Contour furrows overcome this problem because they are placed on a gradient of about 0.5 % across the main slope.
等高沟克服了这个问题，因为这些沟垂直于主坡方向布置，沟道坡度约为0.5%。
2
Secondly, for the image edge detection, methods including the gradient method, the sharp-processing method, and the Hough transformation were used, and the contour tracing was also conducted.
边缘检测处理部分采用了梯度处理法、锐化处理法、哈夫变换处理法，并对图像作轮廓跟踪处理。
3
Two observation models (color and gradient) targeting the head contour are added to work together with the face detector in head tracking.