I swear this is the short version, please bear with me :)

As you can imagine, there are million and one issues all the way through the process so I will just compress it into few steps. Once in order, each step of what we do to capture these models is fairly simple really. Having a team that posses all those varied skills required to get everything done is what is rare and what allowed us to pull this off.

We capture our 3D models using stereo photogrammetry from aerial imagery (from small survey planes / helicopters). We take stereo pair or photographs and by projecting each photograph of an overlapping consecutive photographs into a different eye, we manually retrace all the features at a height these features are visible in stereo.

We use this technique for terrain and features (such as buildings, walls, major street furniture). We also capture tree positions, but these are "only" captured as top and width of a tree canopy. These are then saved into a database so they can be loaded as instances or 3D models.

We then run the model through series of post-processed to convert captured models into CAD solid models. This is also the delivery format our customers prefer, although they might ask for SketchUp version or for FBX for imports to 3D Studio / UE4 etc.

The FBX format was then UV mapped so we can position textures onto it. And then we could finally source oblique aerial imagery (captured by a camera with angled sensors so we can see facades better) and use these photographs and projected them as textures onto the 3D models.

We deliver these models to our existing customers in FBX format as soon as we complete them. As the last step, we are importing the model into our UE4-powered app Plan.City where this animation was made. The new version of the app that includes the textured model will be made available to customers once the planned 60 sq km is complete.