  Horizon line (or sea line) detection (HLD) is a critical component in
multiple marine autonomous navigation tasks, such as identifying the navigation
area (i.e., the sea), obstacle detection and geo-localization, and digital
video stabilization. A recent survey highlighted several weaknesses of such
detectors, particularly on sea conditions lacking from the most extensive
dataset currently used by HLD researchers. Experimental validation of more
robust HLDs involves collecting an extensive set of these lacking sea
conditions and annotating each collected image with the correct position and
orientation of the horizon line. The annotation task is daunting without a
proper tool. Therefore, we present the first public annotation software with
tailored features to make the sea line annotation process fast and easy. The
software is available at:
https://drive.google.com/drive/folders/1c0ZmvYDckuQCPIWfh_70P7E1A_DWlIvF?usp=sharing
