A mark-based interaction paradigm for free-hand drawing

Author:Thomas Baudel

Summary:
This paper gives a different view of editing splines. This paper claims this method of editing splines is more closer to our interaction model than the editing splines with control points and tangents.
This method is very suitable for the graphical designers (closer to their conceptual model). Sketch recognition is used to provide complex modifications and re parametrization.
The method can decomposed into 2 operations:
Given a first F and second m,
1. find the starting point S and end point E that would match best with m. These points are found by finding the visually closest points on F from m. Equal length matching is done and a list of all possible candidate curves are maintained for the user to choose. This search can be further optimized. When the curves are discretized to poly-lines, the search is reduced to the number of poly-lines.
2. Transform F(SE) into r (the resulting stroke) with the help of m. This method encourages for large imprecise strokes and short n fast strokes which start and end within the curve F.First f and m are converted into poly-lines and the resulting curve r is a poly-line which will be smoothed. The algorithm defines a smoothness factor 'k' and a transitional polynomial to provide smoothness in transition. An extension segment each at the start(S') and at the end(E') of curve F is defined for smooth transition between S' -> S and E->E' while re - parametrization.

Evaluation this method showed this method needed lesser effort from the user for editing.
This method allows complex re-parametrization in one single action rather than specifying lot of control points.
Future Work: Use of pressure information to re-parametrize the width/ density of the stroke.

Discussion:
This is a totally different approach to the problem of editing strokes. But it requires a mode switch to understand which stroke is the base stroke and which one is (m) stroke that edits the previous one.
I would like to know how this algorithm be applied when there is no mode switch. There would be a problem of identifying (m). For every stroke drawn by the user, should the next stroke be considered the editing stroke(m)/ should it based on some distance threshold?. Would the user like the automatic adjustments?
I do not think there would any necessity to re-parametrize strokes width. I do not think the editing stroke captures the user-intended width. So the re-parametrized stroke should have the same density pattern as the original stroke.