  Although fully autonomous mapping methods are becoming more and more common
and reliable, still the human operator is regularly employed in many 3D
surveying missions. In a number of underwater applications, divers or pilots of
remotely operated vehicles (ROVs) are still considered irreplaceable, and tools
for real-time visualization of the mapped scene are essential to support and
maximize the navigation and surveying efforts. For underwater exploration,
image mosaicing has proved to be a valid and effective approach to visualize
large mapped areas, often employed in conjunction with autonomous underwater
vehicles (AUVs) and ROVs. In this work, we propose the use of a modified image
mosaicing algorithm that coupled with image-based real-time navigation and
mapping algorithms provides two visual navigation aids. The first is a classic
image mosaic, where the recorded and processed images are incrementally added,
named 2D sequential image mosaicing (2DSIM). The second one geometrically
transform the images so that they are projected as planar point clouds in the
3D space providing an incremental point cloud mosaicing, named 3D sequential
image plane projection (3DSIP). In the paper, the implemented procedure is
detailed, and experiments in different underwater scenarios presented and
discussed. Technical considerations about computational efforts, frame rate
capabilities and scalability to different and more compact architectures (i.e.
embedded systems) is also provided.
