Week 1: Sketchpad

"Sketchpad," Sutherland

Sutherland's paper begins with an example illustrating the capabilities of Sketchpad, highlighting features such as object oriented design and constraint solving. Then next sections detail the inner workings of the various components of the system, beginning with storage. Objects are stored in a doubly-linked list that ties together connected components such as points and edges. Additionally, as new objects are created from the composition of lower level objects, a hierarchy of objects is formed. Modification of the lower level component bubbles up through the hierarchy altering higher level object that make use of it. Next, the light pen used for input is described. The light pen can observe objects on the display and is able to focus the users aim on objects within 1/8 of the center of the light pen's field of vision, allowing a range of freedom for targeting an object. The method used to display drawings is discussed next. For each "spot" on the screen the coordinates of the spot as well as a link to the object responsible for the spot are stored. Drawings can be magnified by up to a factor of 2000 and intersections between the objects an screen edges are computed. Line and curves are generated using simple difference equations, while text and digits rely on pre-generated tables to determine spot locations. Sketchpad also uses recursive, generic methods that allow complex objects to be altered in the same manner as simple ones. Objects are able to be deleted and merged in this fashion, and dependent objects are merged or deleted as necessary. When displayed objects refer to the objects they are composed of to determine how they are drawn. An instance of an object can be copied and modified independently of the original. The final section describing how Sketchpad works deals with constraints. Constraints are enforce with a one pass method and are relaxed should the method fail. Next, several examples are provided, such as patterns, electrical circuits, and bridges.

The Sketchpad paper provides an interesting view into the beginnings of pen based computer input. Though the numerous buttons needed for determining the appropriate mode of operation seem burdensome at first, modern CAD or drawing programs require the use of a similar mode selection procedure, though it is graphical in nature and some efficiency improvement do exist.

Week 1: Intro to Sketch Recognition

"Introduction to Sketch Recognition, Tracy Hammond and Kenneth Mock

The paper begins with a brief history of pen-based computer input, then describes current pen-based computer systems, including several types of hardware (form, size, etc) and available software (OS support, display recording, pen input), as well as describing two methods used to determine where the input device is in relation to the what is displayed. In the next section, uses of pen-based computer input in the classroom are discussed, including lectures/presentations, note taking, and other uses along with advantages and disadvantages of these techniques. Several example systems developed for specific academic environments are described, such as art, music, chemistry, engineering, and computer science, as well as military packages. These systems recognize specific shapes drawn with the pen to represent objects and actions. Finally in this section, a package that allows development of new systems that recognize pen input and associate it with specific actions is described. Next, the paper describes some challenges facing pen interface device. Also, two case studies are presented in which pen devices are used in the classroom and the reaction to their use by the the teacher and students is recorded. The paper finishes with a brief discussions of the use of pen devices in distance learning and possible future use of pen devices.

Overall, the paper provides a fairly comprehensive view of pen-input devices and their use in education. Though educational uses were the primary focus of the examples, the same uses also exist in the business world. Many business presentations could benefit from the interactivity the pen interface provides. The text recognition features available on later model tablets could be useful for improved legibility in professions that tend handwrite documents. The discussion of distance learning uses seems misplaced towards the end.