RTK/PPK Terrestrial photogrammetric survey
Building facade survey at HubCréatic in Nantes
The Tetrarc agency inaugurated the Hub Créatic in Nantes on June 17, 2014. This building is dedicated to young companies developing new digital applications. Under the invigorating yellow of its facades, the building thus concentrates seventy Start-Up. Its architecture conveys the image of an abundant activity thanks to cell-shaped windows and a honey color that suggest the image of a hive in full activity and highly productive.
Survey area preparation:
The stereo preparation time, which consists in posing, measuring and recovering the 2 targets, was 15 minutes.
The 3 passages needed to cover the 4000m² study area took 2 hours and 30 minutes or 50 minutes per passage.
The raw data of the survey (images, logs ..) are processed in the HASK Geoprocessor software, making it possible to increase the RTK georeferencing accuracy before being imported into the Pix4D software.
For this project, we have two targets around HubCréatic. These are measured using a Spectra ProMark500 GNSS receiver.
• Target n°1: 0,020 m (XYZ precision)
• Target n°2: 0,020 m (XYZ precision)
The images are acquired thanks to a FoxyWalk, terrestrial photogrammetric survey tool in pedestrian mode. Equipped with a RTK DroneBox and a calibrated Sony Alpha 6000 camera, with a fixed focus lens of 16mm. The facades were measured at a distance of 6 meters from the building for the first pass, 8 meters at the second and 10 meters at the third pass. Maneuvering a lateral movement of 2 meters manually between each shot to ensure the good recovery of photos.
The FoxyWalk: RTK / PPK terrestrial photogrammetry tool
The total processing time to generate the point cloud and orthophoto from the 476 photos took 11 hours and 40 minutes with a Windows 10 Pro, 64 Bit, CPU: Intel(R) Xeon(R) CPU E5-2609 v2 @ 2.50GHz, RAM: 32GB, GPU: NVIDIA Quadro K4200 computer setup.
Checkpoints are targets measured by a GNSS receiver. The RMS error represents the difference between the coordinates measured by the GNSS receiver and the coordinates calculated by photogrammetry.
So we can observe on the table above that the precision in X is 0,014m, Y is 0,005m and Z is 0,087m is 1cm in X, 5mm in Y and 9cm in Z.