It looks like most options have been covered, but I'll throw in what we use. The retro-reflective tape will direct a reflected light directly back to its source, rather than at an angle like with a mirror, so this is how most teams (including ours) work it out. We use the Axis camera (available on AndyMark) with a LED ring around it (we got it here and it works well
http://www.superbrightleds.com/morei...ent-lights/49/.) Just wire the camera into the 5V built-in wago on the PDB and hook the ethernet up to the D-LINK. We hooked the LEDs up to a spike with a 5A breaker that would turn on when the robot is enabled. From there, the programmers can use vision processing to detect the location of the robot and which goal is hot based on the proportion of the rectangle and if a horizontal rectangle is visible or not. Good luck!