Figure 2 illustrates the relation between the distance of an object point k to the sensor relative to a reference plane and the measured disparity d. To express the 3D coordinates of the object points we consider a depth coordinate system with its origin at the perspective center of the infrared camera. The Z axis is orthogonal to the image plane towards the object, the X axis perpendicular to the Z axis in the direction of the baseline b between the infrared camera center and the laser projector, and the Y axis orthogonal to X and Z making a right handed coordinate system.