Deep Geo-Constrained Auto-Encoder for Non-Landmark GPS Estimation

This paper addresses the problem of geotagging images, i.e., assigning GPS coordinates (i.e., latitude, longitude) to images using image contents. Due to the huge appearance variability of visual features across the world, the images' contents and their GPS coordinates may be inconsistent. This means images captured from geographically close areas may appear visually distinct; and images with visually similar contents may be taken from geographically distant areas. In this paper, we propose a deep Geo-constrained Auto-encoder (DGAE) to solve these inconsistency problems. Using clustered GPS data and visual data, our approach identifies inconsistent data pairs (i.e., image, GPS). We then propose a novel deep learning framework that can learn similar feature representations for geographically close images and distinct feature representations for geographically distant images. We introduce two new constraints: the same-area constraint and the easy-confusing constraint to our feature learning networks. The former one penalizes images from the same area but with very distinct visual features, and the latter one penalizes images from distant areas but with very similar visual features. A deep architecture is developed to further improve learning discriminative features, which can disambiguate different geometric locations. Our approach is extensively evaluated on a newly-compiled large image geotagging dataset from large-scale community-contributed images with 664,720 images and outperforms comparison approaches.