template<typename _Scalar, int _Options>
 class Eigen::Quaternion< _Scalar, _Options >
 The quaternion class used to represent 3D orientations and rotations. 
 This is defined in the Geometry module.
#include <Eigen/Geometry> 
- Template Parameters
-   
| _Scalar | the scalar type, i.e., the type of the coefficients |  
| _Options | controls the memory alignment of the coefficients. Can be # AutoAlign or # DontAlign. Default is AutoAlign. |  
 
This class represents a quaternion \( w+xi+yj+zk \) that is a convenient representation of orientations and rotations of objects in three dimensions. Compared to other representations like Euler angles or 3x3 matrices, quaternions offer the following advantages: 
 - 
compact storage (4 scalars) 
- 
efficient to compose (28 flops), 
- 
stable spherical interpolation
The following two typedefs are provided for convenience: 
 - 
Quaternionfforfloat
- 
Quaterniondfordouble
- Warning
- Operations interpreting the quaternion as rotation have undefined behavior if the quaternion is not normalized.
- See also
- class AngleAxis, class Transform 
   |  | 
 | template<typename Derived1 , typename Derived2 > | 
 
| Quaternion< Scalar, Options > | FromTwoVectors (const MatrixBase< Derived1 > &a, const MatrixBase< Derived2 > &b) | 
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|  | Quaternion () | 
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|  | Quaternion (const AngleAxisType &aa) | 
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 | template<typename Derived > | 
 
|  | Quaternion (const MatrixBase< Derived > &other) | 
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 | template<typename OtherScalar , int OtherOptions> | 
 
|  | Quaternion (const Quaternion< OtherScalar, OtherOptions > &other) | 
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 | template<class Derived > | 
 
|  | Quaternion (const QuaternionBase< Derived > &other) | 
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|  | Quaternion (const Scalar &w, const Scalar &x, const Scalar &y, const Scalar &z) | 
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|  | Quaternion (const Scalar *data) | 
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 |  Public Member Functions inherited from Eigen::QuaternionBase< Quaternion< _Scalar, _Options > > | 
 
| Vector3 | _transformVector (const Vector3 &v) const | 
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| internal::traits< Quaternion< _Scalar, _Options > >::Scalar | angularDistance (const QuaternionBase< OtherDerived > &other) const | 
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| internal::cast_return_type< Quaternion< _Scalar, _Options >, Quaternion< NewScalarType > >::type | cast () const | 
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| internal::traits< Quaternion< _Scalar, _Options > >::Coefficients & | coeffs () | 
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| const internal::traits< Quaternion< _Scalar, _Options > >::Coefficients & | coeffs () const | 
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| Quaternion< Scalar > | conjugate () const | 
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| Scalar | dot (const QuaternionBase< OtherDerived > &other) const | 
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| Quaternion< Scalar > | inverse () const | 
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| bool | isApprox (const QuaternionBase< OtherDerived > &other, const RealScalar &prec=NumTraits< Scalar >::dummy_precision()) const | 
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| Scalar | norm () const | 
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| void | normalize () | 
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| Quaternion< Scalar > | normalized () const | 
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| bool | operator!= (const QuaternionBase< OtherDerived > &other) const | 
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| Quaternion< typename internal::traits< Quaternion< _Scalar, _Options > >::Scalar > | operator* (const QuaternionBase< OtherDerived > &other) const | 
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| Quaternion< _Scalar, _Options > & | operator*= (const QuaternionBase< OtherDerived > &q) | 
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| Quaternion< _Scalar, _Options > & | operator= (const AngleAxisType &aa) | 
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| Quaternion< _Scalar, _Options > & | operator= (const MatrixBase< MatrixDerived > &xpr) | 
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| bool | operator== (const QuaternionBase< OtherDerived > &other) const | 
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| Quaternion< _Scalar, _Options > & | setFromTwoVectors (const MatrixBase< Derived1 > &a, const MatrixBase< Derived2 > &b) | 
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| QuaternionBase & | setIdentity () | 
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| Quaternion< typename internal::traits< Quaternion< _Scalar, _Options > >::Scalar > | slerp (const Scalar &t, const QuaternionBase< OtherDerived > &other) const | 
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| Scalar | squaredNorm () const | 
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| Matrix3 | toRotationMatrix () const | 
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| VectorBlock< Coefficients, 3 > | vec () | 
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| const VectorBlock< const Coefficients, 3 > | vec () const | 
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| NonConstCoeffReturnType | w () | 
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| CoeffReturnType | w () const | 
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| NonConstCoeffReturnType | x () | 
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| CoeffReturnType | x () const | 
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| NonConstCoeffReturnType | y () | 
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| CoeffReturnType | y () const | 
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| NonConstCoeffReturnType | z () | 
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| CoeffReturnType | z () const | 
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 |  Public Member Functions inherited from Eigen::RotationBase< Derived, _Dim > | 
 
| Derived | inverse () const | 
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| RotationMatrixType | matrix () const | 
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 | template<typename OtherDerived > | 
 
| internal::rotation_base_generic_product_selector< Derived, OtherDerived, OtherDerived::IsVectorAtCompileTime >::ReturnType | operator* (const EigenBase< OtherDerived > &e) const | 
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 | template<int Mode, int Options> | 
 
| Transform< Scalar, Dim, Mode > | operator* (const Transform< Scalar, Dim, Mode, Options > &t) const | 
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| Transform< Scalar, Dim, Isometry > | operator* (const Translation< Scalar, Dim > &t) const | 
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| RotationMatrixType | operator* (const UniformScaling< Scalar > &s) const | 
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| RotationMatrixType | toRotationMatrix () const | 
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   template<typename _Scalar , int _Options> 
  template<typename Derived1 , typename Derived2 > 
   
 Returns a quaternion representing a rotation between the two arbitrary vectors a and b. In other words, the built rotation represent a rotation sending the line of direction a to the line of direction b, both lines passing through the origin.
 
- Returns
- resulting quaternion
Note that the two input vectors do not have to be normalized, and do not need to have the same norm.