Great timing on Vox's part in explaining this magical yellow virtual first-down line in the NFL. Today is the Super Bowl game between the Carolina Panthers and the Denver Broncos and if you've always wondered how that wonderful yellow line crosses the field without going over players' uniforms -- making it seem like the yellow line is actually on the field itself no matter what camera angle -- then this video is for you. Lots of tech, engineering, and mathematical calculations involved as you can imagine.
The company behind it is Sportvision and they do a ton of other on-screen graphics during live broadcasts of sports games.