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transformations.md

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description
Frame hopping.

Transformations

Use minkindr to represent transformations.

{% embed url="https://github.com/ethz-asl/minkindr" %}

Further details on the transformation notation, frame names and conventions can be found on the wiki page.

{% embed url="https://github.com/ethz-asl/mav_tools_public" %}

TF2

tf-remapping

Here,

  • old: contains the name of tf that needs to be remapped
  • new: new name of tf
<launch>
 
 <!--tf remmapper node-->
  <node pkg="tf" type="tf_remap" name="tf_remapper" output="screen">
    <rosparam param="mappings">
      [{old: /imu, new: /base_link}]
    </rosparam>
  </node>

 <!--node whose tf needs to be remapped-->
  <node pkg="rosbag" type="play" name="player" args="/home/drive/test.bag">
    <remap from="tf" to="tf_old" />
  </node>

</launch>

The topic subscribed to is:

/tf_old (tf/tfMessage) -- Old transform tree. This is usually published by remapping playback of a bag file. You may need to set use_sim_time as true for the bag file transforms to be accepted.

The topic published is:

/tf (tf/tfMessage) -- Current transform tree. This is the normal /tf topic.

publish-static-transforms

static_transform_publisher x y z yaw pitch roll frame_id child_frame_id period_in_ms

Publish a static coordinate transform to tf using an x/y/z offset in meters and yaw/pitch/roll in radians. (yaw is rotation about Z, pitch is rotation about Y, and roll is rotation about X). The period, in milliseconds, specifies how often to send a transform. 100ms (10hz) is a good value.

static_transform_publisher x y z qx qy qz qw frame_id child_frame_id period_in_ms

Publish a static coordinate transform to tf using an x/y/z offset in meters and quaternion. The period, in milliseconds, specifies how often to send a transform. 100ms (10hz) is a good value.

static_transform_publisher is designed both as a command-line tool for manual use, as well as for use within roslaunch files for setting static transforms. For example:

<launch>
<node pkg="tf" type="static_transform_publisher" name="link1_broadcaster" args="1 0 0 0 0 0 1 link1_parent link1 100" />
</launch>