The video below is provided by Qastar News (www.qps.il). It shows the position and course and speed of the Costa Concordia before, during and after the grounding. Some of what you see here is conjecture and some is derived right from the AIS (Automated Identification System) data stream. Clearly, the ship's captain erred in his initial navigation. He got too close to the rocks that damaged the ship, probably because he miscalculated the ship's dead reckoned position. It has been reported he was navigating by line of sight observations of landmarks on the island.
A point of interest here is the change of color of the graphic for the ship's position. It changes from green to yellow. In the AIS color scheme; Red indicates an identified ship that is considered a potential danger; green indicates an identified ship that is not a potential danger; yellow indicates an "unidentified" ship that is not a potential danger.
So why did the Costa Concordia become an unidentified ship? Perhaps it went from green to yellow because it lost power to the equipment that transmitted some of its data. Or perhaps Qastar interpolated the data for the ship when its speed dropped below a certain value. If this happened, the AIS plotter could no longer determine exactly how it was moving through the water.
Meanwhile, given what we're seeing here, it was quite a piloting feat to lay the ship on that sandbar.