Question about the code that handles the standard deviation of a Gaussian kernel

[liangchengbeibian]

May I ask what these codes below are doing? Where does the "300" come from? Looking forward to your reply, thank you very much.
view_angle_degree = 5
view_angle_radian = math.radians(view_angle_degree)
r = 300/np.pi
gau_filter = int(np.round(view_angle_radian*r))