Automatic scale estimation of structure from motion based 3D models using laser scalers in underwater scenarios

Abstract

A B S T R A C TRecent advances in structure-from-motion techniques are enabling many scientific fields to benefit from the routine creation of detailed 3D models. However, for a large number of applications, only a single camera is available for the image acquisition, due to cost or space constraints in the survey platforms. Monocular structure-from-motion raises the issue of properly estimating the scale of the 3D models, in order to later use those models for metrology. The scale can be determined from the presence of visible objects of known dimensions, or from information on the magnitude of the camera motion provided by other sensors, such as GPS.This paper addresses the problem of accurately scaling 3D models created from monocular cameras in GPS-denied environments, such as in underwater applications. Motivated by the common availability of underwater laser scalers, we present two novel approaches which are suitable for different laser scaler configurations. A fully-calibrated method enables the use of arbitrary laser setups, while a partially-calibrated method reduces the need for calibration by only assuming parallelism on the laser beams, with no constraints on the camera. The proposed methods have several advantages with respect to the existing methods. By using the known geometry of the scene expressed by the 3D model, along with some parameters of the laser scaler geometry, the need for laser alignment with the optical axis of the camera is removed. Furthermore, the extremely error-prone manual identification of image points on the 3D model, currently required in image-scaling methods, is eliminated as well.The performance of the methods and their applicability was evaluated on both data generated from a realistic 3D model and data collected during an oceanographic cruise in 2017. Three separate laser configurations have been tested, encompassing nearly all possible laser setups, to evaluate the effects of terrain roughness, noise, camera perspective angle and camera-scene distance on the final estimates of scale. In the real scenario, the computation of 6 independent model scale estimates using our fullycalibrated approach, produced values with standard deviation of 0.3%. By comparing the values to the only possible method usable for this dataset, we showed that the consistency of scales obtained for individual lasers is much higher for our approach (0.6% compared to 4%).

Quantification of Gravitational Mass Wasting and Controls on Submarine Scarp Morphology Along the Roseau Fault, Lesser Antilles

“…While the data presented here provides little constraints on whether mass wasting primarily occurs in the coseismic, postseismic, or interseismic period, a comparison of seismicity data with further observations from three-dimensional outcrop models, photomosaics, and ROV video imagery indicates strong evidence for coseismic mass wasting with some minor postseismic erosion (Escartín et al, 2016(Escartín et al, , 2020. Elsewhere in the Lesser Antilles, evidence for coseismic triggered mass wasting of sediments has previously been identified from sediment cores and seismic data between Guadeloupe and Nevis (Beck et al, 2012).…”

“…The imagery was corrected to improve the illumination, equalization, and color shift and we employed structure from motion techniques to create three-dimensional terrain models of each outcrop at ∼1 cm resolution (e.g., Campos et al, 2015). We used texture-mapped models to facilitate visualization of features visible at the outcrop scale, while providing proper scaling for quantitative studies (Campos et al, 2015;Istenič et al, 2019Istenič et al, , 2020. The data used in this study is a subset of 14 out the 41 three-dimensional models from the Roseau fault system (Figures 4b and S1; Table S2).…”

Estimating reef fish size distributions with a mini remotely operated vehicle-integrated stereo camera system

“…The accuracy of length measurements collected with laser-based methods are ultimately limited by 1) the parallax effect, 2) laser separation distance, 3) size bias towards larger individuals, 4) the frequency of scaling events at appropriate AOIs, or 5) beam contact distortion [ 36 , 38 , 53 , 58 ]. In a controlled pool experiment, Patterson et al [ 38 ] estimated that an RLS with 100 mm baseline provided accurate (mean PE within ±5%) length estimates of fish models at distances ≤2.5 m and AOIs ≤15°.…”

Underwater 3D Scanner Model Using a Biaxial MEMS Mirror

“…This information comes from different simultaneous viewpoints or from the movement between consecutive image frames. Well-known passive techniques in underwater environments are stereo vision [12,14] and structure from motion (SfM) [15,16].…”