Annotation in outdoor augmented reality

Annotation, the process of adding extra virtual information to an object, is one of the most common uses for augmented reality. Although annotation is widely used in augmented reality, there is no general agreed-upon definition of what precisely constitutes an annotation in this context. In this paper, we propose a taxonomy of annotation, describing what constitutes an annotation and outlining different dimensions along which annotation can vary. Using this taxonomy we also highlight what styles of annotation are used in different types of applications and areas where further work needs to be done to improve annotation. Through our taxonomy we found two primary categories into which annotations in current applications fall. Some annotations present information that is directly related to the object they are annotating, while others are only indirectly related to the object that is being annotated. We also found that there are very few applications that enable the user to either edit or create new annotations online. Instead, most applications rely on content that is created in various offline processes. There are, however, many advantages to online annotation. We summarize and formalize our recent work in this field by presenting the steps needed to build an online annotation system, looking most closely at techniques for placing annotations from a distance.