Using Lidar data to establish the Ecological Index in urban Belgrade

Against the backdrop of a 6% expansion in non-porous surfaces, a project in Belgrade analysed the potential for increasing the Ecological Index through various greening scenarios. A combination of aerial photography and Lidar scanning technologies was used to collect and process high-quality spatial data as the basis for generating a full 3D digital twin of the city infrastructure and trees.

Today, urbanization – the rapid expansion of cities – is a global phenomenon that we anticipate and embrace as an inescapable reality. Characterized by notable advancements in technology and infrastructure, increased job prospects and enhanced transportation and communication systems, the transformations all appear advantageous and even desirable to the populace in urban areas. However, beneath the glamour of urbanization, it’s crucial to acknowledge its environmental consequences and how they affect the residents of these rapidly evolving urban landscapes.

In 2022, five experts in landscape architecture, green infrastructure, urban planning and environmental protection published a report of findings and suggestions defined in their project titled ‘Green Infrastructure in a Compact City – Ecological Index as an Instrument of Resistance to Climate Change’. Centered around Serbia’s capital city, Belgrade, the research investigated the escalating built-up areas in Belgrade over the past two decades. The increase was 6% – a number which at first glance seems insignificant. However, behind the single-digit figure lies a noteworthy expansion of non-porous territories by over 4,400 hectares. Non-porous surfaces such as asphalt, concrete or cement prevent rainwater from recharging the groundwater. They also retain heat, making urban areas warmer than their surroundings. This increase in non-porous surfaces has predominantly occurred at the expense of agricultural land and natural ecosystems. This is impacting public green areas within urbanized parts of Belgrade municipalities, and contributing to issues like urban heat islands, flooding and a decline in biodiversity.

Ecological indicators

The project’s methodology centered around the use of the Ecological Index (EI) as a practical tool for enhancing urban greenery on plots of different land use. Also known as an ecological indicator or environmental index, the EI serves as a numerical metric to evaluate the quantity and quality of vegetation within city plots, thereby assessing their ecological significance and contribution to residents’ quality of life. These indices are typically derived from a set of physical and ecological inputs like landcover, building heights, tree crown cover and more parameters that provide information about the state of the environment, such as flood resilience, biodiversity, water quality, air quality, habitat integrity and other relevant factors.

Evaluating five scenarios

The project conducted a comprehensive pilot study across six locations in Belgrade to analyse the potential for increasing the EI through various greening scenarios. The following five distinct scenarios were evaluated, ranging from minimal ground-level planting to comprehensive rooftop and vertical wall greening, with the aim of maximizing ecological functionality and EI:

Scenario 1 considered all vegetation forms and ecological functional spaces (EFP) on the parcel, including ground level, building vertical surfaces and roofs.

Scenario 2 simulated a design with minimal additional ground-level planting (improved Scenario 1).

Scenario 3 added green walls on suitable vertical surfaces without structural changes (improved Scenario 2).

Scenario 4 simulated greening building roofs without structural changes (improved Scenario 3).

Scenario 5 simulated new construction per planning documents, with structural changes to maximize EFP and EI.

The presentation of the existing condition and EFP on the pilot area parcels, as well as the evaluation of the existing EI, was based on collected spatial data. To perform the evaluation according to predetermined criteria, it was necessary to vectorize 3D objects, trees and land cover using georeferenced point clouds and aerial photographs.

Point cloud classification

Before vectorization, the point cloud was first classified into terrain points, vegetation (low, medium, high), buildings and other content. Each 3D object consisted of a base, exterior walls and a roof, represented by closed polygons. The level of detail used was LOD2. Roofs were represented by surfaces following their construction, shape and slope, exterior walls were represented by vertical surfaces, and bases were represented by closed horizontal polygons. Roof geometry was used to calculate area, aspect and slope, which were added as roof attributes for analysis and selection.

Trees were represented by two layers: trunk (3D point) and canopy (circle). For each tree entity, alphanumeric attributes were calculated from the classified point cloud geometry, including tree height, base elevation, top height, projected surface area and diameter, with the canopy including surface, top and diameter information. Land cover was represented by closed 3D polygons for each type, such as soil, shrubs, turf, concrete, asphalt and artificial grass. These polygons facilitated the application of EI assessment criteria and simplified calculations and element relationships.

Leveraging Lidar

The primary source of data for the study was gathered by aerial imaging and Lidar scanning, while field methods were used as auxiliary sources. Lidar technology is increasingly being used as a tool in ecological studies, providing unparalleled data precision for characterizing the shapes, size and colour of natural and built environments. Lidar data can model the city floor, extract 3D models of buildings, compute roof slopes and extract tree height and crown size, all of which are used in calculating the EI.

In the study of six locations in Belgrade, Lidar data was leveraged to construct an EI that served as a comprehensive measure of the ecosystem’s health. Various processing methodologies were employed in utilizing Lidar technology to derive essential metrics and subsequently formulating an index for ecological assessment.

Quantification and scenario modelling

MapSoft, a geomatics company based in Belgrade, specializes in executing projects related to software development and spatial data collection. The firm’s expertise lies in utilizing a combination of aerial photography and Lidar scanning technologies to collect and process high-quality spatial data. By applying these technologies for the needs of the project, MapSoft was able to generate a full three-dimensional digital twin of the city infrastructure and trees. Through that quantification and scenario modelling (e.g. what if more trees were planted, with a certain height, in a certain location?), it would ultimately be possible to help decision-makers to develop policies aimed at improving the urban quality of life and diminishing air pollution. Examples could include urban planning bylaws that would maintain a minimum number of trees in future developments.

To provide answers, MapSoft used the Teledyne Geospatial Optech Galaxy on a fixed-wing aircraft to map the entire city. This produced a map of urban landcover, 3D building models and footprints, rooftops classified by slope, and tree locations and crowns. The analysis leveraged the richness in the data to derive the EI, describing the health of a city plot.

MapSoft was able to provide the aerial imaging and Lidar point cloud of the area. The images had a spatial resolution of 5cm, while the density of the point cloud was 25pts/m². Specialized software for spatial data processing and manipulation was used for vectorization. Field methods were deployed to supplement aerial mapping with ground-based spherical images as well as control points. The data product delivered was in accordance with the required standards.

Given the dense urban area with tall buildings, it was necessary to collect detailed data within the building blocks, ensuring all blind spots were covered. Therefore, the flight was conducted at a lower altitude, utilizing the Optech Galaxy Lidar scanner to select the optimal field of view and signal strength for better penetration through vegetation and smaller openings. In consultation with MapSoft, the project team concluded that the collected spatial data (ground sampling distance (GSD) of 5cm/pixel, point cloud density of 25pts/m²) would be of sufficient quality to generate geometric elements (with all associated attributes) for a realistic evaluation of the existing EI. All the collected data was verified through field checks.

Conclusion

MapSoft’s work with landscape architects has been crucial for completing various environmental projects, such as GIS mapping of city biotopes, tracking local pollutants and documenting urban green spaces. This project was a pioneering effort in local urban planning and management, requiring the expertise and equipment that MapSoft could provide, proven through multiple airborne laser scanning initiatives. The case study highlights the role of green infrastructure and the Ecological Index in enhancing urban resilience to climate change, as well as the contribution of Lidar technology to ecological assessments. By incorporating ecological considerations into urban planning, policymakers in Belgrade can address environmental challenges and improve the quality of life for the city’s residents.

Further reading

‘Green Infrastructure in a Compact City – Ecological Index as an Instrument of Resistance to Climate Change’, by Anica Teofilović, Andreja Tutundžić, Vesna Šabanović, Katarina Čavić-Lakić and Bojana Jovanović.