At the Electronic Imaging symposium of 2013, Steve Seitz from Washington University and Google presented a very interesting keynote entitled “a trillion photos”.
The principle is to exploit the millions of images found in databases such as Flickr. The aim of the project Building Rome in a Day is to harvest images from Flickr by simply typing the keywords “Rome” or “Venice”. Many images are unusable because they can not be matched with other images – such as pictures of a restaurant, of a family, etc. On the other hand, the most touristic places such as “San Marco” are taken in picture from many different angles. By using a standard processing stream such as SIFT + RANSAC + FLANN it is possible to match the images and then to do the 3D reconstruction.
In this video , the pyramids represent the estimated shooting positions. The reconstruction was made by using 14,079 pictures. The reconstruction of Venice is made by using 250,000 images, 496 computing cores. 27h are necessary for matching and 38h for reconstruction.