Video - Measurement of the Long and Triple Jump (VDM). How does it work.
It was the year 2005, and an idea began to emerge in athletics. if it were not necessary for a judge to choose at the foot of the pit the correct print to measure the athlete's result jump in Long and Triple jump? It was an idea that came from the Technical Committee of the IAAF, and some picked up the glove: SEIKO and two Spanish athletics judges.
Gabriel Abad, member of the Technical Committee of the IAAF, asked Pere Guillaumes and me if that idea of the Technical Committee was feasible. Then, with a Webcam on the dining room table and a graph paper I began to look for a proportionality between the number of pixels and the size of the squares of the paper, and it turns out that it worked! Pere corroborated him by measuring tiles in the countyard of his house.
In 2006, on the occasion of the celebration of the World Championships in the Cantons of La Coruña, I had the honour of meeting César Moreno, then a relevant member of the IAAF Council. A year later, I remember fondly of that dinner, in which I had the opportunity to show him a little software that managed to make longitudinal measurements from a video image. Then he told me, "This invention will be at the Pan American Games of Guadalajara 2011", I just took it for crazy.
In parallel, SEIKO at the World Athletics Championships in Osaka was beginning to test a video measurement system.
In 2009, I founded Sport Solution (www.sportsolution.es) merged with a group of judges and other professionals in electronics and computing, and was aware that the Royal Spanish Athletics Federation would need a system of video recording of the competition for support in the decision making of the jury for the Barcelona European Championships in 2010, I offered a system with the sole purpose of introduce a video camera that recorded the competitions of Long and Triple jump, and perform video measurements "in real time". We did it! We introduced the camera and a computer, we started testing and we knew the result before it was published in the scoreboard! Once, we checked that it worked, we started inviting technicians and relevant members of the IAAF to see the system working. Chance! César Moreno (Mexican) was in Europeans to teach the organization of the Daegu World Championships different aspects of the organization of athletic events.
In the 2011 IAAF Council, when the new VDM systems were presented, it was decided to include these systems in their regulations.
And finally, we received an order for our system to be official in Guadalajara 2011.
Today is the official system of the European Championships, two countries already have them for their national championships Mexico, and Turkmenistan, and soon will have the system, Poland.
But how does it work?
Graphics (Principles of operation)
A pixel or pixel (acronym of picture element) is the smallest homogeneous unit in color that is part of a digital image, be it this, a photograph, a video frame, or a graphic.
Zooming enough a digital image can be observed the pixels that make up the image. The pixels appear as small squares or rectangles each with a single color. The images are formed as a rectangular matrix of pixels, where each pixel forms a relatively small area with respect to the total image.
In bitmap images or graphical devices, each pixel is encoded by a set of bits of determined length (the so-called color depth), for example, a pixel can be coded with one byte (8 bits), so that each pixel admits 256 variations (28 variations with repetition of 2 possible values in one bit taken from 8 in 8). In the "true color" images, we usually use three bytes to define a color, that is, in total we can represent a total of 224 variations, which add up to 16,777,216 color options.
With this number we will make up the color of a single pixel. The color model RGB (Red-Green-Blue), used in computers, allows you to create a color by composing three basic colors: red, green and blue. In this way, depending on the amount of each of them that we use, we will see one result or another. For example, the yellow color is obtained by mixing red and green. The different shades of yellow are obtained by varying the proportion in which both components are involved. In the RGB model it is common to use 8 bits to represent the proportion of each of the three primary components. In this way, when one of the components is 0, it means that it does not intervene in the mix and when it is 255 (28 minus 1 because we started counting to 0) it means that it intervenes, providing the maximum of that tone.
Today there are two standard resolutions in the video market, the HD (High Definition) of 1920x1080 pixels, and the UHD (Ultra High Definition) or 4k definition of 3840x2160 pixels, both RGB.
The basic principle of system operation is based on the fact that the same distance in an image is related to a certain number of pixels depending on how far away from the point of capture of the image (video camera), and the variation of this distance is inversely proportional to the distance of said point.
That is to say, in other words, once the relationship between a distance (for example a meter) and a number of pixels is established, that same distance corresponds to a smaller number of pixels when going further away from the video camera.
To establish this proportionality, we must know the meter-pixel relation in the closest part, and the meter-pixel relation in the farthest point. Once these figures are known, we will perform an interpolation to obtain the distances in intermediate points of distance.
That is, once we determine the closest point of the athlete's bodyprint to the take off line, the system will calculate the number of pixels in a straight line up to said line, or the start of the pit (because the distance from the take off line to the pit is fixed and known), and multiply this number of pixels by the proportional amount of distance that corresponds to them depending on their distance from the video camera.
In order for the system to calculate the proportionality of distances on the closest side of the pit, and on the farthest side of the pit, it is necessary to place markers of pre-established proportions, or to point exact distances. This is that is called calibration.
The designs of the markers (figures that the system recognizes automatically or semiautomatically) depend on each manufacturer. In the case of Sport Solution, black 5x5 cm squares are placed on the edges of the pit.
These markers are used to calculate the proportionality of distances, exact points of distance to the take off line because this line does not appear in the image of the fall pit, and to verify at every moment that the cameras are static and have not moved regarding the original calibration. If the camera was moved, a re-calibration would be necessary before measuring a result again.
For the detection of the bodyprint, after clearing the pit and before the athlete's jump, the operator of the system will take a photograph from which it will then be compared with the image of the sand after the athlete's jump.
This is where the RGB values come into play. As we have said, each pixel is associated with three magnitudes between 0 and 255: one for the Red, another for the Green and another for the Blue. The computer will compare the magnitudes of each pixel in the previous photo, and the magnitudes in the pixels that occupy the same position in the current image. Any variation of magnitude in the Red, Green or Blue will suppose that it is a variation of the state of the arena respect before the athlete fell on it.
Configured in the opinion of the VDM operator, the tolerance margins to consider that there is a new mark on the arena, the system will automatically detect these changes, and allow the judge to select one of them, thus determining the athlete's result.
Margins of tolerance are necessary, especially in outdoor competitions, given the variations in luminosity that can occur during a competition, and to rule out variations such as the sand expelled by the athlete at the moment of impact.
Sport Solution's system, on the real image the system superimposes a series of graphs that help the judge to make the final decision that can be different from the one suggested by the system.
Tells the judge if the calibration marks are not in the same location as when the calibration was made.
It indicates in black to the judge if there is a variation of magnitudes in the colors Red, Green or Blue for each pixel, that is, the state of the sand has varied between the before and after the athlete's attempt and the system point in black all the points where the sand changed.
Shows the judge what is called perspective line that allows the judge to determine with certainty which is the closest print to the take off line. This is a basic tool because the rectangle that makes up the fall pit, in the video image is transformed into a trapezoid, therefore, the further we move away from the center of the trapeze two prints that are exactly the same distance from the edge Left or right will appear in the image more to the right and left respectively even though the same measurement. This triangle effect, also occurs in human vision, and therefore, the error of the measurement without VDM more common is that in even prints the judge always choose the closest print to him although this is not correct by several millimeters, or even centimeters.
Popularly when using EDM (not VDM), the judges do not measure all the prints, only one, so the measurement between pairs of prints is arbitrary and in some cases incorrect.
To all these advantages joins the fact that all jumps are recorded. The system has continuous video recording with what does not depend on the operator interaction for video recording of a jump. Take a picture before and after the jump, and save several photos of augmented reality with the calculations made by the system to help the judge in his decision making.
The recovery of the photo of the measurement, or the video that reproduces the fall, is fast and simple.
With this, the protests of the athletes can be attended without stopping the competition, and especially in case of claiming a fault jump, the athlete will never be given a new jump because the measurement can be made on the recording. Sport Solution with its system recommends that all jumps are always measured regardless if they are fault or not, becuase many times the athletes dismiss claim when they know that the dubious jump is not his best jump. The overmeasure without visual impact for the public is aware of it is also another added benefit that benefits the show.
The accuracy of the system is guaranteed, with the proper configuration of the system to the environmental characteristics, especially luminosity, the system will detect the slightest movement of a grain of sand. Detecting bib number drag as Spanovic in the recent World of London 2017, or impacts with the hair ponytail on the sand, things that at first glance are not so easy to detect.
The final accuracy will depend on the model and number of cameras used and the distance covered by each camera.
With two HD cameras, 1920 pixels, covering three meters each the final resolution will be of 3000/1920 = 1.5 mm theoretical, in practice between 2 and 3 mm. In Ultra HD, 3000/3840 = 0.78 mm theoretically, in practice between 0.9 and 1.5 mm.
Is it an expensive system? The HD system can be purchased from € 12,000