A television/computer system is used to measure the apparent distortion of a line of light as it is scanned over an object. A projector and camera are fixed relative to one another in a swinging frame which rotates at a constant speed through a vertical arc. The displacement of the line in the television picture is a function of the distance of the object from an imaginary cylinder about the axis of rotation, while the position of the frame is also read by the television interface from a spot inserted into the video signal. The geometrical configuration of camera, projector and frame allows simple analysis of the data to yield an output consisting of scattered three-dimensional points. Calibration is achieved by measuring an object of known dimensions. The use of the system is illustrated by application to a project for the assessment of scoliotic deformity of the back. In this, the advantage of an instant digital data acquisition method is that analysis of the data can proceed immediately, without the intervening lengthy, expensive and error-prone digitising stage required by moire topography. The patient can receive his analysis within minutes, and the information can be used by the physician immediately at the clinic, rather than days later.