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# SCNParticleBirthDirection.surfaceNormal

The emitting direction for each particle is along the surface normal vector at the point where the particle is emitted.

```
case surfaceNormal
```

## Discussion

The particle system creates new particles at points in space defined by the [`emitterShape`](/documentation/SceneKit/SCNParticleSystem/emitterShape) geometry. When a new particle is emitted, the geometry’s surface normal vector at the point nearest the particle determines the particle’s initial direction. (Note that the [`birthLocation`](/documentation/SceneKit/SCNParticleSystem/birthLocation) property defines where particles may be created relative to the [`emitterShape`](/documentation/SceneKit/SCNParticleSystem/emitterShape) geometry.)

This value has no effect if the [`emitterShape`](/documentation/SceneKit/SCNParticleSystem/emitterShape) property value is `nil`.

---

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