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Case study

Inspecting a church roof for repair and scaffolding

Old city centers, like the Brussels old town, provide a multitude of challenges for contractors and heritage maintenance. Having a complex roof shape, and little to no space around to put down a cherry picker or any other machinery, this church was a perfect example of how drones and photogrammetry can save a lot of money and time in heritage renovation.

overview

Capture

Process

Deliver

Introduction

The roof of the church shows signs of damage on the inside of the dome, but it is unclear what the damages are on the outside. To make an accurate quote for the necessary reparations the contractor needs to know what the damages are, and where they are positioned on the complex roof layout.

They chose to map the entire roof with a drone. Using the 3D model and orthomosaics to assess the damages and plan the required maintenance works.

As the roof does not have straightforward layout, the model was also used to plan the scaffolding in detail.

01

Capture

In total 2706 images were captured with a DJI Mavic 3E. A mobile phone was used to support the RTK corrections through LTE thanks to the FLEPOS network

The wide angle lens (24mm equivalent) allows for a very close flight while still easily maintaining overlap. With the 20Mpix camera and global shutter provide high quality pictures for photogrammetry. 

As we were dealing with a rather complex building we tend to capture too much data, as it’s easier to filter out data than to come back to the site and do a new/additional capturing session.

Drones in the City center

Flying a drone in the city center of course isn’t without its challenges. Along with all the necessary legal steps, there are a few things we needed to consider: controlling the ground area and maintaining line of sight. 

For the ground area, we made sure to block parts of the street off with red-white tape, and we involved enough personnel to keep people away from multiple sides. 

The line of sight issue was solved by gaining acces to the back terrace of the adjoining building, giving us the perfect launch platform to do the mission on the back side of the church.

02

Process

The imagery was processed using Agisoft Metashape 

The overcapture problem

15m 28s

Subtitle (eg: analysis)

larger image left template

03

Deliver

repeat of initial request

Subtitle (eg initial processing)

Method, specifics, softwares used, specific challenges, processing times on certain hardware

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Author

Dries Speybrouck

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