In the nature light, there are shadows on the area of reference points.Infinite impulse response (IIR) filter was used to detect ridge edge and avoid the effect of shadows in nature light.

• 在自然光照条件下，标定点区域不可避免地存在阴影等干扰，采用无限脉冲响应(IIR)递归滤波器对脊线边缘进行检测，可以有效排除阴影干扰。