Surface reconstruction of ancient water storage systems an approach for sparse 3D sonar scans and fused stereo images

This work presents a process pipeline that addresses the problem of 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 water systems and gather data. As a preprocess to the reconstruction pipeline, a 3D evidence grid is created by mosaicing horizontal and vertical sonar scans. A volumetric representation is then constructed using a level set method. Fine-scale details from the scene are captured in stereo cameras, and 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 fine details to the rough sonar-generated 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.