Machine Referee’ ABS is also possible error

The automated ball-strike system, or ABS, is the most popular work of the KBO League in 2024. Machines are replacing strike and ball judgments from this year, which have long been the exclusive property of human referees.안전놀이터

Many baseball fans welcome the article, saying, “The judgment has become fair.” The May 2 column of The Kyunghyang Shinmun said, “All traditional systems work in favor of vested interests. Young players play an active role as the bias (psychological) of judges is removed from ball judgment.” Politicians also contributed. Lee Jae-myung, the leader of the main opposition Minjoo Party of Korea, introduced the column on social media and commented, “Objectivity and rationality are the driving forces behind the development.”

ABS has elements as important as “mechanical measurement.” This defines a strike zone. This is because the zone that was actually applied in the baseball field is quite different from the zone defined in the baseball rules (see article No. 863, “Robot referee is coming, who else is it favorable to?”). ABS also adopts a different zone from the definition of the baseball rules. Players who play in the field were given a difficult task of adapting to the new zone.

However, there are also questions about the ABS’s reliability. One example is the argument that “the zones vary from stadium to stadium.” Multiple clubs and players make such remarks. Of course, a person’s senses could have caused a mistake. However, the same argument was made in the U.S. minor league, which adopted ABS before the KBO league. The U.S. sports media The Athletic introduced Kyle Mansardo, a promising player with the Cleveland Guardians, in a report in August last year, saying, “The zones seem to be slightly different for each stadium.” The article added, “Mansardo is not the only one saying this.” If multiple people say the same thing at different times and places about similar systems, it is worth listening to.

Can a mechanical umpire’s strike zone change from stadium to stadium? I asked Shin Dong-yoon, director of the Korea Baseball Organization. Shin is an expert on tracking systems that chase pitches and hits, and has participated in the construction of systems currently used by KBO League clubs. ABS is based on a tracking system called PTS. “It is theoretically possible that the tracking system tends to be biased toward each stadium,” Shin said.

PTS is a system manufactured by Sports Vision Corporation in the U.S. and tracks a pitch using three cameras. In Korea, PTS is operated by Sports2i, the official KBO record label. Prior to ABS, PTS was used to evaluate judges’ zone decisions. PTS was first introduced to the Major League under the name “Pitchf/x” in 2006. Since then, a radar-based system “Trackman” and a “Hawk-Eye” that uses 15 cameras have appeared.

The PTS recognizes and tracks where the ball is on the camera screen. The image coordinate value is two-dimensional (2D), but the actual baseball coordinate is three-dimensional (3D). Therefore, it has to go through World Coordinate Conversion, which obtains 3D coordinates from different viewpoint camera images and matches them with the actual coordinates in the ballpark again. To this end, it is necessary to establish a relationship between the image coordinate value recognized by the camera and a specific point in the ballpark. In a tracking system, it is common to input where the home plate vertex, the center of the mound, and the arbitrary coordinates on the straight line connecting the two correspond to in the image coordinate system.

Errors can occur in this process. Location values can be entered incorrectly and computational errors can be amplified under certain conditions in the conversion operation. Errors can be classified by type as follows.

First, “human error.” System operators typically zero a certain spot in the ballpark before a game by taking pictures of it. Wrong zeroing will result in “tipping”. There is also a possibility that a system that automatically adjusts the zero can cause errors in the recognition of a certain location.

Second, the ground variable. The coordinate transformation assumes that the ground is completely flat and that all positions on the ground are at exactly the same height as the home plate vertex. It is assumed that the mound is also consistent with the baseball rules and regulations. However, if the actual ground conditions are different from the regulations, errors will inevitably occur. Of course, the tracking system has the function to set the mound height. However, the input value and the actual value may be different.

Third, sensor location information. Even if the information collected by the sensor is accurate, if there is an error in the information where the sensor is located, the coordinate transformation result will also have an error. A baseball stadium is a reinforced concrete building. The structure that supports the sensor contracts or expands depending on temperature or humidity. The exact location information when first installed may vary during the operating period. The location can be misplaced due to unexpected vibrations. So, pre-game inspections should be carried out. If the sensor location in a specific stadium is different from that of the rest of the stadiums and is out of optimal location due to stadium conditions, “Tall” appears.

For this reason, several tracking systems operated by Major League Baseball frequently experienced errors in the early stages of their introduction. Even the most recent Hawk Eye was unable to be free from this issue. As a result, the Major League Baseball installed this system at all stadiums, corrected errors, and provided formal services a year before its formal introduction.

Sports2i, which runs the ABS, says, “Because coordinate measurement is set based on home plate, it cannot differ from stadium to stadium.” Sports2i may be right in its explanation. However, as we have seen “theoretically” above, there is always a possibility of errors in the operation process. No system can be perfect from the first year of its introduction. This is why thorough and routine inspection is necessary as it is the most important strike zone issue in baseball’s judgment.

The above problem occurs in the operation process, not the accuracy or precision of the system itself. There is also an accuracy problem required by the system. The minimum unit of camera screen is pixels. However, the number of pixels occupied by a baseball is not large.

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