Beyond Minimum-of-N: Rethinking the Evaluation and Methods of Pedestrian Trajectory Prediction

Pedestrian trajectory prediction is an essential task in real-world applications, aimed at predicting plausible future trajectories based on limited observations. In this work, we rethink the standard evaluation metric of the pedestrian trajectory prediction task: Minimum-of-N Average Displacement Error (MoN-ADE). As for multi-modal prediction models that generate multiple trajectories for each pedestrian, this metric typically evaluates the model by only considering the one that is closest to the ground-truth trajectory. However, such an evaluation protocol cannot comprehensively evaluate the predictive ability of the model, and potentially encourage models to generate high-variance and dispersed trajectory distributions. This is quite impractical especially for many real-world scenes like autonomous driving that require precise and convergent trajectory predictions. To address these limitations, we design a novel metric towards comprehensive evaluation in pedestrian trajectory prediction, which moves beyond the traditional reliance on the closest prediction. Specifically, we replace the Minimum-of-N strategy with an insightful Random-Sampling-K strategy to calculate the expectations of the minimum ADE and formulate a novel metric: Area Under the Curve (AUC). Furthermore, motivated by the proposed metric, we introduce a novel objective function named K-Ensemble Loss, which guides the state-of-the-art models to optimize the whole prediction distribution and reduce the uncertainty caused by the high-variance predictions. Extensive experiments on three real-world datasets demonstrate that the proposed metric and objective function are provided with significant effectiveness and flexibility.