LIO-PPF: Fast LiDAR-Inertial Odometry via Incremental Plane Pre-Fitting and Skeleton Tracking

As a crucial infrastructure of intelligent mobile robots, LiDAR-Inertial odometry (LIO) provides the basic capability of state estimation by tracking LiDAR scans. The high-accuracy tracking generally involves the kNN search, which is used with minimizing the point-to-plane distance. The cost for this, however, is maintaining a large local map and performing kNN plane fit for each point. In this work, we reduce both time and space complexity of LIO by saving these unnecessary costs. Technically, we design a plane pre-fitting (PPF) pipeline to track the basic skeleton of the 3D scene. In PPF, planes are not fitted individually for each scan, let alone for each point, but are updated incrementally as the scene 'flows'. Unlike kNN, the PPF is more robust to noisy and non-strict planes with our iterative Principal Component Analyse (iPCA) refinement. Moreover, a simple yet effective sandwich layer is introduced to eliminate false point-to-plane matches. Our method was extensively tested on a total number of 22 sequences across 5 open datasets, and evaluated in 3 existing state-of-the-art LIO systems. By contrast, LIO-PPF can consume only 36% of the original local map size to achieve up to 4x faster residual computing and 1.92x overall FPS, while maintaining the same level of accuracy. We fully open source our implementation at https://github.com/xingyuuchen/LIO-PPF.

ImplantFormer: Vision Transformer based Implant Position Regression Using Dental CBCT Data

Implant prosthesis is the most optimum treatment of dentition defect or dentition loss, which usually involves a surgical guide design process to decide the position of implant. However, such design heavily relies on the subjective experiences of dentist. To relieve this problem, in this paper, a transformer based Implant Position Regression Network, ImplantFormer, is proposed to automatically predict the implant position based on the oral CBCT data. The 3D CBCT data is firstly transformed into a series of 2D transverse plane slice views. ImplantFormer is then proposed to predict the position of implant based on the 2D slices of crown images. Convolutional stem and decoder are designed to coarsely extract image feature before the operation of patch embedding and integrate multi-levels feature map for robust prediction. The predictions of our network at tooth crown area are finally projected back to the positions at tooth root. As both long-range relationship and local features are involved, our approach can better represent global information and achieves better location performance than the state-of-the-art detectors. Experimental results on a dataset of 128 patients, collected from Shenzhen University General Hospital, show that our ImplantFormer achieves superior performance than benchmarks.