The challenge of obtaining ground truth for GPS processing

The increasing use of GPS as a source of travel survey data has brought with it an increasing need for a reliable source of ground truth. Recently, the main source that has been used for providing ground truth is the prompted recall survey. However, the prompted recall survey is subject to many of the same shortcomings as most self-administered surveys. In this paper, we review some of the common problems encountered in prompted recall surveys. Following this, we describe a recent experiment in using life-logging cameras to record a person's travel, together with GPS, thereby providing a new source of ground truth data.