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Thread: Alternative view on FOV calculation.

  1. #1
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    Lightbulb Alternative view on FOV calculation.

    The problem with all these FOV calculators and all these "proper" and "mathematically correct" values is the assumption that the FOV setting in the game should be equal to the angle of your view to your monitor. This usually explained as the window you are looking through. So the field of view (FOV) should depend on distance you are standing from this window.

    But, THIS IS WRONG !!!

    Imagine you are looking at a 30x40cm photograph hanging on the wall in front of you. The picture is taken with some standard camera with standard lens, which has it's own parameters - focal length, field of view, frame size, and many other.

    Now try to step back few steps. Then a few more. Did the FOV on the picture change? Think of it? Does it?

    The answer is NO!

    The same is with the games. You are looking at the PICTURE, and the FOV does not depend on the distance how far you are sitting/standing from it.

    Let me introduce a new term from world of photography, which is tightly related to all the lens and optical parameters - and the term is PERSPECTIVE.

    Every experienced photographer knows about it. And he (she) knows that the wide-angle lenses (have wider FOV) extends the perspective - distance between the objects in the field of the picture looks increased comparing to a "normal" perspective. But, the telephoto lenses (narrow FOV) compress the perspective, so the objects look closer to each other and to a viewer than they are "normally". Both these cases are called PERSPECTIVE DISTORTION.

    Actually, when you are changing the FOV in the game (actually this should be called AOV - Angle of View, or Angular Field of View), two things happen and they are tied togehter:

    1. The field of view (proper FOV term) changes - the visible part of the image, so you can see more - that's why most of the users set this higher, so they see more of the scene.
    2. The perspective also changes. And if you set too high or too low, you've got the perspective distortion.

    So actually we want the "NORMAL" perspective, to avoid the perspective distortion, right?

    I'm a photographer, so I know that the "normal" lens, which does not have (or have minimal) perspective distortion is the f=50mm lens (f=focal length, on full frame camera with 24x36mm frame size, 3:2 aspect ratio). So we can calculate the "normal" field of view (horizontal angular FOV) for 16:9 image, which is 45 degrees.

    This will give you the "natural" view without the perspective distortion. But in real life this view will be too narrow and pretty limited for driving, so it's usually can be expanded to a moderate wide-angle view (horizontal 50-70 deg). The more you change it from "normal", the wider picture will be, but more perspective distortion you will get.

    And remember: the FOV is NOT related to a distance you are sitting from the screen! This is wrong assumption.

    References:
    https://en.wikipedia.org/wiki/Perspe..._(photography)
    https://en.wikipedia.org/wiki/Angle_of_view
    https://en.wikipedia.org/wiki/Normal_lens
    https://www.nikonians.org/reviews/fov-tables
    http://themetalmuncher.github.io/fov-calc/

    P.S. Sorry for my English.
    Last edited by Tepp; 26-05-2017 at 08:31.
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  2. #2
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    Perspective and FOV (as implemented in sim racing games) are related concepts, but are not the same. When you view a photograph, there is no expectation that objects will appear to be "actual size". In sim racing, that expectation is not just present, it is implicit.

    I actually wrote this up for another forum, but you may find it useful:

    FOV is both subjective (preference) and objective (factual).

    The size of objects, their location within your view, and the translation (movement) of objects across your screen are all dictated by simple geometry. That is to say, for a given screen size and viewing distance, the correct field of view will render objects at the same size as if you were sitting in an actual car. Likewise, objects will translate (move) through your view in the same proportions as real life. This is fact, not preference.

    Unfortunately, many console gamers are playing on a couch (more than 1 meter away) with a reasonably sized television 36"-55". If the geometry of your viewing setup doesn't work well for optimal FOV, you have to compromise. That's where preference comes in: how much are you willing to compromise?

    To get a sense of how poor the geometry of a typical couch setup is, just imagine someone built a black box around a car. The wall in front of you is the same distance as your TV. Now imagine that someone cut a hole in the wall that is the size of your TV. It's like viewing the world through a keyhole.

    In order to see more, you have two options: make the window larger (bigger TV), or move closer to the window (sit closer to the TV). When you look at the geometry, something interesting is revealed. Moving closer yields much greater improvement than making the window larger. This is why it is so important to sit as close as possible to your TV.
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  3. #3
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    bradleyland,

    Yes you are right, Perspective and FOV are different concepts, but they are tightly tied together.

    If you increase the FOV, the perspective expands, so the distant objects appear further than they actually are. If you decrease FOV, the perspective contracts, so the objects appear closer than they actually are (like in binoculars).

    About "actual" size of the objects - there is nothing to do with FOV, just buy a larger TV or sit closer. Or use the VR ...

    I'm just trying to tell that if you sit further, you don't have to change the FOV accordingly. It's independent of the viewing distance.
    Last edited by Tepp; 26-05-2017 at 08:04.
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  4. #4
    LMP2 Pilot hkraft300's Avatar
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    Quote Originally Posted by bradleyland View Post
    In order to see more, you have two options: make the window larger (bigger TV), or move closer to the window (sit closer to the TV). When you look at the geometry, something interesting is revealed. Moving closer yields much greater improvement than making the window larger. This is why it is so important to sit as close as possible to your TV.
    Option 3: move the wall
    I've noticed many 3-screen setups using dash/bonnet cam.
    Last edited by hkraft300; 26-05-2017 at 09:59.
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  5. #5
    WMD Member MaximusN's Avatar
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    Quote Originally Posted by hkraft300 View Post
    Option 3: move the camera
    I've noticed many 3-screen setups using dash/bonnet cam.
    I prefer a closer monitor/TV(my 32" is as close to my wheel as possible). You cannot move the camera forward without also moving the side view forward. And the left/right view is all-important in knowing where your opponent is. You might even say that you're giving back some of the extra spatial-awareness you bought the 3 monitors for...
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  6. #6
    LMP2 Pilot hkraft300's Avatar
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    I thought the same, seeing others' 3-screen view.

    I sit ~a meter away from a 42". As close as I can get.
    But I run Hugh fov to compensate and have better side vision.
    Sure the view is slightly warped. Compromise.
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  7. #7
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    Quote Originally Posted by Tepp View Post
    bradleyland,

    Yes you are right, Perspective and FOV are different concepts, but they are tightly tied together.

    If you increase the FOV, the perspective expands, so the distant objects appear further than they actually are. If you decrease FOV, the perspective contracts, so the objects appear closer than they actually are (like in binoculars).

    About "actual" size of the objects - there is nothing to do with FOV, just buy a larger TV or sit closer. Or use the VR ...

    I'm just trying to tell that if you sit further, you don't have to change the FOV accordingly. It's independent of the viewing distance.
    The further away you are, the smaller your TV appears, and by proxy, the objects in your screen. This necessitates a change in FOV, which effectively magnifies what is displayed on screen.

    In order to maintain 1:1 scale, display size, viewing distance, and FOV must all be balanced. You might be tempted to make the argument that you don't care about the size of objects on screen, but because the game is projecting 3D objects onto a 2D plane, correct FOV is required for translation to occur correctly. This is actually the most significant impact, because it relates to our ability to judge distance to objects; i.e., depth perception.

    A perfect display would be hemispherical, but because most displays are flat, you'll always have some degree of distortion.
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  8. #8
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    Again, this all relates to the objective aspect of FOV. Subjectively, compromise is a fact of life. It all gets rather academic, but IMO, it's important to be accurate in our assessment of what is objectively accurate, and what we do out of compromise.
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  9. #9
    GT5 Pilot inthebagbud's Avatar
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    I need to ask here as FOV is a little soapbox of mine in the game. On xbox FOV settings only move your position in the car (you get nearer the windscren or further from the windscreen) they do not alter the distance too objects outside of the car.

    I have always presumed this is incorrect as FOV should alter the distance too objects outside of the car .

    Am I correct?

    And if so I assume pc and ps4 work correctly it's just xbox that doesn't work
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  10. #10
    GT5 Pilot Fanapryde's Avatar
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    Quote Originally Posted by hkraft300 View Post
    I thought the same, seeing others' 3-screen view.

    I sit ~a meter away from a 42". As close as I can get.
    But I run Hugh fov to compensate and have better side vision.
    Sure the view is slightly warped. Compromise.
    Until VR
    Triple 27" monitors angled at 45, all three about 54cm from my eyes (which is as close as I can physically get them as I need to have the middle of the screen at eye height).
    I don't remember right now what value I use for FOV, but I can change that on the fly if wanted.
    Apart from the warped view in the side monitors (which is not going to be an issue in pCars2, since we will have proper triple screen support) it is great.
    Tried VR three times now, got upcoming nausea after about 10 minutes each time, so I ruled that out (for several other reasons too).

    About a year ago I made a cardboard frame representing the bezels of the triples and took it inside my car to check what I see IRL and I must say that the view in my rig is pretty close (apart from the side screens with the warped view and huge mirror on the drivers side - not even seeing the one on the other side).
    I only use cockpit view with my real wheel matching the place of the disabled virtual wheel, and I can rely on the dash instruments/gauges.
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