Journal for Geometry and Graphics

The singular coincidence in 2022, 25th anniversary of the publication of the first issue of the Journal of Geometry and Graphics (JGG), 30th anniversary of the establishment of the International Society for Geometry and Graphics (ISGG), and 80th birthday of Hellmuth Stachel, Professor of Geometry at the Technical University of Vienna (now retired), founder and former Editor in Chief of the JGG, and co-founder of ISGG, suggested the idea of this special issue. The Editorial Board, formed by the current Editor in Chief who launched the proposal, the President, the Vice-Presidents, and the Treasurer of ISGG, decided to publish the issue as part of the JGG series, in order to reach the audience of readers familiar with the journal, and with the person to whom this issue is dedicated. The volume includes two editorial sections, “Personal Memories” and “Scientific Contri butions”, in the aim of reflecting the wide spectrum of competences and interests of Hellmuth Stachel, deepened and shared in a life actively spent between research and education, without missing some personal items and anecdotes. “Personal Memories” consist of short contributions written by people being, or having been, closely connected with Hellmuth Stachel over more than three decades, who share their personal records about his role in science, education, and community services. “Scientific Contributions” refer to the world wide scientific impact of Hellmuth Stachel, and consist of a number of papers on topics related to Geometry and Graphics, written by authors of various backgrounds and generations, invited from the three ISGG world regions (Asia/Australia/Oceania, Europe/Near East/Africa, North America/South America). May this special issue celebrating such an exemplary academic profile, inspire all the readers, as well as the whole JGG and ISGG communities, and, why not, initiate a new editorial line inside the JGG series. On behalf of JGG and ISGG, we warmly address to Professor Hellmuth Stachel our birthday wishes, and cordial greetings to his family and his wife Mrs. Henrike. The Guest Editorial Board of JGG 26/1 Liang-Yee Cheng, Luigi Cocchiarella, Hans-Peter Schr¨ocker, Kumiko Shiina