# halfExtent A location marking the end of the field’s area of effect. ``` var halfExtent: SCNVector3 { get set } ``` ## Discussion To define a field’s area of effect, use the [`position`](/documentation/SceneKit/SCNNode/position) property of the node that contains the field and the field’s [`halfExtent`](/documentation/SceneKit/SCNPhysicsField/halfExtent) property. The center of the area of effect is the node’s position. The half-extent, a position vector in the local coordinate space of the node containing the field, marks one corner of a box, and the negative of the half-extent vector marks the opposite corner of the box. For example, if a node’s position is the vector `{2.0, 2.0, 2.0}` and it contains a physics field whose half-extent is the vector `{0.5, 0.5, 0.5}`, the field’s area of effect is the box extending from `1.5` to `2.5` along each axis of the scene’s coordinate system. By default, a field’s area of effect is the interior of this box shape. Use the [`usesEllipsoidalExtent`](/documentation/SceneKit/SCNPhysicsField/usesEllipsoidalExtent) property to instead make the area of effect an ellipsoid bounded by this box. Use the [`scope`](/documentation/SceneKit/SCNPhysicsField/scope) property to choose whether the area of effect is the interior or exterior of the box (or ellipsoid). The default half-extent is the vector `{INFINITY, INFINITY, INFINITY}`, specifying that the field affects bodies located anywhere in the scene. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)