MyCockpit ® Presents "Mikes Tips" by Mike Powell
Immersion & Scenery Display
Immersion is the feeling that you’re part of a virtual world. It’s what we aim for in our creation of ever more realistic flight simulators. We want to be a part of a virtual aviation world which allows us to experience flight as realistically as possible.
Vision is a big part of immersion. High quality imagery surrounds us in the real world. It’s easy to tell what’s close and what’s farther away. We get different visual perspectives simply by shifting to the side a bit. All this is a normal part of seeing. It feels natural. The more a scenery display system can duplicate this, the more realistic the virtual world feels, and the deeper the feeling of immersion.
Here are several display system characteristics which promote immersion.
1 – Image Width
Increasing the field of view is probably the single best thing you can do to boost immersion. Normal vision spans about 200 degrees horizontally, so make your display as wide as you can. Using a head tracker to slew your viewpoint around is a poor substitute. It’s like wearing blinders. For the best results display a wide panorama that extends into your peripheral vision.
2 – Resolution
The image quality needs to be good. Early hobby experience with projectors showed that an 800 x 600 resolution gave poor results when used for a 60 degree field of view. Bumping up to 1024 x 768 was a bit better, but still marginal. This was due in part to the “screen door” effect these early projectors suffered from. While your mileage may well vary, 1280 x 1024 is a good minimum resolution for a 60 degree field of view. This means you’ll need several projectors or displays to produce a panoramic system.
3 – Contrast
Contrast has been and continues to be a problem. The vast majority of light from display devices doesn’t find its way to the viewers’ eyes. Instead it bounces around, and some of it ends up hitting the display surface where it lowers contrast. Large display systems produce even more light and tend to suffer most. Improve contrast by controlling extraneous light. Keep the sim room light tight and dark. Use light absorbing curtains, wall coverings, paint, furnishings, etc. to reduce the amount of light which is reflected onto the display surface.
4 – Geometric Distortion
A display system should not distort the imagery. Straight lines should remain straight. Objects should not change shape as they move across the screen. Of course, they do. The goal is to minimize these imperfections.
Projection systems have an advantage over multiple flat panel displays because multiple projectors can create a seamless panoramic image on a curved screen. This requires edge blending and image-warping software to stitch the individual images together and to correct for the geometric distortion the curved screen brings.
Flat panel displays can’t produce a continuous image because each display has a bezel which frames the unit. Even removing the display cases won’t remove the gaps between images. (On the other hand, flat panel displays lead to a lower cost, more compact display system.) Proper image set up, however, can accommodate these gaps so objects spanning these gaps don’t appear to have a joggle where crossing the gap.
5 – Screen Positioning
We bring a 3D understanding to everything we look at, even a 2D rendering of a virtual 3D world displayed on a (more or less) 2D screen. And therein is a problem.
We develop an understanding of the 3D nature of our surroundings by subconsciously collecting many different depth clues. As long as these clues are all in agreement the whole process stays quietly buried in the subconscious bothering no one. However, when depth clues disagree, that’s no longer the case, and we’re distracted from the virtual world.
Game developers use embedded depth clues to communicate the three-dimensional nature of the virtual world. Here are just two examples: If one object occludes the view of another, it’s in front. If a large object appears small, it must be distant. Embedded depth clues can be seen with one eye closed.
Binocular vision develops depth clues from the perspective differences between the left and right eye views. This is such a powerful process that it works even with one eye if you move your head. Perspective-differences, whether from binocular vision or motion, are the strongest source of depth clues.
When we look at a desktop monitor, perspective-difference depth clues correctly tag the display surface as flat even though the imagery being displayed is a rendering of a 3D virtual world. The conflict between the perspective-difference depth clues and the embedded depth clues limit the sense of immersion.
Fortunately, perspective-difference depth clues are strongest for objects close to the viewpoint. Beyond 30 feet they are mostly absent because our eyes don’t have the resolving power to see differences between the left and right eye views.
Moving the display screen away from the viewpoint will reduce the conflict among depth clues by suppressing perspective-difference depth clues. You’re left with the embedded depth clues, and immersion gets better. You don’t need a full thirty feet, even a few feet makes a difference.
Another thing you can do, even if you don’t have a sim cockpit, is separate the instrument panel imagery from the external scenery. Display the panel close to you. Place the scenery on a different display device some distance away. The difference in perspective will enhance immersion.
6 – Distractions
A final step is to block out the real world. Display systems rarely fill the entire field of view. Make sure the unfilled portion does not allow the real world to leak in and pull you out of the flight illusion.
Mike Powell, author of
Building Recreational Flight Simulators
Building Simulated Aircraft Instrumentation
Building Simulator Display Systems
. (A work in progress)