getTransform from ROS2 bag

Hi,

I want to access Transform from a ROS2bag, the same way you can with the tf2_msgs/LookupTransform action.

I first tried to use getTransform but it only seems to work with ROS1Bags.

>> bag = ros2bag(rosbag_path);

getTransform(bag,'F_FDB','F_RER1',bag.EndTime);

Check for incorrect argument data type or missing argument in call to function 'getTransform'.

I can still access the tf2_msgs/TFMessage in the bag so I worked out a way to convert them to a ROS1bag and access the TF.

bag_tf = readMessages(select(bag,"Topic",["/tf", "/tf_static"]));

bag_writer = rosbagwriter('tf_ros1.bag');

tf2Msg = rosmessage('tf2_msgs/TFMessage',"DataFormat","struct");

tf2Msg.Transforms=rosmessage('geometry_msgs/TransformStamped',"DataFormat","struct");

for bag_idx = 1:length(bag_tf)

bag_msg=bag_tf{bag_idx};

for tf_idx = 1:length(bag_msg.transforms) %Some message contain multiple TFs

tf = bag_msg.transforms(tf_idx);

tf2Msg.Transforms.Header.Stamp.Sec = uint32(tf.header.stamp.sec);

tf2Msg.Transforms.Header.Stamp.Nsec = uint32(tf.header.stamp.nanosec);

tf2Msg.Transforms.Header.FrameId = tf.header.frame_id;

tf2Msg.Transforms.ChildFrameId = tf.child_frame_id;

tf2Msg.Transforms.Transform.Translation.X = tf.transform.translation.x;

tf2Msg.Transforms.Transform.Translation.Y = tf.transform.translation.y;

tf2Msg.Transforms.Transform.Translation.Z = tf.transform.translation.z;

tf2Msg.Transforms.Transform.Rotation.X = tf.transform.rotation.x;

tf2Msg.Transforms.Transform.Rotation.Y = tf.transform.rotation.y;

tf2Msg.Transforms.Transform.Rotation.Z = tf.transform.rotation.z;

tf2Msg.Transforms.Transform.Rotation.W = tf.transform.rotation.w;

write(bag_writer, "/tf", tf2Msg.Transforms.Header.Stamp, tf2Msg);

end

end

delete(bag_writer)

clear bag_writer

reader = rosbagreader('tf_ros1.bag');

getTransform(reader,'F_FDB','F_RER1')

It does work but it's really unpractical. So i was wondering if I missed something to make getTransform directly work with a ROS2bag ?

Thank you in advance for any help !

Antoine H.

Answer 1

[Jagadeesh Konakalla]

Hi Antonie,

Unfortunately, we do not have easy workaround to provide you.

We are working on adding getTransofromations capability to ros2bag. This feature will be available in future releases of MATLAB.

Thanks,

Jagadeesh K.