This book is the sixth issue in the EurographicSeminars Series. This series has been set up by Eurographics, the European Association for Computer Graphics, in order to disseminate surveys and research results out of the field of Computer Graphics. Computer Graphics constitute a powerful and versatile tool for various application areas. The rapidly increasing use of Computer Graphics techniques and systems in many areas is caused by the availability of more powerful hardware at lower prices,' by the concise specification of Computer Graphics Interfaces in commonly·.agreed standards, and by the inven tion of new and often astonishing methods and algorithms for com position andpreserit~ti6n of pictJres and for graphical interaction. While s,o~e issues of this se.ries contain latest research results, e.g. the issues in window management systems or user interface manage ment systems, this book has the character of a state-of-the-art survey on important areas .of Computer Graphics. Starting from current practice and agreed consens, it will lead to the latest achievements in this field. The contributions in this issue are largely based on tutorials and seminars held at the Eurographics conferences 1984 in Copen hagen and 1985 in Nice.