The present application claims priority from Finnish patent application number 20085876, filed 17 Sep. 2008.
The invention relates to techniques for determining velocity of a sport object. A representative but non-restrictive list of exemplary sport objects includes balls, pucks, arrows and comparable items.
In many games, the velocity of sport object is crucial to the athlete's performance, which is why athletes aim at improving the initial velocity, or start velocity, of the sport objects. It is customary to measure the initial velocity of sport object by means of Doppler radar. A problem with this approach is that the Doppler radar is prohibitively expensive to most amateur athletes. Accordingly, there is a need for simpler equipment for measuring the velocity of a sport object.
An object of the invention is to develop techniques for measuring the velocity of a sport object with a simpler and less costly equipment than in conventional methods. The object of the invention is achieved by a method, apparatus and software product as specified in the attached independent claims. The dependent claims as well as the present patent specification and drawing relate to specific embodiments and implementations of the invention.
The invention is partially based on the idea of determining the object's velocity by means of a mobile telephone. Mobile telephones are ubiquitous, sophisticated pieces of equipment, many of which support additional program modules which can be used to direct the mobile telephone's processor to perform the necessary processing acts and calculations. The invention is also based on the idea of using the mobile telephone's built-in microphone or some microphone operatively coupled to the mobile telephone to receive an audio signal based on which the start and end times of the sport object's movement can be detected. In addition, a span length traversed by the object is determined by the mobile telephone, by receiving this information from the mobile telephone's user interface, for example. The start and end time plus the span length suffice to provide an approximation for the object's average velocity.
Most athletes wish to know the object's initial (start) velocity, which can be estimated by applying some correction to the average velocity. Such a correction can be determined empirically, for example by performing a statistically sufficient number of experiments in which the object's average velocity is determined by dividing the span length traversed by the object by the travel time, while the object's initial velocity is determined with some other means, such as Doppler radar. Such a statistically sufficient number of experiments will yield an empirical correction by which the initial velocity can be determined on the basis of average velocity and span length. It is also possible to entirely bypass the determination of the average velocity and generate an empirically determined function or lookup table whose inputs are the span length and travel time and the output of the function or lookup table is the initial velocity.
Based on the preceding description of the invention alone, it would seem that the invention is merely based on performing simply physical calculations by a mobile telephone's processor. Those skilled in the art will realize, however, that implementing the invention requires solutions to several residual problems,
A first residual problem is the fact that in the application programming interface (API) of conventional mobile telephones, it is problematic to determine the time of an event with a resolution which is sufficient for accurate timing of the object's movement. For instance, the resolution of various timers varies between platforms and telephone models.
A second residual problem is the fact that most mobile telephones are not designed for accurate and objective measurement of sound. Nor are they designed for post-processing of measured sound within the mobile telephone. Instead, mobile telephones are designed to take audio samples called “codebook samples” of human speech and transfer the codebook samples via a traffic channel to a base station in a wireless radio network. For example, it is a well-known fact that the audio circuitry of a conventional mobile telephone and the voice coding algorithm of GSM telephones are incapable of reliably transmitting DTMF (dual-tone, multi-frequency) sounds, which is why various bypass techniques for conveying DTMF sounds have been developed. Some features and embodiments of the invention aim at solving these residual problems.
Provided that the mobile terminal's processor has sufficient processing power, the audio samples can be captured and processed as a real-time operation. Real-time processing does not have a universally adopted definition, but for the purposes of the present invention and its embodiment, real-time processing of audio samples means that the mobile terminal, including all hardware and firmware involved, such as the processor, system firmware, application programming interface and audio processing circuitry are capable of detecting the first and second shapes that indicate the start and end times of the object movement as fast as the audio samples are captured. Typical mobile terminals built on Symbian® platforms are capable of operating in this mode. A benefit of real-time operation is that there is no need to buffer the audio samples for a longer time that what is required for the detection of the first and second shapes. This means that the audio buffer can be re-used or re-filled in a circular fashion and the mobile terminal, under control of the inventive program module, can wait indefinitely for the first shape that indicates the start time of the object's movement. In other words, the mobile terminal can buffer audio samples only as much as is required for detecting either of the first and second shapes, and then discard the audio samples, for example by re-using the buffer memory area. As far as buffer memory consumption is concerned, the mobile terminal could wait indefinitely for the second shape, ie the one that indicates the end of the object's movement, but it is reasonable to utilize some sanity check which rejects the second shape if it occurs too long after the first shape.
In case the mobile terminal, including hardware and firmware resources, is incapable of real-time operation, an embodiment of the inventive program module may cause the mobile terminal to capture and buffer all the audio samples which include the first and second shapes, and any audio samples in between, prior to detecting the first and second shapes from among the buffered audio samples. A residual problem in such environments is that the captured audio samples must be buffered in a buffer memory, and the memory may be a scarce resource in low-power mobile terminals. The buffer memory requirements can be minimized by providing the user with a signal that indicates the time when the audio buffering begins. In some implementations, the signal can even set up to precede the beginning of audio buffering by a couple of seconds. This is useful in situations like a penalty kick in soccer, wherein the player may run for a couple of second before actually kicking the ball, which results in the first shape to be detected.
In the following the invention will be described in greater detail by means of specific embodiments with reference to the attached drawings, in which:
The microphone MP is separated from the span start SS and span end by respective distances d1 and d2. If the difference d2−d1 is large and/or the typical velocity of the object is high, it is beneficial to divide d2−d1 by the speed of sound and subtract the quotient from the travel time (whose determination will be described in connection with
As to the processing of “time” by the mobile terminal, any times discussed herein, such as the start time T1 or end time T2, need not be times on an absolute scale. In other words, the inventive program module being executed by the mobile terminal does not have to know the current time. It is rather the relative times that matter. In addition, the relative times need not be measured or expressed in seconds or milliseconds, and the times and time differences can be conveniently processed via sample numbers. Each sample has a sample length which is the inverse of the sampling rate.
Reference numeral 204 denotes some reference level, such as 0 dB, but the magnitude of the reference level is insignificant. Reference numeral 206 denotes a noise level such that for a significant proportion of time, the sound profile 200 remains below the noise level 206.
The portion of the sound profile 200 shown in
The inventive program module being executed by the mobile telephone's processor converts the presence of the peaks 210 and 212 to start and end times, respectively. Firstly, a specific moment of time should be associated with each peak. In one representative but non-restrictive implementation, the time associated with each peak 210, 212 is the time when the sound profile 200 exceeds a predetermined threshold 208 which is above the noise level 206. In the scenario shown in
In an alternative implementation, the start and end times 216, 218 can be determined based on the presence of the peaks' maximum values. In another alternative implementation, the start and end times 216, 218 can be determined based on times when the sound intensity increases by a predetermined step in a predetermined time window.
The notations 216 (≈T1) and 218 (≈T2) mean that the times denoted by reference numerals 216 and 218 no not precisely coincide with the start and end times T1, T2 of the object movement over the span length SL; rather the times 216 and 218 are the start and end times T1, T2 as measured by the mobile telephone MP under control of the inventive program module. For example, the times 216 and 218 lag the true start and end times T1, T2 at least by the propagation of sound from the start and end positions SS, SE over the distances d1, d2 to the microphone MP. Moreover, as stated above, the program module being executed in the mobile terminal need not know any of the times shown in
Because the sounds generated at the start and end of the object movements have finite lengths, it is beneficial to employ sleep times 220, 222 such that crossing of the threshold 206 during the sleep time 220 is ignored. The sleep times 220, 222 also help suppress echoes from nearby objects. Reference numerals 214A and 214B denote two such echoes.
Based on the preceding description alone, the inventive program module cannot distinguish between the object movement's start time and end time. There are various ways to do so. In one implementation, each measurement event is triggered via the mobile telephone's user interface, for example by pressing a key. After the trigger, the first and second peaks which exceed the threshold 206 are considered the start and end of the object's movement, respectively. A problem with this somewhat crude approach is that the athlete or assistant must trigger each measurement event separately.
In a more user-friendly implementation a sliding time window is employed. After any period without detected sound intensity peaks, any detected peak 210 is assumed to correspond to the start time 216 of the object's movement. After that, any intensity development in the sleep time 220 is ignored and the next detected peak 212 is assumed to correspond to the end time 218 of the object's movement. However, a maximum time period 224 from the start time 216 is employed so as to be able to handle cases in which the end of the object movement goes undetected. For instance, the object may miss its intended target and thereby fail to produce a detectable sound. If the maximum time period 224 expires without the detection of the second peak 212 and end time 218, the previously-detected first peak 210 and start time 216 are ignored and the next peak to be detected will be processed as the first peak.
The time difference between the start time 216 and end time 218 may be used as the object's travel time TT. In an enhanced implementation the travel time TT may be corrected to compensate for unequal distances d1, d2 from the span start SS and span end SE to the microphone MP.
In order to solve the problems underlying the present invention, the mobile terminal's memory MEM is provided with a program module 350 which performs the required measurements and calculations. The program module 350 uses the mobile terminal's memory MEM for storing parameters and variables, collectively denoted by reference numeral 360. Their significance will be described in connection with
In a simple implementation, the only user-entered parameter is the span length SL, ie the span from the object's initial position to the target. The program 350 detects the sound peaks corresponding to the start time T1 and end time T2 of the object's movement over the span length. As stated earlier, in connection with
In an enhanced implementation the program 350 may query the user for the distances d1, d2 from the span start SS and span end SE to the microphone MP. Alternatively the program 350 may query the user for the difference d2−d1. The difference d2−d1 divided by the speed of sound VS yields a time correction Tcorr which can be subtracted from the difference T2−T1 to obtain a more accurate value for the object's travel time TT.
The span length SL and the travel time TT are applied to a function, routine or lookup table denoted by G. In the following description, the term “function” will mean any data structure which accepts at least one input value and outputs at least one predetermined output value based on the at least one input value. Accordingly, the element G this element will be called function G although, in terms of programming, it can be implemented as calculation (sub)routine, lookup table or any comparable data structure. The input values for the function G include the span length SL and the travel time TT, and the output values include the object's velocity. In the implementation shown in
Regardless of whether the correction from average velocity to initial velocity is determined empirically or by physical modelling, it is also possible to implement the program 350 such that it entirely bypasses the determination of the average velocity and employs such an empirically-determined or physically-modelled function G whose inputs are the span length SL and travel time TT and the output of the function is the initial velocity VI.
In order to eliminate a need for the mobile terminal user to read the determined object velocity for each attempt, the mobile terminal may maintain a top-n list of velocities, wherein “n” stands for some convenient number of best scores, such as a number from 1 to 20. The top-n list may be maintained separately for each sport and user. In case the object velocity just determined exceeds the previous record, the mobile terminal may produce some audible and/or visible alert, such as a recognizable tone or flashing of its display. The user may be given an opportunity to accept or reject the new record or a new entry into the top-n list. For instance, new records or top-n entries may be rejected in situations wherein a spurious sound has been detected as one of the shapes 210, 212 corresponding to the start and end times T1, T2 of the object's traversal of the span length SL. Alternatively, the new records or top-n entries may be rejected in situations wherein some of the operating parameters have been entered incorrectly.
The flow chart shown in
The flowchart for Java-based platforms, as shown in
As stated earlier, the application programming interface (API) of mobile terminals may not offer programming functions for measuring time with sufficient accuracy. Accordingly, time-related quantities, such as the length of the audio capturing period, may be determined indirectly. For instance, the inventive Java applet may direct the mobile terminal's processor to capture a predetermined number of audio samples. Alternatively, an appropriate maximum length may be assigned to the capture buffer, wherein the maximum length may be defined as the number of audio samples that the capture buffer can hold. An overflow condition of the capture buffer may then indicate of the expiry of the audio capturing period.
Execution of step 714 involves an operation which solves another residual problem of typical mobile terminals, namely the fact that the beginning of the capture buffer, ie, a few first audio samples, are frequently noisy. This phenomenon may be caused by a finite settling time of the various components of the audio processing circuitry. For instance, if automatic gain control (AGC) is being utilized, the AGC circuitry may need some time to settle. Accordingly, the noisy beginning of the audio capture buffer should be ignored and the shape detection operation in step 716 should only be performed on the relatively noiseless part of the audio capture buffer. In one implementation, the Java applet may automatically determine an appropriate length of time (number of audio samples) that should be ignored, by requesting the user of the mobile terminal to place the mobile terminal into a quiet location, after which the Java applet captures that relative silence and detects the number of noisy audio samples in the beginning of the buffer. As this is a terminal-specific calibration operation, it only has to be performed once for each terminal (or terminal type) and stored as one of the operating parameters (see item 360 in
It is readily apparent to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims
Number | Date | Country | Kind |
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20085876 | Sep 2008 | FI | national |