The big game will be played this weekend so I thought it might be interesting to review the technology behind the lines that TV adds to the field for down markers. Before the game begins, technicians make a digital 3-D model of the field, which is not flat. It is subtly curved with a crown in the middle to help water flow away. Each field is unique.
Technicians also put together two separate color palettes before
each game. One palette contains the colors for the field’s turf to
automatically be converted into yellow (or whatever color is used)
when the line is drawn onto the field. All other colors, such as
player and official uniforms, shoes, the ball, etc., go into the
other palette. Colors that appear on this second palette are never
converted. If a player’s foot is situated on the line, everything
around it will turn yellow, but not his foot.
Each camera used for the game contains sensors that record its
location, tilt, pan, zoom and transmit this data to the graphics
computers. These sensors allow the computers to process exactly
where each camera is within the 3-D model, along with the
perspective of each camera so the lines can be added to the picture.
One version requires a four-man crew and costs about $25,000 per
game to project the lines onto the field.