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# extent

The size of the reference object’s space-mapping data.

```
var extent: simd_float3 { get }
```

## Discussion

The [`extent`](/documentation/ARKit/ARWorldMap/extent) and [`center`](/documentation/ARKit/ARWorldMap/center) properties together define a bounding box for the data recorded in the reference object in its local coordinate system. You define that coordinate system with the transform parameter when calling `extractReferenceObject(transform:center:extent:)`, and can modify it by creating another reference object with [`applyingTransform(_:)`](/documentation/ARKit/ARReferenceObject/applyingTransform(_:)).

---

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