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There may be additional helper functions or an entire wrapper but in bouncy I go through the set_parameters service interface.

class MinimalClientAsync(Node):

    def __init__(self):
        super().__init__('minimal_client_async')
        self.cli = self.create_client(SetParameters, 'v4l2ucp/set_parameters')
        while not self.cli.wait_for_service(timeout_sec=1.0):
            self.get_logger().info('service not available, waiting again...')
        self.req = None

    def send_request(self):
        self.req = SetParameters.Request()

        param = Parameter()
        param.name = "controls/Brightness"
        param.value.type = ParameterType.PARAMETER_INTEGER
        param.value.integer_value = 20
        self.req.parameters.append(param)

        param = Parameter()
        param.name = "controls/Contrast"
        param.value.type = ParameterType.PARAMETER_INTEGER
        param.value.integer_value = 15
        self.req.parameters.append(param)

        self.future = self.cli.call_async(self.req)

def main(args=None):
    rclpy.init(args=args)

    minimal_client = MinimalClientAsync()
    minimal_client.send_request()

    while rclpy.ok():
        rclpy.spin_once(minimal_client)
        if minimal_client.future.done():
            if minimal_client.future.result() is not None:
                response = minimal_client.future.result()
                minimal_client.get_logger().info(
                    'Result of set parameters: for %s' %
                    (str(response)))
            else:
                minimal_client.get_logger().info(
                    'Service call failed %r' % (minimal_client.future.exception(),))
            break

    minimal_client.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

https://github.com/lucasw/v4l2ucp/blob/3449f89628c37f5558bf7b48fb255e56d1f475ca/v4l2ucp/scripts/set_param.py

Adapted from https://github.com/ros2/examples/blob/bouncy/rclpy/services/minimal_client/client_async_member_function.py