Abstract: Freehand sketch is an efficient way for expression,communication and record of ideas at the conceptual design stage of products．The paper presented a novel method for feature extraction and the correction for online freehand conic section and developed a human-computer interface prototype system (FSR) for assisting designers during conceptual design stages,which maks system interface easy and friendly to use．Firstly,this paper classified the conic section to central curve and non-central curve and correspondingly introduced its parameter feature extraction method．Secondly,the paper proposed the parameter characteristic correction method of the circle (arc),the parabola．Consequently,it provided the parameter interface for CAD system that sustains the online freehand sketching．The system was tested with a number of sketched inputs of 2D geometry．The effectiveness of the algorithm was demonstrated preliminarily by experiments．This feature extraction and the revision method may carry on the classification well to the recognition result of online freehand sketch.

Key words: Online freehand sketch,Recognition,Conic section,Feature parameter extraction,Feature parameter correction