Abstract: Apparatus to control the automatic placing of material along a junction between surfaces with reference to the form and position of the junction including means controllably movable to deposit material progressively along the junction in response to a control signal, means linked to the movement of the means to deposit material to produce an image of the surfaces and junction, filter means to remove from the image information resulting from illumination at other than a specific wavelength with a tapped delay line to provide a specific impulse response, means to extract from the image that portion unambiguously defining the junction form and position, means responsive to said image portion to derive said control signal to control the means to deposit material to move in a required manner along said junction to deposit material.