter.

The method according to the invention can further comprise the steps of: providing a transducer in the same position of the acoustic receiver; detecting the value of a physical quantity at the previously calculated position of the acoustic receiver by means of said transducer; wherein the transducer is, for example, a temperature transducer and the physical quantity is the temperature measured by the transducer located at the position of the acoustic receiver.

The steps of acquiring the received acoustic signal; obtaining the position identification signals; obtaining the times of flight; calculating the distances; and calculating the position; they can be cyclically repeated while the acoustic receiver moves into the three-dimensional measuring space in order to detect a topographical or architectural feature.

Namely, the method of the present invention can be advantageously employed to perform real-time position measurements intended for example to create planimetries of rooms, buildings or geological and archaeological sites. The steps of acquiring the received acoustic signal; obtaining the position identification signals and the possible test identification signal; obtaining the times of flight; and obtaining or detecting the value of the physical quantity; can be cyclically repeated with the acoustic receiver located in different positions for mapping the value of the physical quantity within the three-dimensional measuring space.

As a skilled person will easily understand, by varying the position of the acoustic receiver it is possible to obtain the real-time level of sound pressure, at different points of the three-dimensional measuring space, thus obtaining the acoustic field in the measured environment. In the event that a transmitter coupled with the acoustic receiver is used, by moving the acoustic receiver it is possible to obtain in real time a mapping of the physical quantity measured by the transducer in the measurement environment. Particularly, if the transducer measures the temperature, the value of such physical quantity can be obtained when the position varies.

Advantageously, the position acoustic emitters and the respective position acoustic signals are in the number of four, possibly arranged in a not coplanar manner. Such configuration allows to obtain a univocal measurement of the position of the acoustic receiver. However, in order to obtain the coordinates identifying the position of the acoustic receiver, three position acoustic emitters can be sufficiently employed, provided that a suitable configuration thereof and a suitable measurement geometry are used. In so doing, only one out of the two possible obtained positions will fall within the three-dimensional measuring space and will be considered valid to identify the position of the acoustic receiver.

Advantageously, each of the position acoustic signals is decoded from a different pseudo-random sequence, each position identification signal is further preferably obtained by applying the fast Hadamard transform.

The fast Hadamard transform allows to calculate the signal in an accurate, fast and efficient manner.

Furthermore, the method according to the invention can comprise a step of analysing each identification signal, which consists in distinguishing the component of the identification signal actually due to the position acoustic signal by identifying the characteristic peak with the impulse response obtained applying the Hadamard transform by implementing the following steps: - searching, along the time axis of each impulse response, the peak with maximum amplitude in absolute value; identifying the characteristic peak with the first peak of amplitude greater than a threshold proportional to the amplitude of the background noise moving from left to right along the time axis of each impulse response. Advantageously the method can further comprise the steps of: calculating a signal/ noise ratio as the ratio between the amplitude of the peak with maximum amplitude in absolute value and an indicative amplitude of the background noise; validating the measurement only where the signal/ noise ratio exceeds a predetermined threshold value.

The analysis of the identification signal described previously allows thus to discriminate the useful signals from a possible noise due to the movement of the receiver and/ or reverberation phenomena and possibly to set aside the measurements in case the noise is too high.

The technical problem is also solved by a measuring apparatus comprising: - at least three position acoustic emitters adapted to be located with a known relative position at a three-dimensional measuring space; at least one acoustic receiver adapted to be located and possibly moved into the three-dimensional measuring space; a computerized system connected to the position acoustic emitters and to the acoustic receiver so as to send and receive signals from them, the computerized system implementing a software adapted to:

• making each position acoustic emitter emit a position acoustic signal, the position acoustic signals being discriminable from each other;

• acquiring a received acoustic signal by the acoustic receiver, the received acoustic signal comprising contributions associated with the individual position acoustic signals;

• obtaining a position identification signal for each position acoustic signal starting from the received acoustic signal;

• obtaining the time of flight that each position acoustic signal spent to travel the distance between the position acoustic emitter and the acoustic receiver by means of analysis of said position identification signals;

• calculating the distances starting from the times of flight;

• calculating the position of the acoustic receiver in the three- dimensional measuring space starting from the distances. The features and advantages of the method and the apparatus of the present invention will be apparent from the description, made hereafter, of a preferred embodiment, given by indicative and non-limiting example, with reference to the accompanying drawings.

Brief description of drawings Figure 1 shows a photographic image of part of the components of the measuring apparatus according to the present invention; figure 2 shows a schematic representation of the measuring apparatus according to the present invention located into three-dimensional measuring space;

Figures 3 and 4 show two different views of a reproduction of the position acoustic emitters A, B, C, D of the measuring apparatus of figure 2 and the three-dimensional measuring space wherein points are represented, whose position is measured by moving the acoustic receiver until almost the entire length of one side of the three-dimensional measuring space parallel to the axis X is covered.

Figures 5 and 6 show two different views of a reproduction of the position acoustic emitters A, B, C, D of the measuring apparatus of figure 2 and the three-dimensional measuring space wherein points are represented, whose position is measured by moving the acoustic receiver until almost the entire length of one side of the three-dimensional measuring space parallel to the axis X is covered.

Figure 7 shows an example of graphic interface of the software implemented in the computerized system of the measuring apparatus of figure 2, wherein impulse responses considered valid by the analysis protocol are shown.

Figure 8 shows an example of graphic interface of the software implemented in the computerized system of the measuring apparatus of figure 2, wherein one of the impulse responses has such a high noise, it could not be considered valid by the analysis protocol, and so the measurement of the current position is set aside;

Figure 9 shows a summary block diagram of the signals and the components of the measuring apparatus of figure 2 employed in the method of the present invention. Detailed description of a preferred embodiment

With reference to the above-mentioned figures, and in particular to figures 1 and 2, an apparatus for measuring the position in a generic three- dimensional measuring space 10 by acoustic waves is globally indicated by 1. The phrase "measuring space" identifies an ideal volume not necessarily delimited, within which the measurement is performed. It can optionally be an internal or external space. The measuring apparatus 1 firstly comprises a plurality of position acoustic emitters A, B, C, D of acoustic signals, which in the explanatory embodiment described here are in the number of four and consist of simple speakers provided with respective amplifiers.

This does not exclude the use in alternative embodiments of a different type of emitters, such as for example piezoelectric transducers for ultrasound transmission.

As one may notice from figures 1 and 2, the above-mentioned position acoustic emitters A, B, C, D are placed at the vertices of a substantially flat support structure 20 which defines the perimeter of a square. Thus, the relative distance between the position acoustic emitters A, B, C, D is known and corresponds to the length of the sides of the square L.

The support structure 20 is in an elevated position with respect to the ground, is maintained in position by means of a support bar 21 connected to it; such support bar 21 is again stabilised to the ground by means of a tripod 22 and comprises adjustment means 23 to direct the support structure 10 in the space.

The measuring apparatus 1 further comprises an acoustic receiver R of acoustic signals, which in the explanatory embodiment described here consists of a microphone or microphone capsule. This does not exclude the use in alternative embodiments of a larger number and/ or different type of receiver, for example an ultrasound detector, in the event that also the emitters A, B, C and D are suitable for emitting ultrasounds.

It is observed that the configuration of the position acoustic emitters described above has emitters arranged on the same plane and so does not allow to discriminate between specular points with respect to the above- mentioned plane. An advantageous alternative is represented by a configuration wherein one of the position acoustic emitters does not lie on the same plane of the other three, thus ensuring a univocal measurement of the position of the acoustic receiver R.

In the accompanying figures, a Cartesian axis system X, Y, Z with origin O which identifies the three-dimensional measuring space 10 is defined.

The acoustic receiver R is located in a position P within the three- dimensional measuring space 10 which will have coordinates Px, Py, Pz not known with respect to the reference system X, Y, Z.

The position acoustic emitters A, B, C, D are instead located near the three- dimensional measuring space 10. In particular, as you may notice from figure 2, the support structure 20 is arranged orthogonal to the ground and lying on a plane identified by the axes X and Y and with two of the position acoustic emitters with position A, B aligned along the axis Y.

In an alternative embodiment the position acoustic emitters A, B, C, D can be of the omnidirectional type and be arranged within the three-dimensional measuring space 10.

Considered the above-mentioned configuration, each position acoustic emitter A, B, C, D will be at a not known prior distance Dl , D2, D3, D4 from the acoustic receiver R. The measuring apparatus 1 further comprises a computerized system C, wherein a multichannel sound card SA is integrated and on which a dedicated software for generating, acquire, and process signals and calculating signal-related physical quantities is implemented.

The output of the sound card SA is electrically connected to the position acoustic emitters A, B, C, D by means of as many amplifiers, whereas the input of the sound card SA is electrically connected to the acoustic receiver R, possibly by means of suitable preamplifier.

Using the simple above-mentioned apparatus, once the position of the position acoustic emitters A, B, C, D is known, it is possible to obtain the position P, namely the coordinates Px, Py, Pz, of the acoustic receiver R into the three-dimensional measuring space 10. Hereinafter, the method for performing the measurement of the position P of the acoustic receiver R will be described.

Firstly, pseudo-random sequences (also named maximum length sequences) MLS1 , MLS2, MLS3, MLS4, will be generated by means of the software in the same amount of the position acoustic emitters A, B, C, D, and with suitable time length. As a skilled person knows, the pseudorandom sequences are particular 0 and 1 digital sequences known in the field. They are deterministic signals having spectral characteristics similar to those of a white noise and are characterized by particular mathematical features. For the use described here, the 0 and 1 of the sequence are transformed into - 1 and 1 respectively.

Each pseudo-random sequence MLS1 , MLS2, MLS3, MLS4 is conveyed as input to the sound card SA which converts the digital signal into an electric signal, with suitable amplitude, which in turn is sent to a specific position acoustic emitter A, B, C, D. Each position acoustic emitter A, B, C, D will emit a position acoustic signal XI , X2, X3, X4 corresponding to the pseudo-random sequence MLS 1 , MLS2, MLS3, MLS4. Thanks to the properties of the pseudo-random sequences, the acoustic signals XI, X2, X3, X4 by the position acoustic emitters A, B, C, D are sounds similar to a rustle or white noise. The acoustic receiver R will receive the position acoustic signals XI, X2, X3, X4 that propagate in the three-dimensional measuring space 10 and will produce a corresponding electric signal sent in turn to the sound card SA.

The resulting digital signal, which will be identified as the received signal J, is obtained by the sum of the contributions linked to the individual position acoustic signals XI , X2, X3, X4. Alternatively, instead of simultaneously sending and detecting the position acoustic signals XI , X2, X3, X4, they can also be sent and detected individually and spaced over time; in this case the received signal J will be due only to the contribution of the individual position acoustic signal. The received signal J is processed and analysed as will be subsequently described by the same software that generated the pseudo-random sequences MLS1 , MLS2, MLS3, MLS4. By exploiting the mathematical properties of the pseudo-random sequences, the received signal J is separated into the different contributions due to the individual position acoustic signals XI , X2, X3, X4. This process, known in the field, is possible since a pseudo-random sequence itself is immune to background noises, namely noises not related to the specific sequence.

Thus, an identification signal HI , H2, H3, H4 is obtained corresponding to the individual transmitted acoustic signal XI , X2, X3, X4. The identification acoustic signal HI , H2, H3, H4 is nothing but the impulse response of the system.

In that specific case, the considered system is that represented by the environment interposed between the individual position acoustic emitter A, B, C, D and the acoustic receiver R; such system inputs an impulsive position acoustic signal XI , X2, X3, X4 decoded by a pseudo-random sequence MLS1 , MLS2, MLS3, MLS4 and outputs a signal that comprises the received signal J. The impulse response is represented by the time- based trend of the sound pressure level at the acoustic receiver R due to the infinitesimal temporal length stress, namely the position acoustic signal XI, X2, X3, X4, introduced into the environment at the individual position acoustic emitter A, B, C, D.

Each identification signal HI , H2, H3, H4 is automatically obtained by the software by means of suitable mathematical operations which employ the fast Hadamard transform. This does not prevent other types of transforms or other mathematical operations from being used. The fast Hadamard transform allows to obtain a high-quality signal wherein the characteristic peak SI , S2, S3, S4 the impulsive response is easily identifiable and not soiled by spurious waviness.

Subsequently, also by the software, the peak SI , S2, S3, S4 of each impulsive response HI , H2, H3, H4 is identified. Once the characteristic peak SI , S2, S3, S4 is identified, the flight time Tl , T2, T3, T4 is then extracted corresponding to the value of the axis of the abscissas at the newly identified peak SI, S2, S3, S4. The flight time Tl, T2, T3, T4 represents the time taken by the single position acoustic signal XI , X2, X3, X4 to travel the distance D l , D2, D3, D4 which separates the position acoustic emitter A, B, C, D which emitted the signal from the acoustic receiver R.

Starting from the flight time Tl , T2, T3, T4, once the speed of sound in the air is known, the distance D l , D2, D3, D4 between the single position acoustic transmitter A, B, C, D and the acoustic receiver R is immediately obtained.

In alternative embodiments the medium wherein the sounds propagate may be other than air. For example, in the case of sound propagation in a liquid, such as water, in the performed calculations it will be appropriate to consider the propagation speed of sound in the specific liquid.

Subsequently, starting from the value of the distances D l , D2, D3, D4, the software automatically calculates the coordinates Px, Py, Pz of the position P of the acoustic receiver R by performing simple trilateration calculations. Such calculations imply the knowledge of the position of the position acoustic emitters A, B, C, D with respect to the reference system X, Y, Z defined when the measuring apparatus 1 is positioned.

As a skilled person will understand, by moving the acoustic receiver R in the three-dimensional measuring space 10 it is possible to calculate the coordinates of the new position by repeating the process described above. By keeping moving the acoustic receiver R in the measuring space 10, and performing measurements of the position P at certain time intervals, it is possible to have real time information about the position P of the moving acoustic receiver R. The acoustic receiver R can be advantageously located near an object to know the position of the latter.

Furthermore, the acoustic receiver R can be moved along a determined path to calculate the length of the path itself which will result from the sum of the location of the points identified by the positions of the moving acoustic receiver R detected at regular time intervals. This last approach can be useful to perform measurements aimed at obtaining planimetries of rooms, buildings or structures such as archaeological sites. Figures 3 and 4 show a reproduction of the position acoustic emitters A, B, C, D and the three-dimensional measuring space 10 obtained by the software implemented in the computerized system C wherein points are represented, whose position is measured by moving the acoustic receiver R until almost the entire length of one side of the three-dimensional measuring space 10 parallel to the axis X is covered.

Figures 5 and 6 show a reproduction of the position acoustic emitters A, B, C, D and the three-dimensional measuring space 10 obtained by the software implemented in the computerized system C wherein points are represented, whose position is measured by moving the acoustic receiver R until almost the entire length of one side of the three-dimensional measuring space 10 parallel to the axis Z is covered.

In a real situation, the movement of the acoustic receiver R can determine the onset in the impulsive response HI , H2, H3, H4 of further peaks, in addition to the characteristic peak SI , S2, S3, S4, whose number and amplitude vary according to the speed the acoustic receiver R is moved at. If the impulse response were ideal we would only have a characteristic peak SI , S2, S3, S4 of uniform width.

Further important conditions which determine the onset of spurious peaks in the impulsive response HI , H2, H3, H4 are the consequence of echo phenomena that can occur if the acoustic receiver R is placed near an obstacle.

The above-mentioned obstacle can be for example a wall. In particular, if the measurement of position P is performed in a room, the acoustic receiver R will also capture the acoustic signals deriving from the reflection by the walls or objects of the position acoustic signals XI , X2, X3, X4, which result in spurious peaks present in the impulsive response HI , H2, H3, H4.

In order to detect the peak SI , S2, S3, S4 from each impulse response HI , H2, H3, H4 even in the presence of noise caused by the microphone movement or reverberation, the software implements a signal analysis protocol that includes the following phases: searching, moving from right to left along the time axis of each impulsive response HI , H2, H3, H4, the peak of maximum amplitude in absolute value; the peak of maximum amplitude may not be the characteristic peak SI , S2, S3, S4 but will have the same order of magnitude of the latter; calculating the dB amplitude of the background noise in the initial part II, 12, 13, 14 of the impulsive response HI , H2, H3, H4; the initial part II , 12, 13, 14 is placed to the left of the first peak from the left having amplitude of the same order of magnitude of the peak of maximum amplitude obtained previously maintaining a predetermined minimum distance of the acoustic receiver R from the position acoustic emitters A, B, C, D; - calculating a signal/ noise ratio PNR1 , PNR2, PNR3, PNR4 as the ratio between the amplitude of the maximum peak and the amplitude of the background noise; check if the signal /noise ratio PNR1 , PNR2, PNR3, PNR4 is higher than a predetermined minimum tolerance threshold; - if the signal/ noise ratio PNR1 , PNR2, PNR3, PNR4 is lower than a threshold value in at least one of the impulsive responses HI , H2, H3, H4, namely the noise is too high (too fast microphone movement or excessive reverberation) measurement is not considered valid; if the signal/ noise ratio PNR1 , PNR2, PNR3, PNR4 is higher than the threshold value for all the analysed impulse responses HI , H2, H3, H4, the measurement is valid and a research is carried out, moving from left to right along the time axis of each impulsive HI , H2, H3, H4, of the first amplitude peak greater than the multiplication of the amplitude of the background noise and a constant of a predetermined value (since the amplitude is measured in dB the multiplication becomes a sum), the peak thus obtained is the characteristic peak SI , S2, S3, S4.

The phase of calculating the dB amplitude of the background noise can be alternatively performed taking into account the final portion of the impulsive response HI , H2, H3, H4, namely the signal portion to the right of the first peak from the right having amplitude of the same order of magnitude of the maximum amplitude peak previously obtained.

The protocol, after verifying the presence of other peaks in addition to the first one with greater amplitude than the multiplication of the background noise amplitude and a predetermined value constant, signals to the user the presence of secondary peaks in addition to the characteristic peak SI , S2, S3, S4, but still maintains the valid measurement. Thus, the protocol described above allows to obtain accurate measurements even in the presence of causes of error such as the excessive movement speed of the acoustic receiver R or any reverberations present in the measurement environment, and to automatically invalidate the individual measurement in the event that the signal/ noise ratio is below a certain threshold.

The time taken by the apparatus to measure the position P, namely the number of measurements that can be performed in one second, depends on environmental factors: outdoor, without reflections on walls (but only on the ground) and without room reverberation, the maximum speed can be obtained, namely the maximum number of measurements per second (which depends on the power of the computerized system C). Indoor and/ or in the presence of walls, obstacles, reverberation of the environment, the time of each individual measurement, namely the time length of the pseudorandom sequences, is to be increased. This is because the pseudo-random sequence must have a greater time length than the reverberation time of the environment.

The described explanatory embodiment of the measuring apparatus 1 comprises a further test acoustic emitter ET suitably located in the three- dimensional measuring space 10. As will become apparent below, the test acoustic emitter ET is preferably used to perform an acoustic field measurement. Obviously if the user has to perform only one position measurement, such acoustic test emitter ET may not be present.

Analogously as for the other position acoustic emitters A, B, C, D, the acoustic test emitter ET is connected to the computerized system C from which it receives a test pseudo-random sequence MLST different from the other pseudo-random sequences MLS1 , MLS2, MLS3, MLS4 sent to the position acoustic emitters A, B, C, D. The test acoustic emitter ET will accordingly transmit a test acoustic signal XT and the received signal J from the acoustic receiver R will also comprise the contribution of the test acoustic signal XT. The test acoustic emitter ET can consist of a speaker similar to those used as position acoustic emitters A, B, C, D or be of a different type.

Starting from the received signal J, the test impulsive response HT is obtained and then analysed by applying the protocol described above.

This last test impulsive response HT is not used to calculate the position P but to obtain the value of a physical quantity F different from the flight time Tl, T2, T3, T4 and preferably connected to the acoustic properties of the environment in the position P of the acoustic receiver R. In particular, this physical quantity F may be the value of the sound pressure level (SPL) which can be obtained from the data of the test impulsive response HT.

As a skilled person will understand, by moving the acoustic receiver R it is possible to obtain a measurement of the acoustic field at various points of the three-dimensional measuring space 10. Starting from the test impulsive response HT, other physical quantities F of acoustic concern (such as the reverberation time) or acoustic properties of a material located near the acoustic receiver R (such as the absorption coefficient) can also be obtained.

In alternative embodiments, the acoustic receiver R can furthermore be coupled to a transducer T which allows to directly measure a physical quantity F - not connected to the acoustic field - in the position of the acoustic receiver R. In particular, by associating the moving acoustic receiver R a temperature transducer it is possible to obtain the value of the temperature range at various points of the three-dimensional measuring space 10.

Figures 7 and 8 show two examples of a graphic interface of the software implemented in the computerized system C wherein examples of impulsive responses HI , H2, H3, H4, HT are shown, obtained by the measuring apparatus 1. In particular, figure 7 shows impulsive responses HI , H2, H3, H4, HT considered valid by the analysis protocol and thus characterized by an acceptable signal/ noise ratio. Figure 8 shows instead one of the impulsive responses, H3, with such a high noise that it can not be considered valid by the analysis protocol and thus in that case the measurement of the position P of the acoustic receiver R is set aside. Figure 9 shows instead a summary block diagram of the signals and the components of the measuring apparatus 1 employed in the method described above.

The method for calculating a position and possible mapping of a space- related variable by means of acoustic signals and the corresponding apparatus for implementing the method according to the invention solve the technical problem and achieve numerous advantages.

Advantageously, the measuring apparatus provides hardware components, such as the speakers (and respective amplifiers), the microphone, a computerized system whereon the software is implemented and the sound card mounted, which are significantly inexpensive with respect to, for example, optical position measurement systems known in the art.

Advantageously, the measurement apparatus includes the possibility to analyse signals transmitted by at least three speakers and to obtain a univocal measurement of the position. Advantageously, the coding and decoding of the pseudo-random sequences is performed by means of a software implemented in a computerized system and thus the measurement apparatus does not require hardware circuits, such as chips and microprocessors, adapted to this function. The software allows to enter adjustment parameters and view the measurements through a graphic interface that significantly simplifies the usability of the measurement.

Advantageously, the impulsive response of the environment does not require equalization and is obtained by applying the fast Hadamard transform which allows to obtain a very clear characteristic peak. Advantageously, the impulsive responses are analysed by means of an analysis protocol which allows to obtain a measurement of the position even in case of echoes or reverberations present in the environment. The above- mentioned protocol also allows the measurement to be set aside in the event that at least one impulsive response has excessive noise based on the signal/ noise ratio evaluation.

Advantageously, the method and the apparatus according to the invention allow a measurement of the position with a deviation of about 3-5 mm and thus resulting in a precision equal to or greater than systems known in the art.

Advantageously, the method and the apparatus according to the invention allow a precise measurement of the position even indoor, such as in underground archaeological sites, wherein the GPS systems known in the art do not work properly.

Advantageously, by using an auxiliary emitter, the measuring apparatus allows to associate to the position the value of a physical quantity of an acoustic type, such as the pressure level of the received sound in order to obtain the acoustic field in the measuring space. By adding the auxiliary emitter, it is also possible to derive some acoustic properties of a material located near the receiver.

Furthermore, by associating a suitable transducer to the receiver, it is possible to derive the value of a physical quantity not related to the acoustic field, relating it to the position of the receiver in the three-dimensional measuring space.

Advantageously, the method and the apparatus according to the invention allow a real-time measurement of the position - and of any physical variable related thereto - so that a spatial exploration by moving the receiver allows a mapping of the results.

Claims

1. Method for calculating a position and possibly mapping of a space- related variable by means of acoustic signals comprising the following steps: providing at least three position acoustic emitters (A, B, C, D) with known relative position at a three-dimensional measuring space (10); providing at least one acoustic receiver (R) located at a not known distance (D l , D2, D3, D4) from each of said position acoustic emitters (A, B, C, D) into the three-dimensional measuring space (10); making each position acoustic emitter (A, B, C, D) emit a position acoustic signal (XI , X2, X3, X4), said position acoustic signals (XI , X2, X3, X4) being discriminable from each other; acquiring a received acoustic signal (J) by means of the acoustic receiver (R), said received acoustic signal (J) comprising contributions associated with the individual position acoustic signals (XI , X2, X3, X4); obtaining a position identification signal (HI , H2, H3, H4) for each position acoustic signal (XI , X2, X3, X4) starting from said received acoustic signal

(J); obtaining the time of flight (Tl, T2, T3, T4) that each position acoustic signal (XI , X2, X3, X4) spent to travel the distance (D l , D2, D3, D4) between the position acoustic emitter (A, B, C, D) and the acoustic receiver (R) by means of analysis of said position identification signals (HI , H2, H3, H4); calculating the distances (D l , D2, D3, D4) stating from the times of flight (Tl , T2, T3, T4); calculating the position (P) of the acoustic receiver (R) in the three- dimensional measuring space (10) starting from said distances (D l , D2, D3, D4).

2. Method according to claim 1 , further comprising the following steps: providing also a test acoustic emitter (ET) into the three-dimensional measuring space (10); making the test acoustic emitter (ET) emit a test acoustic signal (XT), said test acoustic signal (XT) being discriminable from the position acoustic signals (XI , X2, X3, X4); said received acoustic signal (J) comprising a contribution even associated with the test acoustic signal (XT); obtaining a test identification signal (HT) related to the test acoustic signal (XT) starting from said received acoustic signal (J), obtaining the value of a physical quantity (F) different from the time of flight that the test acoustic signal (XT) spent to reach the acoustic receiver (R), such as the level of sound pressure of the test acoustic signal (XT), from said test identification signal (HT).

3. Method according to one of the preceding claims, further comprising the following steps: providing a transducer (T) in the same position (P) of said acoustic receiver (R); detecting the value of a physical quantity (F) at the previously calculated position (P) of the acoustic receiver (R) by means of said transducer (T); wherein said transducer (T) is, for example, a temperature transducer and said physical quantity (F) is the temperature measured by the transducer (T) located at position (P) of the receiver (R).

4. Method according to claim 1 , wherein said steps of: acquiring the received acoustic signal (J); obtaining the position identification signals (HI , H2, H3, H4); obtaining the times of flight (Tl , T2, T3, T4); calculating the distances (D l , D2, D3, D4); and calculating the position (P); are cyclically repeated while the acoustic receiver (R) moves into the three-dimensional measurement space (10) in order to detect a topographical or architectural feature.

5. Method according to one of the claims 2-3, wherein the steps of: acquiring the received acoustic signal (J); obtaining the position identification signals (HI , H2, H3, H4) and the possible test identification signal (HT); obtaining the times of flight (Tl , T2, T3, T4); and obtaining or detecting the value of the physical quantity (F); are cyclically repeated with the acoustic receiver (R) placed into different positions (P) for mapping the value of the physical quantity (F) within the three-dimensional measurement space (10).

6. Method according to any one of the preceding claims, wherein the position acoustic emitters (A, B, C, D) and the respective position acoustic signals (XI , X2, X3, X4) are in the number of four, arranged in a coplanar or not coplanar manner.

7. Method according to one of the preceding claims, wherein each of said position acoustic signals (XI , X2, X3, X4) is decoded from a different pseudo-random sequence (MLS1 , MLS2, MLS3, MLS4), each position identification signal (HI, H2, H3, H4) being obtained by applying the fast Hadamard transform.

8. Method according to claim 7, wherein the step of analysing each identification signal (HI , H2, H3, H4) consists in distinguishing the component of the position identification signal (HI , H2, H3, H4) actually due to the acoustic signal (XI , X2, X3, X4) by identifying the characteristic peak (SI , S2, S3, S4) with the impulse response obtained applying the Hadamard transform by implementing the following steps: searching, along the time axis of each impulse response (HI , H2, H3, H4), the peak with maximum amplitude in absolute value; identifying the characteristic peak (SI , S2, S3, S4) with the first peak of amplitude greater than a threshold proportional to the amplitude of the background noise moving from left to right along the time axis of each impulse response (HI , H2, H3, H4).

9. Method according to claim 8, further comprising the following steps: calculating a signal/ noise ratio (PNR1 , PNR2, PNR3, PNR4) as the ratio between the amplitude of the peak with maximum amplitude in absolute value and an indicative amplitude of the background noise; validating the measurement only wherein the signal/ noise ratio (PNR1 , PNR2, PNR3, PNR4) exceeds a predetermined threshold value.

10. Measuring apparatus (1) comprising: at least three position acoustic emitters (A, B, C, D) adapted to be located with a known relative position at a three-dimensional measuring space (10); at least one acoustic receiver (R) adapted to be located and possibly move into the three-dimensional measuring space (10); a computerized system (C) connected to said position acoustic emitters (A, B, C, D) and said acoustic receiver (R) so as to send and receive signals from them, said computerized system (C) implementing a software adapted to: making each position acoustic emitter (A, B, C, D) emit a position acoustic signal (XI , X2, X3, X4), said position acoustic signals (XI , X2, X3, X4) being discriminable from each other; acquiring a received acoustic signal (J) from said acoustic receiver (R), said received acoustic signal (J) comprising contributions associated with the individual position acoustic signals (XI , X2, X3, X4); obtaining a position identification signal (HI , H2, H3, H4) for each position acoustic signal (XI , X2, X3, X4) starting from said received acoustic signal