  Vision is one of the most important of the senses, and humans use it
extensively during navigation. We evaluated different types of image and video
frame descriptors that could be used to determine distinctive visual landmarks
for localizing a person based on what is seen by a camera that they carry. To
do this, we created a database containing over 3 km of video-sequences with
ground-truth in the form of distance travelled along different corridors. Using
this database, the accuracy of localization - both in terms of knowing which
route a user is on - and in terms of position along a certain route, can be
evaluated. For each type of descriptor, we also tested different techniques to
encode visual structure and to search between journeys to estimate a user's
position. The techniques include single-frame descriptors, those using
sequences of frames, and both colour and achromatic descriptors. We found that
single-frame indexing worked better within this particular dataset. This might
be because the motion of the person holding the camera makes the video too
dependent on individual steps and motions of one particular journey. Our
results suggest that appearance-based information could be an additional source
of navigational data indoors, augmenting that provided by, say, radio signal
strength indicators (RSSIs). Such visual information could be collected by
crowdsourcing low-resolution video feeds, allowing journeys made by different
users to be associated with each other, and location to be inferred without
requiring explicit mapping. This offers a complementary approach to methods
based on simultaneous localization and mapping (SLAM) algorithms.
