3D City Modelling of Istanbul
3D City Modelling of Istanbul | Terrain Surveys | 3D Surveys
Istanbul, a major city in Turkey has developed a 3D model of the city to assist with urban planning within the area. To create a 3D model, airborne Lidar, aerial images and 2D maps containing footprints of buildings was used. When creating 3D models you face many challenges which include excessive data storage requirements, the need for manual editing, incompleteness and other data quality problems.
For this project, they overcome these challenges using in creating a 3D city model of Istanbul using a helicopter. It flew over the city over between 2012 and 2014 at a height of 500m and a speed of 80 knots (150km/h) for the surveys.
The helicopter was equipped with a Q680i Lidar system from RIEGL (Austria), a DigiCam 60MP camera, an AeroControl GNSS/IMU navigation system and an IGI CCNS-5 flight management system. The Lidar point cloud was captured with an average point density of 16 points/m2. The images were recorded with a ground sampling distance (GSD) of 5cm and with 60% along-track and 30% across-track overlap. To ensure high geometric accuracy, eight GNSS base stations were used. The recording of the whole city covering 5,400km2 required thorough flight planning as the flying height and overlap determine a major part of the data quality. Added to this, data accuracy is directly affected by how good the boresights of IMU, GNSS and camera are calibrated and remain stable during the surveys.
The creation of the 3D city model of Istanbul is still a work in progress. Presently, the main data sources consist of an airborne Lidar point cloud, simultaneously recorded aerial images and the building footprints from the 2D base map of Istanbul. Ground-based data collection has been scheduled to increase the level of detail, with respect to both the geometry and the image texture. The preferred technology is laser scanning and 360⁰ panoramic imaging simultaneously captured from a moving car. Many streets in downtown Istanbul are small and narrow and thus inaccessible for cars. It is planned to capture these parts of the city with backpack mobile mapping systems. For the whole of Istanbul, the ground-based data will cover 32,000 kilometres of roads and streets resulting in 2.73 petabytes of panoramic image data. The 3D city model is not yet connected to a database containing semantic building information, but this is part of the future development work.
This just goes to show you how 3D modeling surveying techniques can produce an accurate model of something so complex, such as the city of Istanbul.