I am utilizing a built in function named "getVerticalViewAngle()" to get the Vertical View Angle of Android Device Camera. The above function returns "63.8146" degrees as the Vertical Angle.

Now if I use the tablet on a tripod so that tilt is eliminated (Keeping tablet camera lens height as 900mm) and capture a picture of a wall at a distance of 1500mm, then 1800mm of the wall(vertical) is included within the picture. Calculating the Vertical Angle based on above scenario yields 61.9275 degress which is not equivalent to 63.8146.

Can anyone please explain why there is difference between Angle values?