Title: Transcendental Idealism of Planner: Evaluating Perception from Planning Perspective for Autonomous Driving. Abstract: Evaluating the performance of perception module in autonomous driving is one of the most critical tasks in developing these complex intelligent systems. While module-level unit test methodologies adopted from traditional computer vision tasks are viable to a certain extent, it still remains far less explored to evaluate how changes in a perception module can impact the planning of an autonomous vehicle in a consistent and holistic manner. In this work, we propose a principled framework that provides a coherent and systematic understanding of how perception modules affect the planning of an autonomous vehicle that actually controls the vehicle. Specifically, planning of an autonomous vehicle is formulated as an expected utility maximisation problem, where all input signals from upstream modules jointly provide a world state description, and the planner aims to find the optimal action to execute by finding the solution to maximise the expected utility determined by both the world state and the action. We show that, under some mild conditions, the objective function can be represented as an inner product between the world state description and the utility function in a Hilbert space. This geometric interpretation enables a novel way to formulate, analyse and evaluate the impact of noise in world state estimation on the solution to the problem, and leads to a universal quantitative metric for such purpose. The whole framework resembles the idea of transcendental idealism in the classical philosophy literature, which gives the name to our approach.