SPRINT: Subgraph Place Recognition for INtelligent Transportation

Visual place recognition is an important problem in mobile robotics which aims to localize a robot using image information alone. Recent methods have shown promising results for place recognition under varying environmental conditions by exploiting the sequential nature of the image acquisition process. We show that by using k nearest neighbours based image retrieval as the backend, and exploiting the structure of the image acquisition process which introduces temporal relations between images in the database, the location of possible matches can be restricted to a subset of all the images seen so far. In effect, the original problem space can thus be restricted to a significantly smaller subspace, reducing the inference time significantly. This is particularly important for scalable place recognition over databases containing millions of images. We present large scale experiments using publicly sourced data that show the computational performance of the proposed method under varying environmental conditions.