diff options
Diffstat (limited to 'vendor/github.com/golang/geo/s1/chordangle.go')
| -rw-r--r-- | vendor/github.com/golang/geo/s1/chordangle.go | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/vendor/github.com/golang/geo/s1/chordangle.go b/vendor/github.com/golang/geo/s1/chordangle.go index 5f5832a..7fe06bb 100644 --- a/vendor/github.com/golang/geo/s1/chordangle.go +++ b/vendor/github.com/golang/geo/s1/chordangle.go @@ -164,8 +164,8 @@ func (c ChordAngle) Add(other ChordAngle) ChordAngle { return ChordAngle(math.Min(4.0, x+y+2*math.Sqrt(x*y))) } -// Sub subtracts the other ChordAngle from this one and returns the resulting value. -// This method assumes the ChordAngles are not special. +// Sub subtracts the other ChordAngle from this one and returns the resulting +// value. This method assumes the ChordAngles are not special. func (c ChordAngle) Sub(other ChordAngle) ChordAngle { if other == 0 { return c @@ -181,12 +181,18 @@ func (c ChordAngle) Sub(other ChordAngle) ChordAngle { // Sin returns the sine of this chord angle. This method is more efficient // than converting to Angle and performing the computation. func (c ChordAngle) Sin() float64 { + return math.Sqrt(c.Sin2()) +} + +// Sin2 returns the square of the sine of this chord angle. +// It is more efficient than Sin. +func (c ChordAngle) Sin2() float64 { // Let a be the (non-squared) chord length, and let A be the corresponding // half-angle (a = 2*sin(A)). The formula below can be derived from: // sin(2*A) = 2 * sin(A) * cos(A) // cos^2(A) = 1 - sin^2(A) // This is much faster than converting to an angle and computing its sine. - return math.Sqrt(float64(c * (1 - 0.25*c))) + return float64(c * (1 - 0.25*c)) } // Cos returns the cosine of this chord angle. This method is more efficient |