The nadir channel, oriented perpendicular to the Martian surface, and the stereo channels of the HRSC camera allow digital terrain models of the Martian surface to be derived with an accuracy of up to 10 metres per pixel. These colour-coded representations clearly portray the absolute altitudes above a reference level, the areoid (the equivalent of sea level on Mars; derived from the Greek word for Mars, Ares). These altitude values can be determined using the colour scale in the top right-hand corner of the image.