Simulators of visual environment of aviation and space simulators

. The development of synthesis systems for human 3 D -models of reference objects allowing them to be used in simulators of visual environment of aviation and space simulators follows the way of development: 3 D -devices of indication; computer image generators and databases. Negative conditions of the USSR collapse led to the fact that the development of domestic computer image generators was stopped. However, the accumulated experience of development and serial production of visual environment simulators makes it possible to define available trends of their further development. Modern achievements of science and technology allow not only to solve the problem of synthesis of 2 D - projections of 3 D -models on the screen plane connected to the computer image generator but also, depending on the Customer's requirements, to synthesise for a person visually observed 3 D -objects with the possibility to form separate components of his cognitive model, in which his experience of orientation in space is accumulated. For example, to orientate in space by selected reference objects with simultaneous training of the trainee's eye-sight, or to orientate in space by observing 2 D -projections of 3 D -models of reference objects additionally using information from simulators of cabin equipment devices. The article gives an overview of the main parts of visual simulators of aviation and space simulators.


Introduction
The Institute of Automation and Electrometry of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk) together with the Research and Production Association "Era" (Penza) have conducted joint work since the 80s of the last century on the creation of software and hardware systems of machine graphics for real-time synthesis of 2D-projections of 3D-models of reference objects caught in the observation camera of the visual simulator of the aviation simulator [1].The aim was to create confidence in the pilot, who was trained on the flight simulator, that during the flight on the flight simulator [2] through the cockpit glazing he sees a sufficient number of 3D-reference objects to perform the flight task, in particular, to learn how to land a real aircraft on the runway [3].In the aviation simulator for the pilot synthesises the 3D-image of the surrounding space by an ergatic optical-softwaretechnical system called "Visual Environment Simulator" (the term ergatic means that the technological process forcing a person to see a 3D-object involves the specified components of his visual apparatus, purposefully activated by the design of the 3D-indicator).Let us consider in more detail its ergative parts and define the directions of their improvement.

Materials and methods
The task of the visual simulator is to synthesise for the pilot a 3D-model of the surrounding space, observing it through the cockpit glazing during flight in the flight simulator, the pilot estimates the speed and direction of movement of the controlled aircraft model [4].When controlling an aircraft in real flight and when controlling a model aircraft during flight on an aircraft simulator, a pilot acquires professional skills that are stored in certain components of his cognitive model.
It is impossible to create a complete model of any object (it is impossible to create a complete model of that part of 3D-space which the pilot sees during flight, for example, when landing an aircraft on the runway of a real aerodrome).Therefore, the task of forming the i h -th pilot's cognitive model.
X selection of those 3D-objects from the whole set of 3D-objects located on the terrain specified by the Customer, the type of 3D-models of which is necessary and sufficient for pilot training in a specific situation called "training situation"; 2 X defines the use of a software and hardware system called "computer image generator" -the purpose of which is to synthesise in real time (currently set to 80 ms cycle on the connected screen 2D-projection of all 3D-models of reference objects caught in the surveillance camera); 3 X defines the use of an ergatic 3D-indicator, the design of which, taking into account the peculiarities of the video sequence from synthesised 2D-projections of 3D-models of reference objects, affects the specified components of the human visual apparatus forcing it to see 3D-objects and at the same time to professionally estimate the distance to them with the help of the oculometer (quite often there is another sub-task -to train the visual apparatus of a particular person to see a 3D-object, while he sees a video sequence from 3D-projections of 3D-models specially generated for the 3D-indicator).
When developing an aviation simulator, the choice of 1 X is always left to the customer.

3
X depends on the conditions of pilot training set by the Customer (observation distances of 3D-models of reference objects and tasks of pilot's visual orientation training taking into account readings of cockpit equipment instruments) and can be described by the functionality: here L -the minimum possible observation distance of the nearest 3D-model of the reference object specified by the Customer;  

, D F K O 
-3D-indicator design: at K=1, a glasses-free, single-channel 3Dindicator with a "narrow" speculum is assumed to be used.
1 O  (volume of space in the cockpit of the aircraft simulator (obtained by using a mirror collimator of the OKU type (Fig. 1) [5], where the pilot's eyes should be located to ensure comfortable observation of 3D-objects, the "narrow" pupil implies the placement of one person's eyes in this space),  ≥ E3S Web of Conferences 458, 03014 (2023) EMMFT-2023 https://doi.org/10.1051/e3sconf/202345803014 2 30 ; at K=2 the use of a glasses-free, single-channel 3D-indicator with a "wide" speculum is assumed as 2 O  ("wide" speculum (obtained by using a mirror collimator of WIDE type) (Fig. 2) [6] assumes that all crew members of a wide-body aircraft can be accommodated in this space)  ≥ 30 ; at K=3, the use of a glasses-free, single-channel 3Dindicator with a high-definition screen with a "wide" speculum is expected for 2 O  allowing the pilot to successfully track the horizon line and the observed 3D-models of reference objects, which allows the pilot to successfully acquire professional aircraft control skills by obtaining additional information from simulators of cockpit equipment devices  ≥ 50  (Fig. 3) [7]; at K=4 a dual-channel 3D-indicator with disparate glasses is supposed to be used, allowing the pilot to see 3D-objects at the shortest possible distance  ≥ 1  (Fig. 4) [5].The choice of a specific type of 3D-indicator according to the Customer's task determines the possibilities of the aviation simulator to train the pilot for professional training of the oculomotor (if the 3D-indicator acting on the specified components of the visual apparatus of a trained person makes him think that he sees a 3D-object, then the aviation simulator can be used for training a complex visual landing on a limited runway (for example, on a shortened runway of an aircraft carrier cruiser), otherwise the synthesised for the pilot during the flight on the aviation simulator, the 3D-indicator can be used for training a complex visual landing on a limited runway (for example, on a shortened runway of an aircraft carrier).In all cases, a video sequence is first synthesised on a screen connected to a computer image generator from 2D-projections of 3D-objects caught in the surveillance camera in the time moment i t .Further, due to indication devices, a trained person, viewing this screen through optics, considers that he sees either a 3D-object (the term "trained person" means that experiments have shown that for some people to be able to perform tests, their visual apparatus should be able to view 2D-projections to allow a person to consider that he sees a 3D-object and thus can professionally train his eyesight), or to observe with good quality a 2D-projection of a 3D-model, which in case of a mobile observer can be considered by him as a 3D-model (but in this case the 3D-indicators allowing a person to see a 3D-model and not a 3D-object are used in specialised aviation simulators and training complexes for astronauts training, where the trainee has to perform tests in order to see a 2D-projection of a 3D-model.3D-indicators allowing a person to see a 3D-model, and not a 3D-object are used in specialised aviation simulators and in simulator complexes for astronaut training, where the trainee must additionally receive information about the observed 3D-models from simulators of cabin equipment. Analysing  2 it should be noted that In our country, computer image generators as multiprocessor software and hardware systems were developed for visual situation simulators.The best known are computer image generators "Aksai", "Albatross", "Arius".Their development and further operation allowed to define the following processes of sequential information processing: -scenario process, when from the database where data on all 3D-models of reference objects are stored in the form of primitives, which can be located on a 3D-model of the Earth surface up to 1500×1500 km in size, at the same stage the problems of eliminating the undesirable effect of shining of the far 3D-model through the near 3D-model (one of the actual tasks of machine graphics with a mobile observer) can be solved; -geometric process, when all 3D-models of the reference objects, which have entered the observation camera in the time moment   ; -clipping process, when excessive parts of 2D-projection of 3D-models that go beyond the screen frame are "clipped"; -video processor translating mathematical models of 2D-projection of 3D-models into TV signals R, G, B for colouring of corresponding pixels of the screen.
Negative processes of the USSR collapse period did not allow to continue the development of domestic computer image generators.A new stage in the synthesis of 2D-projections of 3D-objects on the screen plane began with the appearance of Graphics Processing Units (GPU) of different companies, which allowed to reduce the size of computer image generators and their dimensions.The first domestic computer image generator "Aksai", which was a part of mass-produced simulators of visual environment for aviation and space simulators, occupied a room with four computing machines, two ordinary mini-computers "Elektronika-79" and two multiprocessor mini-computers (for parallel data processing in the implementation of geometric and clipper processes).The following versions of computer image generators in our country are Albatross (Fig. 5) and Arius (Fig. 6), MaxWue TM abroad are as follows -are specialised multiprocessor stands.A graphics processor, or several graphics processors are placed on a single personal computer board and significantly exceed the performance of previously developed computer image generators.Currently, the leadership in the production of graphics processors has been seized by Nvidia.Miniaturisation and significant reduction of hardware cost allowed to change the technology of image synthesis towards processing of data streams, but the stages of information processing remained the same.Currently, developers of visual simulators are generally unable to interfere with data processing at the geometry process, clipper process and video process.The quality of the final image currently depends on the organisation of information processing during the scenario process -the fastest possible selection of data from the database of the computer image generator and solving the problems of correct closure of one 3D-model with another 3D-model (existing solutions to this problem through the use of hardware Z-buffer, can be considered successful but not always acceptable in practice).Scenario process management is carried out by developing the structure of the computer image generator database and placing visual and control primitives in it, from which 3D-models of reference objects located over the entire area of the modelled region of the Earth's surface are selected, in accordance with  1 .

Conclusions
1. Visual simulators for aviation and space simulators, which allow the trainee to form separate components of his cognitive model responsible for solving the tasks of orientation in space, are being developed in four directions: -development of the list of reference objects that the trainee should see during flights on aviation and space simulators; -development of 3D-display devices; -improvement of the hardware part of computer image generators; -development of the structure of databases of computer image generators with 3D-models of reference objects.
2. 3D-indication devices are divided into two classes: the first class allows a trained person to observe 3D-object and at the same time to train his or her eye-sight professionally; the second class allows a person to observe 3D-models that allow a person to orientate in space taking into account additional information from simulators of cabin equipment devices.
3. At present, the developers of simulator complexes have access to scenario process control and the final quality of the image of the modelled space observed by trainees during flights on aviation and space simulators depends on the solution of this problem.