How do you catch regi ice regi steel and regi rock in Pokemon platinum?

First you need the special event Regigigas in order to activate Regirock, Regice and Registeel. All 3 of them are in different caves scattered through the Sinnoh region in Platinum. Regirock is in a cave within Route 228, Regice is in a cave in Mt. Coronet which is near the exit to Route 216 and Registeel is in a cave within Iron Island.