# Correct FOV?

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What is a correct fov? And is it dependent on aspect ratios? (Does it differ from normal 4:3 resolutions and widescreen resolutions) In FPS games like Quake and Unreal Tournament the standard is 90, is it as simple as that? EDIT: If it matters I want to do a fantasy game with 3rd person view and sometimes change to 1st person view.

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I usually use anywhere from 35 to 45 degrees. This works for me, but may not work for you. Just play around with the values and see what looks the best to you. Good luck.

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Above poster means 70-90 degrees. FOV is measured as the field of view from the left edge of the screen to the right edge; thus, it is really the horizontal FOV. The vertical FOV is smaller, depending on the aspect ratio. VerticalFOV = HorizontalFOV / AspectRatio.

A 4:3 view with an FOV of 90 has a vertical FOV of 90 / 1.33, which is 67.5. A widescreen monitor with a horizontal FOV of 90 would have a vertical FOV of 90 / 1.6, which is 56.25. However, some games might choose to preserve the vertical FOV of 67.5 and expand the horizontal FOV to 108 degrees (67.5 * 1.6). The first method gives the player a smaller field of view; the latter method gives them a wider one.

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There do seem to be some standards for FOV in some types of games, but generally I link the fov up to a slider and let the designer choose what they like the best :) (as long as they are aware of the rendering implications of the fov)

Of course some games use fov changes for special effects i.e. nitro boost

Paul

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A bit off topic but here we go (it's getting DirectX related)

After reading the reply from CGameProgrammer I started to check up what kind of fov (vert or horiz) I set in DirectX and VS intellisense says "fieldOfView". I use a beta version of Managed DirectX but the docs (for the other versions of DirectX) calls this parameter fieldOfViewY, not just fieldOfView so I assume that it is vertical fov that I set in DirectX, not horizontal.

So I think I'll try a few different values as you suggest, but I thought it looked a bit weird and the reason could be that I used 90 as vertical fov. Anyways, I'll try some different values. Thanks for the replies!

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Quote:
 Original post by CGameProgrammer... A 4:3 view with an FOV of 90 has a vertical FOV of 90 / 1.33, which is 67.5. A widescreen monitor with a horizontal FOV of 90 would have a vertical FOV of 90 / 1.6, which is 56.25. ...

You were doing great until you got to this point. The aspect ratio doesn't apply to angles. If the horizontal FOV of 90° and the aspect ratio is 4:3, then the vertical FOV is 73.9°, not 67.5°. Here is the formula:
    h is the horizontal FOV    v is the vertical FOV    a is the aspect ratio (width/height)        v = 2 * tan-1( tan( h/2 ) / a )

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Quote:
Original post by JohnBolton
Quote:
 Original post by CGameProgrammer... A 4:3 view with an FOV of 90 has a vertical FOV of 90 / 1.33, which is 67.5. A widescreen monitor with a horizontal FOV of 90 would have a vertical FOV of 90 / 1.6, which is 56.25. ...

You were doing great until you got to this point. The aspect ratio doesn't apply to angles. If the horizontal FOV of 90° and the aspect ratio is 4:3, then the vertical FOV is 73.9°, not 67.5°. Here is the formula:
    h is the horizontal FOV    v is the vertical FOV    a is the aspect ratio (width/height)        v = 2 * tan-1( tan( h/2 ) / a )

Oh, right. What I described would be true if it weren't for 'fish-eye correction' which straightens out curves. So yeah, you're right, my bad.

My post still stands though, even if the exact numbers are off. The vertical FOV is inversely proportional to the aspect ratio, and for widescreen monitors you can either expand the horizontal FOV or shrink the vertical FOV.

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Quote:
 Original post by CGameProgrammerOh, right. What I described would be true if it weren't for 'fish-eye correction' which straightens out curves. So yeah, you're right, my bad.My post still stands though, even if the exact numbers are off. The vertical FOV is inversely proportional to the aspect ratio, and for widescreen monitors you can either expand the horizontal FOV or shrink the vertical FOV.
Just to make sure it's completely clear to the OP, the horizontal and vertical fields of view are not linearly related via the aspect ratio, no matter how you look at it. That may be what you were saying above, but I wasn't sure.

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Technically, the "correct" FOV depends on two things: the width of the monitor (assuming we're discussing horizontal FOV) and the distance of the viewer from the monitor. fov_x = atan((width/2)/dist)*2. The idea being to put the virtual center of projection in the same place as the actual center of projection, so that there is no reprojection error.

"Correct", though, may not be what you want. For common values of width and dist, the monitor does not fill a very large area of our total field of vision, meaning that we can't see very much in the game if we go with this. So FOV is commonly bumped up a good deal to make the display more useful.

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Quote:
 Original post by SneftelTechnically, the "correct" FOV depends on two things: the width of the monitor (assuming we're discussing horizontal FOV) and the distance of the viewer from the monitor. fov_x = atan((width/2)/dist)*2. The idea being to put the virtual center of projection in the same place as the actual center of projection, so that there is no reprojection error."Correct", though, may not be what you want. For common values of width and dist, the monitor does not fill a very large area of our total field of vision, meaning that we can't see very much in the game if we go with this. So FOV is commonly bumped up a good deal to make the display more useful.

To illustrate: If one has a monitor 20" wide and sits with their head two feet from the monitor, the "correct" FOV is 44 degrees (22 degrees left and right). If you sit one foot away, the "correct" FOV would be 78 degrees (39 each way).

Those calculations, based on Sneftel's formula, assume we normally have a 180-degree FOV. Basically a 20" monitor less than a foot away would take up half your field of vision, so its FOV should be half of yours.

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