Monday, November 8, 2010

Reading #6: Protractor: A Fast and Accurate Gesture Recognizer (Li)

Summary
In this paper, Li introduces his gesture recognizer named Protractor. It works similar to the $1 Recognizer presented by Wobbrock but is faster and can be made to be orientation-sensitive. Protractor first resamples to N points and then rotates based on the indicative angle or to one of eight orientations if it is specified to be orientation-sensitive. It then calculates the optimal angular distance against each template and returns the top choice of the N-best list of results

Discussion
Protractor uses the same concepts presented in the $1 Recognizer but also makes some key improvements. Protractor is able to recognize gesture which are orientation-sensitive by only rotating to certain angles and not scaling to avoid distorting the input. It also uses a closed-form solution to find the rotation that leads to the minimum angular distance instead of using the iterative approach utilized in $1. This helps Protractor to produce a higher accuracy in shorter amounts of time.

Reading #5: Gestures without Libraries, Toolkits or Training: A $1 Recognizer for User Interface Prototypes (Wobbrock)

Summary
In this paper, Wobbrock introduces his "$1 recognizer". This recognizer is easy to implement compared to other methods of gesture recognizing, such as Rubine's method. The simple algorithm consists of resampling the point path, rotating the gesture based on "indicitave angle", scaling and translating to a reference square, and then finding the optimal angle for the best score. The score is computed as a function of the distance between the template points and the points of the gesture. 

Discussion
This paper introduces a simple gesture recognizer that requires less processing to implement than many recognizer before it. The $1 recognizer provided accuracy rates of over 99% for a selection of gestures. However, since it changes the orientation and scale of each gesture that is input, it would not perform well with gestures such as arrows or shapes that may be similar such as squares and rectangles. 

Thursday, November 4, 2010

Reading #4: Sketchpad: A Man-Made Graphical Communication System (Sutherland)

Summary
In this paper, the author describes the Sketchpad system. Since the hardware of the time was limited, the author uses a light pen and a combination of push buttons, on and off switches, and turning knobs to input and manipulate data in the system. The system is only able to use lines, circles, and points but the data structure for each was well defined along with the types of constraints that may be used. Several examples of Sketchpad projects were given including bridge drawings, artistic drawings, and electrical circuit diagrams.

Discussion
This paper introduces many ideas that are still used in sketch input systems today such the data structures and constraint systems presented. The idea of copying instances and being able to have sub-pictures within sub-pictures allows for more efficient sketches to be created. The constraint system introduced is very useful for defining components composed of subcomponents.