the meaning of function lookupTransform

asked 2021-10-06 20:18:53 -0500

Laura
35 ●1 ●5 ●7

\param target_frame The frame to which data should be transformed
\param source_frame The frame where the data originated
\param time The time at which the value of the transform is desired. (0 will get the latest)
\return The transform between the frames

geometry_msgs::TransformStamped lookupTransform(const std::string& target_frame, const std::string& source_frame, const ros::Time& time) const;

I don't know it returns the transform from target_frame to source_frame ,or the transform from source_frame to target_frame .This makes me a little confused. I would be very grateful if anyone could help me

answered 2021-10-07 09:11:35 -0500

Mike Scheutzow
4918 ●2 ●430 ●45

updated 2021-10-07 09:13:00 -0500

The argument names for this function assume a very specific use case.

If I rename the arguments lookupTransform(a, b, time) then what this function does is return an object specifying the pose of frame_b relative to frame_a. For a simple planar 2D example, if frame_a and frame_b are initially aligned and have yaw=0, shifting frame_b to the right 1 meter will result in this function returning transform.translation.x = 1.0.

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Thank you very much for your answer! As a beginner, I am not very familiar with some common terms in ROS.But I found through a little experiment thatlookupTransform(T2,T1,time)(T1 and T2 are two coordinate systems)will return transform.translation.x which is the coordinates of the origin of T1 coordinate system in the T2 coordinate system. And I think this is the same as what you explained. So I guess, suppose the coordinate of an object in the T2 coordinate system is X2, and the coordinate in the T1 coordinate system is X1, then X2=R21*X1+τ21, R and τ are the rotation transformation and translation transformation returned by the function , and 21 means transform from 1 to 2, which corresponds exactly to 1 as source and 2 as target. In the sense of matrix theory, this may be a transformation matrix between the ...(more)

Laura ( 2021-10-07 11:12:19 -0500 )edit

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