Init commit of example_4.

example_4.md

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+## Example 4
+
+![image](images/balloon.png)
+
+
+```
+python marker.py
+```
+
+![image](images/balloon.gif)
+
+```python
+#!/usr/bin/env python
+
+import rospy
+import sys
+from visualization_msgs.msg import Marker
+
+class Balloon():
+	def __init__(self):
+		self.publisher = rospy.Publisher('balloon', Marker, queue_size=10)
+		self.marker = Marker()
+		self.marker.header.frame_id = '/base_link'
+		self.marker.header.stamp = rospy.Time()
+		self.marker.type = self.marker.SPHERE
+		self.marker.id = 0
+		self.marker.action = self.marker.ADD
+		self.marker.scale.x = 0.5
+		self.marker.scale.y = 0.5
+		self.marker.scale.z = 0.5
+		self.marker.color.r = 1.0
+		self.marker.color.g = 0.0
+		self.marker.color.b = 0.0
+		self.marker.color.a = 1.0
+		self.marker.pose.position.x = 0.0
+		self.marker.pose.position.y = 0.0
+		self.marker.pose.position.z = 2.0
+
+	def publish_marker(self):
+		self.publisher.publish(self.marker)
+
+
+if __name__ == '__main__':
+	rospy.init_node('marker', argv=sys.argv)
+	ballon = Balloon()
+	rate = rospy.Rate(10)
+
+	while not rospy.is_shutdown():
+		ballon.publish_marker()
+		rate.sleep()		rate.sleep()
+```