Horisontal AOV?

[thomthom]

This is why I think SU mixes up the terms FOV and AOV. Because in the Camera Debug window you have Fov(H) and Fov(W) - both two different values. By default Fov(H) is enabled.

[Chris Fullmer]

FOV(H) is the angle of view (AOV) from top to bottom where FOV(W) is the AOV from side to side.

So yes, its confusing. I think I just got the trig worked out to solve it all. Let me put it together so it works and I'll post what I have, in case it helps.

Chris

[thomthom]

Thanks for looking into this.
I want to be able to make a tool where the AOV can be set in Horizontal, Vertical or Diagonal direction. So I need to be able to work this out.

[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

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[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

( 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.

[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.