Apparatus and method for estimating camera orientation relative to ground surface

A method for estimating camera orientation of a camera relative to a ground, comprising:

• initializing a priori camera orientation and its corresponding priori camera orientation uncertainty with a best guess or random camera orientation of the camera;
• executing an iterative multi-image camera orientation estimation, comprising:
• capturing a new image or extracting a new video frame from a video of a scene before the camera;
• detecting one or more line segments in the scene in the image or video frame;
• classifying and grouping the line segments of the image or video frame into a frontal, a lateral, and a vertical line segment groups;
• computing a maximum likelihood (ML) camera orientation by taking a calibrated matrix of the camera and maximizing a likelihood objective by rotating a X-Y-Z coordinate system under the camera orientation such that it is being optimally aligned with the line segments in at least two of the frontal, the lateral, and the vertical orthogonal directions;
• estimating a maximum a-posteriori (MAP) camera orientation that maximizes an a-posteriori objective such that the MAP camera orientation is an optimal value in between the priori camera orientation and the ML camera orientation, and is closer to the one with smaller uncertainty;
• comparing the MAP camera orientation with a pre-defined MAP camera orientation uncertainty;
• and
• if the MAP camera orientation uncertainty is higher than the MAP camera orientation uncertainty threshold, iterating the multi-image camera orientation estimation with the priori camera orientation and its corresponding priori camera orientation uncertainty set to the computed MAP camera orientation and its corresponding MAP camera orientation uncertainty respectively;
• and
• if the MAP camera orientation uncertainty is equal and lower than the MAP camera orientation uncertainty threshold, taking the MAP camera orientation that is corresponding to the MAP camera orientation uncertainty that is equal and lower than the MAP camera orientation uncertainty threshold value as the camera orientation estimation method result.