Considering the objects related to the building（round corner）, I think the best approach to measure the radius of it is to measure the length of the arc ,then calculate the radius by some maths formula. Hope it helps, GOOD LUCK!!

To find the radius, this is a formula you can use. Circumference = Diameter x 3.14. Measure round the corner until the wall is flat, if the round corner part is say 48" this will be ¼ of the circumference. Multiply x 4 = Circumference. 48" x 4= 192". 192 divided by 3.14 = the Diameter (61.15) half it = 30.6".