BICAM SLAM

Joan Sola talks in his article on BICAM SLAM explaining the benefits of mounting mono-vision cameras on SLAM robots equipped for stereo cameras. He summarizes saying " By using monocular algorithms on both cameras, the advantages of mono-vision (bearing-only, with infinity range but no 3D instant information) and stereo-vision (3D information only up to a limited range) naturally add up to provide interesting possibilities, that are here developed and demonstrated using an EKF-based monocular SLAM algorithm. Mainly we obtain: a) fast 3D mapping with long term, absolute angular references; b) great landmark updating flexibility; and c) the possibility of stereo rig extrinsic self-calibration, providing a much more robust and accurate sensor. Experimental results show the pertinence of the proposed ideas, which should be easily exportable (and we encourage to do so) to other, more performing, vision-based SLAM algorithms."  Basically this means that mono-vision cameras, which have a flat lens allow for an extended field of view.  Typically these mono-vision cameras are uses singularly and have the issue of having a difficult time with depth perception.  However the benefits to mono vision cameras include no lens distortion (of which long range cameras provide) resulting in with absolute angular references(more accuracy) and a larger field of view.  This field of view increases efficiency immensely.  The reason is more of a view the camera can get from a single screenshot, the less it needs to move and recalibrate.  This also results in less of a need to correct errors between screenshots, resulting in once again, more accuracy.  Not with a second mono-vision camera providing stereo vision with flat lenses, a robot is able to use its second camera as a point of reference to calibrate itself to get a better feel for depth. Now by far the biggest benefit mono-vision cameras have is their superior visual range to stereo cameras.  Sola goes into this stating "The drawback of stereo-based systems is a limited range of 3D observability (the dense-fog effect: remote objects cannot be considered), and that they strongly depend on precise calibrations to be able to extend it.". This means that although typical stereo cameras can look a decent maximum distance, the preparation work for capturing a scene an maximum distance is quite tedious. In Sola's writings he also goes over how the identification of landmarks will occur by the camera stating “As a general idea, one can simply initialize landmarks following mono-vision techniques from the first camera, and then observe them from the second one: we will determine their 3D positions with more or less accuracy depending on if they are located inside or outside the stereo observability region.”. In layman's terms, this means the cameras have a slave master relationship in regards to identifying landmarks. The master camera identifies landmarks throughout its field of view, followed by the second camera attempting to work with the first camera to decide were the two are in regards to a 3d environment. The best part about these two cameras working together, is there is no radial distortion(the distortion causes by long range cameras) to skew the inputs. I see a bright future for Bi-mono-vision SLAM in the future.