The 3-D capability of science and engineering cameras on the ExoMars rover

The ExoMars Programme will send a rover to Mars in 2022 equipped with a 2 m drill which will search for evidence of extinct life below the surface. This project is focused on the stereo vision systems of the rover, and how better 3-D information can be extracted from the camera images. This is explored through both experimental and simulation-based approaches. The experimental approach was to build a hardware emulator of the three stereo pairs: the Wide-Angle Cameras (WACs) from the Panoramic Camera instrument (PanCam), and the Navigation Camera (NavCam) and Localisation Camera (LocCam) systems. Point clouds were generated from the emulator data and compared against a (LIDAR) generated point cloud to determine which combination of cameras yields the best point clouds. The comparison methods were as follows: the number of tie points, the number of dense cloud points, coordinate extent, surface density, nearest neighbour distance (NND) to the LIDAR cloud, and measurement of a known target. One set of experiments compared the four mast head stereo cameras (WACs and NavCams) and the second set compared all six stereo cameras (WACs, NavCams, and LocCams). The six-view point cloud was the closest match to the LIDAR in terms of mean NND to the LIDAR point cloud, but it was only marginally better than the five-view point clouds and the four-view point cloud made of the WACs and NavCams. The conclusions from both sets of experiments are that the three stereo camera pairs do not contribute equally to improvements in the point clouds generated through photogrammetry. The emulator WACs are the most suited to photogrammetric reconstruction, followed by the emulator NavCams and finally the emulator LocCams.