disclosed herein is a method for auto - depicting trends in object contours . at the heart of adtoc is a sifting process to determine a significant angular value via evaluating a plurality of angular values in a predefined range . adtoc is characterized in that a probe - ahead concept is applied to obtain a reference angular value along the current route , and then the probed angular value is used to modify the significant angular value in order to timely correct the subsequent trace direction , thus achieving more accurate trace result . contours with discontinuous segments caused by noise , obstacles , illumination , shading variations , etc . can also be auto - depicted without requiring a predefined auxiliary route .