Defining Hatch Boundaries: Using Island Detection Methods in AutoCAD

Island detection methods specify whether to include objects within the outermost boundary as boundary objects when you are using Pick Points. These internal objects are known as islands. By default, AutoCAD uses the Flood island detection method. The Flood method includes islands as boundary objects, as shown in the following illustration. How AutoCAD hatches the detected islands depends on the island detection style. The following illustration uses the Normal island detection style, meaning that islands remain unhatched and islands within islands are hatched.

If you do not want to include islands as boundary objects when using Pick Points, use the Ray Casting island detection method. Ray Casting runs a line from the point you specify to the nearest object and then traces the boundary in a counterclockwise direction, thus excluding islands from boundary detection.
You can find these options on the Advanced tab of the Boundary Hatch dialog box.
When you define boundaries by selecting objects rather than specifying points, the island detection method has no effect on how AutoCAD derives the boundary definition.

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