[OSM-talk] [OSM-dev] OpenStreetView: Digital Photos: Getting the field of view angle

[Richard Weait]

On Sun, Aug 16, 2009 at 9:47 AM, Vincent MEURISSE<osm-dev at meurisse.org> wrote:

> In fact you don't really need the size of film (captor size). Most of the
> camera store the focal in both real and equivalent distance.
> If I take a random picture from a nikon D300 the exif information contain
> this:
> Focal Length: 70mm
> Focal Length In 35mm Film: 105mm
> Digital zoom ratio: 1.0
>
> So with the equivalent focal and the digital zoom, you can get your angle.

Vincent is correct.  Those calculations will help as a rule of thumb.

Back before I had to tell you kids to get off my lawn, everybody used
35mm film and dimensions were set in stone.  43.3, 36, 24.  We had it
all memorized, then those wacky CCDs came along with their 2/3"-format
and 1/2"-format in which none of the dimensions are actually the
dimension for which the format is named.  Oh, those were heady days.
Slide rules and drafting tables for everyone!  But you kids these
days, you know better, with your CCDs and your CMOS sensors and your
varying aspect ratios.  The old rules of thumb are likely to break
your brain.  So go to first principles and get off my lawn.

Ideally, you'll find the actual dimensions of the camera sensor in
your device.  This can be hard to find.  "N95", you say?  I see links
that suggest a CMOS sensor of 2582x1944 pixels[1].  Kodak has a
similar 5MP CMOS device with 2592x1944 and 2.2 micron (square) pixels.
 Other manufacturers may vary in ways that matter to you on the
details.  Find the real sensor data sheet if you can.

http://www.kodak.com/global/en/business/ISS/Products/DiscontinuedProducts/index.jhtml

Sensor width: 2592 x 2.2 microns = 5.7024mm
Sensor height: 1944 x 2.2 microns = 4.2768mm
Focal length: 5.6 mm[1]

Tan(angle/2)=size of film/(2*focal)

aFOV(h)=  14.28 degrees, thank you Wolfram Alpha
aFOV(v)=  10.81 degrees

But this is still an approximation, and based on an ideal lens with no
aberrations. It should get you started. ;-)

Best regards,
Richard

[1] http://www.allaboutsymbian.com/reviews/item/Nokia_N95-part_3_the_Camera.php