Volumetric 3D Reconstruction and parametric shape modeling from RGB-D Sequences

The recent availability of low-cost RGB-D sensors and the maturity of machine vision algorithms makes shape-based parametric modeling of 3D objects in natural environments more practical than ever before. In this paper, we investigate the use of RGB-D based modeling of natural objects using RGB-D sensors and a combination of volumetric 3D reconstruction and parametric shape modeling. We apply the general method to the specific case of detecting and modeling quadric objects, with the ellipsoid shape of a pineapple as a special case, in cluttered agricultural environments, towards applications in fruit health monitoring and crop yield prediction. Our method estimates the camera trajectory then performs volumetric reconstruction of the scene. Next, we detect fruit and segment out point clouds that belong to fruit regions. We use two novel methods for robust estimation of a parametric shape model from the dense point cloud: (i) MSAC-based robust fitting of an ellipsoid to the 3D-point cloud, and (ii) nonlinear least squares minimization of dense SIFT (scale invariant feature transform) descriptor distances between fruit pixels in corresponding frames. We compare our shape modeling methods with a baseline direct ellipsoid estimation method. We find that model-based point clouds show a clear advantage in parametric shape modeling and that our parametric shape modeling methods are more robust and better able to estimate the size, shape, and volume of pineapple fruit than is the baseline direct method.