How to Build a Simulator – Part VI – Visual Systems


This post is Part-6 of the “How To Build a Simulator” series. Previously published was the “How To” intro, which includes a summary of the series and a detailed schedule.

Image Generator

The image generator (IG) predominantly creates the OTW display as well as drives images to the multi-purpose/function displays (MPD/MFD) and sensor displays like forward-looking infrared (FLIR), night vision goggles (NVG) or radar. Since the image generator’s sole purpose is to supply the simulator with images, it can come in many forms. Desktop personal computers (PCs), one or multiple racks of computers, tablets, game consoles, and anything else that can display an image can be considered an image generator.

an Image Generator in use

Before computer software became widely accessible, image generators were made with “terrain” boards, or “map” boards. These were simple in design, yet complex in creation. They consisted of a large surface to draw or shape an Area of Interest (AOI). A model aircraft would hover above the board and below a camera that connected to a movable mechanism and a set of input controls to create the view of an aircraft in flight. These were the predecessors to the modern computer-generated (CG) IGs.

There are also many requirements placed upon image generators which are mainly dependent on the budget, the deadline, and what is needed for training. They determine factors like the type of database (DB), the display output, the number of channels used, the content details, the special effects, the power supply, the cooling system, and the communication networks. These choices can completely change the functionality of the IG.


Image generators are also the interface of the database. The database is a collection of CG objects within an AOI and is used to create synthetic training environments (STEs). Databases were not used until computing assets were introduced to simulation. Instead, large physical models and map/terrain boards were utilized. Databases greatly improve the possibilities of training as they allow the user to train anywhere in the world and beyond without the need for a large room simply devoted to mapping.

The capability of the image generator determines how limited the database will be. IGs can focus more so on data-preparation or on processing as a trade-off. They can focus on both data-prep and processing, but this is dependent on the quality and tools necessary. The better the image generator or the more channels and nodes used, the larger or more detailed the database can be. Because of the required real-time processing, content details and special effects must be prioritized.

Database for an Image Generator. Computer-generated town below a forested mountain.

There are also different types of databases and AOI. A DB’s AOI can either be geo-specific or geo-typical. Geo-specific means the AOI is specific to an actual location in the world or at least has data specific features that can be used to locate the aircraft. Examples include cities, airports, airfields, or military bases. Geo-typical means the AOI is a generic or typical location, as in a desert or a plain. databases themselves can be very different as they are used for different reasons. The most common kinds of DBs are the Hight Flyer, which has a large AOI and much less detail, helicopter sims, which are focused on terrain and terrain flight (TERF), and pilot trainers, which are more concerned with higher resolution terrain and coastlines, and more detail in powerlines, trees, buildings, and towers.


The display output can be anything from a projector to a head-mounted display (HMD). These outputs can be used differently for specific reasons. This display spectrum includes the out the window display (OTW), the multi-function/purpose display (MFD/MPD), the interior cockpit display (ICD), and the head-worn/mounted display (HWD/HMD). Each display has its own use. The OTW shows the pilot’s view of the exterior environment, the MFD and MPD are small screens inside the cockpit used to relay information to the pilot, and the HMD can be used to view an ICD which is a fully VR cockpit interior.

out the window and muti-function displays


The number of channels required is largely dependent on the size of the IG, the resolution of the visual display, and the field of vision (FOV). The more channels mean more information can be sent and received much like a piping system. If you have reservoir-A filled with water that needs to be in reservoir-B you can either use one pipe which slowly fills reservoir B or multiple which fills it quicker. Every pipe (channel) added increases the flow of water (data).

Details and Special Effects

Content details and special effects are chosen by preference. Simulators can run easily without special effects, but they also make the experience much more immersive. Special effects can include tank tracks, smoke, explosions, shadows, weather, missile trails, destroyed vehicles, bomb craters or any content that is generated or synchronized as part of the simulation. This definition of “special effects” is otherwise known as “persistence”. Persistence may or may not be included due to the limitations set in place. This is because they require plenty of processing power and may need a secondary GPU or entire IG (node) to offload the real-time physics workload and avoid lag.

Power Supply

Much like the number of channels, the power supply is dependent upon the size of the IG. The number of channels used, the content displayed, and the special effects added all determine how much power will be required and allotted in the “wattage budget”. The larger the IG, the more power is required.


The more power, the more heat. Therefore, a cooling system is required. A cooling system is extremely necessary because the IG generates more heat than any other associated device in a simulator. IGs account for most of the overall temperature in an enclosed space, depending on the channel count. Cooling systems can be air or liquid-based. Air cooling uses a fan or series of fans to lower the temperature of certain areas. Liquid cooling uses tubing to transport cooled water or thermal paste throughout the entire system. As the liquid moves along in a loop, it absorbs the heat from critical components like the CPU and the GPU and is then cooled separately in a radiator to be cycled again.

Cooling system of an image generator
Cooling System of an IG


As previously mentioned, the IG connects to other components to display generated images. It does this by communicating through multiple networks. The Common Image Generator Interface (CIGI) network is for communicating between nodes, passing relevant traffic, and isolating traffic for reduced latency. It is the primary network for communicating with the host and is required in all IGs. The maintenance network is for powering the IG nodes and is the main control for the IG to launch and kill processes. Finally, the data network is used to reduce and isolate other communication traffic. It transfers data to the nodes from a central “master” node. The data network is only necessary if multiple nodes are utilized to lessen the workload on the IG.


Once the DB and the IG are complete comes time for testing. The IG is initially issued a field acceptance test (FAT) upon delivery. This is a functionality test to ensure everything is working and nothing has been damaged in shipping. Next, after the IG is fully integrated, is system-level testing, which checks the compatibility between the IG, the display output, the visual cables, and the networking cables. Then the element level is tested. This is to test the validation of the databases and content requested.

IGs truly are the brain of the visual system. They communicate, comprehend, translate, and display all required imagery to allow for effective training. Without them, there would not be any way to use the STEs created by databases. We here at the AVT Training Center hope you have learned from our “How to Build a Simulator” series and tune in next week.

This post is Part-6 of the “How to Build a Simulator” series. Previously published was the “How To” intro, which includes a summary of the series and a detailed schedule. You can find it here.

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Initially, Applied Visual Technology Inc., AVT has been developing modeling and simulation expertise through engineering services since 1998. This is due to our founder who has accumulated over 30 years of military MS&T expertise in aviation applications. Nonetheless, everyone at AVT specializes in making old training systems new again and making new ones for less. Consequently, for 20 years AVT has served our Air Force, Army, Navy, and Marine customers by providing the highest quality of service and solutions. Following its inception, AVT’s highly specialized staff of engineers has included some of the top leaders in the simulation industry. With over 20 years of simulation experience, our dedicated team provides specialized solutions for customers with complex problems.




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