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Based on the most recent image flight from 2022, the Office for Land Management and Geoinformation has updated the aerial images and 3D city model in high resolution. The resolution is close to the limit of what can be achieved with aerial surveys today.
At Digital Day 2021, the web application "Bonn in 3D (opens in a new tab) " - a three-dimensional city visualization - was presented as a virtual 3D model.
The 3D city model was positioned by the city as the first basic building block of a "digital representation" of the city's morphology.
Since 1997, the Office for Soil Management and Geoinformation has been regularly taking high-resolution aerial photographs in cooperation with Bonn's public utilities and the state surveying administration.
This also includes the Bonn 3D city model, which is derived in high resolution from the aerial survey data. The aerial image products have now been updated again. The data basis is the image flight from September 12, 2022.
The resolution of the images is even higher than in the 2019 photo flight and is close to the limit of what can be achieved with large-area flights with an aircraft these days. This means that even small details are clearly visible in the images. The high resolution is a particular quality feature of the aerial images and the 3D model of the city of Bonn derived from them.
The city administration also provides the aerial image products from Geobasis NRW (e.g. from the years 2021 and 2023). However, these have a much lower ground resolution. We are therefore able to offer you up-to-date aerial images of the city area every year. To do this, select the relevant aerial image vintages as described above.
From aerial image to 3D city model
Users are familiar with and appreciate the high-resolution aerial image for official activities, which, in addition to the city map, is a frequently used background map for mapping topics of all kinds. This also applies to the detailed 3D city model, which enables impressive city views and daring camera flights through the city. The product is particularly interesting for planning in urban areas.
But how are these fascinating and useful products created?
Why are the pixels in the true orthoimage - as the georeferenced aerial image is correctly called - exactly where they belong? How is a digital three-dimensional model of the city created from the flat, two-dimensional images?
It's no secret that the images come from an airplane. You may have noticed the sonorous humming of the picture plane on the warm, cloudless Monday in the fall (September 12, 2022), which happened to be flying at quite low altitude right above the City Hall at lunchtime. From east to west and vice versa, again and again, over the entire extent of the city.
At very short intervals (about one second), the special camera in the airplane takes pictures of the city with a lens pointing vertically downwards at pre-planned trigger points. At the same time, oblique aerial images (45° angle of attack) are taken by four other cameras. It is very important that the images are taken in such a way that they overlap generously.
Human depth perception
This overlap makes it possible to obtain three-dimensional information from the two-dimensional images. Think of the human eye: here, too, two overlapping individual images are brought together and thus enable us to perceive spatial depth. If you were to transparently superimpose the overlapping images of both eyes, you would see that they are the same: Identical objects that are far away from the observer are close together in the overlap (we also say: the parallax is small), identical objects that are close in front of our face are far apart in the overlap (the parallax is large). We have a "built-in" perception for this so-called depth information.
What our brain transforms into an intuitive perception of spatial depth without calculating can also be cast into mathematical formulas. The most important elements here are the exact positions and viewing directions of the eyes (or cameras) as well as the exact position of an object in the individual two-dimensional images. This results in the exact size of the parallax. This information can then be used to calculate three-dimensional object coordinates.
Weeks of calculations
Only modern computers and advances in photogrammetry and computer science in the last decade have ensured that nowadays a three-dimensional object point can be calculated for each image pixel in high-resolution images.
The greatest difficulty, and therefore the greatest computational effort, lies in automatically finding the identical pixels in the overlapping images (which can sometimes be 20 or more) - known as image matching. The pure computing effort for the 3D model of the Bonn city area from the aerial images is measured in several weeks - several computing cores and hundreds of gigabytes of RAM were used. In the end, the city model and other by-products created during the calculations took up almost 18 terabytes of memory (1 terabyte is 1000 gigabytes)!
