A system for the transformation of steering control signals from a plane cartesian coordinate system to a polar coordinate system is disclosed. The system is designed to be self-contained on board a missile. The system is synchronized with roll position, by virtue of a start pulse and generates pulse increments corresponding to increments of roll angle change. A digital counter counts pulses which are referenced to the missile. The counted pulses are supplied to read-only memories which are pre-programmed with sine and cosine information. A pair of digital-to-analog converters respond to the outputs of the memories. An appropriate Y or Z steering signal is supplied to the converters for multiplication. The outputs of the converters are summed and then supplied to the missile steering device. Means for taking into account the launch of a missile from a mobile launch site is disclosed.