Surface Reconstruction of Ancient Water Storage Systems An Approach for Sparse 3D Sonar Scans and Fused Stereo Images

This work presents a new approach to reconstructing surfaces of underwater structures from stereo images and sonar scans collected with a micro-ROV on the islands of Malta and Gozo. Using a limited sensor load, sonar and small GoPro Hero2 cameras, the micro-ROV is able to explore small hard to reach water systems and gather data. Our algorithm is able to reconstruct geometric models of explored regions, even when the data is noisy and sparse. As a preprocess to the reconstruction pipeline, a 3D evidence grid is created by mosaicing horizontal and vertical sonar scans. A rough implicit surface representation can then be reconstructed using a level set method. Small stereo cameras mounted to the ROV capture fineand medium-scale details from the scene and store them in stereo image pairs, which are transformed into point clouds and projected into the volume. A raycasting technique is used to trim the volume in accordance with the projected point clouds, thus reintroducing finer details to the previously rough model. The resulting volume is surfaced, yielding a final mesh, which can be viewed and interacted with for archaeological and educational purposes. Initial results from both steps of the reconstruction pipeline are presented and discussed.