Photometrically consistent real-time rendering pipeline for street-lighting digital twins: a road-section study

Abstract This paper proposes a photometrically consistent real-time rendering pipeline for digital twins of street lighting systems, designed to bridge the gap between offline lighting simulation tools and interactive visualization environments. The approach integrates high-resolution illuminance data generated by Relux and DIALux into a real-time graphics engine, with the objective of preserving photometric fidelity while maintaining interactive performance. The proposed framework is demonstrated on a campus road section through a street lighting digital twin implemented in Unity. A modular rendering pipeline is introduced, including photometric data preprocessing, illuminance-grid interpolation, texture generation, and consistency checks between offline simulations and real-time outputs. Three real-time lighting modes are implemented and evaluated: an analytical cone-based spotlight model, a texture-masked cookie spotlight mode, and a full-resolution photometric sampling approach based on Unity’s universal Render Pipeline (URP) Shader Graph. A static validation between Relux and DIALux confirms consistent photometric inputs, with mean absolute errors below 5%. Evaluation results show that richer photometric sampling improves agreement with the Relux reference: the Shader Graph mode achieves the best in-engine luxmeter validation (root mean square error (RMSE) 3.82 lx, Pearson correlation (Corr) 0.705) while sustaining real-time performance at approximately 140 frames per second (FPS). Overall, the proposed pipeline enables aligned and interactive street lighting digital twins suitable for simulation-driven visualization and evaluation.