A (relatively) inexpensive 2 projectors sim full immersion display

August 22, 2018 / Comments (0)

AFSBI Standard Building Tips

/ By Editorial Staff

Introduction

A recent study, conducted by a manufacturer of professional simulators, concluded that the perception of motion is 83% visual. An immersive, wraparound (>150°) display around the POV of the pilot, can produce many of the clues a human needs to believe to be moving. Airline-grade simulators add motion as well, but most general aviation training devices found in well-established training centers, stick to just full-immersion visuals and a realistic cockpit. These simulators are real aircraft cockpits surrounded by cylindrical or dome-shaped screens. I personally trained at SimCom on a non-motion King Air 200 FTD a few years ago and, after a few engines out, fires and other simulated huge problems,  I vividly remember how quickly I forgot I was in a simulator: the sweat was all real. With this in mind, at AFSBI we embarked in building a cylindrical, 180°projection screen, with two objectives: 1) creating a full-immersion visual environment and, 2) doing it for less than $1,500 all included. We plan to use this screen as the display environment for one of our simulators. We must add that there are other, less expensive solutions to achieve a similar result, but likely not as immersive as this one.

Construction

The first decision was the size of the screen. We wanted to be able to walk around our 4′ wide by 5′ long simulator, so  we picked a 7′ radius and 7′ height. This allowed the simulator to be completely within the footprint of the screen, while allowing a 2′ walkway in front, plenty space on the sides and ample vertical view. In retrospective, a 6′ radius, or perhaps even less, may have been enough, but other considerations would have applied, as we will see later, for anything smaller. We constructed the frame of the screen using a 3/4″ plywood base and top ‘plates’ with 2×2 uprights in between. Cutting the round frames was easily done by marking a plywood sheet using a long protractor-type device and a jigsaw. Once the pieces (6 at approximately a third of the curve each, for the top and bottom plates, about 2″ wide) were marked and cut,  we ripped the 2×4 in two, length-wise to produce some of the uprights, and cut them to the length required to cover the distance from floor to ceiling, approximately 7′, where the simulator is installed. We left two uprights as 2x4s to support the 5mm ply sheets used for the screen at their edges meeting points. The uprights were assembled starting from the center,  between the two plates  which were screwed into the ceiling and floor and plumbed and measured for accuracy. We installed uprights at about 2′ intervals, then a full 2×4 where the screen’s 5mm plywood sheets joints fell and so on until the edges of the structure. You will have to calculate your own, but ours came at 7’xΠ=21.99′ (rounded up to 22′). This measurement required three of 5mm 4’x8′ sheets for the top part, one of which was cut to 6′ wide. We only used two at the bottom, cut to 3′ high, leaving 6′ uncovered at the bottom-center, in front of the simulator and practically out of sight. We covered this later with a removable sheet of white PVC, to allow access to the back of the wall. We screwed the 5mm ply sheets very sparingly and sunk the head of the screws just enough to be covered by painter’s putty and sanded smooth.  We left the joints between sheets floating but screwed an alignment block half way between the uprights. Two rich coats of white satin paint completed the job. The 5mm plywood responded well to the curve resulting from the choice of a 7′ radius and was easy to handle. It may not bend as easily to a tighter radius. Here is the part list for this project:

ItemQtyPriceTotal $
3/4" 4'x8' Plywood144.9844.98
4'x8' 5mm Plywood514.9874.90
2"x4"
uprights
73.2222.54
White Satin Paint144.9844.98
Projectors
Optoma GT1080 (ebay lightly used with <100hrs lamp time)
2480960
Ceiling mount216.9933.98
DP to HDMI cables, 15' 214.9929.98
Immersive Display Pro, 3 projectors, locked license1225.54225.54
Miscellaneous
(screws, painter
putty, etc)
-3030
Total $1,466.90

Projection

As for the number of projectors, we decided on two – the pros and cons of two or three projectors are described later. We opted for two  Optoma GT1080  gaming projectors, mounted on the ceiling. If you plan to use these type of short-throw projectors, which we recommend, you will mount them so to cross their beams (left projects to right screen, and vice versa). Use a calculator to confirm you are in the ballpark distance for your setup. The beam crossing will allow enough distance to cover a larger area. Ours were placed at 7’4″ each from the far edge of the screen and 7′ from the center. It’s better if you can mount them so that lateral position adjustments can be made. Ours can be moved sideways across the ceiling glulam overhang.  Expect some light obstruction, e.g. the body of at least one of the projectors to be slightly blocking the beam of the other. Since lenses may not be centered on the body of the projector, on one side of the screen you will have a worse block  than the other. Also please note that Optoma GT1080’s all use the same remote IR code. Since one remote will affect both projectors, they will have to be adjusted manually, except for turning them both on and off.  We provided an outlet on the ceiling to power them, and two DP to HDMI cables – use the shortest run possible – to connect them to an Nvidia 1080 video board.

Alignment

Once the projectors are installed, the alignment, warping and blending process begins, followed by the simulator’s graphic setup. An important note: if your simulator blocks some of the light from reaching the lower part of the front of the screen you may have to move it. We mounted our sim on bench lift casters to make moving easy. We use X-Plane 11 on this sim, and we will describe the process for that simulator. Essentially there are three stages to make this work:

  1. Rough alignment and overlap of the two projected images, using the grids in the projector setup;
  2. Warping, blending and masking of the projected images to correct geometry for cylindrical screen, distance variations, overlap bands, and color and luma differences;
  3. Setup of the perspective and POV within your flight simulator software.

Rough Alignment

This is done by displaying (from the projectors’ internal menu) the white grid on black background. Nothing complex here, just make sure you have a substantial overlap in the center between the two projectors, and the top and bottom of the image is as close to the same lines as possible. The projectors we used do not have a zoom, and the adjustment is done by manually moving the projectors across their mount axes. Make also the best use of the projectors’ keystone adjustment to obtain lines as straight as possible.

Warping and Blending

We used Immersive Display Pro (IDP). While we quoted a locked license in our price table, we actually purchased the USB dongle, in order to have more flexibility in changing hardware. IDP allows precise control on all parameters involved. IDP comes with a 30 days trial version, which we used before we decided to buy it. It allows you to setup the software but displays a “Unregistered Version” notice on screen. As a general rule, do not use the Nvidia surround function to make your projectors  appear as one screen on your computer. This will not work in X-Plane as you will need to adjust the two sides separately. You will need to follow the instructions provided by the software vendor, Fly Elise, for more details on the setup. They have an X-Plane-specific setup guide (here). I will only mention here that we used a simple but effective alignment system, using little round stickers to establish a 7×5 square grid on each half of the screen to aid in the exact calibration. In geometry adjustment mode you will then make each grid point fall over one of your predetermined stickers to make the process fast and reliable (some math involved). Blending and masking make for a smooth transition between the two projectors’ images. All the parameters in IDP can be finely modified. Use the keyboard (Ctrl-Arrow), not the mouse, for finer one-pixel increment adjustments.

X-Plane internal setup

Once you have a reasonably good picture, you should adjust the displays within X-Plane. In our setup, we covered 160° and we had similar, but not identical, settings for the left and right projectors. The differences come from the slightly different positions of the projector as related to the screen. Once you display the full screen from X-Plane, you will find the need to go back to IDP and fine tune it even more. It’s an easier task if you remain in X-Plane, Window Key +D and then display the IDP configuration screens to fine tune. Esc, Esc will take you back to X-Plane to verify your adjustment.

Pros and cons of a two projector vs. three projector setup.

Pros

↑ Reduced cost, not only for the actual purchase of two projectors only, but also because you can drive the resulting pixels (3840×1080) with one video card. Driven by a fast processor, a video card such as the Nvidia 1080 will handle the projectors and  offer adequate frame rate up to a good level of detail. You will have to experiment for yourself with your setup, processor, etc. We run consistently above 30 fps.

↑  Ease of setup, electrical consumption, heat, etc. These may be minor items but still worth to take into consideration.

↑ You have most of the elements needed to add a projector later, if you wish.

Cons

↓ A line in the center of the screen, which can be minimized substantially but not completely eliminated. There are workarounds that make this less relevant, as shifting the entire projection to one side a few degrees, so as to have the runway mainly falling on one screen on landing.

↓ You will get less than 180° total view, likely between 150°-160°. Three projectors will give you a full 180° or more and will allow for wider overlap which will give you a better control of the blending.

If you intend to take this route, we hope this is useful information. The difference a full display makes is quite substantial, vs. computer monitors, and the overall effect does exactly what we described at the beginning: transport you into a full immersion experience.


If you like to share you experience, provide suggestions, or ask for more details please comment below.

 

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