Image Geometry

International audienc

A virtual object point model for the calibration of underwater stereo cameras to recover accurate 3D information

The focus of this thesis is on recovering accurate 3D information from underwater images. Underwater 3D reconstruction differs significantly from 3D reconstruction in air due to the refraction of light. In this thesis, the concepts of stereo 3D reconstruction in air get extended for underwater environments by an explicit consideration of refractive effects with the aid of a virtual object point model. Within underwater stereo 3D reconstruction, the focus of this thesis is on the refractive calibration of underwater stereo cameras

Seabed scour around marine structures in mixed and layered sediments

The inherent uncertainty in the prediction of seabed scour depth at offshore structures such as wind turbines is currently a significant barrier to realising optimised, cost effective foundation design. One significant aspect thought to contribute to this uncertainty which has not been extensively studied is the variation in the sediment properties in the marine environment where sediment beds often consist of complex mixtures of materials stratified with depth. This research project encompasses the design and execution of an extensive laboratory study investigating this aspect of the scour problem. Two uniformly graded sands were used to build a range of simplified mixed and layered sediment beds, as a first step to improving understanding of scour behaviour in these situations. A variety of hydrodynamic conditions including unidirectional current, tidal and wave-current flows were tested to ensure relevance to the marine environment. As part of the experiment design a detailed review of scour measurement techniques was conducted leading to the implementation of a photogrammetry system which delivered high resolution, high accuracy scour hole profiles. This study has led to a number of original results. In a layered bed of fine sand overlying coarse sand interaction effects at the grain scale resulted in an enhancement of scour depth in the underlying coarse sand. Bimodally distributed mixed sands were found to alter significantly the scour time development curve. Novel scour tests under a spring-neap tidal cycle in the clear water regime indicated a considerable lengthening of the time to equilibrium. A review of prediction methodologies was undertaken and modifications proposed to take into account the research outcomes. This project has demonstrated that the configuration of the sediment bed is highly influential on scour development, and will contribute towards the future development of more sophisticated design models for implementation in industry

Multi-View Geometry of the Refractive Plane

Transparent refractive objects are one of the main problems in geometric vision that have been largely unexplored. The imaging and multi-view geometry of scenes with transparent or translucent objects with refractive properties is relatively less well understood than for opaque objects. The main objective of our work is to analyze the underlying multi-view relationships between cameras, when the scene being viewed contains a single refractive planar surface separating two different media. Such a situation might occur in scenarios like underwater photography. Our main result is to show the existence of geometric entities like the fundamental matrix, and the homography matrix in such instances. In addition, under special circumstances we also show how to compute the relative pose between two cameras immersed in one of the two media.