Localization, using robot_localization and robot_pose_ekf

edit

To add to the second answer, you probably don't want to find the transform between odom_frame and base_frame if you're trying to calculate a distance on a map. The transform between map_frame and base_farme is generally more useful. The difference can be small, but odom_frame can move relative to the map.

Also amcl_pose topic publishes a coordinate system. Why we don't use amcl_pose topic to calculate distance.

Maybe there is a misconception in my head....

if i subscribe amcl_pose and take the x and y coordinate, will it equals the <map_frame and="" base_frame="" &gt;="" calculation.<="" p="">

Another thing i confused ....

My odom file publish odom0 topic and odom_frame-->base_link transformation... My ekf file subscribe odom0 topic and imu/data topic and publish odom topic... And also publish odom_frame-->base_link transformation.

In that way 2 different node publish same transfer function odom_frame--> base_link... Is this right way or do i need to change frames name , tf.

Using the amcl_pose topic is probably fine and should yield similar results for simple applications, but using the transform tree tends to be more versatile and robust; you can control the timing more easily for example.

Yes, renaming the frame(s) to avoid redundancy is a good idea. You will have issues if multiple sources publish conflicting transforms. Your robot may start jumping around the map.