How does one get the x and y coordinates of a robot?

edit

This is a very open, non-specific question, so I can only answer about what I find most useful. If you use MoveIt! you should check out the get commands for MoveGroupInterface like getCurrentPose etc.

Depends on what topics are being published and in what language you are developing C++/python. Look for topics, such as /odom or /amcl/ From thos you can extract the position information. Beware, distances are in m and rotations are in quaternions or radians.

def odom_callback(odom_message):

    if not settings.odomData_valid:
        settings.odomData_valid = True
        rospy.loginfo("odomData validity!")
    else:
        # < code >
        # rospy.loginfo("odom_callback!")
        # settings.nop = 0

        # position x/y
        settings.pose_odom_x = odom_message.pose.pose.position.x
        settings.pose_odom_y = odom_message.pose.pose.position.y

        # rotation quaternion
        settings.pose_odom_rot_quat[0] = odom_message.pose.pose.orientation.x
        settings.pose_odom_rot_quat[1] = odom_message.pose.pose.orientation.y
        settings.pose_odom_rot_quat[2] = odom_message.pose.pose.orientation.z
        settings.pose_odom_rot_quat[3] = odom_message.pose.pose.orientation.w

        # rotation euler
        settings.pose_odom_rot_euler = calc.euler_from_quaternion(settings.pose_odom_rot_quat)

        # rotation degree
        settings.odom_rot_deg = calc.euler_to_degrees(settings.pose_odom_rot_euler)

def euler_from_quaternion(quat):
    """
    Convert a quaternion into euler angles (roll, pitch, yaw)
    roll is rotation around x in radians (counterclockwise)
    pitch is rotation around y in radians (counterclockwise)
    yaw is rotation around z in radians (counterclockwise)
    """
    # print("<euler_from_quaternion>")
    # print("----------------------------")
    x, y, z, w = quat
    # t0 = +2.0 * (w * x + y * z)
    # t1 = +1.0 - 2.0 * (x * x + y * y)
    # roll_x = math.atan2(t0, t1)

    # t2 = +2.0 * (w * y - z * x)
    # t2 = +1.0 if t2 > +1.0 else t2
    # t2 = -1.0 if t2 < -1.0 else t2
    # pitch_y = math.asin(t2)

    t3 = +2.0 * (w * z + x * y) 
    t4 = +1.0 - 2.0 * (y * y + z * z)
    yaw_z = math.atan2(t3, t4)

    #return roll_x, pitch_y, yaw_z # in radians
    return yaw_z 

# -----------------------------------------------------------------------------
def euler_to_degrees(angle_euler):
    # print("<euler_to_degrees>")
    # print("----------------------------")
    angle_deg = angle_euler * 180 / 3.141592654
    return angle_deg

You will have to remove the "settings.", "calc." etc leading statements, as I have my code highly organized into different files Best to try it out is throwing everything into a single file.