„Digital twins are tools“

Thomas Eichhorn from the State Office for Geoinformation and Surveying in Hamburg in conversation with INTERGEO editor Monika Rech-Heider.

There is no one digital twin, says Thomas Eichhorn from the Hamburg State Office for Surveying and Geoinformation. But there is the basic geo-twin, which feeds theme- and subject-specific twins in a broker function. Version 0.9 of the basic geo-twin and theme twins are already available in Hamburg.

Mr Eichhorn, you are the Managing Director of the State Office for Geoinformation and Surveying in Hamburg. You are responsible for the areas of digital urban development and urban data management. What is a digital twin in your definition?

There is no such thing as a digital twin, and perhaps there never will be. Cities will have topic- and subject-specific digital twins with time reference and in different degrees of detail. They will be purpose-bound digital twins that are designed task-specifically. The connecting element is a base twin from which the other instances are derived. This creates the spatial reference and contains basic elements that occur in all twins. The base twin is able to pass on changes to the other instances. It thus has a kind of broker function, which is there for the spatial merging of different instances.If, for example, you want to bring together twin A and twin B in order to display certain effects or to create district analyses, you might need parts of the traffic twin, but also of the planning twin or of a socio-spatial twin. The basic twin brings all these twins together and makes them calculable and evaluable.

Is the connecting element between the different instances the 3D city model?

Exactly not. That would be abbreviated. The 3D city medell belongs in the basic twin. But it is not alone. Properties and methods belong to it. This has to be specified again, just as you have to consider whether the e-charging station belongs in the climate twin or the mobility twin. But: Elements of the 3D model must be elements of the basic twin; for example, the buildings, roads, cadastral boundaries, bodies of water, administrative boundaries. But this may also change from administration to administration. There is no exhaustive list of everything that belongs in a geographic base twin.
The elements have to be fixed and then kept ajour with fully automated processes and passed on to the other twins. There is a certain intelligence involved. This digital twin is not just a data set. It must have certain methods and properties that enable it to pass on changes in the real world to the other instances. To do this, the base twin must provide the uniform spatial reference. Machine learning or artificial intelligence methods will be used for all of this.

Do you deal with the concept of digital twins within the digitalisation of the city?

Smart City is the strategy to make cities smarter with the help of digitalisation. Digital twins are part of this digital strategy. How do I get from A to B in an environmentally friendly way, how do we avoid heat islands? How do we get good fresh air mixing in inner cities? Simulations in the event of a disaster. In these examples, digital twins are tools that can be used to bring the digital strategy to fruition. In Hamburg, the digital strategy is divided into digital spaces such as mobility, social affairs and health. This concept must be continued in the Digital Twins and use them as a tool to move the city forward.

Where do you stand in terms of the digital twin?

I would say that the basic geo-twin exists in version 0.9. And we also already have specialist twins in version 0.9. That varies from specialist domain to specialist domain. We are very far along in the areas of planning and building and mobility, because there were a lot of projects due to the ITS World Congress in Hamburg.

How does real-time data fit in with the theme of the digital twin?

Sensors have a strong impact on the mobility twin. Traffic is very dynamic. Real-time data is already available on the charging infrastructure, for example. Is it occupied or not? If you have long-term data, you can deduce in advance when a charging point is occupied and when it is not, and where additional charging points need to be installed. Another topic for real-time data is traffic counting, i.e. traffic volume measurement. For this purpose, there are infrared cameras at every traffic light in Hamburg that record the traffic lane by lane and in compliance with data protection regulations. This is the basis for intelligent traffic control. The traffic light circuits are integrated into the traffic twin. For networked autonomous driving, this means that the dual control principle applies. The autonomous vehicles detect the green light with their own sensors, but also receive feedback from the digital twin traffic about the status of the traffic lights.

So the traffic twin already exists?

It is still in project status, but the data stream in real operation is already available. Not all traffic lights have sensors yet. In a project with a car manufacturer, for example, it is being investigated how the data stream can help to calculate the "time to green", i.e. the speed to reach the next green. This is then integrated into a navigation system. Another example is the project on sensors on parking cells. The sensor system reports whether parking spaces are free or occupied and will thus lead to a significant reduction in traffic searching for parking spaces. There are other examples as well.

Do you have other examples from other digital spaces?

A large field is social space management, i.e. socio-spatial analyses in urban districts. Questions are, for example: How do urban districts develop? How do the needs of different population groups develop in urban districts? What is the age distribution and is the infrastructure adapted to the age of the population? How many people have access to bus stops within a five-minute walk? These questions are to be answered by the Social Spatial Twin. The third major topic is the planning area. Planning scenarios are to be modelled in the twin, including the participation of business and citizens, in order to create citizen participation and transparency. This requires digital twins of limited spatial areas with a high level of detail.

What would you like to see on the subject of the digital twin in Hamburg?

I would like to see an agreement on the importance and value of this basic geo-twin. That it be included in the fixed assets, that it be maintained and made available as infrastructure in the sense of digital services of general interest in the city.