Digitizing Brazil’s most important monument is no small feat. Located atop the 700 meter Corcovado Mountain the Christ the Redeemer statue towers over Rio de Janeiro, at 38 meters of height and with a 28 meter arm span. Traditional 3D scanning technologies are unuseable due to the size and location of the statue, the difficult accessibility and challenging weather conditions.
This is the first time ever that Brazil’s most important monument has been digitized in such high quality – all previous 3D models and replicas of the statue have been designed by hand.
Data was collected for six consecutive mornings, on-site in late October. The main challenges for the data acquisition were the changing weather and wind conditions, restricted hours for data acquisition (flights could only take place before and after visiting hours) and inconsistent lighting conditions (shadows in early morning and late afternoon). A total of 3’584 images were acquired during 19 ten-minute flights.
2’090 images were used in Pix4Dmapper Pro desktop software to convert them into the 3D model. The reconstruction was divided into three main projects (statue, base and surrounding area) and nine-sub-projects to help manage the variations in image capture. Signal reflectance was one of the many challenges faced and affected the geotag accuracy; as a result, the sub-projects were processed without geotags. Eighty-two manual tie points were required to merge all sub-projects, while Pix4Dmapper’s point editing tools and annotating feature were used to crop out background points, such as the sky. Finally, a linear measurement, taken onsite by the project team, was used to provide the correct scale for the final result.
The final 3D model, available both as a point cloud of 134.4 million points (97.6 million for the statue, 30.7 million for the terrace and 6.1 million for the surroundings) and as a full 3D textured mesh of 2.5 million triangles with a texture of 16384px x16384px, will be used and presented by PUC University for upcoming projects in the near future.