## 4 Methods--Project Implementation  
Perhaps the most important feature, after the representation of polygonal areas of archeological sites on the interactive digital map, is the automatic conversion between the Stereo70 coordinate system and the World Geodetic System (WGS84) coordinates. This feature is required by both professional archeologists and regular users [3]. From a technical point of view, any data gathered by the web interface (WGS84 or Stereo70 coordinates) is first converted and subsequently graphically presented on the interactive digital map as a polygon area. The biggest benefit of using this approach is avoiding error-prone human intervention or errors in calculation when using multiple conversion tools. To speed up the process of displaying an archeological site's polygonal areas on the digital interactive map, the architecture is divided into two major components, which are accessed through a proxy:  
* the application server;
* the map server. The application block diagram architecture (Figure 9) focuses on the web proxy, which plays an important role in routing each request to the application server and/or the map server. For hardware implementation, we chose a structure based on virtual machines, mainly to enable future-proof expansion. The hardware architecture (Figure 10) is based on a single fully redundant server (processor, storage, memory, power supply) and external shared storage to create snapshot backups for each virtual machine. The main reason for using this approach was to increase the services' availability. This can be achieved due to the ability to easily perform a full backup and/or a full restore for each virtual machine in the case of malfunction. A second benefit of using this approach is the possibility to migrate a complete virtual machine to a different hardware server if more storage space or more processing power are needed. Figure 9: ArchTerr’s application block diagram architecture overview. The following are installed on the hardware (comprised of processors, random access memory, storage, and networking interface access):  
* a type 2 Virtual Machine Monitor (Hypervisor);
* the host operating system;
* the administration and management tools for the entire structure and the backup module;
* Virtual Machine 1;
* Virtual Machine 2. For better security and to increase the web application protection against common web attacks, such as Brute Force attacks, Command Injections, XSS, and SQL Injections, each virtual machine is separated and protected by an individual firewall using a Linux-based kernel. A future development will be the insertion of a frontal Web Application Firewall engine such as NAXSI or Fortinet. To better secure the meaningful data, only the virtual machine hosting the application is exposed to the Internet, rather than the databases stored on the second virtual machine. The first virtual machine architecture is built around the intelligent server applications that enables ArchTerr's functionalities:  
* The web proxy server, which has the role to provide the user-friendly interface. The interface is used both as an entry point to acquire archaeological information and GIS data, and as an interactive display tool for polygons representing each protected area and archaeological site. * The application server, which has the main roles to analyze the coordinates for each archeological site, perform the conversion between Stereo70 and WGS84 when needed, and display an archeological site position on the map. It calculates the overlapping terrain areas and, if necessary, displays error and warning messages. * A security firewall. The web proxy is implemented using NGINX. This web engine is \"an HTTP and reverse proxy server, a mail proxy server, and a generic TCP/UDP proxy server\" and  
Figure 10: System’s hardware architecture based on a fully redundant server. we use it to expose only one virtual machine (the one hosting the web application) to the Internet.