# 3D Modeling of a Virtual Built Environment Using Digital Tools: Kilburun Fortress Case Study
## 2 Materials and Methods  
During this study, methods of observation, analysis, and comparison and a reproduction of the research object in a 3D built environment using appropriate software were applied. The corresponding design scheme for implementing the research methodology is shown in Figure 1.  
In this study, the built environment considered architectural objects that harmoniously fit into the existing environment's surroundings and adapted them to reproduce the historical heritage. The main research stages included analysis of the initial data, detailed descriptions of plans and schemes, overlapping ancient maps onto modern ones, data comparison and analysis, and creating a flexible model in a virtual environment. The research on the available sources was as follows: analytical studies of maps were carried out (cartographic sources of the 16-17 th centuries, modern satellite images in Google Maps, studying the terrain using topography and visual analysis), and descriptions (archival descriptions of eyewitnesses to the events, engravings, drawings, photos, detailed explanations for object plans) and materials (actual search for the remains of building materials, analysis of the building principles, obtaining information about materials) were collected. The results of the analytical experiments were modeled by creating a flexible 3D model, which allowed for the reproduction of an object of cultural and historical heritage. This model enabled changing properties, which can be conducted with any model (e.g., using Revit software), and visualization was achieved using Twinmotion. The design scheme of the proposed approach is presented in Figure 2.  
As a case study, the architectural renovation of the Kilburun Fortress at Kinburn Spit in Ukraine was considered (Figure 3). Kinburn is the site of an ancient settlement of people of the Bronze Age. Nowadays, this is a sandy peninsula with a length of 40 km and an average width of about 8-10 km, which the Black Sea washes on one side. The Kinburn spit separates the Dnipro Bug Estuary and Yagorlytsky Bay. The fortress was an essential strategic object since it controlled the entrance of the trade routes of the Dnipro and the Southern Bug. However, the fortress was destroyed after massive battles in 1787 and during the Crimean war. Nowadays, it is one of the most mysterious and understudied buildings. Figure 1: Research stages. Figure 2: The design scheme of the applied approach. Remarkably, the territory of the Kinkburn Spit is unique not only in its status as a reserve but also in its historical significance for Ukraine, Turkey, and Greece. During modeling, the following obstacles were considered. Firstly, maps and diagrams were scaled appropriately for the reliable reproduction of the 3D object. For this purpose, Autodesk software tools (e.g., AutoCAD) were applied. Secondly, SketchUp was also used for the 3D model creation, considering the application of many different formats. Quixel software can also be used due to its open-access library of materials, their properties, and photo scans. Such software allows for obtaining a photorealistic rendering. After creating the model using the appropriate tools, it was integrated into Revit and ArchiCAD software. Finally, the machining time, as a primary operability factor, was considered for effective modeling. Corresponding software (e.g., Twinmotion, Corona Renderer, V-Ray) can accelerate the rendering process. The method was also supplemented by applying a topogeodetic survey, e.g., using photogrammetry technology. This technology makes the process faster and more informative than the classical method using ground geodetic measuring devices. The stereotopographic method for creating an accurate topogeodetic subbase was applied for this purpose. Firstly, photos of the studied area according to the appropriate scheme were taken and aligned using Agisoft Metashape software. In this case, the model's accuracy was up to 3 cm in width and height. Secondly, the process of creating a cloud of points was started and completed.