  Safety-critical 3D scene understanding tasks necessitate not only accurate
but also confident predictions from 3D perception models. This study introduces
Calib3D, a pioneering effort to benchmark and scrutinize the reliability of 3D
scene understanding models from an uncertainty estimation viewpoint. We
comprehensively evaluate 28 state-of-the-art models across 10 diverse 3D
datasets, uncovering insightful phenomena that cope with both the aleatoric and
epistemic uncertainties in 3D scene understanding. We discover that despite
achieving impressive levels of accuracy, existing models frequently fail to
provide reliable uncertainty estimates -- a pitfall that critically undermines
their applicability in safety-sensitive contexts. Through extensive analysis of
key factors such as network capacity, LiDAR representations, rasterization
resolutions, and 3D data augmentation techniques, we correlate these aspects
directly with the model calibration efficacy. Furthermore, we introduce DeptS,
a novel depth-aware scaling approach aimed at enhancing 3D model calibration.
Extensive experiments across a wide range of configurations validate the
superiority of our method. We hope this work could serve as a cornerstone for
fostering reliable 3D scene understanding. Code and benchmark toolkits are
publicly available.
