Horisontal AOV?

thomthom

@chris fullmer said:

Well don't forget the PC camera tool
Sketchup.send_action 10624

Yea, I use that for debugging.

@chris fullmer said:

and don't forget to use the film and stage plugin. That is always useful to help visualize exactly where the phsical camera is located.

hm... yea. I could have a look at what that does. I've never used it though.

At the moment I manage to draw the viewing frustum so I know exactly where it is. But I want to take it further and make some tools to manipulate the camera. And for that I need to work out the AOV in all possible directions...

I'm reading up on real cameras and how they work. But I'm having some trouble applying that to the SU camera.

Chris Fullmer

Ok, so I'm digging around too and it appears that AOV and FOV are virtually identical, they are just represented differently.

@unknownuser said:

Although related, FOV is not exactly the same as angle of view; FOV is measured in linear, spatial dimensions (feet, inches, metres, etc) whereas AOV (more properly called the angular field of view) is measured in degrees of arc. FOV increases with distance, whereas AOV does not. FOV changes as the camera rotates, AOV does not.

and another good one, using the specs of a 50mm lens:

@unknownuser said:

At a working distance of 10 metres, the horizontal field of view is therefore 7.2 metres; at a distance of 100 feet, the horizontal field of view is 72 feet, etc. (The horizontal AOV is about 39.6º at any distance)

So it appears they are identical in value, just the FOV changes based on the distance away from the camera you are talking about.

Chris

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

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.