Abstract: A device determines a depth value of a 3D irregular surface of an object. The device being at a first viewpoint, 3D position coordinates for the device are initialized, and an imaging system captures a first image comprising at least a portion of the surface. First 3D position coordinates are determined for a first image point. Highest and lowest points of the surface are initialized 5 at the first image point. An inertial sensing unit detects a movement of the device to a current viewpoint. Current position coordinates for the device are determined. A current image comprising another portion of the surface is captured. Current position coordinates are determined for a current image point. The highest or lowest may be updated using the current position coordinates for the current image point. The depth value is updated based on a 0 calculated distance between the highest and lowest points.