Question

I'm trying to convert a Matrix3d rotation to a Quaternion<double>, but I got only weird compiler errors so far. The code I'm using is:

Quaternion<double> getQuaternionFromRotationMatrix(const Matrix3d& mat)
{
    AngleAxisd aa; 
    aa = mat;
    Quaternion<double> q = aa;// conversion error

    return q;
}

And the compiler errors:

path/src/Utils.cpp: In function ‘Eigen::Quaternion<double> Utils::getQuaternionFromRotationMatrix(const Matrix3d&)’:
path/src/Utils.cpp:55:26: error: conversion from ‘Eigen::AngleAxisd {aka Eigen::AngleAxis<double>}’ to non-scalar type ‘Eigen::Quaternion<double>’ requested
In file included from /usr/local/include/eigen3/Eigen/Core:283:0,
                 from /usr/local/include/eigen3/Eigen/Dense:1,
                 from path/include/Utils.h:4,
                 from path/src/Utils.cpp:1:
/usr/local/include/eigen3/Eigen/src/Core/Assign.h: In member function ‘Derived& Eigen::DenseBase<Derived>::lazyAssign(const Eigen::DenseBase<OtherDerived>&) [with OtherDerived = Eigen::Matrix<double, 3, 1>, Derived = Eigen::Block<Eigen::Matrix<double, 4, 4>, 4, -0x00000000000000001, true, true>]’:
/usr/local/include/eigen3/Eigen/src/Core/Assign.h:534:123:   instantiated from ‘static Derived& Eigen::internal::assign_selector<Derived, OtherDerived, false, false>::run(Derived&, const OtherDerived&) [with Derived = Eigen::Block<Eigen::Matrix<double, 4, 4>, 4, -0x00000000000000001, true, true>, OtherDerived = Eigen::Matrix<double, 3, 1>]’
/usr/local/include/eigen3/Eigen/src/Core/Assign.h:574:89:   instantiated from ‘Derived& Eigen::MatrixBase<Derived>::operator=(const Eigen::DenseBase<OtherDerived>&) [with OtherDerived = Eigen::Matrix<double, 3, 1>, Derived = Eigen::Block<Eigen::Matrix<double, 4, 4>, 4, -0x00000000000000001, true, true>]’
path/src/Utils.cpp:34:20:   instantiated from here
/usr/local/include/eigen3/Eigen/src/Core/Assign.h:504:3: error: static assertion failed: "YOU_MIXED_MATRICES_OF_DIFFERENT_SIZES"

Does someone know how to convert between both representations?

Was it helpful?

Solution

The constructors from an AngleAxis or Matrix are explicit meaning you have to write the conversion as follow:

Matrix3f mat;
Quaternionf q(mat);

or

Quaternionf q;
q = mat;

Same for AngleAxis.

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