Editing Artist Help:Pixel Array Tools (section)

=== Alignment Position ===
This box displays the position where the array defined in the Alignment box will be placed. The values are set when you select fixtures in the Fixture View. The position of the first fixture is used to define this value.

Use the Capture button to define another position by moving the mouse over the Fixture View and clicking at the appropriate point. This will define a new point for the array placement.