Transformation in Quaternion space for Geometry_msgs/poseStamped message

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Hi,

I am new to ROS and RTT.

Given the Geometry_msgs/poseStamped message from two topics, how to calculate the transform T (Relative position) at time t1.

T^t1 = Relative_position (Pose_1^t1, pose_2^t1)

so that it can be used to locate the position of one frame from other in the same environment at time stamp t2.

Pose_1^t2 = Inverse_relative_position (T^t1, Pose_2^t2)

Precisely the calculation of Transformation equivalent to Homogeneous Transformation and using this transformation in Quaternion space to calculate the position of a point relative to a base frame.