Department of Computer Science, The University of Tokyo

Abstract. This paper describes an interface for assisting the design and production of pop-up cards by using a computer. A pop-up card is a piece of a folded paper from which a three-dimensional structure pops up when it is opened; it can be folded flat again afterward. Many people enjoy this interesting mechanism in pop-up books and greeting cards. However, nonprofessionals find it difficult to design pop-up cards because of the various geometric constraints required to make the card fold flat. We therefore propose an assistant interface to help people easily design and construct pop-up cards. In this paper, we deal with pop-up cards that open fully to 180◦ . We have designed a prototype that allows the user to design a pop-up card by setting new parts on the fold lines and editing their position and shape afterward. At the same time, the system examines whether the parts protrude from the card or whether the parts collide with one another when the card is closed. Users can concentrate on the design activity because the results are continuously fed back to them. We created several pop-up cards using our system and performed an informal preliminary user study to demonstrate its usability. 1 Introduction A pop-up card is a piece of a folded paper from which a three-dimensional (3D) paper structure pops up when it is opened. The card can be folded flat again afterward.

Many people enjoy this interesting mechanism in pop-up books [1] [2] [3] and greeting cards, and receiving and viewing pop-up cards appeals to people of all ages. Fig. 1 shows an example of pop-up book. Constructing a pop-up card is relatively easy; anyone can simply cut out the pieces and glue them together if a template is available. Unfortunately, it is much more difficult for nonprofessionals to design a pop-up card from scratch. The first problem is correctly understanding the pop-up card mechanism. The second problem is determining the positions of objects so that pop-up parts do not collide. This usually requires repetitive trial and error during design: cutting out component parts out of paper, pasting them on the card, and checking Fig. 1. “Alice’s Adventures in Wonderland”, a typical pop-up book [1]. whether they collide. If an error is found, re-thinking the design and starting over from the beginning. This process requires a lot of time, energy, and paper. Design and simulation in a computer eliminate the boring repetition and save time. Glassner proposed methods for designing pop-up cards [4] [5] [6]. He introduced several simple pop-up mechanisms and described how to use these mechanisms, how to simulate the position of vertices as an intersecting point of three spheres, how to check whether the structure sticks out beyond the cover or if a collision occurs during opening, and how to generate templates. His work is quite useful in designing simple pop-up cards. Our work builds on Glassner’s pioneering work and introduces several innovative aspects. Our system has two new mechanisms based on the V-fold: the box and the cube. We provide a detailed description of the user interface, which Glassner did not describe in any detail. In addition, our system provides realtime feedback to the user during editing operations by examining whether parts protrude from the card when closed or whether they collide with one another during opening and closing. Finally, we report on an informal preliminary user study of our system involving two inexperienced users.