Textbooks are important resources to support learners. In order to explain structures and relations of real existing objects, expository texts are frequently complemented by illustrations. A key role of this complement play annotations which identify illustrations and their parts by their technical terms and consequently may enable the establishment of visual links between expository texts and the depictions. However, the depiction of spatial objects may lead to unintentional ambiguities and due to economic constraints illustrators may be forced to design illustrations as general as possible. Hence, the first part of this book introduces a solution which enables the interactive exploration of 3D models without forgoing annotations similar to those typically found in educational books. Another objective of this book is based on the difficulty that readers of traditional textbooks often encounter mutual search tasks arising from the combined use of expository texts with complementary illustrations.
As a guide for software developers of educational software this book presents solutions for improving electronic versions of textbooks.