OS digital markings, how?

[Color me Dan]

I've been watching some OS swimming (ok, not me but my dad) among other things today and my dad asked me how they do the country markings so perfectly in real time. If you haven't seen what I'm talking about it's when they film the swimming every contestant swim in their own lane. Each lane gets an overlay with the flag and name of the swimmer. Sometimes they add lines to the pool to sho things like previous time and stuff. When they switch camera angles and move the camera it's so well done that there is little to no jitering of the overlays. How do they do it? reflector markers on the sides of the pool to get the accurate perspective and point to lock on to? Since it's live they can't edit it afterwards obviously. Anyone know what they do?

Either way it looks awesome.

 

[Bludd]

OS = Olympiska Spelen

Should be at least OG in english, Olympic Games.

 

[epicstruggle]

very similar to this:
http://www.howstuffworks.com/first-down-line.htm

 

[Color me Dan]

Gah, sorry about that, I obviously mean the Olympic Games! *slaps forehead*