ROS Launch file Issue

Question

I am implementing a simple roslaunch file but I am getting an exit code 2 status I have pasted the exact log below any idea what would cause this and how I can rectify it. It works perfectly when used as a node via rosrun.

PC@PC :~/catkin_ws$ roslaunch apriltag_ros apriltag.launch 
... logging to /home/pc/.ros/log/c7672d6c-479d-11ec-bd02-c56b9aa24743/roslaunch-PC-20782.log
Checking log directory for disk usage. This may take a while.
Press Ctrl-C to interrupt 
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://PC:38583/

SUMMARY
========

PARAMETERS
* /rosdistro: noetic
* /rosversion: 1.15.13

NODES
/
apriltag_ros (apriltag_ros/tagdetector.py)

auto-starting new master
process[master]: started with pid [20790]
ROS_MASTER_URI=http://localhost:11311

setting /run_id to c7672d6c-479d-11ec-bd02-c56b9aa24743
process[rosout-1]: started with pid [20800]
started core service [/rosout] 
process[apriltag_ros-2]: started with pid [20803]
usage: tagdetector.py [-h] [-f FAMILIES] [-B N] [-t N] [-x SCALE] [-b SIGMA] [-0] [-1] [-2] [-c]
tagdetector.py: error: unrecognized arguments: __name:=apriltag_ros __log:=/home/pc/.ros/log/c7672d6c-479d-11ec-bd02-c56b9aa24743/apriltag_ros-2.log
[apriltag_ros-2] process has died [pid 20803, exit code 2, cmd /home/pc/catkin_ws/src/apriltag_ros/scripts/tagdetector.py __name:=apriltag_ros __log:=/home/pc/.ros/log/c7672d6c-479d-11ec-bd02-c56b9aa24743/apriltag_ros-2.log].
log file: /home/pc/.ros/log/c7672d6c-479d-11ec-bd02-c56b9aa24743/apriltag_ros-2*.log

The launch file code is as below

<?xml version = "1.0"?>

<launch>
    <node name = "apriltag_ros" pkg = "apriltag_ros" type = "tagdetector.py"  output="screen" />
</launch>

Edit 1: I have added the function that I am using to publish to ROS where the ROS node is initialised and used.

The function I am using to publish the data is as below

# Import Libraries
from argparse import ArgumentParser
import sys
import cv2
import apriltagbase
import numpy as np
import math
import rospy
from apriltag_ros.msg import tag

def location_publisher():
    """
    ROS Publisher: Publishes X, Y and Yaw values
    """
    # rospy.myargv(argv=sys.argv)
    pub = rospy.Publisher('apriltag_pose', tag, queue_size=10)
    rospy.init_node('apriltag_ros')
    msg = tag()
    msg.location.x = z # z in camera frame of reference is the distance from the tag i.e. x in general frame of reference
    msg.location.y = y
    msg.location.theta = yaw
    msg.status.data = status_tag
    msg.tagid.data = tag_id
    rospy.loginfo(msg)
    pub.publish(msg)

# Detect AprilTag
parser = ArgumentParser(description='Detect AprilTags from video stream.')
apriltagbase.add_arguments(parser)
options = parser.parse_args()

detector = apriltagbase.Detector(options, searchpath=apriltagbase._get_dll_path())

while(video.isOpened()):

    check,frame = video.read()
    
    if not check:
        break

    # overlay box on AprilTag format of detect_tags can be viewd in apriltag.py line 590.
    result,overlay = apriltagbase.detect_tags(frame, 
                                        detector,
                                        camera_params=(565.348501, 565.653872, 326.910261, 226.544390),
                                        tag_size=0.1688,
                                        vizualization=3,
                                        verbose=3,
                                        annotation=True
                                        )
    cv2.imshow('April Tag', overlay)
    

Edit 2: Removed Full code only open source code is now shown

Link to the same question on the ROS Forum: https://answers.ros.org/question/391124/roslaunch-exit-code-2-error/

Answer 1

The output

usage: tagdetector.py [-h] [-f FAMILIES] [-B N] [-t N] [-x SCALE] [-b SIGMA] [-0] [-1] [-2] [-c]

shows, that tagdetector.py is a script which needs to be called with some specific parameters. First of all you should make sure, if the script is a rosnode to ensure launching it via roslaunch like this is correct. Secondly, have a look at the launch documentation which shows how to add arguments to the node.

So you need to add some of the mentioned parameters to your launchfile by adding

args="-h"

to the node launch entry.

Update

The script you've added uses parses arguments defined in apriltagbase.

apriltagbase.add_arguments(parser)
options = parser.parse_args()

argparse fails for all arguments which are not added here. So you need to replace it by

options, unknown = parser.parse_known_args()

to prevent failing due to arguments added automatically by roslaunch.