How to Create Digital Twins of Historical Sites: Alcántara Bridge in Toledo, Spain

Toledo is a central Spanish city renowned for its historical significance and architectural marvels. With thousands of years of history, it has played a significant role in the development of the Iberian peninsula, going as far back as the ancient Roman empire. Many structures built by the Roman Empire remain intact throughout the region. The Alcántara Bridge is one of the oldest and most culturally significant structures that remain intact. Preserving such structures is crucial for maintaining cultural heritage, and modern technology offers innovative ways to document and inspect these buildings. In this article, we explore the process of creating an accurate digital twin model of a historic bridge in Toledo using the DJI Mavic 3 Enterprise (M3E). This Model not only aids in preservation efforts but also enhances surveyors' ability to provide crucial data for infrastructure management.

Pre-Flight Preparations: Compliance and Planning

Before embarking on any drone mission, it's essential to check with local authorities to ensure compliance with all flying regulations. This is particularly important when working in historical or densely populated areas like Toledo. After obtaining the necessary permissions, the first step in the project was to use the DJI Mavic 3 Enterprise to capture rough data for mission planning.

Mission Planning with DJI Mavic 3 Enterprise

The drone operators used the DJI Mavic 3 Enterprise for this specific mission, employing the smart oblique feature to capture rough data and create a mission plan. Based on this information, they planned five missions, each tailored to capture different aspects of the bridge.

The five missions were as follows:

Geometric Missions: Capturing the Pillars on One Side of the Bridge

The first mission focused on capturing the geometric details of one side of the bridge's pillars. This is critical because a 360-degree view of each pillar is necessary for accurate reconstruction. They flew the M3E as close to the pillar as possible while ensuring our safety so that every angle was covered.

Slope Mission on the North Side

The drone operators conducted a slope mission for the north side of the bridge. This mission type is particularly useful for capturing the structure's vertical aspects. Slope missions are beneficial for drone operators because they can livestream their missions, allowing real-time monitoring and adjustments if needed.

Geometric Mission on the South Side

Following the slope mission, they returned to a geometric mission on the south side. This approach ensured the entire bridge was thoroughly scanned from all angles.

Choosing Between Slope and Geometric Missions

When dealing with different structural characteristics, the choice between slope and geometric missions depends on the specific features of the building. For instance, slope missions are better suited for capturing vertical elements, while geometric missions provide a comprehensive view of cylindrical or complex shapes like pillars. An accurate mission plan is essential as it allows you to make the best decisions for capturing detailed images of your structure.

Mapping with FlightHub 2

FlightHub 2 presented five route options for the operator during the mapping process. They opted for the smart oblique mission and selected routes 1, 3, and 5. Each route offered a different angle, which is crucial for capturing the intricacies of the bridge's design.

Manual Mission: Capturing Underneath the Bridge

A critical part of the project was flying the drone manually underneath the bridge. This task required a high level of technical flying skills. The drone operators set the camera to take shots at 1-second intervals, flying the drone approximately 5 meters from the bridge and tilting it slightly to capture data from underneath. This manual mission was essential to combine data from the different missions and stitch together a comprehensive 3D model.

Safety Considerations

Throughout the mission, the paramount concern was ensuring the utmost safety. The DJI Mavic 3 Enterprise proved to be an indispensable asset, thanks to its cutting-edge safety features designed to navigate challenging environments with precision and reliability. Equipped with advanced obstacle avoidance technology, the drone effortlessly detected and avoided potential obstacles, including cables, towers, and intricate structural elements of the bridge.

As the drone operator maneuvered the Mavic 3 Enterprise around the bridge, the real-time alerts provided crucial information to enhance situational awareness. The system intelligently analyzed the environment and alerted the operator to potential risks, such as sudden wind gusts, unexpected turbulence, or nearby objects. These timely alerts allowed for swift decision-making, enabling the operator to adjust the flight path promptly and maintain a safe distance from potential hazards.

Moreover, the Mavic 3E's safety features extended beyond obstacle avoidance and real-time alerts. Its robust GPS positioning system and precise altitude control enabled steady and accurate flight at all times. By leveraging this technology, the drone could adhere to itS pre-programmed flight paths, precisely capturing the intricate details of the bridge's structural elements in a three-dimensional manner.

The safety features of the Mavic 3 Enterprise not only provided a much-needed layer of confidence to the drone operator but also ensured the well-being of the drone itself and the surrounding area. With an acute focus on safety, the mission progressed without any incidents, affirming the reliability and effectiveness of the DJI Mavic 3E's advanced safety features in completing complex 3D missions such as bridge inspections with unparalleled efficiency and peace of mind.

Data Processing: Creating the 3D Model

Once the missions were completed and all of the data was collected, more than 3,500 photos, amounting to 36GB of data, were imported into DJI Terra for processing. The processing took approximately five hours, resulting in a full 3D bridge model. This speed is significantly faster than that of similar processing software.

Refining the Model with DJI Modify

After generating the initial 3D Model with DJI Terra, the team used DJI Modify, a comprehensive 3D model editing software, to adjust the Model. Features such as floating parts removal and water surface repair were used to get a more accurate and precise 3D model. Learn more about DJI Modify by clicking here.

Sharing the Model

One advantage of using DJI Modify is the ability to share the 3D Model via a simple link. This feature is handy for surveyors and engineers collaborating with other professionals or presenting their findings to stakeholders.

The Benefits of 3D Models in Infrastructure Management

Creating a digital twin model of historical structures like the Alcántara bridge in Toledo, Spain, offers numerous benefits. These 3D models are invaluable tools for inspecting old infrastructure, identifying potential issues, and planning maintenance or restoration projects. For surveyors, this technology provides a reliable way to gather and present data, making it easier to communicate with clients and other professionals who rely on accurate information.

Many thanks to Iván from Aerovirtual, a local company that supports us in performing the flights, and thanks to Samuel for always pushing for DJI Enterprise technology and exploring new features in our drones.

Iván, Iving and Samuel during the operations with Alcántara Bridge in the background

For further insights, watch our video featuring our solution engineer and drone expert as they provide an in-depth analysis of this case.