Restricted Skylines

Normal sudoku and killer cage rules apply. Each digit in the grid is a "skyscraper" whose height is the digit in that cell. Taller skyscrapers obscure the view of smaller ones. Clues outside the grid tell how many skyscrapers are visible looking across the row or column from the direction of the clue. Isotropic groups: Each group of nine cells occupying the same relative position in the nine boxes is isotropic: all nine are from {123} or all nine are from {456} or all nine are from {789}.