3D models are created using a technology called Photogrammetry. Roots of this science were layed out in the middle of 19. century. Long story short, this technology allows us to reconstruct a shape of an object based on multiple images.
To get the images we are using UAVs (drones) combined together with terrestrial photography using classic DSLRs.
After we get the images (i.e. a LOT of images) they are processed by a special photogrammetry software. Its not an easy task even for the most powerful machines and sometime takes a whole day of proccesing on 32 cores CPU
When we have the rough model, then a fine work begin. The model needs to be manually cleaned and decimated, as the generated one could easily exceed GBs of data. So in order to be displayd on a web, there is a lot of work to do to make it smaller.