CORSTITCH - A free, open source software for stitching and georeferencing underwater coral reef videos

TL;DR

CorStitch addresses the need for automatic generation of georeferenced reef mosaics from underwater video by employing Fourier-domain image correlation on the green channel, augmented with a central-strip constraint to reduce parallax. The pipeline fuses frame-level stitching with synchronized GPS data and exports KMZ files suitable for Google Earth via SimpleKML, enabling turnkey georeferencing. Validation on two belt transects of the same reef demonstrates consistent placement of coral colonies across time, supporting reliability. The open-source tool aims to broaden access for community mapping, validation, and natural capital accounting of benthic habitats in municipal waters, reducing reliance on proprietary software.

Abstract

CorStitch is an open-source software developed to automate the creation of accurate georeferenced reef mosaics from video transects obtained through Automated Rapid Reef Assessment System surveys. We utilized a Fourier-based image correlation algorithm to stitch sequential video frames, aligning them with synchronized GNSS timestamps. The resulting compressed Keyhole Markup Language files, compatible with geographic information systems such as Google Earth, enable detailed spatial analysis. Validation through comparative analysis of mosaics from two temporally distinct surveys of the same reef demonstrated the software's consistent and reliable performance.

Figures (6)

• Figure 1: CorStitch general workflow.
• Figure 2: Experimental setup.
• Figure 3: Fourier-based image correlation algorithm workflow.
• Figure 4: Sample mosaics from Calatagan, Batangas made by CorStitch.
• Figure 5: KMZ files made by CorStitch as seen in Google Earth Pro.