Pixel based mapping using a sheet laser and camera for generation of coloured 3D seafloor reconstructions

Abstract

There are several approaches for 3 dimensional mapping of the seafloor in the actual colours, many of which require multiple cameras, elaborate algorithms and specially designed vehicles. In this paper a method is presented, which uses minimal equipment and simple algorithms for this task, while treating the data in a fully 3 dimensional way from input to output. Because of the reduced hardware demands, it is well suited for combined missions, where the underwater vehicle records some other data as primary task and the map created with the proposed method acts as a support for visualising that data and the environment where it was collected. I. INTRODUCTIONPhotographing and filming of the seafloor has been performed already for many years, with attempts of using a TV camera for survey dating back to 1964 [1]. As visibility is limited underwater, an image can cover only a few square metres, and so the idea of merging several photos into a mosaic emerged as a practical solution for wide area seafloor imaging. These days reconstruction of the seafloor has been taken to a new level thanks to the use of computers and digital photography. For 2D reconstruction, photos are arranged next to each others, corrected for difference in lighting and the transitions are smoothed [2], [3]. By overlaying such a mosaic on the topography of the seafloor, a 3D model can be generated. If the seafloor topography doesn't have any sudden changes in height, this method yields good results. However, pronounced vertical reliefs lead to geometrical distortions due to the perspective effect, producing artefacts in the mosaic and an inherently incorrect 3D reconstruction.Places of interest underwater often include areas with pronounced reliefs, such as areas where mineral resources are found, hydrothermal vents, manmade underwater installations, shipwrecks, coral reefs or archaeological sites. In these cases a method that handles the images in a fully three dimensional way from input to output is required to produce better results. High resolution 3D reconstruction using stereo photography has been shown by Pizarro, Williams and Mahon [4]. Much effort went into the implementation of the algorithm and an AUV that is perfectly suited for recording the images has been developed.While the above mentioned methods are used for mapping of the seafloor as a main task, we argue that generating a 3D map of the region where a vehicle was deployed while carrying

Snapshot 3D reconstruction of liquid surfaces

“…The ability to reconstruct an object in 3D is of interest for a large number of applications. Examples of three-dimensional optical imaging include the reconstruction of dental pieces for improved accuracy [1], of bridges to aid maintenance work [2], of plants/fruits to measure their growth [3] and to perform 3D mapping of the seafloor [4]. In these mentioned applications a structured light beam was used to illuminate the object of interest and the pattern that was diffusely reflected from its surface was imaged.…”

“…From the analysis of the deformed light pattern, the surface of the object could be reconstructed in 3D. Generally, methods using Structured Illumination require several image acquisitions following a scanning procedure to obtain a single 3D reconstruction [1][2][3][4]. In situations where high temporal resolution is needed this multiple image acquisition is not desired, for example, when imaging fast moving and/or deforming elements such as liquid bodies.…”

Laser based rangefinder for underwater applications

“…Other, similar approaches have been developed for use with different tasks. For example, in ( [3], [4]) the use of a single laser line is used to generate full 3D maps of underwater objects. However, it can be challenging to find the entire laser line in environments that are not extremely dark, thus this approach can not be used in operating environments where large amounts of natural and artificial light may be present.…”

The calibration of a laser profiling system for seafloor micro-topography measurements

“…Finally, the profiler is relatively inexpensive because it uses an off-the-shelf digital camcorder. There are similar systems mounted on autonomous underwater vehicles (AUV), but they use only one laser beam (Bodenmann et al 2010, Kondo et al 2004. The use of multiple lasers increases the coverage rate and improves accuracy.…”