How to inspect building facades using drones

Regular building facade inspections play a vital role in ensuring properties' safety, integrity, and aesthetic appeal. These inspections are usually commissioned by property owners or regulatory bodies and are essential to maintaining a safe and visually pleasing community.

Traditional methods of inspection, which require manual access and scaffolding, pose potential risks and require substantial financial and temporal resources. However, with the advent of drones, vertical building inspections have been significantly simplified. While manual flights can capture the facade, it can be challenging to maintain a consistent distance and overlap between images. On the other hand, automated vertical facade scans can produce an accurate 3D facade model, making it easy to identify defects.

This article aims to guide you through performing vertical building facade inspections with drones using UgCS flight planning software. The inspection site is the San Lorenzo Monastery, located near Madrid in Spain. We used the DJI M300 with a Zenmuse P1 camera in this project. Other drones from DJI , Inspired Flight Technologies Inc. , Harris Aerial , WISPR Systems , and others may be used using the steps described below.

Step 1. (Optional) DSM data import

First, it is essential to identify what elevation data will be used for the flight. UgCS, by default, comes with SRTM 1 Arc-second elevation data, which is usually enough. In this case, an additional digital surface model (DSM) was downloaded from a public source and imported into UgCS as a .tif file. Not only does this even go out the ground in front of the building, but it also gives a better impression of the height of certain building elements.

Step 2. Flight planning for vertical facade capture

Next, the flight plan for vertical facade capture can be created. The "Vertical scan" tool in UgCS is used for this purpose. Since this side of the monastery has two towers, one on each side, three vertical inspection flight segments were used in the route - one for each tower and one for the middle section at a lower maximum altitude to save battery.

The parameters used for the flight plan were as follows:

• Minimum height (set to 5 m)
• Maximum height (set to 45 m for long segments and 60 m for towers)
• Distance to the facade (20 m)
• Camera used (DJI P1 35 mm)
• Forward overlap (80%) - Side overlap (80%)
• Pattern - vertical

Two actions were added here -

1. Set camera attitude: 0 (ensuring camera is looking directly towards the building facade)
2. Set camera by time (setting the camera to automatically take images every certain number of seconds, calculated automatically by UgCS)

Step 3. Performing drone flight and data collection

Flights planned in UgCS can easily be transferred to the drone's remote controller, eliminating the need to open the laptop in the field. Thus, all that is needed is the remote controller and the drone with a camera.

With the flight plan completed, performing the flight and collecting data should be quite straightforward. However, there are some key aspects to remember.

1. Ensure that the area is clear of pedestrians.

Since the flight starts from about 5 meters and goes all along the length of the building, it is crucial to ensure that there is no chance of anyone walking inside the area where the drone is capturing images. Both are for safety and to provide good-quality data.

2. Double-check for any obstacles

Check that the drone's flight path has no unpredicted obstacles, such as vehicles, trees, poles, or powerlines, that may not have been visible on the map during flight planning.

3. Plan for battery swaps.

Long building inspections usually require a few battery sets. So, it is a good idea to plan ahead and ensure that you have enough battery sets for the flight.

4. Check and backup data

The saying goes—if your data is not saved in at least two places, you don't have it. Once the flight is done, make sure to download the data from the camera's SD card onto the computer while still in the field. This allows you to double-check that the collected data is good and ensures you have a backup of it.

Step 4. Data processing and report generation

Different tools can be used to process images collected with vertical surveys. Two popular choices are Agisoft Metashape and @RealityCapture. In this case, we went with RealityCapture. The steps for data processing are as follows:

• Image import and alignment
• Defining calculation region using rough point-cloud
• Model calculation and adjustment if needed
• Texturizing
• Export

Data collected in cooperation with ACRE Surveying Solutions