The analysis of figure captions in anatomy in Section 4 revealed that the structure of these caption is fixed and that short phrases dominates. Hence, we decided to realize a template-based approach to the generation of figure captions. To describe the abstraction techniques and their effect in figure captions, the context expert collects the changes to the visualization (recall Section 6) which are evaluated as to the user preferences (see Section 5.2). The parameters affect single events or entire event-types, events affecting specific object or entire object classes.
Figure: Macrostructure of descriptive figure captions in anatomy according to the analysis in Section 4
The caption should start with a description of the model view which includes the name of the model, the viewing direction and the aspects selected (the structural element model view of the macrostructure presented in Figure 5). In Figure 5 the complete macrostructure is presented. Different realizations are required, depending on, for example, whether one model view is presented or two are presented simultaneously. Figure 6 presents the templates of this category. The structural element text view describes the filtering process of labels (whether all relevant labels could be displayed or not). Other structural elements include descriptions of the abstraction process, especially illustration techniques to emphasize objects, the description of rendering styles and attributes. As a result, these structural elements are arranged in a sequence which represents the order in which they are realized.
Figure 6: Templates of the structural element Model View. [Model] represents the name of a model to illustrate, [Direction] denotes a viewing specification and [AspectList] a set of important categories.
The content of the structural element ``model view'' is realized by four distinct templates. One template is selected by the system as the first sentence of the figure caption according to their application conditions. If there is only one instance of the 3D model depicted, the first template is chosen. If there is a left and a right instance of the 3D model, one of the templates 2, 3 or 4 is chosen.
For the lexical realization of template variables, we need phrases to describe colors, transparency values and viewing directions. The naming of viewing directions considers conventions of the medical domain. In medical images, the frontal view, for example, is referred to as ventral which is more exact because ventral means ``from the stomach''. Thus a reference point of the human body is used to name a viewing direction. By analogy, other viewing directions are named accordingly with reference to the human body.
Figure 7: An illustration conveying a different thematic focus in both symmetric halves. Within the right half the objects of the upper layers where made semi-transparent to prevent occlusion of the lower layer objects. The application of this abstraction technique is described in the figure caption.
Figure 8: The user's request for further information on a very small eye muscle via the selection of its label results in a system-initiated enlargement of that muscle. The first three sentences of the figure caption remain constant, whereas in the fourth sentence the effect of this abstraction technique is explained.
We will illustrate the results from the above mentioned methods with two interactively created illustrations of the human face. In the first illustration (Figure 7) the user has manipulated the presentation so that the left and the right parts of the model look different. The figure caption indicates that the objects near the surface have been rendered semi-translucent in the right part of the model. Figure 8 shows another illustration of the same model. Here the user requested an explanation for a small muscle. The system has automatically enlarged this muscle to emphasize it. This side effect is reflected in the figure caption.
To realize the figure caption in Figure 7, the structural elements ``model view'' and ``focus'' were activated. The caption in Figure 8 was realized using the structural elements ``model view'', ``focus'', ``text view'' and ``adaptive zoom''. In both captions, the structural element ``model view'' was realized with the first template from the template category.