# Calculating the inner angle

I have some polygons and I want to calculate the inner angle of each polygon. Now, I have the geometry of every line of polygons in the same attribute table as shown in the following image. I want to calculate the inner angle using the following equation:

inner_angle= the bearing angle of the previous line - the bearing angle of the following line +180 (in degrees).

How can I write this in the code block in the model builder and do this for each polygon respectively?

I just need code execute that :

( Can the iterate feature in model builder do this loop ( for each polygon)?)

``````for each polygon

for i = 1: last line in the polygon

if i < the last line in the polygon

**angle = the line bearing @ i - the line bearing @ (i+1) +180**

if angle >360

angle= angle -360

end

if angle < 0

angle = angle +360

end
else
angle =   the line bearing @ i - the line bearing @ first line

if angle >360

angle= angle -360

end

if angle < 0

angle = angle +360

end
end

end
``````

The desired result as follows: You can calculate the interior angle of a polygon using this formula: `(n-2) × 180°`, where `n` is the number of sides.