I am trying to find a position sensor that can measure the relative position in respect to a control line (not point) in 2-D. I do not need to know the height of the object, just the XY position. The control sensor I assume would be 2 seperate sensors creating a line in the +- y directions at the x origin. These sensors would be able to determine the x position of the third sensor placed on the object. Essentially I need the perpendicular distance of the third sensor to the control line. The y line created by the 2 control sensors (if that is the best way of doing so) could be anywhere from 1 to 150 feet from the third sensor on the object. Also, the third sensor on the object will be obstructed from view (does this eliminate IR?) by other objects such as people, clothing, weather etc. The sensor needs to be durable (I assume you can create a safe enviroment for any sensor). I am up for using any kind of sensor as long as it is available to the public and can be purchased and setup at a reasonable price. I am highly experienced in matlab/simulink and would prefer using that in my system. So far people are have suggested IR and CNC, are these viable options? Thanks for your help and I hope there is a available solution.