where θ is the angle made from the rough sketch data, φ is the angle made from the data projected onto the rough sketch surface, and i is the angle number counting from the hair strand root. In this equation, the result of each subtraction must be lower than a certain threshold, th. If the subtraction result is higher than th, we do not choose the database sequence with the minimum error. We thereby obtain from the rough sketch the most similar hair form in the motion database