Images for underwater 3D reconstruction of Posidonia seagrass transplantation site

The photographic data, which are the first step for data processing, were acquired with a low-cost action camera (GoPro Hero 9) capable of shooting high quality (20 Mpix images) photos with a specific time-lapse function. To perform the acquisition over a large area (3200 m2) the camera was mounted on a Diver Propulsion Vehicle (DPV) which allowed the SCUBA diver to map the entire area in only 1h and 10’. Consecutive (2 seconds interval) photos were acquired in raw format to allow further manual editing aimed at improving the result via colour grading and correction. Subsequently, each image was processed in a photogrammetric software (Agisoft Metashape) based on Structure from Motion (SfM) processing algorithms to generate 2D raster outputs (orthophoto mosaics and Digital Elevation Models, DEM),3D dense point clouds and 3D triangular mesh with texture. Finally, the open-source software Blender 2.93 was used to render the 3D scene to create a realistic view of the transplanted area by adding water effects and Posidonia leaves that otherwise cannot be well reproduced by only SfM data.

作为数据处理首要环节的摄影数据，由一款具备特定延时摄影功能、可拍摄高质量（2000万像素）影像的低成本运动相机（GoPro Hero 9）采集。为实现3200平方米大面积区域的影像采集，将该相机搭载于潜水推进器（Diver Propulsion Vehicle, DPV）之上，仅需1名水肺潜水员（SCUBA diver）即可在1小时10分钟内完成全区域测绘。采集的连续影像（间隔2秒）采用原始格式存储，以便后续通过色彩分级与校正开展手动编辑以优化画质。随后，基于运动恢复结构（Structure from Motion, SfM）算法，在摄影测量软件（Agisoft Metashape）中对每张影像进行处理，生成二维栅格产品（正射影像镶嵌图与数字高程模型，Digital Elevation Models, DEM）、三维密集点云以及带纹理的三维三角网格模型。最终，借助开源软件Blender 2.93对三维场景进行渲染，通过添加水面效果与波西多尼亚海草（Posidonia）叶片来还原移植区域的真实场景——仅依靠SfM数据无法很好地呈现此类细节。