How to subscribe to a static_transform_publisher node?

asked 2021-11-19 22:00:37 -0600

jasr gravatar image


I have a bunch of frames that I created using the static_transform_publisher option from tf2 in ros2. I created them as follows:

Node( package='tf2_ros', executable='static_transform_publisher', arguments = ['0', '0', '0.5', '0', '0', '0', 'robot-base', 'robot-base_CoM'] ),

So now I want to create a listener package that access the new frames positions and publishes a new frame, but I can't make that work. Right now this is what I have following the tf2 tutorials:

class CoM_listener(Node):

def __init__(self):

    # Declare and acquire `target_frame` parameter
    self.declare_parameter('target_frame', 'right_hand_CoM')
    self.target_frame = self.get_parameter('target_frame').get_parameter_value().string_value

    self.tf_buffer = Buffer()
    self.tf_listener = TransformListener(self.tf_buffer, self)

    # Call on_timer function every second
    self.timer = self.create_timer(1.0, self.on_timer)

def on_timer(self):
    # Store frame names in variables that will be used to
    # compute transformations
    from_frame_rel = self.target_frame
    to_frame_rel = 'robot-base'

    # Look up for the transformation between target_frame and CoM frames
        now = rclpy.time.Time()
        trans = self.tf_buffer.lookup_transform(to_frame_rel, from_frame_rel, now)
    except TransformException as ex:
            f'Could not transform {to_frame_rel} to {from_frame_rel}: {ex}')

    msg = Pose()
    msg.position.x = trans.transform.translation.x * 2
    msg.position.y = trans.transform.translation.y * 2
    msg.position.z = trans.transform.translation.z * 2


def main(): rclpy.init() node = CoM_listener() try: rclpy.spin(node) except KeyboardInterrupt: pass rclpy.shutdown()

But I keep getting errors like:

AttributeError: 'CoM_listener' object has no attribute 'publisher'


[listener]: Could not transform CoM to robot-base_CoM: "CoM" passed to lookupTransform argument target_frame does not exist.

Any guidance would be appreciated please.

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