[tf_eigen] Intended use of toMsg specialization

[artivis]

I wonder what is the intended use of the following conversion specialization (tf2_eigen.h#L154) introduced in #294,

geometry_msgs::Vector3& toMsg(const Eigen::Vector3d& in, geometry_msgs::Vector3& out)

since it does not seems to follow the specialization pattern of toMsg. Is it meant to be called directly rather than through tf2::convert ??

Adding the following test snippet to tf2_eigen's tests results in a compilation error:

TEST(TfEigen, ConvertVector3dToVector3)
{
  const Eigen::Vector3d v(1,2,3);

  Eigen::Vector3d v1;
  geometry_msgs::Vector3 p1;
  tf2::convert(v, p1);
  tf2::convert(p1, v1);

  EXPECT_EQ(v, v1);
}

Error:

geometry2/tf2/include/tf2/impl/convert.h: In instantiation of ‘static void tf2::impl::Converter<IS_MESSAGE_A, IS_MESSAGE_B>::convert(const A&, B&) [with A = Eigen::Matrix<double, 3, 1>; B = geometry_msgs::Vector3_<std::allocator<void> >; bool IS_MESSAGE_A = false; bool IS_MESSAGE_B = true]’:
geometry2/tf2/include/tf2/convert.h:51:113:   required from ‘void tf2::convert(const A&, B&) [with A = Eigen::Matrix<double, 3, 1>; B = geometry_msgs::Vector3_<std::allocator<void> >]’
geometry2/tf2_eigen/test/tf2_eigen-test.cpp:65:21:   required from here
geometry2/tf2/include/tf2/impl/convert.h:65:5: error: no match for ‘operator=’ (operand types are ‘geometry_msgs::Vector3_<std::allocator<void> >’ and ‘geometry_msgs::Point {aka geometry_msgs::Point_<std::allocator<void> >}’)
   b = toMsg(a);
   ~~^~~~~~~~~~
In file included from /opt/ros/melodic/include/geometry_msgs/Transform.h:18:0,
                 from /opt/ros/melodic/include/geometry_msgs/TransformStamped.h:19,
                 from geometry2/tf2/include/tf2/transform_functions.h:37,
                 from geometry2/tf2_eigen/include/tf2_eigen/tf2_eigen.h:32,
                 from geometry2/tf2_eigen/test/tf2_eigen-test.cpp:30:
/opt/ros/melodic/include/geometry_msgs/Vector3.h:22:8: note: candidate: constexpr geometry_msgs::Vector3_<std::allocator<void> >& geometry_msgs::Vector3_<std::allocator<void> >::operator=(const geometry_msgs::Vector3_<std::allocator<void> >&)
 struct Vector3_
        ^~~~~~~~
/opt/ros/melodic/include/geometry_msgs/Vector3.h:22:8: note:   no known conversion for argument 1 from ‘geometry_msgs::Point {aka geometry_msgs::Point_<std::allocator<void> >}’ to ‘const geometry_msgs::Vector3_<std::allocator<void> >&’
/opt/ros/melodic/include/geometry_msgs/Vector3.h:22:8: note: candidate: constexpr geometry_msgs::Vector3_<std::allocator<void> >& geometry_msgs::Vector3_<std::allocator<void> >::operator=(geometry_msgs::Vector3_<std::allocator<void> >&&)
/opt/ros/melodic/include/geometry_msgs/Vector3.h:22:8: note:   no known conversion for argument 1 from ‘geometry_msgs::Point {aka geometry_msgs::Point_<std::allocator<void> >}’ to ‘geometry_msgs::Vector3_<std::allocator<void> >&&’

Clearly the 'proper specialization' is not found.

---

os: ubuntu 18.04 ros: melodic-devel

[IanTheEngineer]

Good find and test @artivis . I need to go back through my notes on this, but I believe your assessment is correct. I needed this function to exist to do some conversions for MoveIt to fully convert to tf2, using the toMsg or fromMsg directly where appropriate, and sometimes using the convert methods. I don't recall if I used the convert method directly for these functions.

[artivis]

Thanks for the reply. This issue is unfortunate as it gives the false feeling that convert would work for those types too. Looking at the convert traits mechanism there doesn't seems to be a simple fix without breaking something.