---
title: "simd_axis(_:)"
framework: simd
role: symbol
role_heading: Function
path: "simd/simd_axis(_:)-56wzs"
---

# simd_axis(_:)

Returns the normalized axis about which the action of the specified quaternion rotates.

## Declaration

```swift
func simd_axis(_ q: simd_quatf) -> simd_float3
```

## Parameters

- `q`: The source quaternion.

## Return Value

Return Value The normalized axis about which the action of the source quaternion rotates.

## Discussion

Discussion This function returns a vector filled with nan if the source quaternion has a rotation of zero radians.

## See Also

### Applying geometric operations to quaternions

- [simd_act(_:_:)](simd/simd_act(_:_:)-2liww.md)
- [act(_:)](simd/simd_quatf/act(_:).md)
- [simd_angle(_:)](simd/simd_angle(_:)-zu9h.md)
- [simd_bezier(_:_:_:_:_:)](simd/simd_bezier(_:_:_:_:_:)-1z3gf.md)
- [simd_conjugate(_:)](simd/simd_conjugate(_:)-98bil.md)
- [simd_imag(_:)](simd/simd_imag(_:)-2c837.md)
- [simd_negate(_:)](simd/simd_negate(_:)-3yt2y.md)
- [simd_real(_:)](simd/simd_real(_:)-75sl3.md)
- [simd_slerp(_:_:_:)](simd/simd_slerp(_:_:_:)-u2db.md)
- [simd_slerp_longest(_:_:_:)](simd/simd_slerp_longest(_:_:_:)-3qens.md)
- [simd_spline(_:_:_:_:_:)](simd/simd_spline(_:_:_:_:_:)-1ok51.md)
- [simd_dot(_:_:)](simd/simd_dot(_:_:)-7frqx.md)
- [dot(_:_:)](simd/dot(_:_:)-2en8e.md)
- [simd_length(_:)](simd/simd_length(_:)-52nf5.md)
- [simd_normalize(_:)](simd/simd_normalize(_:)-uch9.md)