## 2 Case Studies
### Migrating Annotations across Multiple Representations of Museum Artefacts  
The 3D Semantic Annotations (3 DSA) project [17] aims to develop simple, semantic annotation services for 3D digital objects (and their sub-parts) that will facilitate the discovery, capture,  
Figure 4: OA instance illustrating a reply to an existing Annotation/TextualNote. Figure 3: OA instance for textual note. inferencing and exchange of cultural heritage knowledge. The 3 DSA annotation tool enables users (curators, scholars, students and the general public) to search, browse, retrieve and _annotate_ 3D digital representations of cultural heritage objects via a Web browser. The first step involves generating a collection of 3D models of artefacts from the UQ Antiquities Museum (Greek Vases and Roman Sculptures) and the UQ Anthropology Museum (Indigenous carvings from the Wik community in Western Cape York). The 3D representations have been created using a Konica Minolta 9i 3D laser scanner. The 3 DSA annotation client, shown in Figure 5, is a Web application that allows ontology-based (semantic) tags and/or free text comments to be attached to 3D objects. Annotations can be attached to the whole object or to a point, surface region or 3D volumetric segment of the object. The central panel provides an interactive 3D viewer that allows the user to pan, zoom and rotate the 3D object. Existing annotations on the object are indicated by the colored markers attached to the object, and are listed on the right-hand side. Clicking on an annotation on the RHS, rotates and zooms the object, so that that selected annotation is central and its details described in the panel at the bottom centre. The laser scanner produces archival quality models, with each model being on average between 50-200 MB, containing 0.5-2 million polygons and with surface textures scanned as high resolution bit maps. However, many of the users accessing the collection from remote locations have limited bandwidth, poor graphics capabilities and limited compute power--and hence are unable to render very high resolution, archival-quality models. In order to support users with variable Internet connectivity and computing resources, each model is converted into a high resolution and low-resolution X3D format, as well as a \"2.5D\" FlashVR file constructed from a sequence of 2D images. Table 2 outlines the characteristics of the three formats for the web. Figure 5: 3 DSA Annotation client. In order to allow users to collaborate regardless of which format they are using to access the museum objects, 3 DSA supports the automatic migration of annotations between the high res 3D model, low res 3D model and 2.5D representations. The annotation client automatically migrates annotations attached to a point or region on one representation of the model across to the other formats. In the case of the X3D format files, the segments being annotated are identical as the 3D representations share the same local matrix. However, when migrating to the FlashVR image sequence, points need to be projected from a 3D space (identified using X, Y and Z co-ordinates) onto a 2D plane (X and Y only). Figure 6 illustrates an OA model instance for a sample annotation after it has been migrated across the three formats. Rather than having to manage three separate annotations, and ensure that their contents remain synchronized, the OA model allows all of the derivative models to be targeted within a single annotation. The body of this annotation is specified inline using _cnt:chars_ (to represent the content) and _cnt:characterEncoding_ (to specify the type of the content) from the \"Representing Content in RDF\" ontology. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Attribute**} & \multicolumn{3}{c}{**Format**} \\ \cline{2-4}  & **High quality 3D** & **Low quality 3D** & **2.5D VR** \\ \hline Format & X3D & X3D & Flash \\ File size & 18–21 MB & 4–6 MB & 1 MB \\ Polygon count & 0.3 million & 65, 000 & N/A \\ \hline \hline \end{tabular}
\end{table} 
Table 2: 3D object characteristics.