I was the lead environments modeler on this build with an extremely talented crew. This environment used procedural workflows in Houdini (shown in darker grey). It was made using height maps to shape the terrain, then procedural masks were made for shaders and layout to drive textures and dressing. The whole environment became a symbiotic relationship between departments. Kevin Smith's (VFX supervisor) does a full breakdown at https://youtu.be/b7TDcvQjGuE or scroll down below for video clip.
Houdini was also used to populate city building elements and for simulations of debris after the wall was destructed.
Photogrammetry was used for cliff creation and key rock formation builds where vertical surfaces could not be resolved by height fields alone.
Full VFX breakdown by Kevin Smith:
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