Guo Kai, Zhang Zhixiang, Zhang Zhongsen, Tian Ye, Chen Honglin
Northwest Institute of Nuclear Technology, Xi'an 710024, China.
Sensors (Basel). 2022 Oct 28;22(21):8253. doi: 10.3390/s22218253.
Estimating camera pose is one of the key steps in computer vison, photogrammetry and SLAM (Simultaneous Localization and Mapping). It is mainly calculated based on the 2D-3D correspondences of features, including 2D-3D point and line correspondences. If a zoom lens is equipped, the focal length needs to be estimated simultaneously. In this paper, a new method of fast and accurate pose estimation with unknown focal length using two 2D-3D line correspondences and the camera position is proposed. Our core contribution is to convert the PnL (perspective-n-line) problem with 2D-3D line correspondences into an estimation problem with 3D-3D point correspondences. One 3D line and the camera position in the world frame can define a plane, the 2D line projection of the 3D line and the camera position in the camera frame can define another plane, and actually the two planes are the same plane, which is the key geometric characteristic in this paper's estimation of focal length and pose. We establish the transform between the normal vectors of the two planes with this characteristic, and this transform can be regarded as the camera projection of a 3D point. Then, the pose estimation using 2D-3D line correspondences is converted into pose estimation using 3D-3D point correspondences in intermediate frames, and, lastly, pose estimation can be finished quickly. In addition, using the property whereby the angle between two planes is invariant in both the camera frame and world frame, we can estimate the camera focal length quickly and accurately. Experimental results show that our proposed method has good performance in numerical stability, noise sensitivity and computational speed with synthetic data and real scenarios, and has strong robustness to camera position noise.
估计相机位姿是计算机视觉、摄影测量和SLAM（同时定位与地图构建）中的关键步骤之一。它主要基于特征的二维与三维对应关系来计算，包括二维-三维点对应和线对应。如果配备了变焦镜头，则需要同时估计焦距。本文提出了一种利用两组二维-三维线对应关系和相机位置快速准确地估计未知焦距位姿的新方法。我们的核心贡献是将具有二维-三维线对应的透视n线（PnL）问题转化为具有三维-三维点对应的估计问题。一条三维直线和世界坐标系中的相机位置可以定义一个平面，三维直线在相机坐标系中的二维直线投影和相机位置可以定义另一个平面，实际上这两个平面是同一个平面，这是本文估计焦距和位姿的关键几何特征。我们利用这一特征建立了两个平面法向量之间的变换，该变换可视为一个三维点的相机投影。然后，将利用二维-三维线对应关系的位姿估计转化为中间帧中利用三维-三维点对应关系的位姿估计，最后可以快速完成位姿估计。此外，利用两个平面之间的夹角在相机坐标系和世界坐标系中都不变的特性，我们可以快速准确地估计相机焦距。实验结果表明，我们提出的方法在合成数据和真实场景下的数值稳定性、噪声敏感性和计算速度方面具有良好的性能，并且对相机位置噪声具有很强的鲁棒性。
