TABLE TENNIS BALL HAVING MARKING TO MAKE A BALL ROTATION DETECTABLE

Abstract

A table tennis ball which has, on the spherical surface thereof, a marking to make a ball rotation measurable. The marking contains a number of marking points, which are distributed on the ball surface in such a way that the standard deviation of the lengths of the orthodromes between each of the marking points and the three nearest neighboring points thereof is at least 12% of the average value of these lengths, and the minimum length of the orthodromes between each of the marking points and the three nearest neighboring points thereof is at least 40% of the average value of these lengths.

Claims

1. A table tennis ball, comprising: a spherical ball surface; and a marking applied to said spherical ball surface for making a ball rotation metrologically detectable, said marking having a number of marking points, said marking points being distributed on said spherical ball surface such that a standard deviation of lengths of orthodromes between each of said marking points and its three closest neighboring marking points is at least 12% of a mean value of the lengths, and that a minimum length of the orthodromes between each of said marking points and its said three closest neighboring marking points is at least 40% of the mean value of the lengths and/or at least 120% of a quotient of a ball radius to a square root of the number of said marking points.

2. The table tennis ball according to in claim 1, wherein said marking points are distributed on said spherical ball surface such that the standard deviation of the lengths of the orthodromes between each of said marking points and its said three closest neighboring points is at least 15% of the mean value of the lengths.

3. The table tennis ball according to claim 1, wherein the minimum length of the orthodromes between each of said marking points and its said three closest neighboring points is at least 50% of the mean value of the lengths.

4. The table tennis ball according to claim 1, wherein the minimum length of the orthodromes between each of said marking points and its said three closest neighboring points is at least 150% of the quotient of the ball radius to the square root of the number of said marking points.

5. The table tennis ball according to claim 1, wherein said marking points are distributed on said spherical ball surface such that a range of the lengths of the orthodromes, which connect said three closest neighboring points of each said marking point to one another, is greater than 30% of the mean value of the lengths of the orthodromes between each of said marking points and its said three closest neighboring points.

6. The table tennis ball according to claim 1, wherein the number of said marking points is between 13 and 25.

7. The table tennis ball according to claim 1, wherein a diameter of each said marking point is between 10% and 24% of the ball radius.

8. The table tennis ball according to claim 1, wherein a diameter of each said marking point is between 2.0 mm and 4.8 mm.

9. The table tennis ball according to claim 1, wherein all of said marking points have a same shape and size.

10. The table tennis ball according to claim 1, wherein said marking points have an infrared absorption and/or infrared reemission characteristic different from remaining said spherical ball surface, so that said marking points stand out from said remaining spherical ball surface in a contrasting manner in an infrared range of an electromagnetic radiation spectrum.

11. The table tennis ball according to claim 1, wherein said marking points have a color different from remaining said spherical ball surface, so that said marking points stand out from said remaining spherical ball surface in a contrasting manner in a visible range of electromagnetic radiation spectrum.

12. The table tennis ball according to claim 1, wherein the minimum length of the orthodromes between each of said marking points and its said three closest neighboring points is at least 60% of the mean value of the lengths.

13. The table tennis ball according to claim 1, wherein the minimum length of the orthodromes between each of said marking points and its said three closest neighboring points is at least 180% of the quotient of the ball radius to the square root of the number of said marking points.

14. The table tennis ball according to claim 1, wherein said marking points are distributed on said spherical ball surface such that a range of the lengths of the orthodromes, which connect said three closest neighboring points of each said marking point to one another, is greater than 35% of the mean value of the lengths of the orthodromes between each of said marking points and its said three closest neighboring points.

15. The table tennis ball according to claim 1, wherein said marking points are distributed on said spherical ball surface such that a range of the lengths of the orthodromes, which connect said three closest neighboring points of each said marking point to one another, is greater than 40% of the mean value of the lengths of the orthodromes between each of said marking points and its said three closest neighboring points.

16. The table tennis ball according to claim 1, wherein the number of said marking points is between 18 and 19.

17. The table tennis ball according to claim 1, wherein a diameter of each said marking point is 17.5%.

18. A table tennis ball, comprising: spherical ball surface; a marking applied to said spherical ball surface for making a ball rotation metrologically detectable, wherein said marking has a number of marking points, said marking having eighteen of said marking points; wherein starting from a first marking point of said marking points: a length of an orthodrome to its closest neighboring marking point in relation to a ball radius is 0.54±20%; a length of an orthodrome to its second-closest neighboring marking point in relation to the ball radius is 0.91±20%; and a length of an orthodrome to its third-closest neighboring marking point in relation to the ball radius is 0.99±20%; wherein starting from a second marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.54±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.72±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.83±20%; wherein starting from a third marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.78±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.84±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.87±20%; wherein starting from a fourth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.72±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.84±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.85±20%; wherein starting from a fifth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.79±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.83±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.85±20%; wherein starting from a sixth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.67±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.73±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.94±20%; wherein starting from a seventh marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.59±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.76±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.90±20%; wherein starting from an eighth marking point of said marking points: a length of the orthodrome to its closest neighboring point in relation to the ball radius is 0.82±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.87±20%; and a length of the orthodrome to its third-closest neighboring point in relation to the ball radius is 0.89±20%; wherein starting from a ninth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.51±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.91±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.95±20%; wherein starting from a tenth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.75±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.75±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.78±20%; wherein starting from an eleventh marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.82±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.88±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.89±20%; wherein starting from a twelfth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.67±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.79±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.84±20%; wherein starting from a thirteenth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.75±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.82±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 1.02±20%; wherein starting from a fourteenth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.51±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.92±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.98±20%; wherein starting from a fifteenth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.82±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.84±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.90±20%; wherein starting from a sixteenth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.59±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.74±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 1.10±20%; wherein starting from a seventeenth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.74±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.75±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.76±20%; and wherein starting from an eighteenth marking point of said marking points: a length of an orthodrome to its closest neighboring point in relation to the ball radius is 0.73±20%; a length of an orthodrome to its second-closest neighboring point in relation to the ball radius is 0.88±20%; and a length of an orthodrome to its third-closest neighboring point in relation to the ball radius is 0.91±20%.

19. The table tennis ball according to claim 18, wherein for the first marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.83±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.57±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.53±20%; wherein for the second marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.24±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 0.85±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 0.91±20%; wherein for the third marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.61±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 0.82±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.45±20%; wherein for the fourth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.39±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 0.79±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 0.83±20%; wherein for the fifth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.39±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 0.72±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 0.84±20%; wherein for the sixth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.88±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 0.97±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.57±20%; wherein for the seventh marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.74±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.60±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.38±20%; wherein for the eighth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.84±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.00±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.59±20%; wherein for the ninth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.39±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 0.96±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.33±20%; wherein for the tenth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.22±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.11±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.45±20%; wherein for the eleventh marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.75±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.45±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.71±20%; wherein for the twelfth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.21±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 0.85±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.51±20%; wherein for the thirteenth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.88±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.84±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.33±20%; wherein for the fourteenth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.12±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.88±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.05±20%; wherein for the fifteenth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.87±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 0.90±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.58±20%; wherein for the sixteenth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.76±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.57±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.67±20%; wherein for the seventeenth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 1.47±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.21±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 0.59±20%; and wherein for the eighteenth marking point: a length of an orthodrome between the closest neighboring point and the second-closest neighboring point in relation to the ball radius is 0.67±20%; a length of an orthodrome between the second-closest neighboring point and the third-closest neighboring point in relation to the ball radius is 1.37±20%; and a length of an orthodrome between the third-closest neighboring point and the closest neighboring point in relation to the ball radius is 1.62±20%.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0062] FIGS. 1 to 6 are six top view illustrations showing from six viewing directions perpendicular to one another, a table tennis ball having a spherical ball surface and a marking applied thereon for making the spin in flight metrologically detectable, wherein the marking is formed from eighteen marking points distributed on the ball surface; and

[0063] FIG. 7 is an illustration according to FIG. 1, showing a subgroup (“four-point network”) of the marking, which is formed from a first marking point of the marking viewed as the central point and its three closest neighboring points.

DETAILED DESCRIPTION OF THE INVENTION

[0064] Parts, dimensions, and structures corresponding to one another are always provided with the same reference signs in all figures.

[0065] Referring now to the figures of the drawings in detail and first, particularly to FIGS. 1-6 thereof, there is shown in six top view illustrations from six viewing directions perpendicular to one another, a (table tennis) ball 2. The spatial relationship of the views shown in FIGS. 1 to 6 to one another is indicated in each of these figures by arrows inscribed with Roman numerals: The Roman numerals each indicate the viewing direction which underlies the respective figure corresponding to the numeric value. Thus, the arrow inscribed by the Roman numeral II in FIG. 1 indicates the viewing direction from which the view according to FIG. 2 results, etc.

[0066] The ball 2 typically has a hollow-spherical shell 4, in particular made of plastic. The ball 2 in particular has a ball radius R of 20 mm (millimeters) or a ball diameter of 40 mm, which conforms to the rules for table tennis.

[0067] In order to make the ball rotation (spin) metrologically detectable in flight of the ball 2, a spherical ball surface 6 of the shell 4 (and thus of the entire ball 2) is provided with a marking 8. The marking 8 consists in the illustrated example of eighteen marking points P.sub.i (with i=1, 2, . . . , 18), which are arranged distributed over the ball surface 6. In FIGS. 1 to 6, the marking 8 is schematically shown for better illustration. Perspective distortions of the marking points P.sub.i located at the edge of the respective visible part of the ball surface 6 are not shown.

[0068] Each of the marking points P.sub.i is formed by a circular area having a diameter d (FIG. 7) of 3.5 mm (corresponding to 17.5% of the ball radius R). The marking points P.sub.i are applied to the ball surface 6 here using a strongly IR-absorbing and/or IR-reemitting paint, a strongly IR-absorbing and/or IR-reemitting printing ink/ink (see, for example, published, non-prosecuted German patent application DE 10 2008 049 595 A1), or another strongly IR-absorbing and/or IR-reemitting coating. In the visible spectral range of the electromagnetic radiation spectrum (thus in the spectral range of visible light), the marking points P.sub.i can have a color here which forms a color contrast to the surrounding ball surface 6. In this case, the marking points P.sub.i also stand out in an optically visible manner from the surrounding ball surface 6. The marking points P.sub.i are preferably transparent to the human eye, however, or have an identical or similar color as the surrounding ball surface 6. In the latter case, the marking points P.sub.i are only clearly recognizable in an infrared image of the ball 2, but in contrast they are not visible or in any case not conspicuous to a human observer and in light images of the ball 2.

[0069] Due to the above-described IR-sensitive embodiment of the marking 8, the marking points P.sub.i stand out in a strongly contrasting manner from the remaining ball surface 6 in an IR image of the ball 2. The ball 2 is optionally additionally provided with an additional structure (for example, an imprint or pattern), which is applied to the ball surface 6 at least by means of an ink that is not IR-absorbing or is less IR-absorbing. The marking 8 also stands out strongly in an IR image in relation to this possibly provided additional structure, so that in reverse the possibly provided structure does not impair or corrupt the information content conveyed by the marking 8 about the orientation of the ball 2 in space.

[0070] The location of the marking points P.sub.i on the ball surface 6 is specified in the following table in spherical coordinates, i.e., as a function of the polar angle Θ and the azimuth angle φ.

TABLE-US-00003 TABLE 3 The location of the marking points P.sub.i on the ball surface of the table tennis ball in spherical coordinates marking point polar angle Θ [°] azimuth angle φ [°] P.sub.1 57.6 306.8 P.sub.2 88.2 301.2 P.sub.3 62.1 147.4 P.sub.4 128.2 313.0 P.sub.5 91.7 348.5 P.sub.6 112.3 56.8 P.sub.7 44.2 84.9 P.sub.8 111.8 151.3 P.sub.9 151.3 206.0 P.sub.10 40.7 199.6 P.sub.11 91.1 199.2 P.sub.12 129.7 16.2 P.sub.13 68.2 241.3 P.sub.14 132.0 242.1 P.sub.15 91.7 107.8 P.sub.16 44.4 35.5 P.sub.17 2.2 19.1 P.sub.18 145.5 91.6

[0071] In this arrangement, the marking points P.sub.i, viewed globally, are distributed homogeneously on the ball surface 6 in a rough approximation. However, the marking points P.sub.i are nonetheless arranged pseudo-randomly offset in a recognizable manner in relation to an ideal uniform distribution.

[0072] These properties of the point distribution are clear in particular upon observation of the local point environments (designated as four-point networks 10), which are each formed by one of the marking points P.sub.i as the central point 12 and by its three closest neighboring points P.sub.i. The marking 8 may be divided into eighteen (partially overlapping) four-point networks 10 in accordance with the number of the marking points P.sub.i.

[0073] The four-point network 10 of the first marking point P.sub.i is shown by way of example in FIG. 7. It is recognizable herein that:

a closest neighboring point 14 of the marking point P.sub.i is formed by the marking point P.sub.2,
a second-closest neighboring point 16 of the marking point P.sub.i is formed by the marking point P.sub.5, and
a third-closest neighboring point 18 of the marking point P.sub.i is formed by the marking point P.sub.17.

[0074] As defined above, the lengths of the orthodromes 20, which connect the central point 12 of each four-point network 10 (in the example according to FIG. 7 the marking point P.sub.i) to in each case one of its neighboring points 14, 16, and 18 (in the example according to FIG. 7 thus the marking points P.sub.2, P.sub.5, and P.sub.17, respectively) are designated as central point distances Z.sub.i,j. The lengths of the orthodromes 20, which connect the neighboring points 14, 16, 18 of each four-point network 10 to one another, in contrast—as also defined above—are designated as peripheral point distances Q.sub.i,k. For the four-point network 10 of the first marking point P.sub.i, the corresponding central point distances Z.sub.1,1, Z.sub.1,2, Z.sub.1,3 and peripheral point distances Q.sub.1,1, Q.sub.1,2, Q.sub.1,3 are entered in FIG. 7.

[0075] For the arrangement of the eighteen marking points P.sub.i indicated in Table 3, the values of the central point distances Z.sub.i,j from the right column of Table 1.

[0076] According to equation 3, a mean value p results for the central point distances Z.sub.i,j, which corresponds to 0.80 times the ball radius R (i.e., μ/R=0.80). At a ball radius R of 20 mm, the average point distance of each marking point P.sub.i from its three closest neighboring points is thus 16.1 mm (i.e., μ=16.1 mm). For the standard deviation a according to equation 2, a value of 0.126 results for the point distribution indicated in Table 3. The standard deviation a normalized to the mean value p is thus 15.7% (i.e., σ/μ=15.7%). The smallest (central) point distance d.sub.min is formed between the points P.sub.9 and P.sub.14 and is 10.1 mm in the case of the ball radius indicated above. This corresponds to 63% of the mean value p (i.e., d.sub.min=min {Z.sub.i,j,|i=1, . . . , N; j=1, 2, 3}=63%.Math.μ).

[0077] The minimum point distance d.sub.min is 53.6% of the typical distance d.sub.G calculated according to equation 6 (equation 6) are—expressed equivalently—at least 214% of the quotient of the ball radius R to the square root of the point number N or 50.5% of the ball radius R.

[0078] With respect to the parameter σ/μ, the point distribution indicated in Table 3 is over the most ideal possible uniform distribution of the marking points P.sub.i; for such a uniform distribution of eighteen marking points P.sub.i, a comparative value of σ/μ=10.1% was found in experiments. On the other hand, the point distribution indicated in Table 3 also differs from an average random point distribution, in which the standard deviation a normalized to the mean value p is significantly higher, but the minimum central point distance regularly infringes the condition according to equation 4.

[0079] The peripheral point distances Q.sub.i,k for the point arrangement from Table 3 result from the right column of Table 2. The range ΔQ.sub.i of this point arrangement normalized to the mean value p according to equation 8 is greater than or equal to 42.8% for all four-point networks 10 (min {ΔQ.sub.i/μ; i=1, 2, . . . , 18}=ΔQ.sub.10/μ=42.8%).

[0080] The minimum value of this parameter ΔQ.sub.i, which represents a measure of the local irregularity of the point distribution, is significantly higher with the point distribution indicated in Table 3 than with the most ideal possible uniform distribution or an average random arrangement of the eighteen marking points P.sub.i.

[0081] The point distribution according to Table 3 is thus distinguished, viewed globally, by a pronounced uniformity, but viewed locally by a particularly high level of irregularity. Both features in combination facilitate the unambiguous identification of the marking points P.sub.i, each visible in arbitrary views of the ball 2, and thus decisively promote the spin ascertainment.

[0082] To determine the spin of the ball 2, a time sequence of images of the flying ball 2 is recorded by means of a camera. An infrared camera is preferably used for this purpose, in order to be able to utilize the strong contrast of the marking points P.sub.i in the IR spectrum. The camera is preferably arranged laterally to a table tennis table at the height of the net, so that it is aligned in parallel to the table transverse direction.

[0083] The recorded images of the ball 2 are evaluated, for example, using the method known from U.S. Pat. No. 7,062,082 B2, in order to determine the spin (in particular with respect to the axis of rotation, rotational direction, and rotational speed of the ball 2).

[0084] The marking 8 according to the invention, in particular in the embodiment shown in the figures and specified in detail in Table 3, enables for this purpose a particularly numerically uncomplicated and thus particularly fast spin ascertainment, by which for the first time a reasonable use of automatic spin ascertainment methods is enabled in table tennis, in particular in quasi-real time.

[0085] The invention is particularly clear in the exemplary embodiments described above, but is not restricted thereto. Rather, further embodiments of the invention can be derived from the claims and the preceding description.

[0086] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention.

LIST OF REFERENCE SIGNS

[0087] 2 ball [0088] 4 shell [0089] 6 ball surface [0090] 8 marking [0091] 10 four-point network [0092] 12 central point [0093] 14 (closest) neighboring point [0094] 16 (second-closest) neighboring point [0095] 18 (third-closest) neighboring point [0096] 20 orthodrome [0097] d diameter (of the marking point) [0098] P.sub.i marking points (i=1, 2, . . . , 18) [0099] Z.sub.i,j central point distance (i=1, 2, . . . , 18; j=1, 2, 3) [0100] Q.sub.i,k peripheral point distance (i=1, 2, . . . , 18; k=1, 2, 3) [0101] R ball radius