On demand Publishing?

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I'm using ROS kinetic with Yumi package from KTH. I am getting some points from the camera and do some processing and send the coordinates back to the robot arms to move. What I'm doing is letting the camera input and processing system on a node (publisher) to publish the coordinates and the control and move of the robot one (subscriber) on another node. The problem is that the camera publish sequence of coordinates to the robot. My question is that how can I publish the first message only and then wait till demand or flag to publish the second message and so on?

Thank you in Advance