Abstract
Abstract. Uncontrolled refraction of optical rays in underwater photogrammetry is known to reduce its accuracy potential. Several strategies have been proposed aiming at restoring the accuracy to levels comparable with photogrammetry applied in air. These methods are mainly based on rigours modelling of the refraction phenomenon or empirical iterative refraction corrections. The authors of this contribution have proposed two mitigation strategies of image residuals systematic patterns in the image plane: (i) empirical weighting of image observations as function of their radial position; (ii) iterative look-up table corrections computed in a squared grid. Here, a novel approach is developed. It explicitly takes into account the object point-to-camera distance dependent error introduced by refraction in multimedia photogrammetry. A polynomial correction function is iteratively computed to correct the image residuals clustered in radial slices in the image plane as function of the point-to-camera distance. The effectiveness of the proposed method is demonstrated by simulations that allow to: (i) separate the geometric error under investigation from other effects not easily modellable and (ii) have reliable reference data against which to assess the accuracy of the result.
Highlights
Any measurement process is inevitably affected by errors
The induced residual systematic errors may appear as systematic residual patterns in image observations (Fig. 1) and produce deformations of the photogrammetric model in object space
In Menna et al (2020), we focused on the geometric components of the systematic errors induced by the unmodelled refraction effects through simulations
Summary
Any measurement process is inevitably affected by errors. Observation residuals may be caused by random and gross errors, as well as by systematic errors which derive from an incorrect or incomplete functional model (Vlcek, 1969). The deviation from the standard pinhole camera model is caused by the bending of the light rays as the medium changes. By the way, this effect exists in air and aerial triangulation, but it is far less significant and usually ignored in practice. This effect exists in air and aerial triangulation, but it is far less significant and usually ignored in practice This phenomenon is known, the simple pinhole camera model with Brown/Beyer distortion formulation is still the preferred approach in practice in underwater photogrammetry (Shortis, 2015). The problem of camera calibration and systematic residual patterns in image observations is briefly presented. An overview of the investigation previously conducted
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