Freehand sketching is a natural and crucial part of everyday humaninteraction, yet is almost totally unsupported by current user interfaces. With the increasing availability of tablet notebooks and pen based PDAs, sketchbased interaction has gained attention as a natural interaction modality.We are working to combine the flexibility and ease of use of paper and pencilwith the processing power of a computer, to produce a user interface fordesign that feels as natural as paper, yet is considerably smarter. One of themost basic tasks in accomplishing this is converting the original digitizedpen strokes in a sketch into the intended geometric objects. In this paper wedescribe an implemented system that combines multiple sources of knowledge toprovide robust early processing for freehand sketching. We also show how thisearly processing system can be used as part of a fast sketch recognition system with polynomial time segmentation and recognition algorithms.