1. A system comprising: a robot comprising: an end effector that lays up tows of material; actuators that reposition the end effector; a memory storing a Numerical Control (NC) program; and a robot controller that directs the actuators to reposition the end effector based on the NC program, and instructs the end effector to lay up tows based on the NC program; and a sensor system comprising: an imaging device that acquires images of the tows as the tows are laid-up by the end effector; a measuring device that generates input as tows are laid-up by the end effector; and a sensor controller that receives images from the imaging device and the input from the measuring device, and updates stored data to correlate the images with instructions in the NC program, based on the input.