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Converting Datatypes
Description: This is a quick description of the changes in syntax for converting datatypes.Tutorial Level: INTERMEDIATE
Contents
C++
geometry_msgs
Datatypes from geometry_msgs are used both in tf and tf2:
1 #include "geometry_msgs/TransformStamped.h"
2
3 geometry_msgs::Vector3 vector;
4 geometry_msgs::Quaternion quaternion;
5 geometry_msgs::Transform transform;
6
7 geometry_msgs::Vector3Stamped stampedVector;
8 geometry_msgs::QuaternionStamped stampedQuaternion;
9
10 geometry_msgs::TransformStamped stampedTransformFull;
In tf you would do the following:
tf
Standard datatypes
1 #include "tf/transform_datatypes.h"
2
3 tf::Vector3 vector;
4 tf::Quaternion quaternion;
5 tf::Transform transform;
6
7 tf::Stamped<tf::Vector3> stampedVector;
8 tf::Stamped<tf::Quaternion> stampedQuaternion;
9 tf::Stamped<tf::Transform> stampedTransform;
10
11 tf::StampedTransform stampedTransformFull;
Conversion methods
Hard coded methods for bullet to message only.
Helper methods
tf/transform_datatypes.h has static helper methods for creating quaternions
tf2
Standard datatypes
In tf2, they are the same, just in tf2 namespace:
1 #include "tf2/transform_datatypes.h"
2
3 tf::Vector3 vector;
4 tf::Quaternion quaternion;
5 tf::Transform transform;
6
7 tf2::Stamped<tf2::Vector3> stampedVector;
8 tf2::Stamped<tf2::Quaternion> stampedQuaternion;
9 tf2::Stamped<tf2::Transform> stampedTransform;
10
11 // there's no TF2 counterpart of tf::StampedTransform
12 // tf2::StampedTransform stampedTransformFull;
13
If you want a counterpart of tf::StampedTransform in tf2, you need to go with geometry_msgs::TransformStamped. Please note that tf2::Stamped<tf2::Transform> has no child_frame_id field which is required within the ROS tf/tf2 framework.
Conversion methods
With tf2 there is a templated convert method. This allows a modular design which can convert any datatype which implements the overloaded template methods.
Same result using bullet and message bindings:
Much more extensible to convert bullet to kdl:
These headers are packaged in their own packages and allows packages to only depend on the converters they actually need.
Current implementations include tf2_bullet tf2_eigen tf2_kdl tf2_geometry_msgs
You can also create your own datatype conversions. There are tutorials for C++ and Python
Helper methods
tf2/transform_datatypes.h doesn't have the quaternion helper functions (you should use tf2::Quaternion methods in conjunction with tf2::convert()).
