circle

Documentation

Overview

Circle: Chapter 20, Smallest Circle containing three Celestial Bodies.

Index

• func Smallest(r1, d1, r2, d2, r3, d3 unit.Angle) (Δ unit.Angle, typeI bool)

Examples

• Smallest (A)
• Smallest (B)

Functions

func Smallest

func Smallest(r1, d1, r2, d2, r3, d3 unit.Angle) (Δ unit.Angle, typeI bool)

Smallest finds the smallest circle containing three points.

Arguments should represent coordinates in right ascension and declination or longitude and latitude. Result Δ is the diameter of the circle, typeI is true if solution is of type I.

type I   Two points on circle, one interior.
type II  All three points on circle.

根据三点坐标，求最小圆直径

Example (A)

// Example 20.a, p. 128.
r1 := unit.NewRA(12, 41, 8.64).Angle()
r2 := unit.NewRA(12, 52, 5.21).Angle()
r3 := unit.NewRA(12, 39, 28.11).Angle()
d1 := unit.NewAngle('-', 5, 37, 54.2)
d2 := unit.NewAngle('-', 4, 22, 26.2)
d3 := unit.NewAngle('-', 1, 50, 3.7)
d, t := circle.Smallest(r1, d1, r2, d2, r3, d3)
fd := sexa.FmtAngle(d)
fmt.Printf("Δ = %.5j = %m\n", fd, fd)
if t {
	fmt.Println("type I")
} else {
	fmt.Println("type II")
}

Output:

Δ = 4°.26363 = 4°16′
type II

Example (B)

// Exercise, p. 128.
r1 := unit.NewRA(9, 5, 41.44).Angle()
r2 := unit.NewRA(9, 9, 29).Angle()
r3 := unit.NewRA(8, 59, 47.14).Angle()
d1 := unit.NewAngle(' ', 18, 30, 30)
d2 := unit.NewAngle(' ', 17, 43, 56.7)
d3 := unit.NewAngle(' ', 17, 49, 36.8)
d, t := circle.Smallest(r1, d1, r2, d2, r3, d3)
fmt.Printf("Δ = %m\n", sexa.FmtAngle(d))
if t {
	fmt.Println("type I")
} else {
	fmt.Println("type II")
}

Output:

Δ = 2°19′
type I