Monocular visual Simultaneous Localisation and Mapping (SLAM) has become very popular because it relies only on a standard camera. Since cameras are now easily found in many consumer electronics products, this makes SLAM systems which use only a single camera very appealing, both as an area of research and as a key enabling technology for applications such as augmented reality.
Visual SLAM algorithms are designed to take advantage of the very rich information about the world available from image data. The way that SLAM systems use these data can be classified as sparse/dense and direct/indirect. The former describes the quantity of regions used in each received image frame, and the latter describes different ways in which the image data are used. This means there are four possible types of SLAM system, in terms of how the image data are used.