Horisontal AOV?

matteo

the fov of a real camera is a function of the film frame dimensions. It is commonly related to a standard film with frames of 3624 mm - a 50 mm lens over a 3624 mm film frame is not the some of a 50 mm lens over a 60*60 mm film frame.

i know, it's a bit confusing. all the new digital cameras have show an equivalent fov: that's because it would be too tricky to figure out the real angle of view, since there are somany formats. for more informations give a look to this on wikipedia: http://en.wikipedia.org/wiki/Image_sensor_format

talking about the aov, it is not so difficult to find the horizontal angle when you have the vertical angle values and the aspect ratio.

if you look at the first image, I extract half horizontal aov (1/2 Haov by now) + half vertical aov (1/2 Vaov by now) and unfold them.

we have now quite a simple trigonometric problem. both triangles, blue and yellow, share the some radius: then 1/2 Haov tangent is equal to half screen length - and 1/2 Vaov is equal to 1/2 screen heigth. see figure two.

now the formula is quite simple to obtain

1/2 Haov = arctan [tan(1/2 Vaov)*(length/heigth)]

let's suppose that you have a Vaov of 60° and a screen aspect ratio of 3/2, the Haov is equal to:

Haov = 2* arctan [tan(60°/2)(3/2)] = 2 arctan [tan(30)1,5] = 2 arctan (0,577351,5) = 2 arctan (0,866025) = 2* 40,89339° =

81,786789°

i hope this can help you thom
note: all angles are measured in degrees and not radiants or else.

/matteo bignozzi

aov aspect ratio.jpg

aov aspect ratio 2.jpg

thomthom

It worked!
The true test to if I understood this will be when I try to make functions that calculate between all directions of Vaov, Haov and Daov. At least I can go to bed now.

Chris Fullmer

Oh good. have you got it all worked out then in Ruby Thom?

Chris

thomthom


def self.haov_from_vaov(vaov, ratio)
    return (2 * Math.atan( Math.tan(vaov.degrees / 2) * ratio )).radians 
end

When (if) I get the other conversions worked out I'll post them back here in case anyone else should need them. (Plus, people with better math skills than me can verify if I did it right... )

TIG

@thomthom said:

Camera.fov returns the vertical AOV. But how do I get the horizontal or diagonal AOV?
From Wiki I find this forumla: http://en.wikipedia.org/wiki/Angle_of_view

$http://upload.wikimedia.org/math/a/1/7/a172c67e0c1191e57fdc3e958f596628.png$

( Math.atan == arctan, right?)
Problem is, that assumes a film width and height... Which I don't have for the SU camera. So, how do you go about calculating the various AOV?

After a year or so...
I needed it - so here it is...


### acc is the active camera
### width is the screen width
### height is the screen height
    fol=acc.focal_length
    fovV=acc.fov
### fovV if the vertical fov in degrees
    wid=width.to_f
    hei=height.to_f
    if acc.image_width != 0
      wid=acc.image_width
      if acc.aspect_ratio != 0
        aro=acc.aspect_ratio
      else
        aro=wid/hei
      end#if
      hei=wid/aro
    end#if
    h=2*fol*Math;;tan(fovV.degrees/2)
    w=h*wid/hei
    fovH=(2*Math;;atan(w/(2*fol))).radians
### fovH is the horizontal fov in degrees

thomthom

Ah! I'd forgotten about this! (yet another project in limbo. )

Thanks TIG - I'll play around with this when I get VE over with.

Chris Fullmer

Very odd, I also had to re-visit this to make similar code recently....are we all working on the same project?

Chris

thomthom

I can't even remember exactly what it was any more.

I think it was in regard to making camera objects. But due to observers begin naughty it down-prioritised.

DavidBoulder

I did a quick little diagram, but its been a while since I have had to use any trig to write a formula. aov triangles.png

TIG

My seemingly convoluted code does return the correct horizontal fovH in degrees from the current fov [i.e. vertical] in degrees...
It uses the focal_length of the current camera to get this...
The results matches what appears [on a PC] with the code snippet Sketchup.send_action(10624) for the fovH value... so I am confident in its efficacy.

Dan Rathbun

On this subject.. FOV a registry question.

I noticed a setting in the registry Tools/FovDisplayMode
my setting is 0

What is this ?

Chris Fullmer

You can switch between horizontal and vertical in the dialog window that pops up with:

Sketchup.send_action(10624)

I wonder if that registry setting controls that? That would be nice to be able to switch the user back and forth from horizontal and vertical as needed maybe?

Otherwise, if its not that, I am out of ideas (for now).

Chris

Chris Fullmer

Though FOV being horizontal or vertical seems to be associated with the model, not as an SU global setting. So it is probably not that then?

Chris

thomthom

The global default?

Chris Fullmer

I suppose it could be, but if it is, the template file is overwriting it.

Dan Rathbun

@chris fullmer said:

You can switch between horizontal and vertical in the dialog window that pops up with:
Sketchup.send_action(10624)
I wonder if that registry setting controls that? That would be nice to be able to switch the user back and forth from horizontal and vertical as needed maybe?

I changed the setting to 1, and see no difference, in the model or in any of the settings in that Camera dialog.
Could be an orphan setting left over from some earlier version.

Why is there no menu choice or constant string to bring up that dialog?? Is this a WIN only feature?

Chris Fullmer

Yes, it seems to be Win only.

thomthom

Think it's a debug dialoge.

But I do wonder why one can set vertical or horisontal AOV from the UI. And why camera.aspect_ratio isn't exposed in the UI.

TIG

camera.fov always returns the 'vertical' fov. Many 3rd party apps you export to need the 'horizontal' fov - so fov = 30 degrees fovV >> ~52 degrees fovH...
My method does return fovH in degrees correctly: it's worked out from the only available bits via the API - i.e. camera.fov [vertical, in degrees] & camera.focal_length & the screen's width [ view.vpwith] or the camera.image_width, if that's set [it's >0 if you are using a specific 'camera type']... which can then be combined to get it...
You can get the camera.aspect_ratio as it's the ratio of the two fov's ??

thomthom

@tig said:

You can get the camera.aspect_ratio as it's the ratio of the two fov's ??

?

You do get camera.aspect_ratio via the ruby API. But I was wondering why it is not part of the Sketchup UI to control.