Using UAV to create digital doubles of reality and BIM

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It is possible to distinguish BIM of the object and BIM of the construction site.BIM of the object -is a small object in terms of area and volume.Most often it is a threedimensional model of a single standing building or structure.BIM of a construction site is represented by a 4D model of this site, which allows you to track the dynamics of its construction [12].The use of unmanned aerial vehicles in BIM-technologies allows to increase the speed of data acquisition and processing, their detail, reduce the cost of work and automate the collection and processing of information.However, the use of unmanned aerial vehicles may be by: legislation and natural conditions [19].

Ways of obtaining information from UAVs
Building Information Modelling (BIM) Unmanned aerial vehicles are another important mechanism in solving problems arising during construction or design of a facility.Unmanned aerial vehicle information can be obtained by laser scanning or digital aerial photography [20].
Laser scanning is a method of surveying that allows to quickly obtain the most complete and reliable spatial and geometric information about the objects of the surveyed area [6].Laser scanning results in a point cloud with a correct digital elevation model (DEM).The advantages of laser scanning include: a high rate of data acquisition and processing, the ability to build DEM in populated areas, direct method of measurement, the ability to work at any time regardless of lighting, the equipment is in the register of SI.Its disadvantages: expensive equipment, informativeness in comparison with photo is small, data accuracy decreases with increasing survey height [8,17].
Digital aerial photography is the process of creating high-quality images of the Earth's surface using aerial cameras and digital technology.In the process of digital aerial photography, specialised cameras mounted on aircraft or unmanned aerial vehicles (UAVs) capture a series of photographs from an altitude [11].The result is a point cloud with varying degrees of confidence, an orthophoto and a 3D terrain model.Advantages of digital aerial photography are: more extensive data, including due to the height of photography, equipment is less expensive, and there is a possibility to scale.The disadvantages are: dependence on the time of day, high time consumption for data processing, impossibility to obtain DEM in hard-to-reach places, analytical method of model building [14,16].
A digital twin is a digital copy of an object or process designed to realistically represent a physical model.It can be a digital twin of a single object or SmartCity (a large model of a city that displays processes affecting hundreds of thousands of people at the same time) [7,10].

Comparison of digital twin and BIM technologies
Digital twin technology and BIM technology are related, but they have several differences.The central task of BIM-technology is the design and construction of the object.This is due to the fact that the application of this technology solves a number of issues in the field of design.to the main tasks can be attributed the calculation of structural elements of the object and the compilation of construction documentation.Also, BIM-technologies provide analysis and control in the process of object construction.[10,16].
BIM-technologies do not function in real time, and the digital twin allows the model of the terrain in real time, with all the current moments occurring on the necessary territory, including the state of the ecosystem.This is due to the development of digitalisation and the transition from physical data to information and digital sources of information, which makes it possible to display the situation in real time.Therefore, the digital twin is timely updated, collects and analyses the necessary information, which can then be used in the process of operation of the object.However, BIM-technologies allow to enter information about the object into the digital twin as well as possible, but they do not allow to solve the problems in the process of optimisation [2,9].BIM-technologies do not display information about the object in the process of its operation.The digital twin draws its information from all possible sources, including information from employees of organisations located on the territory of this object or on the surrounding area.It contains a vast array of software that keeps the digital twin continuously updated with real-time changes at the site.This information allows the creation of a more detailed digital copy of the object.It very difficult for BIM technologies to achieve such successes without the use of digital twin technologies [10,19].

Saas and Daas methodologies
Companies providing cloud computing services work on SaaS methodology -Softwareas a Service.This is one of the varieties of cloud computing, represented by software, served by an internet provider.
Recently, with the development of unmanned aerial vehicles, another similar model -DaaS -Unmanned aerial vehicles a Service -has emerged.This is a form of equipment use in which the partner company assumes all costs associated with the ownership and operation of unmanned aerial vehicles, providing the customer with unmanned aerial vehicle services to a predetermined extent.
There are several companies on the Russian market providing SaaS unmanned aerial vehicle technologies for HMI and construction: Skyeer, TraceAir, Sarex, *SAREX, LTRACEAIR.
SaaS provides the following features in its functionality: -viewing of all object metrics: elevations, profile, slopes, height differences, areas, distances, volume; -automatic balance detection (comparison of project documentation received at different times of work execution); -checking and comparing the completed work with the preliminary work plan and working documentation; -preparation of documents and statements of the completed scope of work [1].
For Autodesk, there is a specially developed application called "ReCap" -reality capture, from the English "reality capture".It allows you to convert a point cloud of terrestrial laser scanning, aerial laser scanning, digital aerial photography or all together into one large set of points.The point cloud is then loaded into AutodeskRevit to create a digital copy of an existing object.