navigate to NEAREST goal pos (if goal pos is blocked)

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Hello all,

I am working on a project where my robot needs to navigate to the goal position (and it is easy and working fine). But sometimes the goal position may be blocked and there is a possibilty that the goal planners fail hence resulting in no movement at all. In this case i want my robot to move to the nearest point of the goal position (this can be done by taking a radius around the goal position and assign it a new position and then navigate again but it might take alot of time). Please help me that how can i make my algorithms more robust to implement these changes. (using amcl)

Below is my code for navigation to the goal position. Please share your thoughts:

    import rospy
from move_base_msgs.msg import MoveBaseAction, MoveBaseGoal
import actionlib
from actionlib_msgs.msg import *
from geometry_msgs.msg import Pose, Point, Quaternion

class GoToPose():
    def __init__(self):

        self.goal_sent = False

    # What to do if shut down (e.g. Ctrl-C or failure)
    rospy.on_shutdown(self.shutdown)

    # Tell the action client that we want to spin a thread by default
    self.move_base = actionlib.SimpleActionClient("move_base", MoveBaseAction)
    rospy.loginfo("Wait for the action server to come up")

    # Allow up to 5 seconds for the action server to come up
    self.move_base.wait_for_server(rospy.Duration(5))

    def goto(self, pos, quat):

        # Send a goal
        self.goal_sent = True
    goal = MoveBaseGoal()
    goal.target_pose.header.frame_id = 'map'
    goal.target_pose.header.stamp = rospy.Time.now()
        goal.target_pose.pose = Pose(Point(pos['x'], pos['y'], 0.000),
                                     Quaternion(quat['r1'], quat['r2'], quat['r3'], quat['r4']))

    # Start moving
        self.move_base.send_goal(goal)

    # Allow TurtleBot up to 60 seconds to complete task
    success = self.move_base.wait_for_result(rospy.Duration(60)) 

        state = self.move_base.get_state()
        result = False

        if success and state == GoalStatus.SUCCEEDED:
            # We made it!
            result = True
        else:
            self.move_base.cancel_goal()

        self.goal_sent = False
        return result

    def shutdown(self):
        if self.goal_sent:
            self.move_base.cancel_goal()
        rospy.loginfo("Stop")
        rospy.sleep(1)

if __name__ == '__main__':
    try:
        rospy.init_node('nav_test', anonymous=False)
        navigator = GoToPose()

        # Customize the following values so they are appropriate for your location
        position = {'x': 13.3, 'y' : 3.9}
        quaternion = {'r1' : 0.000, 'r2' : 0.000, 'r3' : 0.000, 'r4' : 1.000}

        rospy.loginfo("Go to (%s, %s) pose", position['x'], position['y'])
        success = navigator.goto(position, quaternion)

        if success:
            rospy.loginfo("Hooray, reached the desired pose")
        else:
            rospy.loginfo("The base failed to reach the desired pose")

        # Sleep to give the last log messages time to be sent
        rospy.sleep(1)

    except rospy.ROSInterruptException:
        rospy.loginfo("Ctrl-C caught. Quitting")


#### code by mark sulliman