Four-centred arch: the flat and wide kind

Geometric analysis of an opening. The arch is composed of four circular segments: two short arcs with small radii starting at the sides, connecting to two very large, gentle arcs at the top that meet slightly in the center. The overall height is only about one-third of the span, making it appear flattened but still pointed. Avoid: drawing a semicircular arch, drawing a tall equilateral pointed arch, having discontinuous arc transitions with sharp angles, making the arch height close to its span.

Translated from Chinese by AI.

一個開口的幾何分析。拱由四段圓弧組成:兩側是半徑小的短弧起拱,上方接兩段半徑很大的緩弧到中央微微相交。整體的高度只有跨度的三分之一左右,看起來被壓扁但仍有尖。避免:畫成半圓拱、畫成高聳的等邊尖拱、讓弧線的轉折不連續出現折角、把拱的高度做到與跨度接近。