Mapping Rio de Janeiro's Christ the Redeemer in High-Definition -

This post is the latest in the Drones and Small Unmanned Aerial Systems Special Series, which profiles interesting information, thoughts and research into using drones, UAVs or remotely piloted vehicles for journalism and photography, that Kike learns about during his travels.

3D UAV mapping technology is delving into uncharted territory, finding applications for the union of UAV hardware and image processing software not before used. Mapping the Christ the Redeemer statue in Rio de Janeiro is one of those applications, as an accurate 3D reconstruction of the icon has never been produced. And for good reason: the 38 meter statue is perched on a narrow terrace atop a 700 meter peak, its location exposing it to high winds and irregular cloud cover.

The NEXT lab of PUC University in Rio de Janeiro had long dreamt of creating an accurate 3D model of the Christ statue, but ran into limitations using LiDAR technology. There were too many facades and high angles to scan the whole statue, not to mention the enormous cost of laser scanning and lack of a highly reliable aerial method with the hardware needed to acquire the data.

So when the lab saw that Pix4D, a Swiss company, had done a 3D reconstruction of the Matterhorn using UAV acquired data, they contacted the image-mapping software startup and asked them to help.

Pix4D and NEXT lab needed a highly controllable and reliable UAV for the flight, one able to withstand strong wind drafts and guarantee no accidental damage to the monument. They chose the small Aeryon Scout, a Vertical Take-Off and Landing (VTOL) quad rotor UAV that allowed for safe operation.

“Creating a model of Christ in Rio was perfect because it has such detail,” said Christoph Strecha, CEO and Founder of Pix4D. “It was the perfect structure to show the possibilities of drone usage in image processing technology, where traditional methods like laser scanning have not been practical.”

The team spent six consecutive days with the Aeryon Scout, collecting what came to a total of 3,584 photos before the visitors arrived each morning. 2’090 of those images were used for the reconstruction with Pix4Dmapper Pro, in addition to an on-site linear measurement taken by the project team, and 82 manual tie points to merge the sub-projects.
The final 3D model came out in complex form: both as a 134.4 million point point-cloud and as a full 3D textured mesh of 2.5 million triangles.