Comparison of Semantic Segmentation Approaches for Horizon/Sky Line Detection
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Horizon or skyline detection plays a vital role towards mountainous visual geo-localization, however most of the recently proposed visual geo-localization approaches rely on user-in-the-loop skyline detection methods. Detecting such a segmenting boundary fully autonomously would definitely be a step forward for these localization approaches. This paper provides a quantitative comparison of four such methods for autonomous horizon/sky line detection on an extensive data set. Specifically, we provide the comparison between four recently proposed segmentation methods; one explicitly targeting the problem of horizon detectionAhmad15, second focused on visual geo-localization but relying on accurate detection of skyline Saurer16 and other two proposed for general semantic segmentation -- Fully Convolutional Networks (FCN) Long15 and SegNetBadrinarayanan15. Each of the first two methods is trained on a common training set Baatz12 comprised of about 200 images while models for the third and fourth method are fine tuned for sky segmentation problem through transfer learning using the same data set. Each of the method is tested on an extensive test set (about 3K images) covering various challenging geographical, weather, illumination and seasonal conditions. We report average accuracy and average absolute pixel error for each of the presented formulation.
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