  Real-time three-dimensional (3D) scene representations serve as one of the
building blocks that bolster various innovative applications, e.g., digital
manufacturing, Virtual/Augmented/Extended/Mixed Reality (VR/AR/XR/MR), and the
metaverse. Despite substantial efforts that have been made to real-time
communications and computing, real-time 3D scene representations remain a
challenging task. This paper investigates the tradeoff between timeliness and
fidelity in real-time 3D scene representations. Specifically, we establish a
framework to evaluate the impact of communication delay on the tradeoff, where
the real-world scenario is monitored by multiple cameras that communicate with
an edge server. To improve fidelity for 3D scene representations, we propose to
use a single-step Proximal Policy Optimization (PPO) method that leverages the
Age of Information (AoI) to decide if the received image needs to be involved
in 3D scene representations and rendering. We test our framework and the
proposed approach with different well-known 3D scene representation methods.
Simulation results reveal that real-time 3D scene representation can be
sensitively affected by communication delay, and our proposed method can
achieve optimal 3D scene representation results.
