Corner work: Useful rounds whch means half rounds

In the Corner of scqare of Japanse catsles gunners cannot focus on the terget well from windows when shooting.
That was just said and explanations as saying.
We could imagine and realise that if we knows about that by shapes in our heads.
In history, shooting points in castle, we think, doesn't suits castle by blinds.
So, they could fight Tokugawa, by use of castle on the hill as symbol of half-rounds in 16th century.

(https://jyo-sai.com/wp-content/uploads/2015/11/8557d77d3627beb7c68714f4255e83a1.jpg)

(http://livedoor.blogimg.jp/bzp17576/imgs/4/e/4e3ef2b0.jpg)

Their fights are very popular and famous in our cultury.
We understand Sanada creates half-rounds castle, which has no problem as understanding and truth.