Normal sudoku rules apply. Draw a non-intersecting loop along some edges of the grid. Aliens are inside the loop and cacti are outside the loop. A digit in a white square indicates the number of that cell’s edges that are part of the loop. A digit in a white circle is inside the loop and indicates the number of cells inside the loop “seen” horizontally and vertically, including the circled cell itself. Cells outside the loop obstruct vision. The loop passes through a white dot in a straight line, then makes a 90-degree turn on one or both of the nearest cell corners along the loop. The loop makes a 90-degree turn on a black dot, and does not turn at the next opportunity in either direction. Diagonally adjacent cells joined by a white dot contain consecutive digits and by a black dot contain digits in a 1:2 ratio.