Photogrammetric drone survey: Town Hall of Béthune

A pilot Hélicéo performs a photogrammetric drone survey

Hélicéo has been requested by the city of Béthune, France to carry out a photogrammetric drone survey above the town hall. This photogrammetric mission aims to raise a sanitary diagnosis of the building in contemplation of potential work.

The 3D reconstruction of the city hall

To establish a real inventory of the building, a terrestrial scanner has been achieved before the drone mission. Indeed, the facade of the city hall was scanned by a LiDAR. Outside and inside the Bell Tower data could be recovered to create a printed miniature in 3D. However, this technology doesn’t allow the realisation of a survey of roof. That’s why the mission was completed by a photogrammetric drone survey.

How is organized a photogrammetric drone survey?

Photogrammetric drone survey

The professional multirotor drone Fox4 flights at 80 m above ground level.

Photogrammetric drone survey

The professional multirotor drone Fox4 carries out a survey of roof.

 

Laurent Tavernier, geomatics engineer at Hélicéo, was asked to recover roof data with the professional multirotor drone Fox4.

First of all, the whole mission has been scheduled in a mission planning software for automatic flight. In this way, the device trajectory is set up in advance.
The pilot carried out two fully automatic flights around the building to collect as much information as possible. The first one is a Nadir flight in crossing lines mode made at 80 m above ground level. Therefore, the camera is positioned in vertical downward direction. The second is an oblique view flight made at two different height (60m and 70m above ground level) in order to get the best point of view.

Then, all photos took by the drone will be processing by Pix4D, a points cloud processing software. With the technic of 80%/60% overlapping, each images overlap each other. In this way, a complete point cloud of the building can be constituted and the Town Hall will be showed in 3D.
In accordance with the drone regulation required in France, a safety perimeter around the city hall and a declaration to the civil aviation were set up.

You will find the video of the drone mission in an article written by La Voix du Nord.