Point/Midpoint,A
Midpoint of Arc
Creates a point at the exact midpoint of an arc — the point at the midpoint of the arc sweep angle.
What It Does
The Point/Midpoint,A operator creates a point at the exact midpoint of an arc — the point on the arc circumference at the midpoint of the sweep angle. This is the point equidistant along the arc from both endpoints.
Syntax
Point/Midpoint, A, Z
Quick Input
A: [arc reference]
Z: 0
Direction Selector
No direction selector is required. The result is uniquely determined by the input geometry.
Worked Examples
Setup:
A0 = Arc: centre (0,0), r=50, start=0°, end=90° CCW
Midpoint angle = (0 + 90) / 2 = 45°
Point/Midpoint, A0, 0
→ P0 = (35.355, 35.355) [at 45° on the arc]
Setup:
A1 = Arc: centre (0,0), r=30, start=30°, end=150° CCW
Midpoint angle = (30 + 150) / 2 = 90°
Point/Midpoint, A1, 0
→ P1 = (0, 30) [at 90° — top of arc]
Analytic Rule
Midpoint angle = (start_angle + end_angle) / 2
For CCW arcs: mid = start + sweep/2
For CW arcs: mid = start - sweep/2
Midpoint coordinates:
x = cx + r * cos(mid_angle)
y = cy + r * sin(mid_angle)
Result: Exact analytic midpoint.
FAQ
Is the arc midpoint the same as the geometric centre of the arc chord?
No. The arc midpoint is the point on the arc circumference at the midpoint of the sweep angle. The chord midpoint is the midpoint of the straight line between the arc endpoints — a different location.
How do I find the arc midpoint angle?
The midpoint angle is (start_angle + end_angle) / 2 for a CCW arc. View arc properties in the Geometry Information Display.