MEL - Angle of View

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Old 02 February 2013   #1
MEL - Angle of View

Hi there,
is there any way to read the Angle of View (instead of the Focal Lenght) of a camera via MEL or and expression? It seems there is no getAttr or setAttr for it.

If this is not possible, how would I calculate the AOV from the Focal Length?

Cheers, Florian
 
Old 02 February 2013   #2
Sure:

You need to known factors: the focal length f and the size of the camera aperture d (actually the film/ccd sensor size, but in Maya this would be the effective aperture). By default, aperture is equal to a 35mm image. While there are actually 3 angles of view (vertical, horizontal and diagonal), Maya only shows us the horizontal angle, as calculated by the following formula:

angle of view = 2 x atan(d / (2xf));

In MEL:

float $d = 35;  // film width
float $f = 50;  // focal length
float $ratio = $d / (2 * $f);
float $a = 2 * atan($ratio); // angle in radians
$a = rad_to_deg($a); // angle in degrees


In Python:
import math

def aov(d,f):
	a = 2 * math.atan(float(d) / (2*float(f)))
	a = math.degrees(a)
	return a

a = aov(35,35)
print a


Note that Maya seems to use some rounding internally, so the resulting values are not exactly identical.
 
Old 02 February 2013   #3
Vielen Dank.
Gonna try it tomorrow.

Cheers, Florian
 
Old 02 February 2013   #4
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