GreenTwins - what has been done?
Urban Digital Twins (UDTs) as digital environments for modelling and simulating change in cities, are promising instruments to overcome the challenges of rapid urbanization, social inequity, anthropogenic climate change, and biodiversity loss. However, in this regard, the representation of the green infrastructure in UDTs, and the interaction between the UDTs and the stakeholders, are limited and recognized as a significant development gap. GreenTwins project addresses these deficiencies by contributing to the UDTs of Tallinn and Helsinki and by creating interfaces between the UDTs and the stakeholders.
GreenTwins has three main research and development directions (Figure 1):
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The layer of dynamic vegetation for UDTs of Helsinki and Tallinn. The information about the vegetation is sourced from existing city registries, and, also, collected through AI analysis of aerial photographs. Plant models are parametric, and simulate the growth, aging, seasonal and maintenance related changes. The temporal component of vegetation models is a key novelty of the project.
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User-friendly digital tools which serve as interfaces between UDTs and the stakeholders, such as active citizens, urban planners, architects, engineers and developers. These tools allow to view three-dimensional city models and interact with them, by adding or removing buildings and trees, and, thus, developing a share ground for discussion.
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A physical space in the city centre of Tallinn at Kaarli pst 1, which is equipped with the state-of-the-art visualization technology. The space is entitled AvaLinn Smart City Planning Hub, it aims to bring together urban professionals and citizens, and involve everyone into digitally aided planning discussions, irrespectively of the digital literacy of participants.
All these developments began in autumn 2020 with the Smart City Challenge, and we expect to get functional prototypes and demos by June 2023.

Figure 1: GreenTwins project ecosystem.
Meanwhile… on 29-31 March 2022 there was a pop-up workshop in the premises of the forthcoming AvaLinn SmartCity Planning Hub at Kaarli pst 1 in Tallinn city centre. In three consecutive days approximately 100 stakeholders, representing the City of Tallinn, as well as active citizens and students, have visited the Hub and tested out the tools (Figure 2). Overall, the Hub concept was perceived with great enthusiasm, and the city of Tallinn has already begun using the space for different planning related public events.

Figure 2. The pop-up event at Kaarli pst 1 on 29-31 March 2022.
In spring-summer 2022 the brand guidelines for AvaLinn and the interior design of the space was developed by Velvet OÜ. The space has a workshop feel, flexible space organisation and lightweight furniture, so that it could be rearranges based on the event type and the number of participants. Currently the city of Tallinn is looking for the construction firm to perform the construction works and for the hardware firm to provide the projection screen and related technology. The opening of the Hub is planned for spring-summer 2023, so, keep the eye on the newsletter, in order not to miss out!

Figure 3. The design of the forthcoming AvaLinn Smart City Planning Hub developed by Velvet OÜ.
The GreenTwins smart city pilot composed by a transdisciplinary and international research team from TalTech, Aalto University and High Performance Computing Centre Stuttgart. The pilot project is financed by the European Regional Development Fund and the Estonian Ministry of Education and Research.