How aerial imagery simplifies surveying workflows in Denmark

Aerial imagery is an essential resource for uncovering unknown insights into how land has been used over time. Denmark’s Digital Orthophoto (DDO) project is a good example of how the evolution of airborne technology has had an impact on the understanding and utilization of the country’s ever-changing landscape.

High-resolution aerial imagery has become an indispensable tool for land administrators and chartered surveyors. It enables accurate measurement and mapping of land features that aid in infrastructure and land-use planning, property boundary determination, and even resolving property disputes.

One good example is Denmark’s Digital Orthophoto (DDO) project, which has been a reliable historical record of Denmark’s geography since 1995. For nearly three consecutive decades, the collection has provided detailed aerial orthoimagery to chartered surveyors, municipalities and other land professionals in Denmark. Conducted every two years, the DDO programme has consistently documented Denmark’s development of landscapes, urban centres and infrastructure. Initially, the first collection was created to support a major infrastructure project. Since then, the DDO series has become part of the HxGN Content Program’s expansive data library, which anyone worldwide can access.

The advancement of airborne technology

The geospatial data industry has seen rapid technological advancements: from film cameras that capture black-and-white photos, to high-performance airborne sensors that simultaneously collect multiple datasets. The innovations also had an impact to the DDO collection, significantly evolving how the national aerial images are updated and shared with customers.

In the beginning, the process of collecting aerial imagery using film cameras was complex and time-consuming work. Thousands of photos had to be developed, scanned and manually processed to create orthorectified images positioned precisely on a map. Photos were delivered to customers on CDs, presenting extensive data management challenges.

Nowadays, software enhances every stage of the process. Flight planning software enables the immersive planning of flights with a virtual 3D world view. While in the air, a flight management and control system automates sensor configuration and release, system monitoring and logging, and flight guidance as part of an integrated and complete system to increase productivity. The only thing software cannot augment during the flights is the weather (which can prove challenging in Denmark, even during the summer!).

The data captured by airborne sensors fully integrates with post-flight processing software, producing a large number of datasets: orthoimagery, point clouds, elevation data, 3D mesh models and more.

Greater accuracy and accessibility

Today’s technology allows vastly more detailed images to be processed. Where once the country was covered by just 6,000 photos, the DDO programme now captures hundreds of thousands of images without concern. The airborne sensors used for the programme offer 12.5cm-resolution imagery, giving land administrators and surveyors greater detail than ever before. High-resolution aerial images provide an accurate view of the world, making it easier to present findings compared to the technical maps used previously.

A key advantage of the DDO programme is that the data is always collected during the summer, ensuring consistent seasonal conditions for like-for-like comparison. Although the Danish government provides lower-resolution imagery for free, Torbjørn Mandahl Pedersen, Partner at LE34, has found the DDO imagery to be more visually appealing. “Hexagon’s aerial imagery is intuitive and aligns with people’s real-world perceptions,” says Pedersen. “And because the images are taken during the summertime, the green trees make for a nice backdrop when presenting to our clients.”

Accessing the DDO series is straightforward. As soon as new editions are processed, the refreshed data is uploaded to servers where users can gain access immediately within their GIS application. Users can choose between different vintage layers of the DDO programme, making it simple to compare changes over time.

Visualizing boundary markings

Historical aerial imagery plays a vital role in documenting land and property changes over time, and the availability of high-accuracy aerial data is transformative in simplifying mapping processes and clarifying boundary disputes. For this reason, the DDO collection is leveraged by many of the over 1,400 members of the Danish Association of Chartered Land Surveyors (PLF). Customers of the PLF surveying firms include private homeowners, developers, utilities, municipalities and government agencies requiring guidance on land management, land-use potential and boundary delineation. Chartered surveyors conduct cadastral surveys to determine boundaries between plots of land, and aerial data provides an intuitive basemap to help clients visualize boundary markings and proposed changes. “Before we had access to aerial images, LE34 relied on technical maps, which were more challenging for clients to understand. We find that a lot of customers struggle to interpret traditional maps. With the aerial image in front of us, we can talk to the customer as if we were in the field together,” states Pedersen.

The DDO programme plays a critical role in land claim validations. Michael Stærk, Partner at Skel.dk, utilizes aerial imagery to compare property boundaries with the actual on-ground situation when advising homeowners or businesses, as mandated by Danish regulations. “The resolution and the placement accuracy are crucial. We often find mismatches between the registered property borders and the actual situation in the aerial imagery – discrepancies that the respective owners need to resolve through negotiation,” explains Stærk.

Morten Knudsen, a chartered surveyor at Kjær, comments: “Working with a dataset that spans almost three decades allows us to document historical land use – a crucial feature considering the Danish legal landscape. Under Danish law, if an individual or entity has occupied and used a plot of land for over 20 years, they can claim it, irrespective of whether they are the registered owner.”

A multipurpose visual record

The DDO series has won supporters in other surveying arenas. Comprehensive datasets of high-resolution aerial imagery can play a role in negotiations with landowners during infrastructure projects involving the laying of new pipes, for example. The images are likewise an important quality assurance tool, verifying that everything within a given area has been measured accurately.

In land management, the DDO collection provides valuable insights for assessing vegetation health, monitoring changes in land use, and supporting conservation efforts. Archaeologists can use the data to examine the structure and elevation of land, and agriculturalists can detect discrepancies in how a crop grows in different areas. The online accessibility of the aerial images enhances their utility, offering immediate references when exploring new areas.

Picturing the future of aerial data

As technology continues to transform possibilities for data gathering and visualization, the DDO project shows how innovations can enable a more intuitive understanding of land conditions over time. 3D mapping, which integrates imagery and Lidar technology, holds the potential to revolutionize how chartered surveyors and planners access and utilize land data, optimizing spaces and informing data-driven decisions.