3D City Modelling (Digital twins) is the process of creating virtual or realistic three–dimensional models that allow you to represent the size, shape, appearance and other detailed characteristics of an object or territory with maximum geometric accuracy by remote sensing methods: space, air or ground (surface, underwater), allows you to represent the observed object or territory from all angles.

3D City Modelling (Digital twins) is applied in various fields, including:

• Cartography purposes;
• Landscape design. Understanding the terrain's shape is essential for planning water accumulation areas and determining suitable locations for planting;
• Building and construction design, BIM construction;
• Construction of roads, highways, interchanges, and railways. The research involves not only studying the terrain but also assessing potential settlement levels and determining groundwater that may affect construction;
• Environmental protection measures;
• Scientific research: many researchers across various disciplines use 3D models for their studies;
• Everyday use in mobile phones, navigators, etc;
• Military and maritime applications;
• Informational support for project decisions;
• Creating models of objects based on design documentation and terrain models using remote sensing data;
• Optimizing the placement of designed objects considering the environment and infrastructure;
• Visualizing changes in landscapes;
• Disaster modeling and personnel training for emergencies, and more.

The tasks are determined by the capabilities of the software, which allows solving the main directions of high-detail imaging and measurements:

• Creating a 3D topographic base for design and survey works;
• Geometric 3D measurements of engineering structures;
• Updating 3D maps of the terrain;
• Building mathematical models using the intensity of laser pulse reflections;
• High-precision decoding of terrain objects;
• 3D models for thematic mapping, especially for complex construction projects (bridges, interchanges, ports, train stations, airports, quarries, etc.), BIM, CAD-CAM, and other modern construction technologies.

Thus, 3D modeling is commonly used in urban planning, industrial and infrastructure construction, forestry, emergency situations, geology, development of coastal marine and river areas, and more.

• Conduct detailed studies from a distance;
• Perform visual assessments of the spatial arrangement of objects considering terrain features and their heights;
• Analyze the spatial arrangement of various industrial infrastructure structures;
• Obtain and evaluate the true relief of the terrain;
• Select objects on the model to obtain semantic information, edit the appearance and characteristics (semantics) of objects, perform measurement and calculation operations, determine coordinates, and conduct detailed terrain evaluations in office conditions.

A three-dimensional model allows relatively accurate determination of building and other structure heights. The absolute accuracy of the model based on satellite images is +/- 3 meters, while for UAV imagery, it is 1-5 cm.