Survey of Pen-and-Paper Computing - Human-Computer Interaction - page 56

visible marks on the document (e.g. an individual word). Instead hot-spot areas can
be freely defined on the paper surface. Tapping with the pen on such an area displays
the associated digital document. Both PaperLink and the Interactive Multimedia
Textbook are limited to links from paper to digital media.
PapierCraft [75] (introduced above) allows the user to create hyperlinks between
two paper documents. A hyperlink is created by drawing two specific pen gestures
on both link anchors (see Fig. 2.17 on p. 53). To create links from or to digital
documents, the same gestures can be used on a Tablet PC on which the digital doc-
ument is displayed. In contrast to the other solutions discussed in this section, it is
not possible to activate a hyperlink on paper, but only in the PapierCraft software
viewer.
The hyperlinking functionality of CoScribe (cf. Chapter 6 of this topic and [144])
focuses on tasks that require integrating and structuring information from a variety
of documents, including printed documents and Web pages. Hyperlinks are created
with pen gestures similar to PapierCraft's gestures. CoScribe introduces the follow-
ing two novel aspects: On the one hand, it integrates the linking interactions; the
same Anoto pen and the same gestures can be used both on paper and on displays.
This avoids the need for switching between different devices and different inter-
action techniques, allowing seamless linking between both realms. A plug-in for
Mozilla Firefox supports pen-based linking within Web pages. On the other hand,
CoScribe automatically integrates linking activities of multiple users and multiple
documents into one workgroup view. This view allows users to identify higher-level
linking patterns that go beyond individual links.
In-place Visual Feedback
Almost all of the solutions discussed above strongly separate paper-based input from
digital output. Digital versions of the documents are made available on a separate
screen. We conclude this section by reviewing several publications that examine
how digital information can be visualized directly within the paper document.
PenLight [138] introduced the concept of a digital pen that features a built-in
projector. The pen projects a superimposed layer of digital information onto the
paper document. This layer shows additional contents, such as annotations made
by other users or additional images, but also provides visual guidance for invoking
commands from pie menus. As current mobile projectors are still too large to be
mounted to a pen, the authors simulat a projecting pen by tracking the position and
orientation of the pen. Contents are then projected by a projector that is mounted at
the ceiling above the table. MouseLight [139] is a follow-up work by the same au-
thors. Here a real mobile projector is used, which however is detached from the pen
and forms a separate device. This device, which resembles a mouse, can be placed
onto paper documents and projects a superimposed layer of digital information. Fig-
ure 2.20 depicts MouseLight. The concept is similar to PenLight, but interaction is
now bimanual. One hand is interacting with the pen while the other hand is manip-