Geospatial Annotations for 3D Environments and their WFS-based Implementation

Abstract

Collaborative geovisualization provides effective means to communicate spatial information among a group of users. Annotations as one key element of collaborative geovisualization systems enable comprehension of collaboration processes and support time-shifted communication. By annotations we refer to user-generated information such as remarks, comments, findings and any other information related to the 3D environment. They have to be efficiently modeled, stored and visualized while precisely retaining their spatial reference and creation context. Existing models for annotations generally do not fully support spatial references and, therefore, do not fully take advantage of the spatial relationships associated with annotations. This paper presents a GML-based data model for geospatial annotations that explicitly incorporates spatial references and allows different types of annotations to be stored together with their context of creation. With this approach annotations can be represented as firstclass spatial features. Consequently, annotations can be seamlessly integrated into their 3D environment and the author's original intention and message can be better expressed and understood. An OGC Web Feature Service is used as standardized interface for storage and retrieval of annotations, which assures data interoperability with existing geodata infrastructures. We have identified three types of annotation subjects, namely geographic features, geometry, and scene views, represented by their corresponding 2D/3D geometry. The model also defines a point-based approximation for complex geometry, such that annotations can also be used by client application with limited abilities regarding display size, band-width or geometry handling. Furthermore we extended our model by annotations that can contain 3D geometry besides textual information. In this way the expressiveness of annotations can be further enhanced for communicating spatial relationships such as distances or arrangements of geographic features.