This study explores how to combine parametric modeling and virtual reality (VR) technology with geographic information system (GIS) to improve the analytical ability and visual performance of urban digital twins. Taking the Dora Riparia and its surrounding urban parks in Turin, Italy as a case study object, this study constructs a cross-platform workflow integrating CityEngine, ArcGIS Pro and Unreal Engine 5 (UE5) integrated through Cesium for Unreal. The main research question examines whether Computer Generated Architecture (CGA) rule-based 3D modeling in CityEngine, when integrated with GIS-based simulation and real-time VR visualization, can deliver a more interactive and efficient urban-analysis framework compared with conventional static GIS approaches.