The Camera System

The camera system (Fig. 2, left) consists of two TerraCAM USB Pro webcams. They are equipped with a manual focus lens and the resolution is limited to 640 $\times$ 480 pixels with 7 fps as the maximum frame rate. To cover the whole area, scanned by the laser range finder, each camera needs to take 6 different images (Fig. 2, right). To handle this, the webcams are mounted on pan-tilt units each of which is based on 2 servo drives (Volz Micro-Maxx), one for the horizontal axis and the other for the vertical axis. Each axis can be rotated by $\pm45^{\circ}$. Due to the high-grade servo drives, an excellent repeat accuracy in positioning is guaranteed.

The webcams are powered over the USB interface and the servo drives are fed by the same batteries as the 3D laser range finder servo (cf. section 3.2).