Brecht

Is there someone who can guide me to some information regarding the 

relation between the lens angle and the distance of the camera?

I want to move the camera away or towards an object in relation to 

the lens angle so that the relative size on screen of the object 

Is there someone who can guide me to some information regarding the  
relation between the lens angle and the distance of the camera?
I want to move the camera away or towards an object in relation to  
the lens angle so that the relative size on screen of the object  
stays the same...

distance-vs-lens-angle

P.S. I have asked a similar question before, but I'm looking for some 

more background info, math explanation or something similar. I've 

been quite some googeling but haven't found anything solid (read: 

On 31 Mar 2008, at 23:11, Brecht Debackere wrote:

> Is there someone who can guide me to some information regarding the 

> relation between the lens angle and the distance of the camera?

> I want to move the camera away or towards an object in relation to 

> the lens angle so that the relative size on screen of the object 

P.S. I have asked a similar question before, but I'm looking for some  
more background info, math explanation or something similar. I've  
been quite some googeling but haven't found anything solid (read:  
what my puny mind can fathom) so far.

> Hi!
>
> Is there someone who can guide me to some information regarding the  
> relation between the lens angle and the distance of the camera?
> I want to move the camera away or towards an object in relation to  
> the lens angle so that the relative size on screen of the object  
> stays the same...
>
> thx!.
> B.


On Mon, Mar 31, 2008 at 9:11 PM, Brecht Debackere 

> Is there someone who can guide me to some information regarding the

> I want to move the camera away or towards an object in relation to

> the lens angle so that the relative size on screen of the object

I guess you're talking about OpenGL no? I've been playing around with camera

stuff recently. This is one of those things I would definitely implement

using a procedural language instead of patching. Disclaimer: I haven't

tested this, and its pseudo code, so it won't work straight out of the box.

Calculate the distance of the object from the camera by subtracting one

point from the other and taking the magnitude of the resulting vector:

distance = magnitude (object_pos - cam_pos)

Set "screen" height to a ratio of your object height:

Now you can calculate the field of view in y direction (fovy) by a simple

trigonometric function (see attached crappy drawing):

Now you should have enough information to set up your camera.

Your "up" and "lookat" vectors are for you to choose. Here's how you

set the projection and modelview matrix to match your camera settings:

gluLookat(cam_x, cam_y, cam_z, lookat_x, lookat_y, lookat_z, up_x, up_y,

You can find more info about this stuff in the opengl redbook and the

opengl.org FAQ. I hope my explanation was somewhat clear. Good luck.

On Mon, Mar 31, 2008 at 9:11 PM, Brecht Debackere 
wrote:

>
> Is there someone who can guide me to some information regarding the
> relation between the lens angle and the distance of the camera?
> I want to move the camera away or towards an object in relation to
> the lens angle so that the relative size on screen of the object
> stays the same...
>
>
Hi Brecht,

I guess you're talking about OpenGL no? I've been playing around with camera
stuff recently. This is one of those things I would definitely implement
using a procedural language instead of patching.  Disclaimer: I haven't
tested this, and its pseudo code, so it won't work straight out of the box.

Calculate the distance of the object from the camera by subtracting one
point from the other and taking the magnitude of the resulting vector:

Set "screen" height to a ratio of your object height:
screen_h = object_h * ratio

Now you can calculate the field of view in y direction (fovy) by a simple
trigonometric function (see attached crappy drawing):

tan x = screen_h / distance
x = arctan(screen_h / distance)

convert x (in radians) to degrees:
fovy = x*(180/PI)

Now you should have enough information to set up your camera.
Your "up" and "lookat" vectors are for you to choose. Here's how you
set the projection and modelview matrix to match your camera settings:

/// SET CAMERA
glMatrixMode(GL_PROJECTION)
glPushmatrix()
glLoadIdentity()
gluPerspective(fovy, aspect, near, far)
glMatrixMode(GL_MODELVIEW)
glPushMatrix()
glLoadIdentity()
gluLookat(cam_x, cam_y, cam_z, lookat_x, lookat_y, lookat_z, up_x, up_y,
up_z)

/// RESET CAMERA
glMatrixMode(GL_PROJECTION)
glPopMatrix()
glMatrixMode(GL_MODELVIEW)
glPopMatrix()

You can find more info about this stuff in the opengl redbook and the
opengl.org FAQ. I hope my explanation was somewhat clear. Good luck.

distance vs. lens angle