Abstract: To outline the silhouette of point cloud or mark some special signs on it,a novel approach for creating curves on point cloud with free-hand sketch is presented.The raw sketch made by free-hand tracing is first recognized as a set of conics and line segments,then the conics are equi-distantly sampled,and all the sampled points are projected back onto the point cloud.Finally,all these projected points are verified to see whether they lie well on a plane.If it does,re-project the conics onto the plane.Else,fit the projected points as a B-spline curve and smooth it.Experiments show that silhouette can be perfectly and quickly outlined based on this free-hand sketching.Conics or smooth 3D B-spline curve can be drawn freely and quickly.