Citigen is a Blender extension. There is no need for HDRIs and no requirement for the rigging of animation cameras for basic drone photos like POI or Course Lock!
With just a few clicks you can design a virtually limitless range of urban environments with traffic lights, streets trees, etc. - as big as your RAMs GPUs, and CPUs can handle. The city props that come with Citigen will appear like real-world objects between 10 and 15 feet in an amount that is sufficient to create drone-like scenes, however, you can create your own building models that are detailed in the Citigen library to take close-up photos!
